The Intra-cavity Mode Competition and Laser Absorption Spectroscopy with CO2 Laser

A mathematical model is developed for analysis the dynamics of an intra-cavity laser spectroscopy and mode competition using the CO₂ laser as the coherent source. The governing equations of system are derived and effect of the absorbing material on the laser modes, as a time-dependent term is considered. Thus, the application of the CO₂ laser for intra-cavity laser spectroscopy with considering an inhomogeneous medium and effect of the absorbing material is investigated.     

Narrow saturation resonances in the spectrum of OsO4 induced by CO2 laser radiation

Narrow saturation resonances in the v₃ band of the rotational-vibrational spectrum of the OsO₄ molecule were observed in the radiation field of a number of lines of the CO₂ laser. The parameters and relative positions of narrow resonances offer the possibility for further improvement of the long-term frequency stability of the CO₂ laser. The OsO₄ molecule is considered a suitable medium for finding the effect suggested by Letokhov; it consists in the γ-radiation narrow resonances on nuclear transitions of Os under the effect of excitation of OsO₄ molecular oscillations by the CO₂ laser radiation.     

Measurements and assignments of new large offset CD3OH FIR laser lines

By using an acoustooptic modulator we extend the 300 MHz tunability of a waveguide CO₂ laser to 480 MHz. The CD₃OH was optically pumped by the 10R(32), 10R(34), and 10R(36) CO₂ laser lines, and 17 new FIR laser lines were discovered. The Stark effect on previously known FIR laser lines was investigated, and some tentative FIR laser lines assignments are suggested.     

The thermal effect in diode-end-pumped continuous-wave 914-nm Nd:YVO4 laser

The thermal effect and the heat generation in diode-end-pumped continuous-wave 914-nm Nd:YVO₄ lasers are investigated in detail. A theoretical model of a diode end-pumped solid-state laser is constructed to analyse the influence of fractional thermal loading on the thermal effect in the Nd:YVO₄ laser based on finite element analysis. The thermal focal lengths and the end-surface deformations of laser rods in Nd:YVO₄ quasi-three-level and four-level lasers are measured and compared with the results obtained by ordinary interferometry for the demonstration of higher thermal loading in 914-nm laser. Finally the fractional thermal loading in the Nd:YVO₄ quasi-three-level laser is calculated by matching the experimental and the simulated end deformations.     

A novel strongly correlated electronic thin-film laser energy/power meter based on anisotropic Seebeck effect

Strongly correlated electronic (SCE) materials including high-temperature superconducting cuprate and colossal magnetoresistance manganite thin films demonstrate tremendous anisotropic Seebeck effect which makes them very promising for developing high-performance laser detectors. In this work, laser-induced thermoelectric voltage (LITV) signals with nanosecond response time have been measured in SCE La_1?x Pb _x MnO₃ thin films based on anisotropic Seebeck effect at room temperature. The magnitude of the LITV signals increases linearly with laser energy/power density in a wide range of laser wavelengths from ultraviolet, visible to infrared based on which a novel SCE thin-film laser energy/power meter has been developed.     

1180 nm Raman laser operation of end-pumping Nd:GdAl3(BO3)4/SrWO4 crystal

We present an end-pumped continuous-wave Raman laser at 1180 nm with a 60 mm long pure crystal SrWO₄ and an Nd:GdAl₃(BO₃)₄ crystal. The highest output power Raman laser at 1180 nm is 15.5 mW corresponding to the pump power of 1.75 W. Results indicate that the intense self-doubling frequency effect of GdAl₃(BO₃)₄ reduces the 1180 nm Raman laser output.     

Superradiance effects on the infrared absorption and vibrational temperature of optically pumped molecules

Using controlled feedback and coincident far infrared absorption, we have shown that the superradiant emission process in NH₃ pumped by the 9R16 line of a CO₂ TEA laser has a marked effect on the absorption of laser energy and vibrational heating of the gas. Since many polyatomic molecules pumped by IR laser are efficient superradiant far infrared sources, the effect is important for laser induced fluorescence studies in these polyatomics.     

Behavioral studies of gain and saturation energy density in a N2 laser with corona preionization

By the use of an oscillator-amplifier (OSC-AMP) TE N₂ laser system, both operating with corona preionizers, the laser parameters (small-signal gain g ₀ and saturation energy density E _s) have been measured at different N₂ gas pressure and for different states of the AMP preionizer. The details of our measurements are presented. In addition, the effect of He buffer gas on the laser parameters has also been investigated; it was found that both laser parameters remain almost constant up to 150 Torr of He gas pressure, indicating that He mainly affects the discharge uniformity. Finally, with the variation of the N₂ laser gain values in the literature, we found that the g ₀-N₂-laser parameter depends strongly on the length of the laser channel. Based on the most recent measurements, a graph showing this dependency is introduced.     

Acoustooptic extension of the frequency tunability of CW CO2 lasers: New FIR lasers emissions from CH3OH and13CH3OH

We have increased the frequency tunability of our CW waveguide CO₂ lasers by means of an acoustooptic amplitude modulator, operating at the fixed frequency of 90 MHz. The up-shifted, or down-shifted, laser optical sideband can be generated independently by adjusting the orientation of the modulator. The efficiency is larger than 50%. The frequency tunability of the CO₂ laser around each laser line is thus increased by 180 MHz. To demonstrate the possibilities of this method, a source composed of the above modulator and of a CW, 300 MHz tunable waveguide CO₂ laser has been used for the search of new large offset FIR laser lines from optically pumped CH₃OH and¹³CH₃OH molecules. As a result 15 and 10 new large offset laser lines were discovered respectively. New assignments of some laser lines are also proposed. We have also measured the Stark effect, the offset, and the polarization of other already known lines. In particular a Stark effect frequency tuning of about 1 GHz is demonstrated for a laser line at 208.399 m.     

Dependence of impurity binding energy on nitrogen and indium concentrations for shallow donors in a GaInNAs/GaAs quantum well under intense laser field

Within the framework of the effective-mass approximation, using a variational method, we have calculated the effect of intense laser radiation on the binding energy of the shallow-donor impurities in a Ga_{1- x} In _x N _y As_{1- y} /GaAs single quantum well for different nitrogen and indium mole concentrations. Our numerical results show that the binding energy strongly depends on the laser intensity and frequency (via the laser dressing parameter) and it also depends on the nitrogen and indium concentrations. Impurity binding energy under intense laser fields can be tuned by changing the nitrogen and indium mole fraction.     

Transient molecular absorptions induced by the absorption of CO2 laser radiation

Laser-induced molecular absorptions are reported for the species SF₆, CF₃I, and CF₃Br. Induced absorptions are observed at frequencies ～ 40 cm^-1 lower than that of a CO₂ TEA laser which is used to vibrationally excite the molecules in a low pressure cell. The dependence of the effect on pump laser intensity indicates that the species that exhibit the induced absorption have absorbed more than one laser photon. Applications of this phenomenon with respect to laser induced isotope separation are discussed.     

New large offset far-infrared laser lines from CD3OH

The CD₃OH molecule has been investigated for new far-infrared laser lines by optically pumping with a cw waveguide CO₂ laser. The increased tunability (300 MHz) with respect to a conventional CO₂ laser permits to pump many new CD₃OH lines. As a consequence 108 new laser lines have been discovered, ranging from 42.9 to 1155 m in wavelength. On some lines the effect of an electric Stark field has been investigated demonstrating a laser frequency tuning. The total number of known FIR laser lines from CD₃OH is increased to about 340 making this molecule the most prolific together with CH₃OH.     

Microstructure of laser melted Al18B4O33w/2024Al composite

The microstructure of a laser treated Al₁₈B₄O₃₃w/2024Al composite has been investigated using transmission electron microscope (TEM), low-angle (glancing angle) X-ray diffraction (XRD) techniques. Various surface microstructures were observed in the laser treated composite. The Al₁₈B₄O₃₃ whisker on the surface of the composite was decomposed during laser surface melting, various decomposition products were studied in the laser treated composite. Eutectic phases and the precipitation in the matrix of the composite with laser-treated were observed. The main phases detected in the molten zone were aluminum and decomposition products Al₂O₃. The effect of laser treatment on the hardness of the composite was also examined. A surface hardness of 400 Hv was noted.     

The use of discharge electric field variations to CO2 laser stabilization

A method is described for detection of CO₂ laser power variations which requires no optical detector. It is based on electric field changes near the laser tube induced by the laser power fluctuations within the optical cavity. This phenomenon called by us “antenna effect” is used for laser stabilization. A simple and inexpensive technique for CO₂ laser power measurements, resonator adjustment, and for observation of the laser signature is described.     

Effect of CO2 laser irradiation on the transport properties of La0.67Ba0.33MnO3 thin film

The effect of CO₂ laser irradiation on La_0.67Ba_0.33MnO₃ epitaxial thin film was investigated. Epitaxial thin films grown by pulsed laser deposition were irradiated by a CO₂ laser in air for 10-60 s. It is shown that after CO₂ laser irradiation treatment, the crystallinity of the film is strongly enhanced. It is found that a dramatic decrease in the resistivity of the CO₂-laser-irradiated film is accompanied by a remarkable increase in its insulator-metal transition temperature and the temperature coefficient of resistance. This significant improvement of its structure and properties is achieved in several dozens of seconds and surpasses that observed in films annealed in an oxygen atmosphere at 900 ^°C for 12 h, suggesting that CO₂ laser irradiation is a new and effective tool to optimize CMR manganites for bolometric applications.     

LD抽运Nd:YVO4晶体中的上转换及其影响

对激光二极管抽运下Nd:YVO₄晶体中的上转换发光做了测量与分析,发现对应⁴G_7/2能级向下跃迁的上转换发光的主导机制为能量传递上转换.接着,对上转换对LD抽运Nd:YVO₄激光器运转的影响进行了理论分析,并特别讨论了上转换对热效应的影响. 关键词： 上转换 固体激光器 热效应     

Raman spectroscopic study of oxidation and phase transition in W18O49 nanowires

W₁₈O₄₉ nanowires were synthesized by a high‐temperature physical evaporation technique. The structure, morphology, and composition of the nanowires were characterized by SEM, EMPA, XRD, XPS, and HRTEM techniques. The intrinsic Raman spectrum of W₁₈O₄₉ nanowires was obtained, and the effect of laser power on the change of their structure was also studied. W₁₈O₄₉ nanowires were first oxidized to tungsten trioxide nanowires under irradiation of a certain laser power, and then the tungsten trioxide nanowires underwent a phase transition from monoclinic to orthorhombic with increasing laser power; this phase transition was reversible on turning down the laser power. Copyright © 2006 John Wiley & Sons, Ltd.     

Optimum conditions for correlation of the temporal shape of an object pulse with a stimulated photon echo response in inhomogeneous external electric fields

We have studied the information locking effect and the effect of correlation of the shape of an object laser pulse with the shape of a stimulated photon echo response in the presence of external spatially inhomogeneous electric fields. We have shown that, for the transition ³H₄-³P₀ in a LaF₃:Pr³⁺ crystal, one can observe the effect of the correlation of the shape of an object laser pulse with the shape of a stimulated photon echo response and, depending on the scheme of the action of external spatially inhomogeneous electric fields, either the information locking effect or the information destroying effect.     

Optical magnetic flux generation in superconductor

The generation of the magnetic flux quanta inside the superconductors is studied as a new effect to destroy superconductivity using femtosecond (fs) laser. The vortices are successfully generated in the YBa₂Cu₃O_7-δ thin film striplines by the fs laser. It is revealed that the vortex distribution in the strip reflects the fs laser beam profile.     

A high polarization microchip green laser with dual Nd:YVO4 crystal

A high polarization Nd:YVO₄/KTP laser with dual crossed gain crystal is reported. Using two optical axis orthogonal Nd:YVO₄ crystal as gain medium, eliminating the depolarization effect of single Nd:YVO₄ crystal, the high polarization green laser is obtained. With 1.8 W diode laser pump power the output power of TEM₀₀ green laser is 366 mW, the light–light conversion efficiency is up to 20.3%, and the polarization ratio is 110:1. This laser has the advantages of being simple and easily attainable at a low cost, and it is suitable for batch production.