Optically (solar) pumped oxygen-iodine lasers

We present the results of theoretical and experimental studies demonstrating the possibility of developing an oxygen-iodine laser (OIL) with direct optical pumping of molecular oxygen involving inter-molecular interaction with charge transfer from donor molecule (buffer gas) to acceptor molecule (oxygen). This interaction lifts degeneracy of the lower energy states of molecular oxygen and increases its absorption cross section in the visible spectral region and the UV Herzberg band, where high quantum yield of singlet oxygen is achieved (QY ～ 1 and QY ～ 2, respectively) at the same time. A pulse-periodic optical pump sources with pulse energy of ～50 kJ, pulse duration of ～25 μs, and repetition rate of ～10 Hz, which are synchronized with the mechanism of singlet oxygen generation, are developed. This allows implementation of a pulse-periodic oxygen-iodine laser with an efficiency of ～25%, optical efficiency of ～40%, and parameter L/T ～ 1/1.5, where T is the thermal energy released in the laser active medium upon generation of energy L. It is demonstrated that, under direct solar pumping of molecular oxygen, the efficiency parameter of the OIL can reach L/T ～ 1/0.8 in a wide range of scaling factors.     

Holographic optical elements (HOE) for semiconductor lasers

A two step method is described to produce off-axis holographic lenses with high diffraction efficiency and without astigmatism for semiconductor lasers. The hologram is recorded in the visible (514 nm) and reconstructed in the infrared (800 nm). The principal parameters (recording and reconstruction angles, astigmatic focal lengths) for each hologram and wavelength are calculated analytically using second order approximation. Numerical methods, based on classical ray-tracing applied to holographic diffraction, have been developed to calculate spot diagrams and to investigate the effects of higher order aberrations.     

Technology of the (Al,Ga)As/GaAs double heterostructure lasers

Conclusion Even thqugh the LPE growth of (Al,Ga)As layers is now largely a matter of industrial development or routine, there still remain some problems that need fundamental study. We have pointed to two of them: growth of very thin layers and the influence of ambient atmosphere. The problem of automation of the growth process, while being connected with industrial LPE installations, also has a bearing on the fundamental research, e.g. it is important for reproducible preparation of very thin layers.We did not include in this paper work done in our laboratories in the field of integrated optics. A hybrid combination of DH coherent source with a MESFET GaAs device has been tested; integrated version of this optoelectronic circuit is in preparation.Invited talk at the International Conference on Radiative Recombination and Related Phenomena in III–V Compound Semiconductors, Prague, 4–7 October, 1983.     

High-resolution (Doppler-limited) spectroscopy using quantum-cascade distributed-feedback lasers

Lasing characteristics were evaluated for distributed-feedback quantum-cascade (QC) lasers operating in a continuous mode at cryogenic temperatures. These tests were performed to determine the QC lasers' suitability for use in high-resolution spectroscopic applications, including Doppler-limited molecular absorption and pressure-limited lidar applications. By use of a rapid-scan technique, direct absorbance measurements of nitric oxide (NO) and ammonia (NH>(3)) were performed with several QC lasers, operating at either 5.2 or 8.5 microm. Results include time-averaged linewidths of better than 40 MHz and long-term laser frequency reproducibility, even after numerous temperature cycles, of 80 MHz or better. Tuning rates of 2.5 cm(-1) in 0.6 ms can be easily achieved. Noise-equivalent absorbance of 3 x 10(-6) was also obtained without optimizing the optical arrangement.     

Application of lasers in precision analytical measurements (review)

Conclusions The foregoing analysis does not exhaust the analytic methods of laser spectroscopy (see, e.g., [6–8, 142, 143]). The methods of traditional [8–10, 144, 145] resonance [8, 146], and active (or CARS) [8, 11, 147] Raman scattering spectroscopy are continuously being expanded. Newer, purely laser methods — optogalvanic spectroscopy [25, 148], optothermal spectroscopy [7, 149], the method of selective photoionization [6, 150], etc. — are also being developed.Further development of laser spectra analysis will primarily require going beyond narrow laboratory, purely research setups, and the development of commercial laser analytic devices. In this connection, in selecting a method as the basis for the device being constructed it is necessary to know not only the technical characteristics, such as sensitivity, selectivity, speed of operation, etc., but also the metrological characteristics, such as the random and systematic measurement errors; in addition, the measurement accuracy is a decisive factor. At the same time there are few works devoted to the questions of accuracy of the measurements performed with laser spectrometers; in the literature available to us there are no reviews and comparisons of analytic methods of laser spectroscopy from this viewpoint.Amongst the foregoing methods the direct absorption method has the highest accuracy. With a definite arrangement of the measurement process this method enables absolute measurements of the concentration of the analyte component, i.e., it does not require precalibration of the apparatus based on gas mixtures (for the gas analyzer). The minimum achievable error of such measurements is limited by the error of the premeasured absorption coefficient for radiation of the molecule being detected at the wavelength of the laser radiation and at the present time can equal 1–3%. Other methods studied are characterized by higher sensitivity, and they are also more accurate, difficult to calibrate, and less versatile. A comparative analysis of the methods and their errors will be performed in the future.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 48, No. 1, pp. 7–26, January, 1988.We thank A. P. Voitovich for useful remarks and a discussion of this work.     

Self-pulsing phenomena in (GaAl) as double-heterostructure injection lasers

Repetitive self-pulsations under CW operation in the frequency range of 200 MHz–2 GHz are observed in many (GaAl)As double-heterostructure injection lasers. About 100 lasers of both low-mesa stripe geometry and with proton-implanted structures have been studied and about half of them exhibited more or less pronounced self-induced pulsations. The experimental results on three typical lasers are discussed more in detail on the basis of existing theories. Self-induced pulsations have often been observed in the non-linear region of the laser light output characteristic. The most probable reason for the instabilities appears to be a repetitive Q-switching process.     

Calculation of beam divergence of pulsed electron-beam-discharge lasers (EBL)

The beam divergence in electron-beam-discharge lasers is determined by the refraction of the radiation by the gradients of the electron and gas densities. At short pump pulse durations ( 1 sec) and, accordingly, at high charged-particle densities (n_e 10¹⁴ cm^-3) the divergence is due to the inhomogeneity of the ionization of the active medium. At long durations ( > 10 sec) the divergence is determined by the refraction of the radiation by the gas-density gradients produced by the hydrodynamic motion of the active medium during the course of the pump pulse. By using unstable telescopic resonators with dimensions smaller than the energy-input region, it is possible to considerably increase the energy of the radiation whose divergence is due to refraction.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva, Vol. 116, pp. 181–187, 1980.     

High-power lasers at the Russian Federal Nuclear Center (VNIIEF)

The development of laser plants with different purposes, which originally began in the mid-1960s, are being successfully carried out at the Laser Physics Research Institute (LPRI). Investigations of the physical fundamentals of the laser operation, nonlinear optics, and the properties of high-temperature dense plasma that is formed under the action of the intensive laser emission on matter are realized at these plants.     

Low threshold current proton-isolated (GaAl)As double heterostructure lasers

Very low threshold current laser sources are desirable for a number of potential applications including optical fibre telecommunications systems. Conventional proton-isolated stripe geometry (GaAl)As lasers can be designed to give threshold currents in the range 10–50 mA by proper optimization of device geometry. Experimentally, it is shown that such devices can be easily fabricated and bonded and that their characteristics are not adversely affected by the optimization procedure.     

Noise of mode-locked lasers (Part I): numerical model

A numerical model for the calculation of noise spectra of actively or passively mode-locked lasers has been developed. Fluctuations not only of the timing error, but also of all other quantities of interest can be quantified. The model is based on a pulse propagation algorithm with quantum noise sources. It allows the study of a much wider class of phenomena than those accessible with analytical techniques, and it is useful for testing the validity limits of analytical results. PACS 43.50.+y, 42.50.Lc, 42.60.Fc     

A replacement solvent for dimethylsulfoxide (SMSO) in cw dye lasers

The use of propylene glycol carbonate as a replacement solvent for dimethyl sulfoxide in a Coherent model 599-21 c.w. dye laser has been investigated. Up to 40 milliwatts of single frequency output was achieved at 875 nm.