Gain characteristics of large volume CuBr laser active media

The paper presents the experimental results on how the active additive HBr and the temperatures of the containers with CuBr influence the gain characteristics of large volume (8 cm bore, 90 cm long) CuBr laser active media with the external heating of the active zone of the gas discharge tube (GDT). It has been demonstrated that an increase in the concentration of CuBr vapors results in the contraction of the gain profile of the active medium, consistent with the increase of the gain factor in the axial region of GDT. The contraction is also imposed by HBr addition. Despite the fact that we used the external heating of GDT at the pump power of 1.5 kW and less, the energy input is still not sufficient to produce the effective generation for large active volume lasers; and it is evident from the small gain profile width. The maximum gain profile width under experimental conditions (consider P_out/P_in > 2) was 3 cm; this value was obtained without HBr-additive within the active volume, while the concentration of CuBr vapors being significantly less than optimal, that corresponds to the maximum average lasing power.     

Numerical modeling of active media of high-pressure group-II-metal lasers

Translated from a preprint (manucript) of the Lebedev Physics Institute, Russian Academy of Sciences, Moscow.     

Generation of picosecond pulses in solid-state lasers using new active media

Results are reported of investigations aimed at generating nanosecond radiation pulses in solid-state lasers using new active media having broad gain lines. Passive mode locking is accomplished for the first time in a BeLa:Nd³⁺ laser at a wavelength 1.354 m, and in a YAG:Nd³⁺ laser on a 1.32–m transition. The free lasing and mode-locking regimes were investigated in an alexandrite (BeAl²O₄:Cr³⁺) laser in the 0.72–0.78–m range and in a synchronously pumped laser on F 2- centers in LiF in the 1.12–1.24–m region. The features of nonlinear perception of IR radiation by the eye, using a developed picosecond laser on F₂ ^– centers, are investigated for the first time.Translated from Lazernye Sistemy, pp. 67–86, 1982.     

Anomalous characteristics of lasers with a large number of quantum wells

Semiconductor lasers with an active region containing six quantum wells are investigated experimentally. The temperature dependences of working characteristics (threshold current density, external differential quantum efficiency, and directional pattern) are analyzed. Anomalous behavior of the temperature dependence of the threshold current and external differential quantum efficiency, associated with a negative characteristic temperature and a decrease in the quantum efficiency of radiation upon a decrease in temperature, is detected. A narrowing of the directional patterns in the plane perpendicular to the p-n junction upon an increase in temperature is revealed.     

Investigation of the active media in pulsed gas discharge lasers by the Rozhdestvenskii hook method

In this review we generalize the results of our experimental investigations in which the Rozhdestvenskii hook method was first used to look for an inverted population in new spectral transitions. An inverted population in new 3p–3s transitions of the neon atom with =588.1, 594.4, 650.6, and 653.2 nm was discovered in the active medium of a Penning plasma laser emitting the =585.3 nm neon line in Ne-H₂ and Ne-H₂-Ar mixtures. Results of investigations of a number of active media are given. An analysis is made of the spatial and temporal distributions of copper atoms in the ground state and of their influence on the lasing efficiency of a copper-vapor laser. Using the rhenium atom as an example, it was shown to be possible to obtain a sufficiently high concentration of refractory metal atoms (>10¹⁴ cm^–3) in an active medium to form active media of lasers utilizing self-terminating transitions and also plasma lasers.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 3–27, December, 1994.     

Effect of longitudinal pump inhomogeneity on the energy characteristics of steady-state raman lasers

The energy characteristics of externally pumped Raman lasers are calculated taking inhomogeneities in the active medium into account. Equations for the power and steady-state lasing threshold in these systems as function of the parameters of the cavity, pump, and Raman active medium are obtained over the entire ranges of their possible variations. The conditions for applicability of the model of averaged (uniform) fields, which is widely used in the theory of Raman lasers, are determined and interrelations among the cavity parameters favor unidirectional lasing in ring cavity Raman lasers are identified.     

Imaging in turbid media with intensity-modulated lasers

We describe the formation of a narrow beam for intensity-modulated electromagnetic radiation propagating through highly scattering materials. We propose to use this beam to reconstruct images, similar to X-ray back-projection techniques. For sufficiently high modulation frequency, the photon density wave is primarily carried by photons that suffer small or no large-angle scattering, which gives rise to the beam’s narrow divergence. The beam-narrowing concept is supported by large-scale numerical simulations to examine the quality of the imaging.     

Resonance frequencies and threshold gains of distributed feedback lasers with strong modulations

In this paper the calculation of resonance frequencies and threshold gains of distributed feedback (DFB) lasers with strong modulations is discussed. The theory is based on the Floquet solutions of a complex Hill differential equation. The dispersion relation of the above solutions is shown to be of importance for the behaviour of the resonances of the DFB laser.     

激活介质热效应对振荡模式的影响研究

理论分析了激活介质热效应对端面泵浦固体激光器激光振荡模式分布的影响,并以光纤耦合半导体激光器端面泵浦Nd∶YAG激光器实验研究了激活介质热效应对激光振荡模式的影响。实验结果表明：由于热效应,基模的模体积随泵浦功率的增加而变大,基模在模式竞争中占优;在泵浦光轴线偏离几何腔轴时,基模光斑中心位置朝泵浦光轴线所在位置移动,偏离量与泵浦光轴线的偏离量近似成线性关系。利用实验结果指导腔调节,可使泵浦光轴线与几何腔轴精确重合,获得了椭圆率为0.98、M2因子为1.01的基模输出。     

Solid-state active media of tunable organic-compound lasers pumped with a laser. I. An XeCl laser

The lasing properties of organic compounds in a polymethylmethacrylate matrix radiating in the blue-green (paraterphenyle and coumarine derivatives) and red (phodamine and phenalemine derivatives) regions of the spectrum pumped by an XeCl laser are studied. The lasing efficiency and photostability of the solid-state active media are compared with corresponding characteristics of the same liquid active media. Received: 14 March 2001 / Published online: 7 June 2001     

键合界面对面发射激光器光与热性质的影响

通过界面有效吸收系数的计算及界面对腔模的反射率的影响可知,采用双面键合技术制备面发射激光器应使键合界面处于驻波场分布零点位置,同时界面厚度应该小于20 nm以使器件光学性能受界面吸收系数的影响较小.采用有限元方法分析VCSEL温度分布,结果证实薄的键合界面使VCSEL有源区温度对界面的热导率和电导率改变不敏感,而厚的键合界面将可能使有源区温度有较大地升高,给器件带来严重的不良影响.亲水键合和疏水键合的SEM照片说明疏水处理界面较薄,适合用于器件的制备.而亲水处理界面厚度>40 nm,对器件的光、热特性不利 关键词： 键合 面发射激光器 热导率 电导率