All solid-state Cr:LiSAF laser

Many kinds of experiments about all solid-state Cr:LiSAF lasers have been reported. A tunable all solid-state cw laser having tunability over more than 100 nm was developed by using the spectrum selection self-injection locking (SSSIL) method in 1992. The authors realize tunable picosecond radiation from an all solid-state laser with 146-200 ps pulses in an 88 nm range. Also, 70 fs pulse generation was achieved using a Kerr-lens mode-locking pumped with an Ar⁺ laser     

Two-photon fluorescence microscopy with a diode-pumped Cr:LiSAF laser

We demonstrate the acquisition of high-quality two-photon fluorescence microscopy images using an all-solid-state self-mode-locked Cr:LiSAF laser. We contrast the performance of the two-photon technique with single-photon confocal fluorescence microscopy images taken with an argon-ion laser. Examples of improved depth penetration and reduced dye bleaching are presented.     

Unstable Cr:LiSAF laser resonator with a variable reflectivity output coupler

The performance of a flash-lamp-pumped Cr:LiSAF unstable laser resonator utilizing a fourth-order super-Gaussian variable reflectivity mirror as an output coupler is described. The super-Gaussian mirror results in a smooth, flattop transverse beam profile in the near field that is advantageous for nonlinear frequency-conversion applications. Long-pulse and Q-switched operation of the Cr:LiSAF unstable laser resonator are described and compared with stable resonator operation. We obtained tunable ultraviolet radiation extending from 267 to 290 nm by frequency mixing theQ-switched Cr:LiSAF laser output with lithium triborate and beta-barium borate nonlinear crystals.     

Multiwavelength output from a Nd:YAG /Cr:LiSAF hybrid laser

A prototype solid-state, multispectral hybrid laser has been designed and tested. The laser provides simultaneous outputs at several wavelengths. The hybrid-laser concept is based on the efficient use of flash-lamp-pump energy distributed between two complementary lasing materials, Nd:YAG and Cr:LiSAF, that share the same pump cavity. The prototype Q-switched hybrid laser provides dual-fundamental-wavelength output at 850 and 1064 nm as well as frequency-doubled output at 532 nm. The laser achieved 3.6% slope efficiency (combined) in free-running operation and 2.4% when Q switched. Higher efficiencies can be obtained with improvements in laser crystal quality and pump cavity configuration.     

氟化物激光晶体Cr:LiSAF的坩埚下降法生长

报道了氟化物激光晶体CrLiSAF的坩埚下降法生长工艺.采用经氟化处理的无水氟化物原料,按照LiFSrF2(AlF3+CrF3)=111的摩尔比配料,控制炉体温度于900～940℃,晶体生长速度为0.4～0.8mm/h,通过密闭条件下的坩埚下降法生长出大尺寸(φ25mm×85mm)的优质完整的CrLiSAF单晶.     

Tunable diode-pumped and frequency-doubled Cr:LiSAF lasers

The performance of a diode-pumped Cr:LiSAF laser and its intracavity frequency-doubled operation is reported. Close to 1 W of quasi-cw power at 870 nm was obtained in multimode operation. Power in excess of 20-mW cw of TEM(00) second-harmonic power at 435 nm has also been obtained by using a lithium triborate crystal with an infrared-to-visible conversion efficiency of 33%. This result is believed to be the highest yet reported for a true cw blue output from a diode-pumped Cr:LiSAF system. However, the maximum attainable output power was limited by thermal fluorescence quenching. The effect of the pump size on the temperature rise and on the small-signal gain is investigated.     

Ultrafast semiconductor laser-diode-seeded Cr:LiSAF regenerative amplifier system

An ultrafast, hybrid mode-locked semiconductor laser-diode system has been used to seed a flash-lamp-pumped Cr:LiSAF regenerative amplifier system, producing subpicosecond pulses with millijoule output pulse energy. This system has the potential to eliminate argon-ion-pumped-based, ultrafast laser systems.     

Diagonal scan measurement of Cr:LiSAF 20 ps ablation threshold

We report the measurement of the 20 ps ablation threshold of pure and Cr(3+) doped LiSAF samples using a simple method that employs a single scan of the sample across a focused laser beam waist. During the scan, a profile is etched in the sample surface, and the measurement of the maximum transversal size of the profile and the pulse peak power determine the ablation threshold, without any further knowledge of the beam geometry. Also, it was possible to measure the depth of the ablation profile, to calculate its effective volume, and to identify that the maximum material removal rate per pulse does not occur at the beam waist, which is not intuitively expected.     

CFD simulation of a miniature coaxial Stirling-type pulse tube cryocooler operating at 128 Hz

A two-dimensional axis-symmetric CFD model of a miniature coaxial Stirling-type pulse tube cryocooler with an overall weight of 920 g operating at 128 Hz is established, and systematic simulations of the performance characteristics at different temperatures are conducted. Both thermal equilibrium and non-equilibrium mechanisms for the porous matrix are considered, and the regenerator losses including the gas and solid conduction, the pressure drop and the imperfect interfacial heat transfer are calculated, respectively. The results indicate that the pressure drop loss is dominant during the first 85% and 78% of regenerator length for the thermal equilibrium and non-equilibrium models, respectively, and it decreases monotonously from warm to cold end due to the steadily decreasing Darcy and Forchheimer terms, whereas other entropy generations share similar changing tendencies, going up gradually near the warm end, increasing dramatically from about 60% of length and then decreasing sharply near the cold end. The reasons for these entropy variations are discussed.     

300 Hz脉冲管制冷机特性研究

从实验和数值计算两个方面研究了1台工作频率为300 Hz的单级脉冲管制冷机的制冷特性.实验方面,验证了平均压力、入口压比、惯性管长度以及均流化元件对其制冷性能的影响,该制冷机在平均压力为3.96 MPa、入口压比为1.21时获得了79.6 K的最低制冷温度;数值计算方面,基于线性热声理论的模拟结果与实验结果进行了比较,以验证程序的有效性.     

Multifrequency erbium-doped fiber laser operating at room temperature

A method to realize room-temperature operation of a multifrequency Er-doped fiber laser with low-frequency shift feedback placed within a linear laser cavity is theoretically proposed and experimentally demonstrated. Simultaneous multiwavelength lasing with 0.5 nm wavelength spacing is experimentally demonstrated by applying a sinusoidal signal of 10 kHz to a fiber phase modulator inserted within the linear cavity to prevent single wavelength steady-state oscillation. In the linear cavity, an all-polarization-maintaining fiber Sagnac loop is used as a periodic filter, and a single-mode fiber loop with a polarization controller is used as a partial reflector and also as an output port.     

Carburation of an Ni70Cr30 substrate by laser solid-state diffusion

Laser surface treatments provide interesting solutions to the problem of accelerated wear of materials. Some results are presented for chromium carbide-rich surface alloys after laser-beam solid-state treatment of an Ni₇₀Cr₃₀ carbon-precoated substrate. The wear results are satisfactory with respect to pure Ni₇₀Cr₃₀ substrate, but are below those obtained by superficial melting of a graphitized Ni₇₀Cr₃₀ substrate.     

Quasi-flat-top frequency-doubled Nd:glass laser for pumping of high-power Ti:sapphire amplifiers at a 0.1 Hz repetition rate

A Nd:glass laser based on a novel design delivers up to 120 J energy pulses with a quasi-flat-top spatial profile at a 0.1 Hz repetition rate. The laser output is frequency-doubled with 50% efficiency and used to pump Ti:sapphire amplifiers. The developed design is perspective for use in the currently contemplated next step in ultra-high-intensity laser development.     

Development of a compact efficient 10 Hz 20 TW Ti:sapphire laser system with a 1 kHz regenerative amplifier

We have constructed a compact efficient Ti:sapphire laser system that generates 30 fs, 630 mJ pulses at a repetition rate of 10 Hz. A new geometry for a single-stage multipass power amplifier is proposed that greatly weakens and even makes use of thermal lensing. Such geometry can realize high output in a single-stage power amplifier; otherwise at least two-stage power amplifiers are required. The new configuration simplifies the laser system and reduces the cost. The key point in this design is that the beam spot size evolution is considered in combination with the pulse amplification.     

Continuous-wave laser performance of Nd:LuVO4 crystal operating at 1.34 microm

A laser-diode-array end-pumped Nd:LuVO4 crystal continuous-wave (cw) laser operating at 1.34 microm has been demonstrated. The maximum cw output power of 1.85 W was obtained at the incident pump power of 17 W for a c-cut 0.5 at. % Nd-doped LuVO4 crystal sample, giving the corresponding optical conversion efficiency of 10.88% and a slope efficiency of 13.5%. Laser experiments of Nd3+ concentration of 0.5 and 0.9 at. % a-cut crystal LuVO4 samples were also investigated; due to the strong excited-state absorption of Nd:LuVO4 at 1.34 microm, the output power was limited.     

A semiconductor whispering-gallery-mode laser with ring cavity operating at room temperature

Whispering gallery mode (WGM) semiconductor lasers with ring and disk cavities (outside diameters 300, 200, and 100 μm) operating in a pulsed regime at room temperature on a λ = 2.4 μm wavelength have been created. A comparative study of the spectral and threshold characteristics of these lasers showed that ring lasers operate, like those with the disk cavities, on WGMs. The level of spontaneous emission in the ring lasers is lower by almost an order of magnitude than that in the disk lasers, which is due to the absence of recombination in the central part of the cavity. The threshold current density in ring lasers is slightly greater than that in the disk lasers, which is related to an increase in the current density at the edges of both cavities and to the appearance of surface leak currents on the inner surface of the ring-shaped cavity.     

A high-performance CO2 laser heterodyne detector operating at 250 K

Abstract

The design, construction and assessment of a CO₂ laser heterodyne receiver based on a Hg_1-x Cd _x Te heterostructure is described. The structure has been designed to minimize the leakage currents at high temperatures while maintaining a high quantum efficiency. Measurements show that over 4dB of shot noise can be obtained with the application of less than 1 mW of laser power. This result can be combined with the measured low-frequency quantum efficiency of 42% to give a noise equivalent power of 7.2 × 10^?20 WHz^?1. The device is mounted on a single-stage thermoelectric cooler and coupled to an amplifier. It is hoped that the availability of high-performance detectors which do not need to be cooled to cryogenic temperatures will greatly improve the attractiveness of laser heterodyne systems.