@article{Münter2021,
   author = {M. Münter, M. Pieper, T. Kohlfaerber, E. Bodenstorfer, M. Ahrens, C. Winter, R. Huber, P. König, G. Hüttmann and H. Schulz-Hildebrandt},
   title = {Microscopic optical coherence tomography (mOCT) at 600 kHz for 4D volumetric imaging and dynamic contrast},
   journal = {BiomedOptE},
   volume = {12(10)},
   Keywords = {CMOS cameras,Full field optical coherence tomography,High numerical aperture optics, Image processing,In vivo imaging,Medical imaging,Ag-Huber},
   pages = {6024-6039},
   DOI = {10.1364/BOE.425001},
  
   year = {2021},
   type = {Journal Article}
}

@INPROCEEDINGS{Schmidt2020ICLO,
  author={M. {Schmidt}, C. {Grill}, R. {Huber} and C. {Jirauschek}},
  booktitle={2020 International Conference Laser Optics (ICLO)}, 
  title={Coherence of Fourier Domain Mode-Locked (FDML) Lasers in the Ultra-Stable Regime}, 
  year={2020},
keywords={AG-Huber_FDML},
  volume={},
  number={},
  pages={1-1},
  doi={10.1109/ICLO48556.2020.9285488},
}

@article{Pfeiffer:20,
author = {T. Pfeiffer, M. G\"{o}b, W. Draxinger, S. Karpf, J.P. Kolb and R. Huber},
journal = {Biomed. Opt. Express},
keywords = {AG-Huber_OCT; High speed imaging; Image quality; Optical coherence tomography; Swept lasers; Swept sources; Systems design},
number = {11},
pages = {6799--6811},
publisher = {OSA},
title = {Flexible A-scan rate MHz-OCT: efficient computational downscaling by coherent averaging},
volume = {11},
month = {Nov},
year = {2020},
doi = {10.1364/BOE.402477},
abstract = {In order to realize adjustable A-scan rates of fast optical coherence tomography (OCT) systems, we investigate averaging of OCT image data acquired with a MHz-OCT system based on a Fourier Domain Mode Locked (FDML) laser. Increased system sensitivity and image quality can be achieved with the same system at the cost of lower imaging speed. Effectively, the A-scan rate can be reduced in software by a freely selectable factor. We demonstrate a detailed technical layout of the strategies necessary to achieve efficient coherent averaging. Since there are many new challenges specific to coherent averaging in swept source MHz-OCT, we analyze them point by point and describe the appropriate solutions. We prove that coherent averaging is possible at MHz OCT-speed without special interferometer designs or digital phase stabilization. We find, that in our system up to \&\#x223C;100x coherent averaging is possible while achieving a sensitivity increase close to the ideal values. This corresponds to a speed reduction from 3.3 MHz to 33 kHz and a sensitivity gain of 20 dB. We show an imaging comparison between coherent and magnitude averaging of a human finger knuckle joint in vivo with 121\&\#x00A0;dB sensitivity for the coherent case. Further, the benefits of computational downscaling in low sensitivity MHz-OCT systems are analyzed.},
}

@InProceedings{Strauch2020,
  author    = {M. Strauch, J.P. Kolb, D. Weng, M. Wacker, W. Draxinger, N. Merg, J. Hundt, S. Karpf and R. Huber},
  booktitle = {104. Jahrestagung der Deutschen Gesellschaft fuer Pathologie},
  title     = {Two-photon microscopy for sectioning-free virtual {H&E} imaging},
URL = {https://www.pathologie-dgp.de/media/Dgp/user_upload/Verhandlungsband_2020_final__kompr._.pdf},
  year      = {2020},
  keywords  = {AG-Huber_NL},
}

@article{schmidt2020self,
  title={Self-stabilization mechanism in ultra-stable Fourier domain mode-locked (FDML) lasers},
  author={M. {Schmidt}, T. {Pfeiffer}, C. {Grill}, R. {Huber} and C. {Jirauschek}},
  journal={OSA Continuum},
  volume={3},
  number={6},
  pages={1589--1607},
  year={2020},
keywords={AG-Huber_FDML},
url={https://doi.org/10.1364/OSAC.389972}, 
  publisher=  {Optical Society of America}
}

@PhdThesis{Strauch2020,
  author      = {M. Strauch},
  title       = {Tunable Optics: Spectral Imaging and Surface Manipulation on Liquid Lenses},
  institution = {Delft University of Technology},
  year        = {2020},
  date        = {2020-03-30},
  type        = {phdthesis},
  subtitle    = {Spectral Imaging and Surface Manipulation on Liquid Lenses},
  language    = {English},
  isbn        = {978-94-028-1994-6},
  pagetotal   = {151},
  doi         = {10.4233/uuid:b61aa64e-cba4-44c0-8d16-93440e028611},
  
  abstract    = {This thesis focusses on two aspects of tunable optics: Fabry-P{\'e}rot interferometers with a variable distance between their mirrors and electrowetting liquid lenses. The need for a device to detect child abuse has motivated us to design and build a camera that can detect the chemical composition of the upper skin layers of a bruise using a self-made Fabry-P{\'e}rot interferometer. The research described in the first part of this thesis has shown that wide-angle spectral imaging can be achieved with compact and cost-effective cameras using Fabry-P{\'e}rot interferometers. Designs with a full field of 90° in which the Fabry-P{\'e}rot interferometer is mounted either in front of an imaging system or behind a telecentric lens system are presented and analysed. The dependency of the spectral resolution on the numerical aperture of the lens system is derived and its value as a design criterion is shown. It is shown that the telecentric camera design is preferable over the collimated design for bruise imaging with a Fabry-P{\'e}rot interferometer.The idea to use a liquid lens for spectral imaging has directed the research towards a new concept of controlling surface waves on the surface of a liquid lens. We investigate and model surface waves because they decrease the imaging quality during fast focal switching. We propose a model that describes the surface modes appearing on a liquid lens and that predicts the resonance frequencies. The effects of those surface modes on a laser beam are simulated using geometrical optics and Fresnel propagation, and the model is verified experimentally. The model of the surface oscillations is used to develop a technique to create aspheric surface shapes on commercially available electrowetting liquid lenses. The surface waves on the liquid lens are described by Bessel functions of which a linear combination can be used to create any circularly symmetrical aspheric lens shape at an instant of time. With these surface profiles, one can realise a large set of circularly symmetrical wavefronts and hence intensity distributions of beams transmitted by the lens. The necessary liquid lens actuation to achieve a desired shape is calculated via a Hankel transform and confirmed experimentally. The voltage signal can be repeated at video rate. Measurements taken with a Mach-Zehnder interferometer confirm the model of the surface waves. The capabilities and limitations of the proposed method are demonstrated using the examples of a Bessel surface, spherical aberration, an axicon, and a top hat structure.},
keywords = {AG-Huber},
  address     = {Delft},
  publisher   = {Delft University of Technology},
  school      = {Delft University of Technology},
}

@inproceedings{Strenge2020,
author = {P. Strenge and B. Lange and C. Grill and W. Draxinger and M. M. Bonsanto and C. Hagel and R. Huber and R. Brinkmann},
title = {{Segmented OCT data set for depth resolved brain tumor detection validated by histological analysis}},
volume = {11228},
booktitle = {Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XXIV},
editor = {Joseph A. Izatt and James G. Fujimoto},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {82 -- 89},
keywords = {AG-Huber_OCT, Optical coherence tomography, OCT, FDML Laser, MHz-OCT, brain tumor, brain imaging, neurosurgery},
year = {2020},

URL = {  https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11228/112282O/Segmented-OCT-data-set-for-depth-resolved-brain-tumor-detection/10.1117/12.2545659.short}
}

@inproceedings{Grill2020,
author = {C. {Grill}, S. {Lotz}, T. {Blömker}, D. {Kastner}, T. {Pfeiffer}, S. {Karpf}, M. {Schmidt}, W. {Draxinger}, C. 
 {Jirauschek} and R. {Huber}},
title = {{Beating of two FDML lasers in real time}},
volume = {11260},
booktitle = {Fiber Lasers XVII: Technology and Systems},
editor = {Liang Dong},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {132 -- 138},
keywords = {AG-Huber_FDML, FDML laser, fiber lasers, beat signal, OCT, Optical Coherence Tomography, Fourier domain mode locking},
year = {2020},
doi = {10.1117/12.2545794},

}

@article{Cecchetti2020,
  doi = {10.1007/s10554-020-01796-7},
  url = {https://doi.org/10.1007/s10554-020-01796-7},
  year = {2020},
  month = feb,
  publisher = {Springer Science and Business Media {LLC}},
  volume = {36},
  number = {6},
  pages = {1021--1029},
  author = {Leonardo Cecchetti and Tianshi Wang and Ayla Hoogendoorn and Karen T. Witberg and Jurgen M. R. Ligthart and Joost Daemen and Heleen M. M. van Beusekom and Tom Pfeiffer and Robert A. Huber and Jolanda J. Wentzel and Antonius F. W. van der Steen and Gijs van Soest},
  title = {In-vitro and in-vivo imaging of coronary artery stents with Heartbeat {OCT}},
  journal = {The International Journal of Cardiovascular Imaging}
}

@InProceedings{Strauch2020a,
  author    = {M. Strauch, J.P. Kolb, N. Merg, J. Hundt, S. Karpf and R. Huber},
  booktitle = {32nd Congress of the ESP and XXXIII International Congress of the IAP},
  title     = {Evaluation of two-photon fluorescence microscopy for sectioning-free {H&E} imaging of different tissues},
  year      = {2020},
  keywords  = {AG-Huber_NL},
}

@article{Lopez-Marin:19,
author = {Antonio L\'{o}pez-Mar\'{i}n and Geert Springeling and Robert Beurskens and Heleen van Beusekom and Antonius F. W. van der Steen and Arjun D. Koch and Brett E. Bouma and Robert Huber and Gijs van Soest and Tianshi Wang},
journal = {Opt. Lett.},
keywords = {Image reconstruction; Light beams; Magnetic fields; Optical coherence tomography; Optical imaging; Reflector design},
number = {15},
pages = {3641--3644},
publisher = {Optica Publishing Group},
title = {Motorized capsule for shadow-free OCT imaging and synchronous beam control},
volume = {44},
month = {Aug},
year = {2019},
url = {https://opg.optica.org/ol/abstract.cfm?URI=ol-44-15-3641},
doi = {10.1364/OL.44.003641},
abstract = {We demonstrate a tethered motorized capsule for unobstructed optical coherence tomography (OCT) imaging of the esophagus. By using a distal reflector design, we avoided the common shadow artifact induced by the motor wires. A synchronous driving technique features three types of beam-scanning modes of the capsule, i.e., circumferential beam scanning, localized beam scanning, and accurate beam positioning. We characterized these three modes and carried out ex vivo imaging experiments using the capsule. The results show that the capsule can potentially be a useful tool for diagnostic OCT imaging and OCT-guided biopsy and therapy of the esophagus.},
}

@inproceedings{10.1117/12.2527034,
author = {Julian Klee and Jan Philip Kolb and Christin Grill and Wolfgang Draxinger and Tom Pfeiffer and Robert Huber},
title = {{Zero roll-off retinal MHz-OCT using an FDML-laser}},
volume = {11078},
booktitle = {Optical Coherence Imaging Techniques and Imaging in Scattering Media III},
editor = {Maciej Wojtkowski and Stephen A. Boppart and Wang-Yuhl Oh},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {110780S},
abstract = {Optical coherence tomography (OCT) applications like ultra-widefield and full eye-length imaging are of high interest for various diagnostic purposes. In swept-source OCT these techniques require a swept light source, which is coherent over the whole imaging depth. We present a zero roll-off 1060 nm Fourier Domain Mode Locked-Laser (FDML-Laser) for retinal OCT imaging at 1.7 MHz A-scan rate and first long-range imaging results with it. Several steps such as improved dispersion compensation and frequency regulation were performed and will be discussed. Besides virtually no loss in OCT signal over the maximum depth range of 4.6 mm and very good dynamic range was observed. Roll-off measurements show no decrease of the point-spread function (PSF), while maintaining a high dynamic range.},
keywords = {optical coherence tomography, OCT, tunable laser, Fourier Domain Mode Locking, FDML, MHz OCT},
year = {2019},
doi = {10.1117/12.2527034},
URL = {https://doi.org/10.1117/12.2527034}
}

@inproceedings{10.1117/12.2526796,
author = {Madita G{\"o}b and Tom Pfeiffer and Robert Huber},
title = {{Towards combined optical coherence tomography and multi-spectral imaging with MHz a-scan rates for endoscopy}},
volume = {11078},
booktitle = {Optical Coherence Imaging Techniques and Imaging in Scattering Media III},
editor = {Maciej Wojtkowski and Stephen A. Boppart and Wang-Yuhl Oh},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {110780Y},
abstract = {We demonstrate a preliminary setup of a combined MHz-OCT and RGB narrowband reflection microscope and investigate the performance of the new RGB branch and different display modes of colored OCT data sets.},
keywords = {MHz OCT, multi-spectral imaging, Optical Coherence Tomography, Fourier Domain Mode Locked , FDML, RGB, Color },
year = {2019},
doi = {10.1117/12.2526796},
URL = {https://doi.org/10.1117/12.2526796}
}

@inproceedings{10.1117/12.2527123,
author = {Yoko Miura and Wolfgang Draxinger and Christin Grill and Tom Pfeiffer and Salvatore Grisanti and Robert Huber},
title = {{MHz-OCT for low latency virtual reality guided surgery: first wet lab experiments on ex-vivo porcine eye
}},
volume = {11078},
booktitle = {Optical Coherence Imaging Techniques and Imaging in Scattering Media III},
editor = {Maciej Wojtkowski and Stephen A. Boppart and Wang-Yuhl Oh},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {110780E},
abstract = {MHz-OCT systems based on FDML swept laser sources combined with the massive parallel processing capabilities of modern computer hardware enable volumetric imaging, processing and stereoscopic display at video rates. The increasing image quality and speed might enable new fields of application where the volumetric OCT completely replaces stereoscopic microscopes instead of being a mere supplement. Aside from the depth resolving capability, a particular advantage is the ability to display a whole image volume from arbitrary points of view without the need to move the actual microscope or to rotate the patient’s eye. Purely digital microscopy is already offered as alternative to traditional through-an-eyepiece surgical microscope. We explore the use of virtual reality to present digital OCT microscopy images to a trained surgeon, carrying out a series of surgical procedures ex-vivo on a porcine eye model.},
keywords = {virtual reality, surgery guidance , real-time OCT, user experience},
year = {2019},
doi = {10.1117/12.2527123},
URL = {https://doi.org/10.1117/12.2527123}
}

@INPROCEEDINGS{8872571,
  author={Weng, Daniel and Hakert, Hubertus and Blömker, Torben and Kolb, Jan Philip and Strauch, Matthias and Eibl, Matthias and Lamminger, Philipp and Karpf, Sebastian and Huber, Robert},
  booktitle={2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)}, 
  title={Sub-Nanosecond Pulsed Fiber Laser for 532nm Two-Photon Excitation Fluorescence (TPEF) Microscopy of UV Transitions}, 
  year={2019},
  volume={},
  number={},
  pages={1-1},
  abstract={Summary form only given. Two-photon microscopy is a powerful technique for in vivo imaging, due to its high penetration depth and axial sectioning. Usually excitation wavelengths in the near infrared are used. However, most fluorescence techniques for live cell imaging require labeling with exogenous fluorophores. It has been shown that shorter wavelengths can be used to excite the autofluorescence of endogenous proteins, e.g. tryptophan. Recently we demonstrated a fully fiber-based laser source built around a directly modulated, ytterbium amplified 1064 nm laser diode with sub-nanosecond pulses for two-photon imaging [2]. The overall system enables to capture high-speed fluorescence lifetime imaging (FLIM) with single pulse excitation. Here, we extend the spectral range of this laser source by frequency doubling it to 532nm to achieve two-photon excited fluorescence microscopy (TPM) in the ultraviolett (UV) range to harness endogenous autofluorescence. In this presentation we explore first TPM results of tryptophan to investigate signal levels and fi delity before transitioning to biological tissues. It has been shown that TPM of endogenous tryptophan can be used to visualize immune system activity in vivo. Our laser source could be a cheap, flexible and fiber-based alternative to the OPO-based Ti:Sa Lasers currently employed. The basic concept of our design is to shift the wavelength of the pulsed fiber-based master oscillator power amplifier (MOPA) by second-harmonic generation (SHG) using phase-matching in a KTP crystal. This generates a coherent output at 532nm at a maximal peak power of 500W. We achieved a maximum conversion efficiency of about 17%. After the SHG module, the 532nm light is coupled into a single-mode fiber and delivered to a home built microscope. A 40x microscope objective is used to excite the sample and epi-collect the fluorescence. The fluorescence is recorded on a UV-enhanced photomultiplier tube (PMT). For a proof of concept measurement, crystalized tryptophan was imaged. Here we show signals of pure tryptophan, with laser parameters of 1MHz repetition rate and 100ps pulse duration. We used spectral bandpass fi lters in order to detect only fluorescence signal, however, from crystalized tryptophan we observed an unexpected short lifetime. We have recently shown that we can shift our laser output from 1064nm to longer wavelengths. By shifting to 1180nm and frequency doubling to 590nm a more efficient fluorescence excitation of tryptophan can be achieved. In the future we aim at in vivo imaging with our setup.},
  keywords={},
  doi={10.1109/CLEOE-EQEC.2019.8872571},
  ISSN={},
  month={June}}

@article{Kolb2019,
   author = {Kolb, J P;Draxinger, W;Klee, J;Pfeiffer, T;Eibl, M;Klein, T;Wieser, W and Huber, R},
   title = {Live video rate volumetric OCT imaging of the retina with multi-MHz A-scan rates},
   journal = {J pone},
 keywords = {AG-Huber_OCT},
   url = {https://doi.org/10.1371/journal.pone.0213144},
   pages = {e0213144},
   ISSN = {1932-6203},
   
   year = {2019},
   type = {Journal Article}
}

@inproceedings{10.1117/12.2507866,
author = {Jan Philip Kolb and Daniel Weng and Hubertus Hakert and Matthias Eibl and Wolfgang Draxinger and Tobias Meyer and Thomas Gottschall and Ralf  Brinkmann and Reginald Birngruber and J{\"u}rgen Popp and Jens Limpert and Sebastian Nino Karpf and Robert Huber},
title = {{Virtual HE histology by fiber-based picosecond two-photon microscopy}},
volume = {10882},
booktitle = {Multiphoton Microscopy in the Biomedical Sciences XIX},
editor = {Ammasi Periasamy and Peter T. C. So and Karsten K{\"o}nig},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {108822F},
abstract = {Two-Photon Microscopy (TPM) can provide three-dimensional morphological and functional contrast in vivo. Through proper staining, TPM can be utilized to create virtual, HE equivalent images and thus can improve throughput in histology-based applications. We previously reported on a new light source for TPM that employs a compact and robust fiber-amplified, directly modulated laser. This laser is pulse-to-pulse wavelength switchable between 1064 nm, 1122 nm, and 1186 nm with an adjustable pulse duration from 50ps to 5ns and arbitrary repetition rates up to 1MHz at kW-peak powers. Despite the longer pulse duration, it can achieve similar average signal levels compared to fs-setups by lowering the repetition rate to achieve similar cw and peak power levels. The longer pulses lead to a larger number of photons per pulse, which yields single shot fluorescence lifetime measurements (FLIM) by applying a fast 4 GSamples/s digitizer. In the previous setup, the wavelengths were limited to 1064 nm and longer. Here, we use four wave mixing in a non-linear photonic crystal fiber to expand the wavelength range down to 940 nm. This wavelength is highly suitable for imaging green fluorescent proteins in neurosciences and stains such as acridine orange (AO), eosin yellow (EY) and sulforhodamine 101 (SR101) used for histology applications. In a more compact setup, we also show virtual HE histological imaging using a direct 1030 nm fiber MOPA.},
keywords = {Multiphoton Microscopy, Four Wave Mixing, FWM, Histology, Laser, Non Linear Microscopy, Two Photon Microscopy, JenLab Young Investigator Award},
year = {2019},
doi = {10.1117/12.2507866},
URL = {https://doi.org/10.1117/12.2507866}
}

@InProceedings{Strauch2019,
  author    = {Strauch, Matthias and Kolb, Jan Philip and Weng, Daniel and Wacker, Melanie and Draxinger, Wolfgang and Karpf, Sebastian and Huber, Robert},
  booktitle = {31st Congress of the ESP},
  title     = {Sectioning-Free Virtual H&E Imaging of Tissue Samples with Two-Photon Microscopy},
  year      = {2019},
  keywords  = {AG-Huber_NL},
}

@inproceedings{Kastner:19,
author = {Kastner, D; Bl\"{o}mker, T; Pfeiffer, T; Grill, C; Schmidt, M; Jirauschek, C and Huber, R},
booktitle = {2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference},
journal = {2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference},
keywords = {Fourier domain mode locking; Image quality; Optical coherence tomography; Phase noise; Ring lasers; Tunable lasers},
pages = {cj_7_5},
publisher = {Optical Society of America},
title = {Measurement of Inter-Sweep Phase Stability of an FDML Laser with a 10 kHz Tunable Ring Laser},
year = {2019},
keywords = {AG-Huber_FDML, AG-Huber_OCT},
doi = { 10.1109/CLEOE-EQEC.2019.8872860},
abstract = {Fourier Domain Mode Locking (FDML) lasers are light sources that generate a sequence of narrowband optical frequency sweeps at the fundamental or harmonic of the cavity repetition rate \[1\]. This frequency swept output can also be considered as a sequence of strongly chirped, long pulses. FDML lasers are mainly used in swept source optical coherence tomography (SS-OCT), a medical imaging technique. The coherence length of the source, i.e. the intra-sweep phase stability of an FDML sweep, is decisive for the image quality and performance of OCT imaging \[2\].},
}

@inproceedings{schmidt2019coexistence,
  title={Coexistence of Intensity Pattern Types in Broadband Fourier Domain Mode Locked (FDML) Lasers},
  author={Schmidt, M; Pfeiffer, T; Grill, C; Huber, R and Jirauschek, C},
  booktitle={2019 Conference on Lasers and Electro-Optics Europe \& European Quantum Electronics Conference (CLEO/Europe-EQEC)},
  pages={1--1},
  year={2019},
  organization={IEEE},
keywords= { AG-Huber_FDML},
url={  https://ieeexplore.ieee.org/document/8872381}

}

@article{Maertz2018,
   author = {Maertz, J; Kolb, J P; Klein, T; Mohler, K J; Eibl, M; Wieser, W; Huber, R; Priglinger, S and Wolf, A},
   title = {Combined in-depth, 3D, en face imaging of the optic disc, optic disc pits and optic disc pit maculopathy using swept-source megahertz OCT at 1050 nm},
   journal = {Graefe's Archive for Clinical and Experimental Ophthalmology},
   number = {2},
   pages = {289-298},
   DOI = {10.1007/s00417-017-3857-9},
   url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85032262413&doi=10.1007%2fs00417-017-3857-9&partnerID=40&md5=a46c315f12cf5e633ea0f7e644116eb3},
   year = {2018},
   Keywords= {En face imaging, Optical coherence tomography, Swept-source OCT, Megahertz OCT, 3D rendering, Optic disc, Optic disc pit, Optic disc pit maculopathy, AG-Huber_OCT},
   type = {Journal Article}
}

@article{Eibl2018,
  doi = {10.1364/boe.9.006273},
  url = {https://doi.org/10.1364/boe.9.006273},
  year = {2018},
  month = nov,
  publisher = {The Optical Society},
  volume = {9},
  number = {12},
  pages = {6273},
  author = {Matthias Eibl and Daniel Weng and Hubertus Hakert and Jan Philip Kolb and Tom Pfeiffer and Jennifer E. Hundt and Robert Huber and Sebastian Karpf},
  title = {Wavelength agile multi-photon microscopy with a fiber amplified diode laser},
  journal = {Biomedical Optics Express}
}

@article{Schulz-Hildebrandt:18,
author = {Hinnerk Schulz-Hildebrandt and Tom Pfeiffer and Tim Eixmann and Sabrina Lohmann and Martin Ahrens and Joshua Rehra and Wolfgang Draxinger and Peter K\"{o}nig and Robert Huber and Gereon H\"{u}ttmann},
journal = {Opt. Lett.},
keywords = {Fiber optics imaging; Endoscopic imaging; Medical and biological imaging; Optical coherence tomography; Fourier domain mode locking; Image quality; Optical coherence tomography; Single mode fibers; Step index fibers; Three dimensional imaging},
number = {18},
pages = {4386--4389},
publisher = {Optica Publishing Group},
title = {High-speed fiber scanning endoscope for volumetric multi-megahertz optical coherence tomography},
volume = {43},
month = {Sep},
year = {2018},
url = {https://opg.optica.org/ol/abstract.cfm?URI=ol-43-18-4386},
doi = {10.1364/OL.43.004386},
abstract = {We present a forward-viewing fiber scanning endoscope (FSE) for high-speed volumetric optical coherence tomography (OCT). The reduction in size of the probe was achieved by substituting the focusing optics by an all-fiber-based imaging system which consists of a combination of scanning single-mode fibers, a glass spacer, made from a step-index multi-mode fiber, and a gradient-index fiber. A lateral resolution of 11 $\mu$m was achieved at a working distance of 1.2 mm. The newly designed piezo-based FSE has an outer diameter of 1.6 mm and a rigid length of 13.5 mm. By moving the whole imaging optic in spirals for scanning the sample, the beam quality remains constant over the entire field of view with a diameter of 0.8 mm. The scanning frequency was adjusted to 1.22 kHz for use with a 3.28 MHz Fourier domain mode locked OCT system. Densely sampled volumes have been imaged at a rate of 6 volumes per second.},
}

@article{Pfeiffer:18,
author = {Tom Pfeiffer and Markus Petermann and Wolfgang Draxinger and Christian Jirauschek and Robert Huber},
journal = {Biomed. Opt. Express},
keywords = {Fiber optics imaging; Lasers, fiber; Optical coherence tomography; Laser stabilization ; Lasers, frequency modulated ; Analog to digital converters; Dark solitons; Image quality; Laser modes; Mode locking; Optical coherence tomography},
number = {9},
pages = {4130--4148},
publisher = {Optica Publishing Group},
title = {Ultra low noise Fourier domain mode locked laser for high quality megahertz optical coherence tomography},
volume = {9},
month = {Sep},
year = {2018},
url = {https://opg.optica.org/boe/abstract.cfm?URI=boe-9-9-4130},
doi = {10.1364/BOE.9.004130},
abstract = {We investigate the origin of high frequency noise in Fourier domain mode locked (FDML) lasers and present an extremely well dispersion compensated setup which virtually eliminates intensity noise and dramatically improves coherence properties. We show optical coherence tomography (OCT) imaging at 3.2 MHz A-scan rate and demonstrate the positive impact of the described improvements on the image quality. Especially in highly scattering samples, at specular reflections and for strong signals at large depth, the noise in optical coherence tomography images is significantly reduced. We also describe a simple model that suggests a passive physical stabilizing mechanism that leads to an automatic compensation of remaining cavity dispersion in FDML lasers.},
}

@article{Schmidt:20,
author = {Mark Schmidt and Tom Pfeiffer and Christin Grill and Robert Huber and Christian Jirauschek},
journal = {OSA Continuum},
keywords = {Doppler effect; Laser modes; Laser sources; Nonlinear effects; Stimulated Raman scattering; Vertical cavity surface emitting lasers},
number = {6},
pages = {1589--1607},
publisher = {Optica Publishing Group},
title = {Self-stabilization mechanism in ultra-stable Fourier domain mode-locked (FDML) lasers},
volume = {3},
month = {Jun},
year = {2020},
url = {https://opg.optica.org/osac/abstract.cfm?URI=osac-3-6-1589},
doi = {10.1364/OSAC.389972},
abstract = {Understanding the dynamics of Fourier domain mode-locked (FDML) lasers is crucial for determining physical coherence limits, and for finding new superior methods for experimental realization. In addition, the rich interplay of linear and nonlinear effects in a laser ring system is of great theoretical interest. Here we investigate the dynamics of a highly dispersion-compensated setup, where over a bandwidth of more than 100\&\#x2009;nm, a highly coherent output with nearly shot-noise-limited intensity fluctuations was experimentally demonstrated. This output is called the sweet-spot. We show by numerical simulation that a finite amount of residual dispersion in the fiber delay cavity of FDML lasers can be compensated by the group delay dispersion in the swept bandpass filter, such that the intensity trace exhibits no dips or high-frequency distortions, which are the main source of noise in the laser. In the same way, a small detuning from the ideal sweep filter frequency can be tolerated. Furthermore, we find that the filter\&\#x2019;s group delay dispersion improves the coherence properties of the laser, and acts as a self-stabilizing element in the cavity. Our theoretical model is validated against experimental data, showing that all relevant physical effects for the sweet-spot operating regime are included.},
}

@article{Kolb:18,
author = {Jan Philip Kolb and Tom Pfeiffer and Matthias Eibl and Hubertus Hakert 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; Image quality; In vivo imaging; Mode locking; Ophthalmic imaging; Three dimensional imaging},
number = {1},
pages = {120--130},
publisher = {Optica Publishing Group},
title = {High-resolution retinal swept source optical coherence tomography with an ultra-wideband Fourier-domain mode-locked laser at MHz A-scan rates},
volume = {9},
month = {Jan},
year = {2018},
url = {https://opg.optica.org/boe/abstract.cfm?URI=boe-9-1-120},
doi = {10.1364/BOE.9.000120},
abstract = {We present a new 1060 nm Fourier domain mode locked laser (FDML laser) with a record 143 nm sweep bandwidth at 2\&\#x2219;\&\#x202F;417 kHz\&\#x202F; $=$ \&\#x202F;834 kHz and 120 nm at 1.67 MHz, respectively. We show that not only the bandwidth alone, but also the shape of the spectrum is critical for the resulting axial resolution, because of the specific wavelength-dependent absorption of the vitreous. The theoretical limit of our setup lies at 5.9 \&\#x00B5;m axial resolution. In vivo MHz-OCT imaging of human retina is performed and the image quality is compared to the previous results acquired with 70 nm sweep range, as well as to existing spectral domain OCT data with 2.1 \&\#x00B5;m axial resolution from literature. We identify benefits of the higher resolution, for example the improved visualization of small blood vessels in the retina besides several others.},
}

@article{Eibl:17,
author = {Matthias Eibl and Sebastian Karpf and Hubertus Hakert and Torben Bl\"{o}mker and Jan Philip Kolb and Christian Jirauschek and Robert Huber},
journal = {Opt. Lett.},
keywords = {Lasers, fiber; Lasers, Raman; Nonlinear optics, four-wave mixing; Scattering, stimulated Raman; Lasers, ytterbium ; Fiber lasers; Master oscillator power amplifiers; Nanosecond pulses; Raman scattering; Stimulated Brillouin scattering; Wavelength conversion},
number = {21},
pages = {4406--4409},
publisher = {Optica Publishing Group},
title = {Pulse-to-pulse wavelength switching of a nanosecond fiber laser by four-wave mixing seeded stimulated Raman amplification},
volume = {42},
month = {Nov},
year = {2017},
url = {https://opg.optica.org/ol/abstract.cfm?URI=ol-42-21-4406},
doi = {10.1364/OL.42.004406},
abstract = {We report on a multi-color fiber laser based on four-wave mixing (FWM) and stimulated Raman scattering (SRS), delivering rapidly wavelength switchable narrowband output at 1064, 1122, and 1186\&\#x00A0;nm. High-power pulses from a nanosecond pulsed fiber master oscillator power amplifier at 1064\&\#x00A0;nm are combined with 1122\&\#x00A0;nm of seed light for Raman amplification at the first Stokes order in a standard single-mode fiber. With increasing power, we observe a narrowband spectral component at 1186\&\#x00A0;nm, without any additional seed or resonator at this wavelength. We analyze this occurrence of a narrowband second Stokes order both experimentally and theoretically and suggest it is a result of FWM seeding of the SRS amplification in the fiber. We demonstrate that the wavelength shifting can be controlled electronically within microseconds for very rapid and even pulse-to-pulse wavelength changes. This wavelength conversion method can extend the spectral coverage of single-wavelength fiber lasers for biomedical imaging.},
}

@article{Wang:17,
author = {Tianshi Wang and Tom Pfeiffer and Min Wu and Wolfgang Wieser and Gaetano Amenta and Wolfgang Draxinger and Antonius F. W. van der Steen and Robert Huber and Gijs van Soest},
journal = {Opt. Lett.},
keywords = {Imaging systems; Medical and biological imaging; Optical coherence tomography; Lasers, pulsed ; Fourier domain mode locking; Functional imaging; Laser beams; Nanosecond pulses; Optical coherence tomography; Phantom studies},
number = {17},
pages = {3466--3469},
publisher = {Optica Publishing Group},
title = {Thermo-elastic optical coherence tomography},
volume = {42},
month = {Sep},
year = {2017},
url = {https://opg.optica.org/ol/abstract.cfm?URI=ol-42-17-3466},
doi = {10.1364/OL.42.003466},
abstract = {The absorption of nanosecond laser pulses induces rapid thermo-elastic deformation in tissue. A sub-micrometer scale displacement occurs within a few microseconds after the pulse arrival. In this Letter, we investigate the laser-induced thermo-elastic deformation using a 1.5 MHz phase-sensitive optical coherence tomography (OCT) system. A displacement image can be reconstructed, which enables a new modality of phase-sensitive OCT, called thermo-elastic OCT. An analysis of the results shows that the optical absorption is a dominating factor for the displacement. Thermo-elastic OCT is capable of visualizing inclusions that do not appear on the structural OCT image, providing additional tissue type information.},
}

@inproceedings{10.1117/12.2287484,
author = {Tom Pfeiffer and Wolfgang Draxinger and Christin Grill and Robert Huber},
title = {{Long-range live 3D-OCT at different spectral zoom levels}},
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 = {104160L},
abstract = {We demonstrate that the 3.2 MHz a-scan rate and the improved coherence of our new low noise FDML laser enables live 3D-OCT with different spectral zooms and up to 10 cm of imaging range.},
keywords = {Optical coherence tomography, Fourier Domain Mode Locking, FDML, OCT},
year = {2017},
doi = {10.1117/12.2287484},
URL = {https://doi.org/10.1117/12.2287484}
}