Near- and mid-infrared laser radiation interaction with eye tissue

Comparison of the eye tissue transmission for laser radiations with the wavelengths 0.75, 1.08, 1.34, 1.44, 1.54, 1.66, 2.01, 2.69, and 2.94 μm was made with the aim to understand the possible tissue injury by the particular light. From the step by step transmission measurements of the various human eye tissues (in vitro) it was recognized that the value of the transmitted energy in particular segments is different for various wavelengths yielding substantial fluence differences on the retina and anterior segments, mainly.     

多光束泵浦中红外激光器

为了获得高功率高效率3 m～5 m中红外激光输出,利用双声光调Q晶体,通过高重复频率驱动调Q同步技术和LD侧面泵浦双棒串接技术,获得高功率高光束质量1.06 m激光双端输出,外置起偏器获得4束激光输出,利用波片偏振旋光原理,实现4束偏振态一致的激光输出,泵浦非线性晶体PPLT进行频率变换,实现高功率3 m～5 m中红外激光输出。在电源输入电流30 A、调Q驱动频率10 kHz的条件下,获得最高功率10.6 W的3.9 m中红外激光,1.06 m～3.9 m转化效率为9.5%。实验结果表明:通过双声光调Q技术和LD侧面泵浦双棒串接技术,可以实现4束高重复频率窄脉宽1.06 m偏振激光输出,泵浦PPLT可获得高功率3.9 m中红外激光输出。     

中红外固体激光器研究进展

本文介绍了中红外固体激光器中新型的Fe²⁺: ZnSe激光器和基于MgO: PPLN、ZnGeP₂晶体的光参量振荡器的发展现状,讨论了它们在发展过程中遇到的技术难题,探讨了中红外固体激光器的未来发展方向。波长为3~5 μm的中红外固体激光器具有效率高、体积小和重量轻等优点,在工业、医疗、军事等方面具有重要应用价值,研制大尺寸、高质量中红外激光晶体和输出波长更长的红外高功率激光泵浦源已成为中红外固体激光器未来发展方向之一。     

Electro-optic detection of continuous-wave mid-infrared radiation

We demonstrate coherent detection of continuous-wave mid-infrared radiation. This radiation is produced by use of conventional difference-frequency mixing and detected via the linear electro-optic effect. The detection process allows for the simultaneous measurement of the amplitude and phase properties of the infrared field. Both processes require an amplitude-modulated optical beam that is derived from the superimposed output of two single-frequency lasers. With appropriate choice of lasers and nonlinear optical crystals, the technique may be applied to any wavelength throughout the far and mid infrared.     

中红外高能激光探测单元

基于光电导探测原理,分析了影响室温光导型InSb探测器在中红外激光功率参数测量中的因素,得到了材料掺杂数密度、环境温度对探测器暗电阻、光谱响应率和光谱探测率的影响规律;开展了探测器在强激光辐照下的热效应理论模拟和实验研究,模拟分析了探测器在激光辐照下的动态响应特性。结果表明:针对测量系统中所使用的探测器,在激光功率密度小于4 W/cm2时,激光热效应对测量结果的影响可忽略;研制了相应的恒流源驱动电路,实现了中红外高能激光功率参数的探测。     

Fiber laser pumped burst-mode operated picosecond mid-infrared laser

We demonstrate a compact periodically poled MgO-doped lithium niobate(MgO:PPLN)-based optical parametric oscillator(OPO) quasi-synchronously pumped by a fiber laser system with burst-mode operation.The pump source is a peak-power-selectable pulse-multiplied picosecond Yb fiber laser.The chirped pulses from a figure of eight-cavity modelocked fiber laser seed are narrowed to a duration of less than 50 ps using an FBG reflector and a circulator.The narrowed pulses are directed to pass through a pulse multiplier and to form pulse bunches,each of which is composed of 13 subpulses.The obtained pulse bunches are amplified by two-stage fiber pre-amplifiers:one-stage is core-pumped and the other is cladding-pumped.A fiberized acousto-optic modulator is inserted to control the pulse repetition rate(PRR) of the pulse bunches before they are power-amplified in the final amplifier stage with a large mode area(LMA) PM Yb-doped fiber.The maximum average powers from the final amplifier are 85 W,60 W,and 45 W,respectively,corresponding to the PRR of2.72 MHz,1.36 MHz,and 0.68 MHz.The amplified pulses are directed to pump an MgO:PPLN-based optical parametric oscillator(OPO).A maximum peak power at 3.45 μm is obtained approximately to be 8.4 kW.Detailed performance characteristics are presented.     

High repetition rate mid-infrared laser source

An efficient, high-power mid-infrared laser source based on ZnGeP₂ (ZGP) optical parametric oscillator (OPO) is presented. Using a Q-switched Ho:YAG laser as the pump source a total output power of 10.6 W was obtained in the 3–5 μm band at 10 kHz and 8.5 W at 20 kHz. The Ho:YAG laser was pumped by two diode-pumped polarization coupled Tm:YLF lasers. Optical-to-optical efficiency achieved is >8.8% (laser-diode 792 nm to mid-IR 3–5 μm). With a commercial PtSi infrared camera (256×256 pixel focal plane array, 24 μm pitch) the pointing stability of Ho pump, signal and idler beam was measured to be better than 30 μrad. Whilst propagating the OPO beams over 100 m, little absorption for the idler beam was observed, resulting in a significant higher peak-to-peak value of ±22%, whereas the peak-to-peak stability of the signal pulses remained unchanged (±13%). To cite this article: M. Schellhorn et al., C. R. Physique 8 (2007).     

中波红外激光技术最新进展

3～5μm中红外波段激光源是近年来备受国内外关注的研究热点,本文综合评述了产生中红外波段激光的5种主要方法（CO2激光倍频技术、泛频CO激光技术、光学参量振荡器、氟化氘激光器、Fe2＋∶ZnSe固体激光技术）的国内外发展现状,总结分析了各种方法的关键技术和存在的问题,指出了该技术的未来发展趋势。     

Combining a DS-DBR laser with QPM-DFG for mid-infrared spectroscopy

Studies into the suitability of a novel, widely tunable telecom L-band (1563?C1613?nm) digital supermode distributed Bragg reflector (DS-DBR) laser for spectroscopy in the mid-IR are presented. Light from the DS-DBR laser was mixed with 1064?nm radiation in a periodically poled lithium niobate (PPLN) crystal to generate mid-IR light by quasi phase matching difference frequency generation (QPM-DFG). The resultant continuous wave radiation covered the range 3000?C3200?cm^?1 with powers of up to 2.6???W. The use of such laser light for spectroscopic applications was illustrated by performing absorption experiments on both narrow-band and broad-band absorbers, namely methane (CH₄) and methanethiol (CH₃SH). Wavelength modulation spectroscopy (WMS) on CH₄ demonstrated that the modulation characteristics of the DS-DBR laser observed in the near-IR were transposed to the mid-IR and yielded a sensitivity of 3.1×10^?6?cm^?1?Hz^?1/2 over a 47?cm path length. In the CH₃SH spectrum, the absorption feature at 3040?cm^?1 was identified as a potential useful region for monitoring this biomarker in exhaled breath at reduced pressures.     

Pulsed laser surface fragmentation and mid-infrared laser spectroscopy for remote detection of explosives

Stand-off technology for the remote detection of explosives and their traces on contaminated surfaces is a field of research that has recently gained much interest. Optical methods are well established in applications for counterterrorism because they facilitate analysis without contact between human being and hazardous materials. In this paper, to our knowledge for the first time, a remote stand-off detection system is developed by combination of pulsed laser fragmentation and pulsed mid-infrared laser absorption spectroscopy. Since the absorption of explosives is more efficient for infrared wavelengths laser radiation in the eye safe region around λ=1.47 μm rather than the conventional Nd:YAG laser line at λ=1.06 μm is preferred for the fragmentation. Generated product gases such as nitric oxide are probed by a synchronized distributed feedback quantum cascade laser (DFB-QCL) at λ≈5.3 μm. The ratio of NO and NO₂ is a measure to distinguish between energetic and non-energetic materials. PACS 42.62.Fi; 07.07.DF; 42.55.Px     

Dynamics of mid-infrared femtosecond laser resonant ablation

Resonant ablation is beneficial to avoiding uncontrollable subsurface damages in the laser ablation of polymers. In this paper the dynamics of mid-infrared laser resonant ablation of polylactic acid and toluene was calculated by using fluid dynamic equations. The merits and drawbacks of mid-infrared femtosecond laser resonant ablation of high molecular weight polymers have been discussed.     

Single-frequency mid-infrared optical parametric oscillator source for coherent laser radar

We report on the design and characterization of a highly coherent mid-IR source at 3.57mum based on a single-frequency optical parametric oscillator. Detailed frequency and amplitude noise spectra have been measured. The rms intensity noise from 1.2 to 1000 Hz was 0.03%, and a rms frequency drift of 8 kHz in 1 ms was observed. We have also demonstrated the utility of this source for coherent laser radar applications by measuring micro-Doppler spectra from vibrating targets.     

Imaging and correlation used for guided laser lithotripsy

High-speed imaging of phenomena akin to laser lithotripsy is performed. A new method for guiding laser light for the stone destruction is proposed. This is based on a combination of signals obtained from the correlation of fluorescent and ballistic images.     

Potentials and limits of mid-infrared laser spectroscopy for the detection of explosives

Optical methods are well-established for trace gas detection in many applications, such as industrial process control or environmental sensing. Consequently, they gain much interest in the discussion of sensing methods for counterterrorism, e.g., the detection of explosives. Explosives as well as their decomposition products possess strong absorption features in the mid-infrared (MIR) spectral region between λ=5 and 11 μm. In this report we present two different laser spectroscopic approaches based on quantum cascade lasers (QCLs) operating at wavelengths around λ=5 and 8 μm, respectively. Stand-off configuration for the remote detection of nitro-based explosives (e.g., trinitrotoluene, TNT) and a fiber coupled sensor device for the detection of triacetone triperoxide (TATP) are discussed. PACS  42.62.Fi; 07.07.Df     

Tunable mid-infrared,high-energy femtosecond laser source for glyco-protein structure analysis

We have developed a 6–12 μm mid-infrared (MIR) femtosecond laser source for glyco-protein structure analysis. The MIR femtosecond laser pulses are generated by a differential frequency generation (DFG) configuration with a combination of Ti:sapphire based regeneratively amplified femtosecond laser pulses (780 nm, 160 fs, 1 mJ) and a β-BaB₂O₄ (BBO) based optical parametric amplifier (OPA). The MIR pulse energy exceeds 4.5 μJ, where a glyco-protein molecule has resonant absorption lines due to the vibrational–rotational transitions. The pulse width is estimated to be less than 1 ps according to the cross correlation measurement between the two OPA output pulses. Using the MIR femtosecond laser pulses, we demonstrated photo-dissociation of the sialyl Lewis X (sLeX) proton added ion, which is the first time to the best of our knowledge. PACS 42.65.Re; 42.62.-b; 42.60.-b; 42.65.-k; 87.50     

Optically pumped mid-infrared laser action in the monohaloacetylenes

Strong optically pumped laser action excited by a TEA carbon dioxide laser has been obtained from monofluoro-acetylene in the 560–610 cm⁻¹ region with outputs of up to 25 mJ and superfluorescent operation readily achieved without optimisation. These result from excitation of a combination of the two bending modes v4+v5. Laser action was also obtained with 9 μm excitation of the v3 C---F stretch, on a difference band terminating in v4, with similar properties. Lasers of this type are rare. As well as being a potentially useful laser source in a region sparsely populated with good lasers, the results are of interest in the context of on going investigations of the spectroscopy of HCCF. Most, but not all lines are assigned. Very weak, erratic laser action was observed from chloro- and bromo-acetylene.     

中红外超快光纤激光器研究进展

中红外波段覆盖重要的分子吸收区与多个大气透射窗口,该波段的超快激光器在多个领域具有广泛应用。基于光纤的中红外超快激光器近年来在激光发射与传输、超快脉冲产生与应用等方面发展迅速,为中红外波段超快激光开辟了新的研究手段与应用领域。综述了近十年来中红外超快光纤激光器的发展概况,介绍了近年来中红外波段的激光传输与增益手段。其中,重点回顾了近年来中红外超快脉冲产生技术的研究进展及其代表性工作,包括非线性偏振旋转、可饱和吸收体以及频移反馈锁模技术。此外,还介绍了中红外超快脉冲的压缩放大技术与超连续谱产生应用。最后讨论并总结了中红外超快光纤激光器面临的挑战与可能的发展方向。

     

Pulsed laser deposition of chromium-doped zinc selenide thin films for mid-infrared applications

We have grown Cr doped ZnSe thin films by pulsed laser deposition on GaAs, sapphire and Si substrates through KrF excimer laser ablation of hot-pressed targets containing appropriate stoichiometric mixtures of Zn, Se, and Cr species and hot-pressed ceramic targets made of ZnSe and CrSe powders in vacuum and in an He background environment (10^-4 Torr). Deposited films were analyzed using X-ray diffraction to determine crystallinity and energy dispersive X-ray fluorescence to confirm Cr incorporation into the films. Photoluminescence measurements on the films show intracenter Cr²⁺ emission in the technologically important 2–2.6 μm spectral range. PACS 78.66.hf; 78.66.-w; 78.55.-m; 78.66.Bz; 78.20.-e     

Non-contact subsurface temperature measurements following mid-infrared laser irradiation

A difficult challenge in laser processing at nanosecond time scales is monitoring substrate temperature in the laser focal volume, particularly for mid-infrared laser irradiation where the absorption depth is relatively large and the attained temperatures are often relatively low. Here, we describe time-dependent measurements of the subsurface temperature of a target material following absorption of pulsed mid-infrared (MIR) laser irradiation, by detecting the luminescence from micron-size ceramic phosphor particles (Gd-doped YAG:Ce) embedded in the target material at a concentration of up to 10 %. Temperature calibrations were obtained by measuring the luminescence decay of the probe particles in an oil-bath heater. A silica-nanoparticle film was irradiated by an Er:YAG laser operating in a free-running mode over a fluence range up to but below the ablation threshold, while the third harmonic of the Nd:YAG laser excited the luminescence of the probe particles. From the temperature calibrations, it was possible to infer the thermal history of the target as a function of time delay between the Er:YAG and Nd:YAG laser pulses.