KEYWORDS: Diodes, Semiconductor lasers, Cryogenics, Oscillators, Optical amplifiers, Crystals, Laser crystals, Laser systems engineering, Temperature metrology, High power lasers
We present our recent developments in high-power, high-efficiency cryogenic Yb:YAG laser systems. Specifically, we
will discuss our 2.3-kW master oscillator power amplifier (MOPA) which has shown optical wall-plug efficiencies
above 30-% (diode-driver input to optical output). This laser system has been operated for long run times with
continuous wave and pulsed output formats. The beam quality factor, M2, of the MOPA has been measured to be less
than 2 and it is currently limited by the master oscillator. We are working to improve the device's beam quality and
output power. In addition, we have demonstrated an all-cryogenic Yb:YAG laser that produced 29 W of optical power.
Use of cryogenic diode laser pumps represents our next step towards achieving greater than 50% efficient high-power
laser systems.
Water vapor is one of the most significant constituents of the atmosphere because of its role in cloud formation, precipitation, and interactions with electromagnetic radiation, especially its absorption of longwave infrared radiation. Some details of the role of water vapor and related feedback mechanisms in the Earth system need to be characterized better if local weather, global climate, and the water cycle are to be understood. A Differential Absorption LIDAR (DIAL) with a compact laser diode source may be able to provide boundary-layer water vapor profiles with improved vertical resolution relative to passive remote sensors. While the tradeoff with small DIAL systems is lower vertical resolution relative to large LIDARs, the advantage is that DIAL systems can be built much smaller and more robust at less cost, and consequently are the more ideal choice for creating a multi-point array or satellite-borne system. This paper highlights the progress made at Montana State University towards a water vapor DIAL using a widely tunable amplified external cavity diode laser (ECDL) transmitter. The ECDL is configured in a Littman-Metcalf configuration and was built at Montana State University. It has a continuous wave (cw) output power of 20 mW, a center wavelength of 832 nm, a coarse tuning range of 17 nm, and a continuous tuning range greater than 20 GHz. The ECDL is used to injection seed a tapered amplifier with a cw output power of 500 mW. The spectral characteristics of the ECDL are transferred to the output of the tapered amplifier. The rest of the LIDAR uses commercially available telescopes, filter optics, and detectors. Initial cw and pulsed absorption measurements are presented.
Since the photorefractive effect was first discovered in 1966, and then photorefractive materials were used in many aspects, such as dynamic holography and optical phase conjugation, the band transport model has become the general explanation for such photorefraction. In this model, diffusion mechanism acts as a main role and in some cases drift mechanism (under applied field) as well as the photovoltaic effect (under uniform illumination) were added. However, experiments and theoretical analysis have shown that the photovoltaic effect should always be considered; in the case of ferroelectrics, e.g., LiNbO3, this effect often exceeds the diffusion and thus dominates. In addition, the circular photovoltaic effect, if it exists, is able to create a phase shift grating. Therefore, theoretically, energy can be transferred between two beams through two-wave mixing.
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