High-power difference-frequency generation at 5-11 µm in AgGaS2

Efficient generation of high peak power and high average power difference-frequency radiation, continuously tunable over the range of5-11 mum, has been achieved by mixing the Nd:YAG laser radiation with the output of an infrared dye laser pumped by the same Nd: YAG laser in AgGaS2. Peak pulse powers as high as 180 kW with an average power output of 14 mW were obtained around 6 μm.     

High-power difference-frequency generation at 4.4-5.7 µm in LiIO3

Efficient generation of high-power difference-frequency radiation, continuously tunable over the range of4.4-5.7 mum, has been achieved by mixing the Nd :YAG laser and Nd :YAG pumped infrared dye-laser outputs in LiIO3. Peak pulse powers as high as 550 kW with an average power output of 45 mW were obtained around 4.9μm.     

Generation of infrared radiation by Raman scattering and difference frequency mixing with a Nd:YAG pump

A repetitivelyQ-switched Nd:YAG laser was used to produce "eye-safe" radiation near 1.55 μm by stimulated Raman scattering in acetonitrile and in methane with photon conversion efficiencies of 14 percent and 22 percent, respectively. The laser and Stokes beams were mixed in lithium niobate to obtain 6-kW peak power pulses at the difference frequency near 3.4 μm with a photon conversion efficiency of 1.1 percent.     

Single-diode end-pumped Nd:YAG laser

Experimental results on the first miniature Nd:YAG laser end-pumped by a single incoherent infrared-emitting diode are given. Laser operation was verified by measurements of relaxation oscillations, angular divergence, wavelength, and nonlinear output. In order to emit in the 0.81- μm pump band of Nd:YAG, the GaAs1-xPxdiode required cooling to 88 K (-185°C). Cooling the diode increased its efficiency while cooling the rod decreased the pump power necessary to reach threshold. With both laser mirrors highly reflecting at 1.06 μm, the maximum pulse powerP_{D}^{th}emitted by the diode at threshold was 6.2 ± 1.2 mW. The diode power required for laser threshold at room temperature was derived and compared with more recent experiments. Miniature size and long-lived solid-state components make this laser attractive for further development.     

Widely and continuously tunable optical parametric generator based on MgO-doped periodically poled LiNbO3 crystal

Pulsed optical parametric generators(OPGs)and op-tical parametric oscillators(OPOs)have beenextensive-ly studied and developedfor generatingtunable coherentsources[1-5]that cover the wide spectral range fromthenear UVto the mid IR.In this letter we report…     

Second-harmonic generation at 0.659 µ in CD*A

The efficient generation of the second-harmonic radiation of an Nd:YAG laser operating at 1.318 μ has been achieved in a deuterated cesium dihydrogen arsenate (CD*A) crystal. An overall peak power conversion efficiency of 40 percent was obtained for the experimental conditions described.     

Configuration of the optical transmission line using stimulated Raman scattering for signal light amplification

Expansion of a repeater spacing of optical transmission line is investigated using forward stimulated Raman scattering generated by a 1.34-μm Nd:YAG laser to amplify the signal light. Achievable repeater spacing at the 1.42-μm wavelength transmission is numerically estimated on the basis of coupled power equations and experimentally obtained Raman gain for various core-cladding index difference. A transmission distance of more than 200 km is predicted for an input signal light power of 100 μw and a pump power of 200 mW using a fiber with a relative index difference of 1 percent.     

2800～4100埃连续可调紫外激光器

报导了Nd:YAG脉冲激光器基波(1.06微米)与它的四次谐波泵浦的参量放大器输出(0.42～0.7微米连续可调)在KDP晶体中进行和频,产生0.3～0.41微米连续可调的紫外激光.以及Nd:YAG脉冲激光器的二次谐波(0.53微米)泵浦的若丹明6G染料激光在ADP晶体中倍频,产生0.28～0.3微米连续可调的紫外激光的实验结果.     

激光辐照对不同饵料微藻生长的影响

利用Nd:YAG激光(波长1.06μm,功率5W,照射时间0.5-3min)和Ar 激光(波长:488nm,功率70mw,照射时间5-20min)分别照射角毛藻和叉鞭金藻,辐照后进行细胞增殖和生长速率的测定。实验结果表明:照射剂量为1min的Nd:YAG激光及剂量为5min的Ar 激光对叉鞭金藻有较明显的促长效果,这两种激光处理组的细胞增殖量在辐照后的两天内较对照组分别高42.9%和48.1%,但这种促长效果随时间的推移逐渐消失。不同剂量的两种激光辐照角毛藻后,在延滞期均出现生长抑制现象,但进入指数生长期或传代培养后,剂量为1min的Nd:YAG激光及剂量为10min的Ar 激光对角毛藻有明显的促长效果,其中在指数生长期1min剂量的Nd:YAG激光处理可促长27.0%,传代培养后10min的Ar 激光处理组生长速率提高达51.2%。本文对不同激光及不同激光参数条件下,两种饵料藻的耐受性及生长特性的差异也进行分析探讨。本实验结果不仅证实了已有研究的推论,还展示出激光技术在饵料藻种选育中的应用前景。     

The stimulated Cerenkov interaction and its applications

Reviewed are the results of two experiments in which momentum modulation of a relativistic electron beam by laser fields using the stimulated Cerenkov interaction was measured, and coherent Cerenkov radiation from the optically bunched electron beam was observed. In the first experiment, light at 1.06 μm from a 30 MW Nd:YAG laser intersected 102 MeV electrons at an angle of 18 mrad in hydrogen gas, which was used as the phase-matching medium. The change in the electron-beam energy spectrum in the presence of the laser was measured, together with its functional dependence on the index of refraction of the phase-matching medium. In the second experiment, the same laser intersected 55.9 MeV electrons at an angle of 17 mrad, again in hydrogen gas. Coherent Cerenkov radiation at the second harmonic of the laser frequency (0.532 μm) was measured and indicated that the electrons were bunched on the order of the laser wavelength as a result of being velocity modulated by the laser. Applications of these results, such as development of optical klystrons and laser-driven particle accelerators, are considered. The characteristics of these devices and possible design configurations are discussed.     

Laser surgery: CO2or HF

Laser surgery may be improved by modifications based on similar processes in industrial applications. A major problem in materials processing is minimizing heat diffusion from the site of laser exposure. The same problem exists in the surgery of tissue with a CO2laser. A model based on vitreous surgery is described which indicates that radiation at 2.9 μm (HF laser) in short duration pulses, shorter than the thermal relaxation time (1.7 μs) of its 1μm thick absorption depth in water, will minimize thermal diffusion, and also take advantage of the large amount of heat removed by the phase change of water into steam. This model suggests that, for deep cuts, many pulses are preferable to a single long duration exposure, and that more delicate surgery may be possible with such short pulse, shallow absorption depth types of energy delivery. For coagulation (hemostasis control) as well as ablation, two simultaneous wavelengths are required: 2.9μm for cutting, and another with less absorption (such as Nd: YAG or argon lasers) for more penetration and heating of deeper layers and blood vessels. Among the secondary benefits of the use of the HF laser at 2.9μm is the ready availability of flexible optical fibers for a delivery system.     

Biomedical Utility of 1.34 ?m Nd: YAG Laser Radiation

Absorption of the 1.34 ?m Nd: YAG laser radiation in whole human blood and animal tissues is compared with 1.06, ?m Nd: YAG and argon laser radiation. Absorption coefficients are determined and the biomedical utility of the 1.34 ?m wavelength is evaluated.     

Clad Nd:YAG fibers for laser applications

We report the implementation of an extrusion method to clad Nd:YAG single crystal fibers with index-matched glasses (Deltan = 0.048). A propagation loss coefficient of 0.08 dB/cm was measured for the fundamental mode of a 41-μm-diameter glass-clad fiber laser, an improvement of about one order of magnitude over unclad fibers. Guided clad fiber lasers operated at 1.064 μm with thresholds as low as 0.3-0.5 mW and up to 65-mW CW output power are also reported. The origins of and means of reducing the residual loss are discussed.     

High-power red beam generation by frequency-doubling of a Nd:YAGlaser

This letter reports the generation of 6.1 W of red laser radiation by frequency-doubling a Nd:YAG laser operating at a wavelength of 1.319 μm with a KTP crystal. The conversion efficiency and the stability of the red output power were both improved through the suppression by means of a thin etalon of two-wavelength operation in the 1.3-μm region     

High-efficiency high-power UV generation at 2128 Å in urea

Urea has been found to be phase matchable for type-1 fifth-harmonic generation by mixing the Nd:YAG laser fundamental and fourth-harmonic radiation at room temperature. A peak power as high as 4.5 MW with an average power of 320 mW was obtained at 2128 Å in a 5 mm long crystal.     

Comparison of Nd 1.06 and 1.33 µm operation in various hosts

Performances of Nd in various hosts including Nd:YAG, Nd:YLF, Nd:BEL, and Nd:Cr:GSGG were characterized and compared for operation on the nominal 1.06 μm and 1.33 μm transitions. Comparison included continuous mode operation, normal mode operation,Q-switched operation, and gain measurements. Continuous lasing of Nd:Cr:GSGG under lamp pumping is reported for what may be the first time. Characterization included operation with different mirror reflectivities to obtain the internal losses, measurement of the upper laser level lifetime, measurement of the beam quality of the lasers operating under nominally similar circumstances, and measurement of the wavelength. These measurements should provide a comparison of the various Nd hosts under similar circumstances for a wide variety of operational modes and at both wavelengths of interest.     

Sensitivity measurement of a 10.6-µm parametric upconverter

The sensitivity of a parametric upconverter for the detection of 10.6-µm radiation was measured. 10.6-µm radiation was mixed with the 1.06 µm beam of an Nd :YAG laser in properly oriented single-crystal proustite. The upconverted output at 0.967 µm was then detected by an S-1 photomultiplier tube. NEP of 1.1×10^-9W . s^½was measured.     

Pulse chirping in a Nd:YAG laser

The 1.06-μm output of a loss-modulation mode-locked and frequency-doubled Nd:YAG laser was examined using a microwave avalanche photodiode with a rise time of ∼40 ps, and a scanning Fabry-Perot. The pulses were found to be transform limited only in the case where the 0.53-μm output of the laser was suppressed. When conversion efficiency was restored, the spectrum exhibited narrowing, but the pulses were much wider than the transform limit, indicating the presence of chirping.     

LED end-pumped Nd:YAG lasers

Experimental results are reported on the room-temperature operation of Nd:YAG lasers end pumped with an LED. The radiation from a 10-percent-efficient 0.46-mm-diam domed LED was coupled to the end of a 0.46-mm-diam × 5.0-mm-long laser rod with a large hemispherical reflector. At 20°C, a multimode laser power of 0.25 mW was obtained at an LED current of 250 mA. By measuring the variation of threshold pump power with rod temperature and the laser power versus pump power just above threshold, both the laser cavity loss and the output mirror transmission were determined. A round-trip cavity loss as low as 0.022 percent was measured. A calculation of the fractional pump power absorbed in the rod for the LED spectrum gave 56 percent for a 5-mm-long rod while measurements showed that 30 to 35 percent of the LED power was being absorbed indicating an LED-to-laser rod coupling efficiency of 54 to 63 percent for this arrangement. With such efficient absorption of pump power and low cavity loss, end-pumped Nd:YAG lasers with high slope efficiencies above threshold are possible.     

Improved germanium avalanche photodiodes

New kinds of germanium avalanche photodiodes with n+-n-p and p+-n structures were devised for improved excess noise and high quantum efficiency performance. Multiplication noise, quantum efficiency, and pulse response were studied and compared with those of the conventional n+-p structure diode. Multiplication noise of the new type of diodes were measured in the wavelength range between 0.63 and 1.52 μm. The effective ionization coefficient ratio of the p+-n diode was lower than unity at a wavelength longer than 1.1 μm and 0.6-0.7 at 1.52 μm, and that of the n+-n-p diode was 0.6-0.7 in the whole sensitive wavelength region. Response times were evaluated by using a mode-locked Nd:YAG laser beam and a frequency bandwidth wider than 1 GHz was estimated. Receiving optical power levels were compared with each other using parameters measured in this study.