Stable diode lasers for hydrogen precision spectroscopy

We report on an external cavity diode laser at 972 nmstabilized to a mid-plane mounted Fabry-Perot (FP) resonator with afinesse of 400000. The 0.5 Hz optical beat note line width betweentwo similar lasers (Allan deviation 2 × 10^-15) is limitedby thermal noise properties of two independent FP resonators. Thelong term drift of the FP resonator and mirror substrates made fromUltra-Low-Expansion glass (ULE) is small and can be well predictedon time intervals up to many hours if the resonator is stabilized atthe zero thermal expansion temperature T_c. Using a Peltierelement in a vacuum chamber for temperature stabilization allowsstabilization of the FP cavity to T_c which is usually below theroom temperature. Beat note measurements with a femtosecond opticalfrequency comb referenced to a H-maser during 15 hours have shown awell defined linear drift of the FP resonance frequency of about 60 mHz/s with residual frequency excursions of less than ±20 Hz.     

Study on the possibilities of controlling the laser output beam properties by an intracavity deformable mirror

The possibilities of controlling the laser beam properties by a deformable mirror introduced into the laser optical cavity were studied theoretically and experimentally. The experiments were performed under conditions of an industrial high power transverse flow cw CO₂ laser operating with a stable resonator of a folded configuration. A deformable bimorph mirror of a surface profile controlled by the voltage applied to the mirror electrodes is implemented to the laser system as a back cavity mirror or as a one of the inner folding mirrors. The near-and far-field characteristics of the laser beam versus the resonator configuration controlled by the changes of the focal length of the deformable mirror are discussed in the paper. The analysis reveals that the resonator with an inner deformable mirror is much more sensitive to the mirror curvature variations than the resonator in which the deformable mirror is used as a back cavity mirror. The presented results show that dynamic and controllable changes in the resonator properties result in the controlled modification and optimisation of the laser output power and spatial parameters of the laser radiation.     

InnoSlab混合腔输出光束质量的理论研究

对InnoSlab Laser用混合腔的输出光束质量问题从热透镜效应和腔镜的不对准两个方面的影响进行理论分析,并从远场光强分布、远场发散角、光腰半径、光束质量因子M²值和桶中功率曲线等几个角度进行了讨论,特别是离轴非稳腔方向上腔镜倾斜对光束质量的影响,利用M²值和PIB曲线两个参数共同评价非稳腔的光束质量,对目前并无统一标准的非稳腔光束质量评价问题提供了有意义的参考. 关键词： InnoSlab 混合腔 光束质量 桶中功率     

High beam quality in a HyBrID copper laser operating with an unstable resonator made of a concave mirror and a plano-convex BK7 lens

This paper presents a very simple unstable resonator, made of a concave mirror (total reflector) and a bare plane–convex BK7 lens working as a convex coupling mirror, which is quite efficient for HyBrID copper laser. In addition to a good quality factor (M²=4.9), experimental results showed that it is possible to control the laser output power by introducing a variable aperture iris inside the cavity, close to the coupling lens, without spoiling beam quality. A rough theoretical model helped to explain these results as a combined effect of unstable resonator plus radial gain distribution.     

Off-beam quartz-enhanced photoacoustic spectroscopy with LEDs

A photoacoustic ozone sensor based on quartz-enhanced photoacoustic spectroscopy is presented. Instead of a laser, a UV-LED at 285 nm is utilized as light source. Using an acoustical resonator in off-beam configuration, it is feasible to align the light of the LED through the resonator tube. The sensor is integrated in a miniaturized flow-through gas cell which allows fast gas exchange. The sensor performance and the influence of the speed of sound on the measurement signal are investigated. For the detection of ozone in the Hartley band, a detection limit of S = 1.27 ± 0.08 ppmv (1σ) and a noise equivalent absorption sensitivity of D = (3.02 × 10^?8 ± 1 × 10^?10) cm^?1W(Hz)^?1/2 have been achieved.     

光泵气体THz激光器用CO2泵浦源腔内光场模式

CO2泵浦源是光泵气体太赫兹激光器的核心器件之一,其性能直接关系到太赫兹激光器的工作稳定性。CO2泵浦源一般由闪耀光栅作为全反射尾镜,构成特殊的光栅腔实现波长的选支输出。采用传输矩阵的特征向量法对光栅谐振腔的腔内光场模式进行了理论分析与数值模拟,计算了光栅腔的一系列本征模式及相应的衍射损耗。结果表明光栅腔的腔内模式特性等效于一个平凹腔,而对于大菲涅尔数的光栅腔, Littrow波长的附近支线也可能具有衍射损耗较低的低阶模,可能优先于Littrow波长的高阶模起振,导致光栅腔的波长选择性降低。     

Hybrid optical resonator type laser proposed for direct coupling into optical fiber

Combining one stable resonator with a concave mirror and a coupling-hole plane mirror, and another unstable resonator having a concave mirror and a convex mirror, a new hybrid optical resonator type laser has been proposed by overlapping the concave mirror as a common one and fitting the convex mirror exactly to the coupling-hole. Using theABCD law, the so-called g-parameters are first found for beam confinement. Then, based on the eigen-equation, the field distribution on the plano-convex mirror is obtained with the g-parameters above. Knowing this field distribution results in an effective transmittanceG _{e e}. Finally, the ratio of the inner convex to outer plane mirror radii can be determined for an optimum coupling in both the limiting cases of homogeneously and inhomogeneously broadened gain media. Some numerical examples will also be given for a CO₂ laser having the proposed hybrid resonator.     

Theoretical analysis of imaging properties of a pressure-actuated deformable mirror for adaptive compensation of rotationally symmetrical wavefronts

Our work presents a theoretical analysis of aberration properties of a simple single-channel deformable mirror from both the aspect of modeling the shape of the mirror reflecting surface and the mechanisms of wave-front correction using such mirror. The proposed mirror can be used for a compensation of rotationally symmetrical wavefronts, e.g. focusing of optical beams, adaptive change of resonator parameters in laser technology, phase shifting, etc. The detailed analysis of possibilities of wave-front correction was performed.     

钛宝石飞秒激光器用色散补偿Gires-Tournois镜的研究

根据钛宝石飞秒激光器的色散补偿要求设计了单次反射平均补偿量为-60 fs²的GT(Gires-Tournois)镜,采用离子束辅助沉积技术结合光学监控技术制作了器件.用分光光度计对650—950 nm波段薄膜反射率进行测试,结果表明反射率测试曲线与设计曲线十分符合,同时利用白光干涉系统对群延迟色散进行了测试,测试结果与设计符合得很好,实际的色散曲线振荡基本控制在±20 fs²以内.应用该GT镜进行钛宝石飞秒激光系统的色散补偿,取得了很好的锁模效果,得到了29 fs的超短脉冲. 关键词： 色散补偿 钛宝石飞秒激光器 GT镜 离子束辅助沉积     

受激布里渊散射相位共轭腔及腔内光学参量振荡器

利用受激布城渊散射相位共轭特性和Ｑ开关特性组成Ｎｄ：ＹＡＧ激光谐振腔,代替传统激光器全反镜和调Ｑ装置,获得能量１００ｍＪ,脉宽１３ｎｓ的线偏振相位共轭激光输出,相应的激光器总体转换效率为０．４７％,同时将单共振ＫＴＰ光学参量振荡器置入腔内,得到波长１．５７μｍ、能量１５ｍＪ的参理振荡激光,实验证实了受激布城渊散射相位共轭腔内光学参量振荡器运行的可行性。     

Spectral properties of a Tm:Ho:YAG laser in active mirror configuration

3+ :Ho³⁺:YAG laser is operated in active mirror configuration. This laser is characterised by a rather thin crystal (3 mm thickness in our experiment) and a very short resonator (about 3.2 mm). Therefore this laser is well suited for operation in a single longitudinal mode. Single-frequency operation is demonstrated with and without an intracavity etalon. It is further shown that single-frequency emission is reached with a stable cw emission. With a slight detuning of the outcoupling mirror, spiking can be achieved, resulting in an emission on different lines. The assignment of the observed laser lines to the known transitions between Stark sublevels of the ⁵I₇ and the ⁵I₈ level is discussed and compared with predictions in the literature. Received: 2 December 1997     

High resolution ethylene absorption spectrum between 6035 and 6210 cm-1

A two-channel photo-acoustic spectrometer (PA spectrometer) with a near infrared diode laser was used for taking measurements of a high resolution ethylene absorption spectrum. A semiconductor TEC-100 laser with an outer resonator generates a continuous single-frequency radiation in the range 6030–6300 cm^-1. A newly designed model of photo-acoustic detector (PAD) in the form of a ring type resonator provides for measurement of weak absorption cross-section equal to 4×10^-23 cm²/mol at a laser radiation power of 3 mW. The PAD threshold sensitivity is 2×10^-9 cm^-1 Hz^-1/2 W, when the signal to noise ratio equals to 1. The ethylene absorption spectrum within the range 6035–6210 cm^-1 was measured for the first time with a spectral resolution of 10 MHz. The reported line centre positions have an uncertainty of ± 0.0005 cm^-1. The precise measurements of ethylene absorption cross-sections were carried out using the mixture of high purity ethylene and broadening gas (nitrogen) at the mixture ratio 1:50–1:200. Measurements were carried out at a mixture pressure of about 4.2 kPa. PACS 42.62.Fi; 42.55.Px     

高功率激光器抗失调谐振腔的实验研究

为简化高功率激光器谐振腔结构,提高激光谐振腔的稳定性,增加基模体积,改善光束质量,提出了两种新型激光谐振腔结构,分别是带角隅反射镜的激光谐振腔和直角内圆锥面反射镜激光谐振腔。使用高功率脉冲CO2激光器,研究了这两种激光谐振腔的输出特性和腔镜失调的关系,并结合平凹稳定腔,对三种激光谐振腔的抗失调稳定性进行了对比。实验结果表明,随着全反镜或平面输出镜失调角的增加,角隅腔激光器的单脉冲输出能量下降速度小于直角内圆锥面全反镜腔。两种新型谐振腔全反镜的抗失调稳定性都超过平面输出镜。角隅全反镜谐振腔和直角内圆锥面全反镜谐振腔的抗失调稳定性均大大超过平凹稳定腔。     

High power operation of a CW 28 μm water vapor laser

This paper describes the best operating conditions and power performance of a CW 28 μm water vapor laser, using a 3 m long discharge in a 3 cm diameter Pyrex glass tube. The laser cavity is a half symmetric conventional Fabry-Perot resonator, the plane mirror of which is a metal mesh used as an output coupler. The addition of a large amount of hydrogen to the water vapor leads to the production of high power laser emission. This laser delivers 230 mW of continuous output at 28 μm, corresponding to a volumetric power of 102 μW/cm³, the highest value ever reported.     

Coherent nitrogen laser with high output energy

Employing an unstable resonator in a nitrogen laser with a short channel and high output energy, spatially coherent ultraviolet radiation with radiance 6.5×10¹² W/sr and output energies ranging from 0.1-0.9 mJ for different geometrical magnifications of the resonator are obtained. These figures are the highest reported for a single channel nitrogen laser.     

Beam parameters,mode structure and diffraction losses of slab lasers with unstable resonators

The properties of unstable resonators in on-axis and off-axis geometry were investigated both theoretically and experimentally. Diffraction loss, mode structure, beam quality and misalignment sensitivity were measured in single-shot operation with a gas-cooled Nd: YAG slab laser (4×12×100 mm³) and compared with theoretical results obtained by solving the Fresnel integral equation numerically. The excellent agreement allowed detailed resonator optimization. Furthermore, the resonator performance in high-power operation was investigated with two water-cooled Nd: YAG slab lasers (6×25×163 mm³ and 7×26×191 mm³) capable of 670 W of output power. Beam quality near the diffraction limit and a maximum output power of 475 W was achieved with an on-axis unstable resonator with variable-reflectivity mirror.     

Diode-pumped orthogonally polarized dual-wavelength Nd3+:LaBO2MoO4 laser

Polarized spectroscopic properties related to 1.07 μm laser operation of a 1.8 at.% Nd³⁺:LaBO₂MoO₄ crystal grown by the Czochralski method were investigated at room temperature. Using a 2.2-mm-thick, Z-cut Nd³⁺:LaBO₂MoO₄ crystal as gain medium, orthogonally polarized dual-wavelength laser at 1,068 and 1,074 nm was first realized in a plano-concave resonator end-pumped by a quasi-continuous-wave 795 nm diode laser. A total output peak power of 1.2 W with slope efficiency of 26 % around 1.07 μm was obtained. The influences of resonator length and pump power on output laser wavelength were also investigated.     

Experimental analysis of a continuously pumped,repetitively Q-switched Nd/YAG laser

The threshold operation and performance of a high pulse repetition frequency Nd/YAG laser are discussed. A rotating mirror Q-switch was used, and detailed studies of the variation of Q-switched threshold with motor frequency, and of the pulse build-up time with input power have been carried out. The results indicate that the switching angle varies with mirror reflectivity but is practically independent of resonator length. The latter is attributed to thermal lens action in the laser rod modifying the nominally plane parallel resonator configuration thereby leading to a spherical configuration. Under these conditions, the switching angle becomes independent of resonator length, but depends strongly on the induced focal length of the lens (laser rod). The degrading effect on the Q-switched laser performance of the mis-match at the laser rod surfaces is then discussed and finally the conditions for achieving maximum energy output in a single pulse are derived and experimentally verified.     

High-power multibeam CO2 laser for industrial applications

Multibeam CO₂ lasers consist of a large number of closely packed parallel glass discharge tubes, all sharing a common plane parallel resonator. This paper describes construction and operation of a CW multibeam CO₂ laser consisting 20 discharge tubes and cooled length of 1500 mm, delivering 1 kW power. A high-frequency pulser is used for producing preionization in all discharge sections for initiating the main DC discharge simultaneously in all discharge tubes. Plane parallel resonator consists of a plane ZnSe mirror of 90 mm diameter having 60% reflectivity and a gold-coated copper mirror of same diameter. This laser operates in waveguide regime and laser power is not critically sensitive to mirror misalignment.     

Non-selective Remote Sensing of Organic Pollutants by Laser Induced IR Fluorescence

A number of papers from this laboratory^1–6 have described work which may be termed “feasibility studies” of the application of laser induced infrared fluorescence to remote sensing of molecular air pollutants. An initial attempt to demonstrate extra-laboratory remote sensing was made⁷ using a cassagrainian telescope system with a 4–1/4 inch aluminum coated primary. The analytical sensitivity of this system was found to be insufficient for remote sensing. It was felt that the power of the laser was too low for the detection of molecules more than a few feet from the detector. Further in the cassagrainian system, several feet of the laser optical path closest to the detector are shielded from the collecting mirror by the reflecting mirror. Since this part of the system is closest to the detector, it was felt that the signal for the most sensitive analytical region was eliminated from observation. In a second attempt to demonstrate remote sensing with this system the optics were redesigned.