Thermal effects are typically considered as obstacles to high-repetition-rate stimulated Brillouin scattering (SBS) pulse compression. In this paper, a novel method is proposed for improving the SBS output characteristics by exploiting thermal effects on the liquid medium. Using HT270, the SBS output parameters with the medium purification and rotating off-centered lens methods are studied at different repetition rates. The results indicate that these two methods can alleviate thermal effects and improve the energy efficiency, but the rotating method reduces the energy stability because of the aggravated optical breakdown at the kilohertz-level repetition rate. For a 35-mJ pump energy, the energy efficiency at 2 kHz without the rotating method is 30% higher than that at 100 Hz and 70% higher than that at 500 Hz. The enhancement of the SBS output characteristics by thermal effects is demonstrated theoretically and experimentally, and 2-kHz high-power SBS pulse compression is achieved with HT270.

In this paper, we propose an effective method to compensate for the performance degradation of optically addressed spatial light modulators (OASLMs). The thermal deposition problem usually leads to the on-off ratio reduction of amplitude OASLM, so it is difficult to achieve better results in high-power laser systems. Through the analysis of the laser-induced temperature rise model and the liquid crystal layer voltage model, it is found that reducing the driving voltage of the liquid crystal light valve and increasing the driving current of the optical writing module can compensate for the decrease of on–off ratio caused by temperature rise. This is the result of effectively utilizing the photoconductive effect of Bi12SiO20 (BSO) crystal. The experimental results verify the feasibility of the proposed method and increase the laser withstand power of amplitude-only OASLM by about a factor of 2.5.

Stimulated Raman-scattering-based lasers provide an effective way to achieve wavelength conversion. However, thermally induced beam degradation is a notorious obstacle to power scaling and it also limits the applicable range where high output beam quality is needed. Considerable research efforts have been devoted to developing Raman materials, with diamond being a promising candidate to acquire wavelength-versatile, high-power, and high-quality output beam owing to its excellent thermal properties, high Raman gain coefficient, and wide transmission range. The diamond Raman resonator is usually designed as an external-cavity pumped structure, which can easily eliminate the negative thermal effects of intracavity laser crystals. Diamond Raman converters also provide an approach to improve the beam quality owing to the Raman cleanup effect. This review outlines the research status of diamond Raman lasers, including beam quality optimization, Raman conversion, thermal effects, and prospects for future development directions.

We present a 2 μm Tm:YAG disk laser multi-pass pumped by a 1 μm laser. The transitions in competition of up conversion (UC) and excited state absorption (ESA) are analyzed in detail based on a numerical model that considers stimulated emission, fluorescence, non-radiative decay, UC, andESA, showing good agreement with experiments. The proportions and fractional thermal loads of all transitions are derived quantitatively. The results show that UC and ESA are critical in Tm:YAG disk lasers, resulting in a decrease in the absorbed pump power and temperature after lasing for two different disk thicknesses. In addition, although the absorbed pump power of the 0.5 mm disk is lower than in the 1 mm case, its relatively weak UC and ESA and low total fractional thermal load can improve laser performance. A 0.5 mm Tm:YAG disk laser thus delivered the maximum output power of1.05 W with beam quality of Mx2 = 2.02 and My2 = 2.03.

Raman spectrometry has been established as an instrument of choice for studying the structure and bond type of known molecules, and identifying the composition of unknown substances, whether geological or biological. This versatility has led to its strong consideration for planetary exploration. In the context of the ExoGeoLab and ExoHab pilot projects of ESA-ESTEC & ILEWG (International Lunar Exploration Working Group), we investigated samples of astrobiological interest using a portable Raman spectrometer lasing at 785 nm and discuss implications for planetary exploration. We find that biological samples are typically best observed at wavenumbers >1100 cm−1, but their Raman signals are often affected by fluorescence effects, which lowers their signal-to-noise ratio. Raman signals of minerals are typically found at wavenumbers <1100 cm−1, and tend to be less affected by fluorescence. While higher power and/or longer signal integration time improve Raman signals, such power settings are detrimental to biological samples due to sample thermal degradation. Care must be taken in selecting the laser wavelength, power level and integration time for unknown samples, particularly if Raman signatures of biological components are anticipated. We include in the Appendices tables of Raman signatures for astrobiologically relevant organic compounds and minerals.

L'influence des effets thermiques et des déformations mécaniques sur les performances des butées hydrodynamiques à géométrie fixe est analysée. Les études menées sur les butées hydrodynamiques à géométrie fixe allient rarement les effets thermiques et les déformations. Après un bref rappel théorique de la lubrification thermohydrodynamique (THD), nous décrivons les méthodes de calculs des déformations mécaniques. L'étude thermoélastohydrodynamique (TEHD), qui prend en compte les effets thermiques locaux et les déformations mécaniques, est réalisée sur une butée hydrodynamique à géométrie fixe à huit patins. Les champs de pression hydrodynamique et de température sont obtenus par une méthode des différences finies et le champ des déplacements de la surface des patins est obtenu à l'aide de la méthode des éléments-finis. Les déformations mécaniques du grain mobile sont également prises en compte pour résoudre le problème TEHD. L'influence des conditions de fonctionnement (charge appliquée et vitesse de rotation) sur les différentes caractéristiques de la butée est également analysée. Il ressort que pour déterminer précisément les caractéristiques de fonctionnement d'une butée hydrodynamique à patins fixes, il ne faut pas négliger les déformations mécaniques du collet et en particulier, lorsque la charge appliquée est élevée.