Conventional diagnosis of laryngeal cancer is normally made by a combination of endoscopic examination, a subsequent biopsy, and histopathology, but this requires several days and unnecessary biopsies can increase pathologist workload. Nonlinear imaging implemented through endoscopy can shorten this diagnosis time, and localize the margin of the cancerous area with high resolution. Develop a rigid endomicroscope for the head and neck region, aiming for in-vivo multimodal imaging with a large field of view (FOV) and tissue ablation. Three nonlinear imaging modalities, which are coherent anti-Stokes Raman scattering, two-photon excitation fluorescence, and second harmonic generation, as well as the single photon fluorescence of indocyanine green, are applied for multimodal endomicroscopic imaging. High-energy femtosecond laser pulses are transmitted for tissue ablation. This endomicroscopic system consists of two major parts, one is the rigid endomicroscopic tube 250mm in length and 6mm in diameter, and the other is the scan-head ( in size) for quasi-static scanning imaging. The final multimodal image accomplishes a maximum FOV up to , and a resolution of is achieved over FOV. The optics can easily guide sub-picosecond pulses for ablation. The system exhibits large potential for helping real-time tissue diagnosis in surgery, by providing histological tissue information with a large FOV and high resolution, label-free. By guiding high-energy fs laser pulses, the system is even able to remove suspicious tissue areas, as has been shown for thin tissue sections in this study.

Here, we present a new handheld multiphoton endomicroscopic system designed for tumor diagnosis in the head and neck region. It consists of an approximate 25-cm-long rigid endomicroscopic probe with two variants (0° and 45° bended tip), connected to a handheld scan-head. The system can achieve a field of view ⪆600 µm for Coherent Anti-stokes Raman Scattering (CARS) and other nonlinear imaging modalities by a non-de-scanned detection and using a de-scanned confocal imaging channel to detect light from tissue labeled with Indocyanine Green (ICG). Furthermore, high-power femtosecond laser pulses can be transmitted through the system for precise tissue ablation which was considered in the optical design of the probe.

We present our progress on developing an innovative compact thulium-based fiber CPA emitting at 2 µm central wavelength. The laser parameters comprise >100 µJ pulse energy at an average power of >30W. The system comes in an industrial-grade platform optimized for long-term operation and its optimized packaging is well suited for the integration in laser machines for materials processing. The laser parameters are ideally suited for processing semiconductors, e.g. silicon by microwelding or cutting of filaments.

Ultrafast fiber laser sources emitting fs-pulses around 2 μm have many applications in medicine, metrology and sensing as well as in various frequency-conversion techniques. Thulium-doped fiber amplifiers are a promising platform for power scalable ultrafast amplification in this wavelength region. Usually, these ultrafast, high-power fiber laser systems were pumped at a wavelength around 790 nm and obtain slope efficiencies in the range of 50 % in the 100 W-class. Due to the high quantum defect obtained with this pump technique and the related high heat loads, considerable thermal challenges still must be overcome when scaling the power further. In this contribution we present a concept on highly efficient, high-power thulium-doped fiber amplifiers pumped at 1692 nm. This pump concept is suitable for high-power, high-energy, ultrafast Tm-doped fiber laser systems. In this proof of principle demonstration, we achieve a slope efficiency of 80% in a standard commercially available, thulium-doped photonic crystal fiber (PCF) with ~60 W of average power when pumping at 1692 nm compared to 47 % slope efficiency by pumping at 793 nm. In the simulation we investigated the heat load and core temperature evaluation along the fiber. These findings demonstrate an improvement in the amplification efficiency of large-mode area fiber amplifiers which are suitable for ultrafast operation on Yb-like efficiencies. The reduced heat load paves the way to even higher average powers from ultrafast Tm-doped fiber lasers with the potential to provide multi-mJ energy fs-pulses at kW-level average power from a single amplifier channel.

We investigate the influence of the pump wavelength on the high-power amplification of large-mode area, thulium-doped fibers which are suitable for an ultrashort pulsed operation in the 2 µm wavelength region. By pumping a standard, commercially available photonic crystal fiber in an amplifier configuration at 1692 nm, a slope efficiency of 80 % at an average output power of 60 W could be shown. With the help of simulations we investigate the effect of cross-relaxations on the efficiency and the thermal behavior. We extend our investigations to a rod-type, large-pitch fiber with very large mode area, which is exceptionally suited for high-energy ultrafast operation. Pumping at 1692 nm leads to a slope efficiency of 74 % with a average output power of 67 W, instead of the 38 % slope efficiency obtained when pumping at 793 nm. These results pave the way to highly efficient 2 µm fiber-based CPA systems.

Herein, the complex pseudodielectric function of Ge and Si from femtosecond pump–probe spectroscopic ellipsometry with 267, 400, and 800 nm pump–pulse wavelengths is analyzed by fitting analytical lineshapes to the second derivatives of the pseudodielectric function with respect to energy. This yields the critical point parameters (threshold energy, lifetime broadening, amplitude, and excitonic phase angle) of and in Ge and in Si as functions of delay time. Coherent longitudinal acoustic phonon oscillations with a period of about 11 ps are observed in the transient critical point parameters of Ge. From the amplitude of these oscillations, the laser‐induced strain is found to be on the order of 0.03% for Ge measured with the 800 nm pump pulse, which is in reasonable agreement with the strain calculated from theory.

Abstract Electric-field oscillations are now experimentally accessible in the THz-to-PHz frequency range1–11. Their measurement delivers the most comprehensive information content attainable by optical spectroscopy – if performed with high sensitivity. Yet, the trade-off between bandwidth and efficiency associated with the nonlinear mixing necessary for field sampling has so far strongly restricted sensitivity in applications such as field-resolved spectroscopy of molecular vibrations12,13. Here, we demonstrate electric-field sampling of octave-spanning mid-infrared waves in the 18-to-39 THz (600-to-1300 cm-1) spectral region, with amplitudes ranging from the MV/cm level down to a few mV/cm. Employing powerful short-wave mid-infrared gate pulses14,15, the field-measurement sensitivity approaches within a factor of 4 the ultimate detection limit of capturing all photons in the temporal gate. This combination of detection sensitivity and dynamic range enables optimum use of newly-emerging high-power waveform-controlled infrared sources12,14,16–22 for molecular spectroscopy. In a proof-of concept experiment, we performed broadband quantitative linear spectroscopy of multiple gases over more than 8 orders of magnitude in concentration, at an interaction length of only 45 cm. Our technique brings fast, label-free, quantitative multivariate detection of volatile organic compounds over the entire known physiologically-relevant molecular landscape23,24 within reach.