@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}}

@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{Muenter2019,
title = {4D microscopic optical coherence tomography imaging of ex vivo mucus transport},
author = { M\"{u}nter, M; Schulz-Hildebrandt, H; Pieper, M; K\"{o}nig, P and  H\"{u}ttmann, G},
url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11078/2527138/4D-microscopic-optical-coherence-tomography-imaging-of-ex-vivo-mucus/10.1117/12.2527138.full},

isbn = {9781510628496},
year = {2019},
date = {2019-01-01},
booktitle = {Proc. SPIE 11078, Optical Coherence Imaging Techniques and Imaging in Scattering Media III},
volume = {11078},
number = {11},
pages = {1--5},
keywords = {OCM},
pubstate = {published},
tppubtype = {inproceedings}
}

@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{Haak2019,
author = {Haak, Rainer and Ahrens, Martin and Schneider, Hartmut and Strumpski, Michaela and Rueger, Claudia and Haefer, Matthias and H{\"{u}}ttmann, Gereon and Theisen-Kunde, Dirk and Schulz-Hildebrandt, Hinnerk},
booktitle = {Proc. SPIE 11073, Clinical and Preclinical Optical Diagnostics II},
doi = {10.1117/12.2527185},
isbn = {9781510628397},
number = {110730W},
pages = {1--4},
title = {{Handheld OCT probe for intraoral diagnosis on teeth}},
keywords = {OCT,Endoskope},
year = {2019},
}

@inproceedings{Strenge2019,
Title = {Ex vivo and in vivo imaging of human brain tissue with different OCT systems},
author = {Strenge, P.; Lange, B; Grill, C; Draxinger, W; Dannicke, V; Theisen-Kunde, D; Bonsanto, M; Huber, R and Brinkmann, R},
abstract = {Optical coherence tomography (OCT) is a non-invasive imaging technique which is currently investigated for intraoperative detection of residual tumor during resection of human gliomas. Three different OCT systems were used for imaging of human glioblastoma in vivo (830nm spectral domain (SD) OCT integrated into a surgical microscope) and ex vivo (940nm SD-OCT and 1310nm swept-source MHz-OCT using a Fourier domain mode locked (FDML) laser). Before clinical data acquisition, the systems were characterized using a three-dimensional point-spread function phantom. To distinguish tumor from healthy brain tissue later on, attenuation coefficients of each pixel in OCT depth profiles are calculated. First examples from a clinical study show that the pixel-resolved calculation of the attenuation coefficient provides a good image contrast and confirm that white matter shows a higher signal and more homogeneous signal structure than tumorous tissue.},
keywords = {Optical coherence tomography, OCT, FDML laser, MHz-OCT, glioblastoma, intraoperative imaging, brain
imaging},
   DOI= {10.1117/12.2526932},
   year = {2019},
   type = {Conference Paper}
}

@inproceedings{Bliedtner2019,
   author = {Bliedtner,K; Seifert, E and Brinkmann,R},
   title = {Dosimetry for microsecond selective laser trabeculoplasty},
   volume = {11079},
   DOI = {10.1117/12.2526987},
   year = {2019},
keywords = {Ophthalmology, ophthalmic optics and devices, selective laser trabeculoplasty, micro bubble detection},
booktitle =    {Proc. SPIE 11079, Medical Laser Applications
and Laser-Tissue Interactions IX},
   type = {Conference proceedings}
}

@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}

}

@inproceedings{Ahrens2019,
title = {An endomicroscopic OCT for clinical trials in the field of ENT (Invited)},
author = { Ahrens, M; Idel, C; Chaker, A; Wollenberg, B; K\"{o}nig, P; Schulz-Hildebrandt, H and H\"{u}ttmann, G},
url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11073/2527099/An-endomicroscopic-OCT-for-clinical-trials-in-the-field-of/10.1117/12.2527099.full},

isbn = {9781510628397},
year = {2019},
date = {2019-01-01},
booktitle = {Proc. SPIE 11073, Clinical and Preclinical Optical Diagnostics II},
number = {110730U},
pages = {1--4},
keywords = {Endoskope, meos, OCM},
pubstate = {published},
tppubtype = {inproceedings}
}

@inproceedings{Schulz-Hildebrandt2019,
author = {Schulz-Hildebrandt, Hinnerk and Meyer-Schell, Naja and Casper, Malte and Evers, Michael and Birngruber, Reginald and Manstein, Dieter and H{\"{u}}ttmann, Gereon},
booktitle = {Proc. SPIE 11073, Clinical and Preclinical Optical Diagnostics II},
doi = {10.1117/12.2527087},
isbn = {9781510628397},
number = {110730L},
pages = {1--3},
title = {{Monitoring temperature induced phase changes in subcutaneous fatty tissue using an astigmatism corrected dynamic needle probe}},
keywords = {OCT, Endoskope},
year = { 2019}
}

@inproceedings{Detrez2019,
   author = {Detrez, N;Miura, Y;Seifert, E;Theisen-Kunde, D and Brinkmann, R},
   title = {Heating and optoacoustic temperature determination of cell cultures},
   publisher = {SPIE},
   volume = {11079},
   series = {European Conferences on Biomedical Optics},
booktitle =    {Proc. SPIE 11079, Medical Laser Applications
and Laser-Tissue Interactions IX},
   url = {https://doi.org/10.1117/12.2527024},
keywords = {Laser, Noninvasive thermometry, hyperthermia, temperature measurement, photoacoustics}, optoacoustics,
   year = {2019},
   type = {Conference Proceeding}
}

@inproceedings{Wang2019-3,
   author = {Wang, Tianshi;Pfeiffer, Tom;Daemen, Joost;Mastik, Frits;Wieser, Wolfgang;van der Steen, AFW;Huber, Robert and van Soest, Gijs},
   title = {Megahertz intravascular Doppler optical coherence tomography enables simultaneous morphological and flow pattern imaging},
   booktitle = {Diagnostic and Therapeutic Applications of Light in Cardiology 2019},
   publisher = {International Society for Optics and Photonics},
   volume = {10855},
   pages = {1085503},
   type = {Conference Proceedings}
}

@inproceedings{Wang2019-1,
   author = {Wang, Tianshi;Pfeiffer, Tom;Wieser, Wolfgang;van Beusekom, Heleen;Draxinger, Wolfgang;van der Steen, Antonius FW;Huber, Robert and van Soest, Gijs},
   title = {Thermo-elastic optical coherence tomography},
   booktitle = {Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XXIII},
   publisher = {International Society for Optics and Photonics},
   volume = {10867},
   pages = {108672C},
   type = {Conference Proceedings}
}

@inproceedings{Vogel2018,
   author = {Uzunbajakava, N E; Varghese, B; Botchkareva, N V; Verhagen, R and Vogel, A},
   title = {Highlighting the nuances behind interaction of picosecond pulses with human skin: Relating distinct laser-tissue interactions to their potential in cutaneous interventions},
   booktitle = {Progress in Biomedical Optics and Imaging - Proceedings of SPIE},
   volume = {10492} ,
   DOI = {10.1117/12.2307804},
   year = {2018},
date = {2018-20-02},
   type = {Conference Proceedings},
year = { 2018}
}

@inproceedings{Hakert2019,
   author = {Hakert, Hubertus;Eibl, Matthias;Karpf, Sebastian;Wollenberg, Barbara;Pries, Ralph and Huber, Robert},
   title = {Label-free imaging of tumorous tissue in the Raman fingerprint region with time-encoded (TICO) stimulated Raman scattering (Conference Presentation)},
   booktitle = {Multiphoton Microscopy in the Biomedical Sciences XIX},
   publisher = {International Society for Optics and Photonics},
   volume = {10882},
   pages = {108821R},
   type = {Conference Proceedings}
}

@inproceedings{Smits2018,
title = {Development and Experimental Validation of a Combined FBG Force and OCT Distance Sensing Needle for Robot-Assisted Retinal Vein Cannulation},
author = {Smits, J; Ourak, M; Gijbels, A;  Esteveny, L; Borghesan, G; Schoevaerdts, L; Willekens; Stalmans, P; Lankenau, E; Schulz-Hildebrandt, H; H\"{u}ttmann, G; Reynaerts, D and  Vander Poorten, E.B},

doi = {10.1109/ICRA.2018.8460983},
year = {2018},
date = {2018-09-20},
journal = {2018 IEEE Intern Conf Robot a Automation (ICRA)},
pages = {129-134},
abstract = {Retinal Vein Occlusion is a common retinal vascular disorder which can cause severe loss of vision. Retinal vein cannulation followed by injection of an anti-coagulant into the affected vein is a promising treatment. However, given the scale and fragility of the surgical workfield, this procedure is considered too high-risk to perform manually. A first successful robot-assisted procedure has been demonstrated. Even though successful, the procedure remains extremely challenging. This paper aims at providing a solution for the limited perception of instrument-tissue interaction forces as well as depth estimation during retinal vein cannulation. The development of a novel combined force and distance sensing cannulation needle relying on Fiber Bragg grating (FBG) and Optical Coherence Tomography (OCT) A-scan technology is reported. The design, the manufacturing process, the calibration method, and the experimental characterization of the produced sensor are discussed. 
The functionality of the combined sensing modalities and the real-time distance estimation algorithm are validated respectively on in-vitro and ex-vivo models.},
keywords = {Endoskope},
pubstate = {published},
tppubtype = {inproceedings}
}

@inproceedings{Cecchetti2019,
   author = {Cecchetti, Leonardo;Wang, Tianshi;Pfeiffer, Tom;Wieser, Wolfgang;van der Steen, Antonius FW;Huber, Robert;van Soest, Gijs and Huber, Robert Alexander},
   title = {Heartbeat optical coherence tomography enables accurate in vivo stents imaging: a quantitative image processing study (Conference Presentation)},
   booktitle = {Diagnostic and Therapeutic Applications of Light in Cardiology 2019},
   publisher = {International Society for Optics and Photonics},
   volume = {10855},
   pages = {1085506},
   type = {Conference Proceedings}
}

@inproceedings{Schulz-Hildebrandt2018a,
title = {Coherence and diffraction limited resolution in microscopic OCT by a unified approach for the correction of dispersion and aberrations},
author = {Schulz-Hildebrandt,H; M\"{u}nter, M; Ahrens,M; Spahr, H; Hillmann, D; K\"{o}nig, P and  H\"{u}ttmann, G},
doi = {10.1117/12.2303755},
isbn = {9781510616745},
year = {2018},
date = {2018-03-05},
booktitle = {2nd Canterbury Conference on OCT with Emphasis on Broadband Optical Sources},
volume = {10591},
pages = {105910O},
abstract = {Optical coherence tomography (OCT) images scattering tissues with 5 to 15 μm resolution. This is usually not sufficient for a distinction of cellular and subcellular structures. Increasing axial and lateral resolution and compensation of artifacts caused by dispersion and aberrations is required to achieve cellular and subcellular resolution. This includes defocus which limit the usable depth of field at high lateral resolution. OCT gives access the phase of the scattered light and hence correction of dispersion and aberrations is possible by numerical algorithms. Here we present a unified dispersion/aberration correction which is based on a polynomial parameterization of the phase error and an optimization of the image quality using Shannon’s entropy. For validation, a supercontinuum light sources and a costume-made spectrometer with 400 nm bandwidth were combined with a high NA microscope objective in a setup for tissue and small animal imaging. Using this setup and computation corrections, volumetric imaging at 1.5 μm resolution is possible. Cellular and near cellular resolution is demonstrated in porcine cornea and the drosophila larva, when computational correction of dispersion and aberrations is used. Due to the excellent correction of the used microscope objective, defocus was the main contribution to the aberrations. In addition, higher aberrations caused by the sample itself were successfully corrected. Dispersion and aberrations are closely related artifacts in microscopic OCT imaging. Hence they can be corrected in the same way by optimization of the image quality. This way microscopic resolution is easily achieved in OCT imaging of static biological tissues.},
keywords = {OCM},
pubstate = {published},
tppubtype = {inproceedings}
}

@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{10.1117/12.2286854,
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{10.1117/12.2287484,
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}
}

@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}
}

@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}
}