@inproceedings{10.1117/12.2286854,
author = {Jan Philip Kolb and Julian Klee and Tom Pfeiffer and Robert Huber},
title = {{1060nm FDML laser with centimeter coherence length and 1.67 MHz sweep rate for full eye length and retinal ultra-widefield OCT}},
volume = {10416},
booktitle = {Optical Coherence Imaging Techniques and Imaging in Scattering Media II},
editor = {Maciej Wojtkowski and Stephen A. Boppart and Wang-Yuhl Oh},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {104160J},
abstract = {We present a new design of a 1060nm Fourier Domain Mode Locked-Laser (FDML-Laser) that combines 1.67 MHz A-scan rate with a centimeter scale coherence length. The extended coherence length is achieved by synchronizing the cavity roundtrip time over the 75 nm sweep with a relative accuracy of 10<sup>-7</sup>. We will show that this requires careful combination of multiple fiber types in the cavity with a gradient heated chirped Fiber Bragg grating.},
keywords = {optical coherence tomograhy, OCT, tunable laser, Fourier domain mode locking, FDML, MHz OCT},
year = {2017},
doi = {10.1117/12.2286854},
URL = {https://doi.org/10.1117/12.2286854}
}

@inproceedings{10.1117/12.2286035,
author = {Matthias Eibl and Sebastian Karpf and Hubertus Hakert and Daniel Weng and Tom Pfeiffer and Jan Philip Kolb and Robert Huber},
title = {{Single pulse two-photon fluorescence lifetime imaging (SP-FLIM) with MHz pixel rate and an all fiber based setup }},
volume = {10414},
booktitle = {Advances in Microscopic Imaging},
editor = {Emmanuel Beaurepaire and Francesco Saverio Pavone and Peter T. C. So},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {1041403},
abstract = {Newly developed microscopy methods have the goal to give researches in bio-molecular science a better understanding of processes ongoing on a cellular level. Especially two-photon excited fluorescence (TPEF) microscopy is a readily applied and widespread modality. Compared to one photon fluorescence imaging, it is possible to image not only the surface but also deeper lying structures. Together with fluorescence lifetime imaging (FLIM), which provides information on the chemical composition of a specimen, deeper insights on a molecular level can be gained. However, the need for elaborate light sources for TPEF and speed limitations for FLIM hinder an even wider application. In this contribution, we present a way to overcome this limitations by combining a robust and inexpensive fiber laser for nonlinear excitation with a fast analog digitization method for rapid FLIM imaging. The applied sub nanosecond pulsed laser source is perfectly suited for fiber delivery as typically limiting non-linear effects like self-phase or cross-phase modulation (SPM, XPM) are negligible. Furthermore, compared to the typically applied femtosecond pulses, our longer pulses produce much more fluorescence photons per single shot. In this paper, we show that this higher number of fluorescence photons per pulse combined with a high analog bandwidth detection makes it possible to not only use a single pulse per pixel for TPEF imaging but also to resolve the exponential time decay for FLIM. To evaluate our system, we acquired FLIM images of a dye solution with single exponential behavior to assess the accuracy of our lifetime determination and also FLIM images of a plant stem at a pixel rate of 1 MHz to show the speed performance of our single pulse two-photon FLIM (SP-FLIM) system.},
keywords = {Nonlinear microscopy, Fluorescence microscopy, Fiber optics imaging, Lifetime-based sensing, Lasers, fiber, Nonlinear optics, fibers},
year = {2017},
doi = {10.1117/12.2286035},
URL = {https://doi.org/10.1117/12.2286035}
}

@inproceedings{10.1117/12.2287947,
author = {Hubertus Hakert and Matthias Eibl and Sebastian Karpf and Robert Huber},
title = {{Sparse-sampling with time-encoded (TICO) stimulated Raman scattering for fast image acquisition}},
volume = {10414},
booktitle = {Advances in Microscopic Imaging},
editor = {Emmanuel Beaurepaire and Francesco Saverio Pavone and Peter T. C. So},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {1041408},
abstract = {Modern biomedical imaging modalities aim to provide researchers a multimodal contrast for a deeper insight into a
specimen under investigation. A very promising technique is stimulated Raman scattering (SRS) microscopy, which can
unveil the chemical composition of a sample with a very high specificity. Although the signal intensities are enhanced
manifold to achieve a faster acquisition of images if compared to standard Raman microscopy, there is a trade-off between
specificity and acquisition speed. Commonly used SRS concepts either probe only very few Raman transitions as the
tuning of the applied laser sources is complicated or record whole spectra with a spectrometer based setup. While the first
approach is fast, it reduces the specificity and the spectrometer approach records whole spectra -with energy differences
where no Raman information is present-, which limits the acquisition speed. Therefore, we present a new approach based
on the TICO-Raman concept, which we call sparse-sampling. The TICO-sparse-sampling setup is fully electronically
controllable and allows probing of only the characteristic peaks of a Raman spectrum instead of always acquiring a whole
spectrum. By reducing the spectral points to the relevant peaks, the acquisition time can be greatly reduced compared to a
uniformly, equidistantly sampled Raman spectrum while the specificity and the signal to noise ratio (SNR) are maintained.
Furthermore, all laser sources are completely fiber based. The synchronized detection enables a full resolution of the
Raman signal, whereas the analogue and digital balancing allows shot noise limited detection. First imaging results with
polystyrene (PS) and polymethylmethacrylate (PMMA) beads confirm the advantages of TICO sparse-sampling. We
achieved a pixel dwell time as low as 35 μs for an image differentiating both species. The mechanical properties of the
applied voice coil stage for scanning the sample currently limits even faster acquisition.},
keywords = {nonlinear microscopy, fiber optics imaging, stimulated raman scattering microscopy, time encoded, sparse sampling, Raman spectroscopy , Fourier Domain Mode Locked Laser, FDML, Lasers, fiber},
year = {2017},
doi = {10.1117/12.2287947},
URL = {https://doi.org/10.1117/12.2287947}
}

@article{Maertz2017,
   author = {Maertz, J. and Mohler, K. J. and Kolb, J. P. and Klein, T. and Neubauer, A. and Kampik, A. and Priglinger, S. and Wieser, W. and Huber, R. and Wolf, A.},
   title = {INTRAPAPILLARY PROLIFERATION IN OPTIC DISK PITS: Clinical Findings and Time-Related Changes},
   journal = {Retina},
   volume = {37},
   number = {5},
   pages = {906-914},
   DOI = {10.1097/iae.0000000000001260},
   year = {2017},
keywords = {AG-Huber_OCT},
   type = {Journal Article}
}

@article{Karpf2017,
   author = {Karpf, Sebastian and Eibl, Matthias and Wieser, Wolfgang and Klein, Thomas and Huber, Robert},
   title = {Shot-Noise Limited Time-Encoded Raman Spectroscopy},
   journal = {Journal of Spectroscopy},
   volume = {2017},
   pages = {1-6},
   url = {https://doi.org/10.1155/2017/9253475},
   year = {2017},
keywords = {AG-Huber_NL},
   type = {Journal Article}
}

@inproceedings{10.1117/12.2251965,
author = {Matthias Eibl and Sebastian Karpf and Hubertus Hakert and Daniel Weng and Torben Bl{\"o}mker and Robert Huber},
title = {{Pulse-to-pulse wavelength switching of diode based fiber laser for multi-color multi-photon imaging}},
volume = {10083},
booktitle = {Fiber Lasers XIV: Technology and Systems},
editor = {Craig A. Robin and Ingmar Hartl},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {100831C},
abstract = {We present an entirely fiber based laser source for non-linear imaging with a novel approach for multi-color excitation. The high power output of an actively modulated and amplified picosecond fiber laser at 1064 nm is shifted to longer wavelengths by a combination of four-wave mixing and stimulated Raman scattering. By combining different fiber types and lengths, we control the non-linear wavelength conversion in the delivery fiber itself and can switch between 1064 nm, 1122 nm, and 1186 nm on-the-fly by tuning the pump power of the fiber amplifier and modulate the seed diodes. This is a promising way to enhance the applicability of short pulsed laser diodes for bio-molecular non-linear imaging by reducing the spectral limitations of such sources. In comparison to our previous work [1, 2], we show for the first time two-photon imaging with the shifted wavelengths and we demonstrate pulse-to-pulse switching between the different wavelengths without changing the configuration.},
keywords = {stimulated raman scattering, two-photon imaging, fiber amplifier, four-wave-mixing, wavelength conversion, non-linear imaging},
year = {2017},
doi = {10.1117/12.2251965},
URL = {https://doi.org/10.1117/12.2251965}
}

@inproceedings{10.1117/12.2255090,
author = {Max-Heinrich Laves and Andreas Schoob and L{\"u}der A. Kahrs and Tom Pfeiffer and Robert Huber and Tobias Ortmaier},
title = {{Feature tracking for automated volume of interest stabilization on 4D-OCT images}},
volume = {10135},
booktitle = {Medical Imaging 2017: Image-Guided Procedures, Robotic Interventions, and Modeling},
editor = {Robert J. Webster III and Baowei Fei},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {101350W},
abstract = {A common representation of volumetric medical image data is the triplanar view (TV), in which the surgeon manually selects slices showing the anatomical structure of interest. In addition to common medical imaging such as MRI or computed tomography, recent advances in the field of optical coherence tomography (OCT) have enabled live processing and volumetric rendering of four-dimensional images of the human body. Due to the region of interest undergoing motion, it is challenging for the surgeon to simultaneously keep track of an object by continuously adjusting the TV to desired slices. To select these slices in subsequent frames automatically, it is necessary to track movements of the volume of interest (VOI). This has not been addressed with respect to 4DOCT images yet. Therefore, this paper evaluates motion tracking by applying state-of-the-art tracking schemes on maximum intensity projections (MIP) of 4D-OCT images. Estimated VOI location is used to conveniently show corresponding slices and to improve the MIPs by calculating thin-slab MIPs. Tracking performances are evaluated on an in-vivo sequence of human skin, captured at 26 volumes per second. Among investigated tracking schemes, our recently presented tracking scheme for soft tissue motion provides highest accuracy with an error of under 2.2 voxels for the first 80 volumes. Object tracking on 4D-OCT images enables its use for sub-epithelial tracking of microvessels for image-guidance.},
keywords = {4D imaging, maximum intensity projection, optical coherence tomography, feature tracking},
year = {2017},
doi = {10.1117/12.2255090},
URL = {https://doi.org/10.1117/12.2255090}
}

@inproceedings{10.1117/12.2250831,
author = {Matthias Eibl and Sebastian Karpf and Hubertus Hakert and Daniel Weng and Robert Huber},
title = {{Two-photon-excited fluorescence (TPEF) and fluorescence lifetime imaging (FLIM) with sub-nanosecond pulses and a high analog bandwidth signal detection}},
volume = {10069},
booktitle = {Multiphoton Microscopy in the Biomedical Sciences XVII},
editor = {Ammasi Periasamy and Peter T. C. So and Karsten K{\"o}nig and Xiaoliang S. Xie},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {100691F},
abstract = {Two-photon excited fluorescence (TPEF) microscopy and fluorescence lifetime imaging (FLIM) are powerful imaging techniques in bio-molecular science. The need for elaborate light sources for TPEF and speed limitations for FLIM, however, hinder an even wider application. We present a way to overcome this limitations by combining a robust and inexpensive fiber laser for nonlinear excitation with a fast analog digitization method for rapid FLIM imaging. The applied sub nanosecond pulsed laser source is synchronized to a high analog bandwidth signal detection for single shot TPEF- and single shot FLIM imaging. The actively modulated pulses at 1064nm from the fiber laser are adjustable from 50ps to 5ns with kW of peak power. At a typically applied pulse lengths and repetition rates, the duty cycle is comparable to typically used femtosecond pulses and thus the peak power is also comparable at same cw-power. Hence, both types of excitation should yield the same number of fluorescence photons per time on average when used for TPEF imaging. However, in the 100ps configuration, a thousand times more fluorescence photons are generated per pulse. In this paper, we now show that the higher number of fluorescence photons per pulse combined with a high analog bandwidth detection makes it possible to not only use a single pulse per pixel for TPEF imaging but also to resolve the exponential time decay for FLIM. To evaluate the performance of our system, we acquired FLIM images of a Convallaria sample with pixel rates of 1 MHz where the lifetime information is directly measured with a fast real time digitizer. With the presented results, we show that longer pulses in the many-10ps to nanosecond regime can be readily applied for TPEF imaging and enable new imaging modalities like single pulse FLIM.},
keywords = {FLIM, TPEF, fiber laser, endoscope, MOPA, Nonlinear microscopy, Fluorescence microscopy, Lifetime-based sensing},
year = {2017},
doi = {10.1117/12.2250831},
URL = {https://doi.org/10.1117/12.2250831}
}

@inproceedings{10.1117/12.2251502,
author = {Tianshi Wang and Tom Pfeiffer and Min Wu and Wolfgang Wieser and Wolfgang Draxinger and Antonius F. W. van der Steen and Robert Huber and Gijs van Soest},
title = {{Short pulse laser induced thermo-elastic deformation imaging}},
volume = {10062},
booktitle = {Optical Interactions with Tissue and Cells XXVIII},
editor = {E. Duco Jansen and Hope Thomas Beier},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {100620C},
abstract = {Absorption of nanosecond laser pulses induces rapid thermo-elastic deformation in tissue, i.e. a sub-micrometer scale displacement happens within a couple of microseconds. In this study, we initially investigate the depth-resolved deformation using a 1.5 MHz phase-sensitive optical coherence tomography (OCT) system. Functional images can be reconstructed based on the detected deformation, which enables a new imaging modality called thermo-elastic deformation imaging (TDI). Our results show that the associated displacement is related to the optical absorption of the short laser pulses. The TDI images can provide tissue type information in addition to the conventional OCT images.},
keywords = {thermal-elastic deformation, optical coherence tomography},
year = {2017},
doi = {10.1117/12.2251502},
URL = {https://doi.org/10.1117/12.2251502}
}

@article{Klein:17,
author = {Thomas Klein and Robert Huber},
journal = {Biomed. Opt. Express},
keywords = {Imaging systems; Optical coherence tomography; Lasers and laser optics; Lasers, tunable; Optical coherence tomography; Full field optical coherence tomography; High speed imaging; Image quality; Imaging systems; Light wavelength; X ray imaging},
number = {2},
pages = {828--859},
publisher = {Optica Publishing Group},
title = {High-speed OCT light sources and systems \[Invited\]},
volume = {8},
month = {Feb},
year = {2017},
url = {https://opg.optica.org/boe/abstract.cfm?URI=boe-8-2-828},
doi = {10.1364/BOE.8.000828},
abstract = {Imaging speed is one of the most important parameters that define the performance of optical coherence tomography (OCT) systems. During the last two decades, OCT speed has increased by over three orders of magnitude. New developments in wavelength-swept lasers have repeatedly been crucial for this development. In this review, we discuss the historical evolution and current state of the art of high-speed OCT systems, with focus on wavelength swept light sources and swept source OCT systems.},
}

@inproceedings{10.1117/12.2254792,
author = {Tom Pfeiffer and Wolfgang Draxinger and Wolfgang Wieser and Thomas Klein and Markus Petermann and Robert Huber},
title = {{Analysis of FDML lasers with meter range coherence}},
volume = {10053},
booktitle = {Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XXI},
editor = {James G. Fujimoto and Joseph A. Izatt and Valery V. Tuchin},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {100531T},
abstract = {FDML lasers provide sweep rates in the MHz range at wide optical bandwidths, making them ideal sources for high
speed OCT. Recently, at lower speed, ultralong-range swept-source OCT has been demonstrated using a tunable
vertical cavity surface emitting laser (VCSEL) and also using a Vernier-tunable laser. These sources provide relatively
high sweep rates and meter range coherence lengths. In order to achieve similar coherence, we developed an extremely
well dispersion compensated Fourier Domain Mode Locked (FDML) laser, running at 3.2 MHz sweep rate and 120 nm
spectral bandwidth. We demonstrate that this laser offers meter range coherence and enables volumetric long range OCT
of moving objects.},
keywords = {Optical coherence tomography, OCT, tunable laser, Fourier domain mode locking, FDML, MHz OCT},
year = {2017},
doi = {10.1117/12.2254792},
URL = {https://doi.org/10.1117/12.2254792}
}

@article{Eibl:17,
author = {Matthias Eibl and Sebastian Karpf and Daniel Weng and Hubertus Hakert and Tom Pfeiffer and Jan Philip Kolb and Robert Huber},
journal = {Biomed. Opt. Express},
keywords = {Fiber optics imaging; Nonlinear optics, fibers; Lasers, fiber; Lifetime-based sensing; Fluorescence microscopy; Nonlinear microscopy; Fourier domain mode locking; Image quality; Imaging techniques; Laser sources; Pulsed fiber lasers; Three dimensional sensing},
number = {7},
pages = {3132--3142},
publisher = {Optica Publishing Group},
title = {Single pulse two photon fluorescence lifetime imaging (SP-FLIM) with MHz pixel rate},
volume = {8},
month = {Jul},
year = {2017},
url = {https://opg.optica.org/boe/abstract.cfm?URI=boe-8-7-3132},
doi = {10.1364/BOE.8.003132},
abstract = {Two-photon-excited fluorescence lifetime imaging microscopy (FLIM) is a chemically specific 3-D sensing modality providing valuable information about the microstructure, composition and function of a sample. However, a more widespread application of this technique is hindered by the need for a sophisticated ultra-short pulse laser source and by speed limitations of current FLIM detection systems. To overcome these limitations, we combined a robust sub-nanosecond fiber laser as the excitation source with high analog bandwidth detection. Due to the long pulse length in our configuration, more fluorescence photons are generated per pulse, which allows us to derive the lifetime with a single excitation pulse only. In this paper, we show high quality FLIM images acquired at a pixel rate of 1 MHz. This approach is a promising candidate for an easy-to-use and benchtop FLIM system to make this technique available to a wider research community.},
}

@article{Karpf:16,
author = {Sebastian Karpf and Matthias Eibl and Benjamin Sauer and Fred Reinholz and Gereon H\"{u}ttmann and Robert Huber},
journal = {Biomed. Opt. Express},
keywords = {Fiber optics imaging; Nonlinear optics, fibers; Lasers, fiber; Fluorescence microscopy; Nonlinear microscopy; Femtosecond pulses; In vivo imaging; Laser sources; Nanosecond pulses; Optical systems; Ultrafast lasers},
number = {7},
pages = {2432--2440},
publisher = {Optica Publishing Group},
title = {Two-photon microscopy using fiber-based nanosecond excitation},
volume = {7},
month = {Jul},
year = {2016},
url = {https://opg.optica.org/boe/abstract.cfm?URI=boe-7-7-2432},
doi = {10.1364/BOE.7.002432},
abstract = {Two-photon excitation fluorescence (TPEF) microscopy is a powerful technique for sensitive tissue imaging at depths of up to 1000 micrometers. However, due to the shallow penetration, for in vivo imaging of internal organs in patients beam delivery by an endoscope is crucial. Until today, this is hindered by linear and non-linear pulse broadening of the femtosecond pulses in the optical fibers of the endoscopes. Here we present an endoscope-ready, fiber-based TPEF microscope, using nanosecond pulses at low repetition rates instead of femtosecond pulses. These nanosecond pulses lack most of the problems connected with femtosecond pulses but are equally suited for TPEF imaging. We derive and demonstrate that at given cw-power the TPEF signal only depends on the duty cycle of the laser source. Due to the higher pulse energy at the same peak power we can also demonstrate single shot two-photon fluorescence lifetime measurements.},
}

@article{doi:10.1021/acs.jpcc.6b02012,
author = {Huber, Robert and Dworak, Lars and Moser, Jacques E. and Grätzel, Michael and Wachtveitl, Josef},
title = {Beyond Vibrationally Mediated Electron Transfer: Coherent Phenomena Induced by Ultrafast Charge Separation},
journal = {The Journal of Physical Chemistry C},
volume = {120},
number = {16},
pages = {8534-8539},
year = {2016},
doi = {10.1021/acs.jpcc.6b02012},

URL = { 
        https://doi.org/10.1021/acs.jpcc.6b02012
    
},
eprint = { 
        https://doi.org/10.1021/acs.jpcc.6b02012
    
}
,
    abstract = { Wave packet propagation succeeding electron transfer (ET) from alizarin dye molecules into the nanocrystalline TiO2 semiconductor has been studied by ultrafast transient absorption spectroscopy. Because of the ultrafast time scale of the ET reaction of about 6 fs, the system shows substantial differences to molecular ET systems. We show that the ET process is not mediated by molecular vibrations, and therefore classical ET theories lose their applicability. Here the ET reaction itself prepares a vibrational wave packet and not the electromagnetic excitation by the laser pulse. Furthermore, the generation of phonons during polaron formation in the TiO2 lattice is observed in real time for this system. The presented investigations enable an unambiguous assignment of the involved photoinduced mechanisms and can contribute to a corresponding extension of molecular ET theories to ultrafast ET systems like alizarin/TiO2. }
}

@article{WANG2016622,
title = {Heartbeat OCT and Motion-Free 3D In Vivo Coronary Artery Microscopy},
journal = {JACC: Cardiovascular Imaging},
volume = {9},
number = {5},
pages = {622-623},
year = {2016},
issn = {1936-878X},
doi = {https://doi.org/10.1016/j.jcmg.2015.08.010},
url = {https://www.sciencedirect.com/science/article/pii/S1936878X15006713},
author = {Tianshi Wang and Tom Pfeiffer and Evelyn Regar and Wolfgang Wieser and Heleen {van Beusekom} and Charles T. Lancee and Geert Springeling and Ilona Krabbendam-Peters and Antonius F.W. {van der Steen} and Robert Huber and Gijs {van Soest}}
}

@inproceedings{10.1117/12.2214758,
author = {Jan Philip Kolb and Thomas Klein and Matthias Eibl and Tom Pfeiffer and Wolfgang Wieser and Robert Huber},
title = {{Megahertz FDML laser with up to 143nm sweep range for ultrahigh resolution OCT at 1050nm}},
volume = {9697},
booktitle = {Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XX},
editor = {Joseph A. Izatt and James G. Fujimoto and Valery V. Tuchin},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {969703},
abstract = {We present a new design of a Fourier Domain Mode Locked laser (FDML laser), which provides a new record in sweep
range at ~1μm center wavelength: At the fundamental sweep rate of 2x417 kHz we reach 143nm bandwidth and 120nm
with 4x buffering at 1.67MHz sweep rate. The latter configuration of our system is characterized: The FWHM of the
point spread function (PSF) of a mirror is 5.6μm (in tissue). Human in vivo retinal imaging is performed with the MHz
laser showing more details in vascular structures. Here we could measure an axial resolution of 6.0μm by determining
the FWHM of specular reflex in the image. Additionally, challenges related to such a high sweep bandwidth such as
water absorption are investigated.},
keywords = {Optical coherence tomography, OCT, tunable laser, Fourier domain mode locking, FDML, MHz OCT},
year = {2016},
doi = {10.1117/12.2214758},
URL = {https://doi.org/10.1117/12.2214758}
}

@article{Wang:15,
author = {Tianshi Wang and Tom Pfeiffer and Evelyn Regar and Wolfgang Wieser and Heleen van Beusekom and Charles T. Lancee and Geert Springeling and Ilona Krabbendam and Antonius F.W. van der Steen and Robert Huber and Gijs van Soest},
journal = {Biomed. Opt. Express},
keywords = {Fiber optics imaging; Three-dimensional image acquisition; Medical optics instrumentation; Scanners; Endoscopic imaging; Medical and biological imaging; Optical coherence tomography; Image quality; Image registration; Imaging techniques; Laser modes; Mode locking; Optical coherence tomography},
number = {12},
pages = {5021--5032},
publisher = {Optica Publishing Group},
title = {Heartbeat OCT: in vivo intravascular megahertz-optical coherence tomography},
volume = {6},
month = {Dec},
year = {2015},
url = {https://opg.optica.org/boe/abstract.cfm?URI=boe-6-12-5021},
doi = {10.1364/BOE.6.005021},
abstract = {Cardiac motion artifacts, non-uniform rotational distortion and undersampling affect the image quality and the diagnostic impact of intravascular optical coherence tomography (IV-OCT). In this study we demonstrate how these limitations of IV-OCT can be addressed by using an imaging system that we called \&\#x201C;Heartbeat OCT\&\#x201D;, combining a fast Fourier Domain Mode Locked laser, fast pullback, and a micromotor actuated catheter, designed to examine a coronary vessel in less than one cardiac cycle. We acquired in vivo data sets of two coronary arteries in a porcine heart with both Heartbeat OCT, working at 2.88 MHz A-line rate, 4000 frames/s and 100 mm/s pullback speed, and with a commercial system. The in vivo results show that Heartbeat OCT provides faithfully rendered, motion-artifact free, fully sampled vessel wall architecture, unlike the conventional IV-OCT data. We present the Heartbeat OCT system in full technical detail and discuss the steps needed for clinical translation of the technology.},
}

@article{10.1167/iovs.15-16670,
    author = {Mohler, Kathrin J. and Draxinger, Wolfgang and Klein, Thomas and Kolb, Jan Philip and Wieser, Wolfgang and Haritoglou, Christos and Kampik, Anselm and Fujimoto, James G. and Neubauer, Aljoscha S. and Huber, Robert and Wolf, Armin},
    title = "{Combined 60° Wide-Field Choroidal Thickness Maps and High-Definition En Face Vasculature Visualization Using Swept-Source Megahertz OCT at 1050 nm}",
    journal = {Investigative Ophthalmology & Visual Science},
    volume = {56},
    number = {11},
    pages = {6284-6293},
    year = {2015},
    month = {10},
    abstract = "{   To demonstrate ultrahigh-speed swept-source optical coherence tomography (SS-OCT) at 1.68 million A-scans/s for choroidal imaging in normal and diseased eyes over a ∼60° field of view. To investigate and correlate wide-field three-dimensional (3D) choroidal thickness (ChT) and vascular patterns using ChT maps and coregistered high-definition en face images extracted from a single densely sampled Megahertz-OCT (MHz-OCT) dataset.    High-definition, ∼60° wide-field 3D datasets consisting of 2088 × 1024 A-scans were acquired using a 1.68 MHz prototype SS-OCT system at 1050 nm based on a Fourier-domain mode-locked laser. Nine subjects (nine eyes) with various chorioretinal diseases or without ocular pathology are presented. Coregistered ChT maps, choroidal summation maps, and depth-resolved en face images referenced to either the retinal pigment epithelium or the choroidal–scleral interface were generated using manual segmentation.    Wide-field ChT maps showed a large inter- and intraindividual variance in peripheral and central ChT. In only four of the nine eyes, the location with the largest ChT was coincident with the fovea. The anatomy of the large lumen vessels of the outer choroid seems to play a major role in determining the global ChT pattern. Focal ChT changes with large thickness gradients were observed in some eyes.    Different ChT and vascular patterns could be visualized over ∼60° in patients for the first time using OCT. Due to focal ChT changes, a high density of thickness measurements may be favorable. High-definition depth-resolved en face images are complementary to cross sections and thickness maps and enhance the interpretation of different ChT patterns.  }",
    issn = {1552-5783},
    doi = {10.1167/iovs.15-16670},
    url = {https://doi.org/10.1167/iovs.15-16670},
    eprint = {https://arvojournals.org/arvo/content\_public/journal/iovs/934564/i1552-5783-56-11-6284.pdf},
}

@article{Reznicek2015,
   author = {Reznicek, Lukas and Kolb, Jan P. and Klein, Thomas and Mohler, Kathrin J. and Wieser, Wolfgang and Huber, Robert and Kernt, Marcus and Märtz, Josef and Neubauer, Aljoscha S.},
   title = {Wide-Field Megahertz OCT Imaging of Patients with Diabetic Retinopathy},
   journal = {Journal of Diabetes Research},
   volume = {2015, Article ID 305084},
   pages = {1-5},
   DOI = {10.1155/2015/305084},
   url = {http://dx.doi.org/10.1155/2015/305084},
   year = {2015},
keywords = {AG-Huber_OCT},
   type = {Journal Article}

}

@inproceedings{10.1117/12.2183768,
author = {Jan Philip Kolb and Thomas Klein and Wolfgang Wieser and Wolfgang Draxinger and Robert Huber},
title = {{High definition in vivo retinal volumetric video rate OCT at 0.6 Giga-voxels per second}},
volume = {9541},
booktitle = {Optical Coherence Imaging Techniques and Imaging in Scattering Media},
editor = {Brett E. Bouma and Maciej Wojtkowski},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {95410Z},
abstract = {We present full volumetric high speed OCT imaging of the retina with multiple settings varying in volume size and volume rate. The volume size ranges from 255x255 A-scans to 160x40 A-scans with 450 samples per depth scan with volume rates varying between 20.8 V/s for the largest volumes to 195.2 V/s for the smallest. The system is based on a 1060nm Fourier domain mode locked (FDML) laser with 1.6MHz line rate. Scanning along the fast axis is performed with a 2.7 kHz or 4.3 kHz resonant scanner operated in bidirectional scanning mode, while a standard galvo scanner is used for the slow axis. The performance is analyzed with respect to various potential applications, like intraoperative OCT.},
keywords = {Optical coherence tomography, OCT, tunable laser, Fourier domain mode locking, FDML, MHz-OCT},
year = {2015},
doi = {10.1117/12.2183768},
URL = {https://doi.org/10.1117/12.2183768}
}

@inproceedings{10.1117/12.2183822,
author = {Matthias Eibl and Sebastian Karpf and Wolfgang Wieser and Thomas Klein and Robert Huber},
title = {{Hyperspectral stimulated Raman microscopy with two fiber laser sources}},
volume = {9536},
booktitle = {Advanced Microscopy Techniques IV; and Neurophotonics II},
editor = {Emmanuel Beaurepaire and Peter T. C. So and Francesco Pavone and Elizabeth M. Hillman},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {953604},
abstract = {A fast all fiber based setup for stimulated Raman microscopy based on a rapidly wavelength swept cw-laser is presented. The applied Fourier domain mode locked (FDML) laser is a fiber ring laser, providing a continuously changing wavelength output over time. This fast swept source allows us to rapidly change the wavelength and, thereby the energy difference with respect to a single color pump laser. The pump laser is a master oscillator power amplifier based on a fiber amplified laser diode and a Raman shifter. By controlled variation of the relative timing between probe and pump laser with an arbitrary waveform generator, the Raman signals are encoded in time and they are directly acquired with a synchronized, fast analog-to-digital converter. This setup is capable of acquiring rapidly high resolution spectra (up to 0.5 cm<sup>-1</sup>) with shot noise limited sensitivity over a broadband (750 cm<sup>-1</sup> to 3150 cm<sup>-1</sup>) spectral region. Here, we show the performance of this system for imaging in the CH-stretch region around 3000 cm<sup>-1</sup> and in the fingerprint region around 1600 cm<sup>-1</sup>. We present hyperspectral images of a plant stem slice with molecular contrast of lignin and a lipid representative as well as images of PS (polystyrene) and PMMA (poly(methyl methacrylate) beads with an acquisition speed of 18 &mu;s per spectral point.},
keywords = {stimulated Raman, multiphoton, microscopy, coherent Raman, fiber laser, FDML, TICO, hyperspectral},
year = {2015},
doi = {10.1117/12.2183822},
URL = {https://doi.org/10.1117/12.2183822}
}

@inproceedings{10.1117/12.2183854,
author = {Sebastian Karpf and Matthias Eibl and Robert Huber},
title = {{Nanosecond two-photon excitation fluorescence imaging with a multi color fiber MOPA laser}},
volume = {9536},
booktitle = {Advanced Microscopy Techniques IV; and Neurophotonics II},
editor = {Emmanuel Beaurepaire and Peter T. C. So and Francesco Pavone and Elizabeth M. Hillman},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {953616},
abstract = {A system is presented that uses a fiber based Master Oscillator Power Amplifier (MOPA) with nanosecond-range pulses for two-photon excitation fluorescence (TPEF) imaging. The robust laser in the extended near infrared is based on an actively modulated electro-optical modulator (EOM), enabling free synchronization of the pulses to any other light source or detection unit. Pulses with a freely programmable duration between 0.4 and 10 ns are generated and then amplified to up to kilowatts of peak power with ytterbium doped fiber amplifiers (YDFA). Since we achieve peak power and duty cycles comparable to standard femto- and picosecond setups, the TPEF signal levels are similar, but realized with a robust and inexpensive fiber-based setup. The delivery fiber is further used as an optional, electronically controllable Raman shifter to effectively shift the 1064 nm light to 1122 nm and to 1186 nm. This allows imaging of a manifold of fluorophores, like e.g. TexasRed, mCherry, mRaspberry and many more. We show TPEF imaging of the autofluorescence of plant leaves of moss and algae, acquired in epi-direction. This modular laser unit can be integrated into existing systems as either a fiber-based, alignment free excitation laser or an extension for multi-modal imaging.},
keywords = {multi-photon imaging, TPEF, MOPA, TPA, fiber laser, Raman shifter, non-linear imaging, multi-modal imaging},
year = {2015},
doi = {10.1117/12.2183854},
URL = {https://doi.org/10.1117/12.2183854}
}

@inproceedings{10.1117/12.2183431,
author = {Wolfgang Wieser and Thomas Klein and Wolfgang Draxinger and Robert Huber},
title = {{Fully automated 1.5 MHz FDML laser with more than 100mW output power at 1310 nm}},
volume = {9541},
booktitle = {Optical Coherence Imaging Techniques and Imaging in Scattering Media},
editor = {Brett E. Bouma and Maciej Wojtkowski},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {954116},
abstract = {While FDML lasers with MHz sweep speeds have been presented five years ago, these devices have required manual control for startup and operation. Here, we present a fully self-starting and continuously regulated FDML laser with a sweep rate of 1.5 MHz. The laser operates over a sweep range of 115 nm centered at 1315 nm, and provides very high average output power of more than 100 mW. We characterize the laser performance, roll-off, coherence length and investigate the wavelength and phase stability of the laser output under changing environmental conditions. The high output power allows optical coherence tomography (OCT) imaging with an OCT sensitivity of 108 dB at 1.5 MHz.},
keywords = {OCT, optical coherence tomography, swept laser, wavelength-swept laser, fiber laser, MHz-OCT, Fourier-domain mode-locking, FDML},
year = {2015},
doi = {10.1117/12.2183431},
URL = {https://doi.org/10.1117/12.2183431}
}

@inproceedings{10.1117/12.2183859,
author = {Sebastian Karpf and Matthias Eibl and Wolfgang Wieser and Thomas Klein and Robert Huber},
title = {{Time-encoded Raman scattering (TICO-Raman) with Fourier domain mode locked (FDML) lasers}},
volume = {9541},
booktitle = {Optical Coherence Imaging Techniques and Imaging in Scattering Media},
editor = {Brett E. Bouma and Maciej Wojtkowski},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {95410F},
abstract = {We present a new concept for performing stimulated Raman spectroscopy and microscopy by employing rapidly wavelength swept Fourier Domain Mode locked (FDML) lasers [1]. FDML lasers are known for fastest imaging in swept-source optical coherence tomography [2, 3]. We employ this continuous and repetitive wavelength sweep to generate broadband, high resolution stimulated Raman spectra with a new, time-encoded (TICO) concept [4]. This allows for encoding and detecting the stimulated Raman gain on the FDML laser intensity directly in time. Therefore we use actively modulated pump lasers, which are electronically synchronized to the FDML laser, in combination with a fast analog-to-digital converter (ADC) at 1.8 GSamples/s. We present hyperspectral Raman images with color-coded, molecular contrast.},
keywords = {swept lasers, FDML, TICO-Raman, fiber lasers, stimulated Raman microscopy, Raman spectroscopy, molecular contrast, multi-modal imaging},
year = {2015},
doi = {10.1117/12.2183859},
URL = {https://doi.org/10.1117/12.2183859}
}

@article{Jirauschek:15,
author = {Christian Jirauschek and Robert Huber},
journal = {Biomed. Opt. Express},
keywords = {Laser theory; Lasers, tunable; Optical coherence tomography; Vertical cavity surface emitting lasers; Distributed Bragg reflectors; Laser light; Laser sources; Quantum well lasers; Swept lasers; Vertical cavity surface emitting lasers},
number = {7},
pages = {2448--2465},
publisher = {Optica Publishing Group},
title = {Wavelength shifting of intra-cavity photons: Adiabatic wavelength tuning in rapidly wavelength-swept lasers},
volume = {6},
month = {Jul},
year = {2015},
url = {https://opg.optica.org/boe/abstract.cfm?URI=boe-6-7-2448},
doi = {10.1364/BOE.6.002448},
abstract = {We analyze the physics behind the newest generation of rapidly wavelength tunable sources for optical coherence tomography (OCT), retaining a single longitudinal cavity mode during operation without repeated build up of lasing. In this context, we theoretically investigate the currently existing concepts of rapidly wavelength-swept lasers based on tuning of the cavity length or refractive index, leading to an altered optical path length inside the resonator. Specifically, we consider vertical-cavity surface-emitting lasers (VCSELs) with microelectromechanical system (MEMS) mirrors as well as Fourier domain mode-locked (FDML) and Vernier-tuned distributed Bragg reflector (VT-DBR) lasers. Based on heuristic arguments and exact analytical solutions of Maxwell's equations for a fundamental laser resonator model, we show that adiabatic wavelength tuning is achieved, i.e., hopping between cavity modes associated with a repeated build up of lasing is avoided, and the photon number is conserved. As a consequence, no fundamental limit exists for the wavelength tuning speed, in principle enabling wide-range wavelength sweeps at arbitrary tuning speeds with narrow instantaneous linewidth.},
}

@article{Huber:15,
author = {Robert Huber},
journal = {Opt. Photon. News},
keywords = {Image processing; Optical coherence tomography; Lasers, tunable; Medical optics and biotechnology; Optical coherence tomography; Image processing; Imaging techniques; Line scan cameras; Medical imaging; Optical coherence tomography; Three dimensional imaging},
number = {6},
pages = {32--39},
publisher = {Optica Publishing Group},
title = {4-D Real-Time Optical Coherence Tomography},
volume = {26},
month = {Jun},
year = {2015},
url = {https://www.optica-opn.org/abstract.cfm?URI=opn-26-6-32},
doi = {10.1364/OPN.26.6.000032},
abstract = {Advances in OCT techniques, combined with the processing power of moderncomputer hardware, are adding a new dimension---time---to a familiar 3-D imaging method.The result could be new applications in research and the biomedicalclinic.},
}

@article{Jirauschek:15,
author = {Christian Jirauschek and Robert Huber},
journal = {Opt. Lett.},
keywords = {Laser theory; Lasers, tunable; Optical coherence tomography; Birefringence; Polarization; Pulses; Cross phase modulation; Mode locking; Optical components; Picosecond pulses; Polarization mode dispersion; Pulse generation},
number = {10},
pages = {2385--2388},
publisher = {Optica Publishing Group},
title = {Modeling and analysis of polarization effects in Fourier domain mode-locked lasers},
volume = {40},
month = {May},
year = {2015},
url = {https://opg.optica.org/ol/abstract.cfm?URI=ol-40-10-2385},
doi = {10.1364/OL.40.002385},
abstract = {We develop a theoretical model for Fourier domain mode-locked (FDML) lasers in a non-polarization-maintaining configuration, which is the most widely used type of FDML source. This theoretical approach is applied to analyze a widely wavelength-swept FDML setup, as used for picosecond pulse generation by temporal compression of the sweeps. We demonstrate that good agreement between simulation and experiment can only be obtained by including polarization effects due to fiber bending birefringence, polarization mode dispersion, and cross-phase modulation into the theoretical model. Notably, the polarization dynamics are shown to have a beneficial effect on the instantaneous linewidth, resulting in improved coherence and thus compressibility of the wavelength-swept FDML output.},
}

@article{Kolb:15,
author = {Jan Philip Kolb and Thomas Klein and Corinna L. Kufner and Wolfgang Wieser and Aljoscha S. Neubauer and Robert Huber},
journal = {Biomed. Opt. Express},
keywords = {Medical optics instrumentation; Lasers, fiber; Medical and biological imaging; Ophthalmic optics and devices ; Optical coherence tomography; Adaptive optics; Full field optical coherence tomography; Image quality; Imaging techniques; Laser scanning; Three dimensional imaging},
number = {5},
pages = {1534--1552},
publisher = {Optica Publishing Group},
title = {Ultra-widefield retinal MHz-OCT imaging with up to 100 degrees viewing angle},
volume = {6},
month = {May},
year = {2015},
url = {https://opg.optica.org/boe/abstract.cfm?URI=boe-6-5-1534},
doi = {10.1364/BOE.6.001534},
abstract = {We evaluate strategies to maximize the field of view (FOV) of in vivo retinal OCT imaging of human eyes. Three imaging modes are tested: Single volume imaging with 85{\textdegree} FOV as well as with 100{\textdegree} and stitching of five 60{\textdegree} images to a 100{\textdegree} mosaic (measured from the nodal point). We employ a MHz-OCT system based on a 1060nm Fourier domain mode locked (FDML) laser with a depth scan rate of 1.68MHz. The high speed is essential for dense isotropic sampling of the large areas. Challenges caused by the wide FOV are discussed and solutions to most issues are presented. Detailed information on the design and characterization of our sample arm optics is given. We investigate the origin of an angle dependent signal fall-off which we observe towards larger imaging angles. It is present in our 85{\textdegree} and 100{\textdegree} single volume images, but not in the mosaic. Our results suggest that 100{\textdegree} FOV OCT is possible with current swept source OCT technology.},
}

@Article{HU_2015_Karpf_a,
  Title                    = {A Time-Encoded Technique for fibre-based hyperspectral broadband stimulated Raman microscopy},
  Author                   = {Karpf, Sebastian and Eibl, Matthias and Wieser, Wolfgang and Klein, Thomas and Huber, Robert},
  Journal                  = {Nature Communications},
  Year                     = {2015},
  Volume = {6},
  pages = {6784 1--6},
keywords = {AG-Huber_NL},
  Doi                      = {10.1038/ncomms7784}
}

@inproceedings{10.1117/12.2214788,
author = {Tom Pfeiffer and Wolfgang Wieser and Thomas Klein and Markus Petermann and Jan-Phillip Kolb and Matthias Eibl and Robert Huber},
title = {{Flexible A-scan rate MHz OCT: computational downscaling by coherent averaging}},
volume = {9697},
booktitle = {Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XX},
editor = {Joseph A. Izatt and James G. Fujimoto and Valery V. Tuchin},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {96970S},
abstract = {In order to realize fast OCT-systems with adjustable line rate, we investigate averaging of image data from an FDML based
MHz-OCT-system. The line rate can be reduced in software and traded in for increased system sensitivity and image
quality. We compare coherent and incoherent averaging to effectively scale down the system speed of a 3.2 MHz FDML
OCT system to around 100 kHz in postprocessing. We demonstrate that coherent averaging is possible with MHz systems
without special interferometer designs or digital phase stabilisation. We show OCT images of a human finger knuckle joint
in vivo with very high quality and deep penetration.},
keywords = {Optical coherence tomography, OCT, Fourier domain mode locking, FDML, MHz OCT, averaging, tunable laser},
year = {2016},
doi = {10.1117/12.2214788},
URL = {https://doi.org/10.1117/12.2214788}
}