Free-running Regime Research Articles

Criteria of optimal pump pulse length of a CO electroionization laser

The dependence of the generation efficiency of a pulsed electroionization CO laser on the excitation duration is investigated experimentally. A criterion is established for the choice of the excitation-pulse duration. Satisfaction of this criterion ensures operation of an electroionization CO laser in the freerunning regime, with an efficiency that is maximal under the given experimental conditions.

Dynamic properties of an electrooptic DKDP switch in the microsecond range

An intracavity method was used in an experimental investigation of the dynamic processes in a Pockels cell made of a DKDP single crystal. The cell was placed inside a laser resonator operating in the free-running regime and characterized by an external negative feedback loop. For the first time the time dependence of the transmission of the switch was determined during the operation of a laser and it was found that acoustic vibrations affected the modulation properties of the switch. Another reason for the excitation of acoustic vibrations was the electric field of radiation of intensity in excess of 104 W/cm2 crossing the crystal. Clearly, this field also altered the anisotropy of the crystal giving rise to abrupt changes in the switch transmission under the influence of the individual lasing spikes. In the presence of a negative feedback loop this effect was manifested by self-excitation of hf (in excess of 106 Hz) fluctuations of the laser radiation power at the peak of a pulse. These two effects (acoustooptic and photorefractive) could alter greatly the modulation efficiency of the switch dealing with stochastic spike radiation of intensity in excess of 104 W/cm2.

Single axial mode Q-switched pulse generation at 1.052 μm by self seeding in a Nd: YAG oscillator

Single axial mode Q-switched pulse generation at 1.052 μm in Nd:YAG by self seeding with free running spikes is discussed. The Nd:YAG, having plane parallel faces without anti-reflection coatings, exhibits modulation-free spikes in the free running regime. By allowing the Q-switching to take place, when the radiation field of any of these pulses is present in the resonator, very reliable and reproducible modulation-free Q-switched pulses are obtained.

Pulsed electron-beam-controlled carbon monoxide laser amplifiers. I. Amplification of radiation from a CO laser operating in the free-running regime

An experimental investigation was made of pulsed electron-beam-controlled carbon monoxide laser amplifiers. Efficient amplification of radiation pulses from electron-beam-controlled CO lasers operating in the free-running regime was achieved under conditions of spectral and temporal matching between the master oscillator and the laser amplifier. The requirements imposed on the master oscillator and laser amplifier in order to provide such matching were formulated. The spectral properties of a multifrequency signal at the output of a laser amplifier were found to depend on the radiation energy density at its input. The saturation energy of the multifrequency signal of ~?5?J???cm???2???amagat??1 and the specific output energy from the laser amplifier of ~?90?100 J???liter??1 ???amagat??1 were greater by a factor of about 5 than the corresponding values in the case of a single-frequency signal. The electrooptic efficiency of the amplifier was found to be ~?15?20%. The radiation energy at the output of an amplifier with an 8-liter active volume (CO:N2 = 1:9, N = 0.25 amagat, T ? 110 K) reached ~?230?J.

Pulsed electron-beam-controlled carbon monoxide laser amplifiers. II. Amplification of radiation pulses from an electron-beam-controlled CO laser with controlled spectral and temporal characteristics

The results are presented of experimental investigations of pulsed electron-beam-controlled CO laser amplifiers operating under conditions of spectral and temporal mismatch of the master oscillator and laser amplifier. The optimal regimes are found for amplifying electron-beam-controlled CO laser radiation pulses with specified spectral and temporal characteristics. It is shown that amplification of radiation pulses having a spectrum with one rotational component in each of 5–7 cascade-coupled vibrational bands can increase the laser radiation spectral energy density by a factor of 4–6 compared with amplification of radiation pulses from an electron-beam-controlled CO laser operating in the nonselective free-running regime, without lowering the efficiency of conversion of the pump energy to laser radiation energy. A specific output energy of ~ 80 J liter − 1 amagat − 1 with an efficiency of ~ 20% was achieved in a superregenerative CO laser amplifier. The peak radiation power increased by two orders of magnitude when multifrequency pulses of microsecond duration were amplified. When the number of microsecond pulses being amplified was increased from one to five and their repetition period was greater than the time for an inverted population to be reestablished, the specific output energy rose from 10 to 25 J liter − 1 amagat − 1.

Photographic recording of YAG:Er3+laser radiation (λ=2.94 μm) by thermal sensitization of the emulsion

A study was made of the possibility of using thermal sensitization of a silver halide photographic emulsion for recording YAG:Er3+ laser radiation (λ = 2.94 μm). Using an FT-101 photographic film it was possible to record the radiation down to energy densities of ~ 1 mJ/cm2 in a dynamic range of ~ 100 with a resolution of at least 50 lines/mm when the laser pulse duration was ~ 150 μsec. This method was employed to determine for the first time the spectral width of a line emitted by a YAG:Er3+ laser operating in the free-running regime.

Chromium- and neodymium-activated yttrium scandium gallium garnet laser with an efficiency of 3.6% emitting linearly polarized radiation of energy of 0.46 J per single pulse, and a pulse repetition frequency 50 Hz

An investigation was made of a YSGG:Cr:Nd laser using a resonator and a polarization method for coupling out radiation. The Q factor was switched electrooptically (pulse duration 10 ns) and the repetition frequency was up to 50 Hz. The differential efficiency was 5.6% and the absolute efficiency was 3.6% when the output energy per pulse was 0.46 J. The highest average output power of single pulses of linearly polarized radiation was 23 W when the average pump power was 640 W. The results indicated that in the pulse-periodic regime the polarization method of coupling out the output radiation ensured near-optimal conditions so that the efficiency was high, approaching that of a YSGG:Cr:Nd laser with a conventional resonator and coupling out of radiation via a transparent mirror operating in the single-pulse free-running regime.

Free running mode of operation of high-power amplifier of PERUN iodine laser

A high power amplifier of a PERUN iodine laser is described and tested in free running regime. Dependences of the output energy on the composition and pressure of the gas filling are explored for the purpose of optimization.

Lasing properties of a multifiber Nd3+-activated glass laser

A study was made of the lasing characteristics of a multifiber neodymium-activated glass laser operating without a resonator in the free-running regime, characterized by a relatively high efficiency (~2%) and energy yield, as well as by a fairly low lasing threshold. A study was made of the influence of reflection at the ends on the energy and threshold characteristics. The passive loss factor at λ = 1.06 μ was determined. Measurements were made of the width of the spectrum, pulse duration, and divergence of laser radiation, and changes in these parameters were studied in the course of variation of the pump energy below and above the threshold.

Pulse-periodic YAG:Nd laser emitting variable-duration (0.2–10 msec) pulses

A pulse-periodic laser operating in the free-running regime with a variable pulse duration in the range 0.2–10 msec was developed. A compact pump-lamp power supply was constructed on the basis of selection of a part of a sinusoidal power-line voltage. Experiments demonstrated the suitability of this laser in physical research on the interaction of laser radiation with various materials, in technology of processing of different materials, and in surgery.

Influence of thermal self-interaction of optical beams on wavefront reversal in the free-running regime

An example of a parallel four-beam interaction in absorbing liquids was used to study the influence of a thermal self-interaction of optical beams on wavefront reversal (WFR) of radiation from a neodymium glass laser having a pulse duration of 2.5–3 msec in the free-running regime. It was found that although the thermal self-interaction substantially rearranged the angular spectrum of the interacting beams, the WFR quality was high due to self-compensation of large-scale optical inhomogeneities in the nonlinear medium. However, some shortening of the duration and deterioration in the efficiency of the WFR process were observed.

Time dependences of the optical properties of a laser erosion jet

A simultaneous determination was made of the time dependences of the transmission, scattering, and absorption coefficients of ruby laser radiation used to probe an erosion jet created by interaction of a zinc target with neodymium laser radiation emitted in the free-running regime and characterized by an energy of ~1.5×103 J and duration ~10−3 sec. The results of the probe experiments and spectroscopic measurements indicated that a considerable role in the transmission of laser radiation by the jet was played by the target particles in the form of liquid drops. There was a change in the particle formation mechanism during the interaction of laser radiation with the metal target.

Comparative tests of lasing characteristics on certain brands of neodymium laser glasses

Comparative tests were made of the lasing characteristics of certain Soviet neodymium laser glasses. The tests were carried out in the free-running, -switched, and pulse periodic regimes. The best parameters were obtained for phosphate glasses with high neodymium concentrations.

Analysis of the characteristics of a pulsed chemical DF-CO2laser under lasing and amplification conditions

Experimental and calculated data are used in an analysis of the characteristics of a pulsed chemical DF–CO2 laser under free-running and amplification regimes. A deviation of the distribution of the populations of the vibrational states of the CO2 molecule from the Boltzmann law was observed in the course of amplification of a saturating 150-nsec pulse. The role of a hot R 23 (0111–1110) transition and the influence of rotational relaxation on the kinetics of lasing of individual vibrational–rotational lines, on the output radiation pulse profile, and on the output energy were considered. The calculated and experimental values of the unsaturated gain and of the output energy in the free-running regime were in good agreement when the degree of initiation (dissociation) was far from the lasing threshold.

Solid-state microlasers pumped by miniature flashlamps

Highly efficient solid-state neodymium microlasers pumped by an energy of 0.2–1 J were constructed. This energy was provided by flashlamps in which the discharge gap was less than 15 mm. In the free-running regime the lasing efficiency reached 2%, whereas in the -switched regime it was 1.3% and the pulse duration was 2 nsec.

Stabilization of the emission frequency of an internal-mirror laser model ILGN-202

The emission frequency of an ILGN-202 internal-mirror laser was stabilized. An experimental study was made of the dependences of the power of the orthogonal components of laser radiation on the frequency tuning in the free-running regime. The laser was stabilized by maintaining a definite relationship between the intensities of the components by an automatic frequency control (AFC) system utilizing the method of thermal control of the resonator length. A theoretical study was made of the ultimate short-term frequency instability and an expression was derived for the transfer function of the optimal AFC system. The relative frequency instability found experimentally was 5 ? 10?9 in 15 min when the averaging time was 1 sec and the change in the frequency in 8 h was 10 MHz.

Output characteristics of a gadolinium scandium gallium garnet laser operating in the pulse-periodic regime

A pulse-periodic neodymium laser was made from a new crystal, which was gadolinium scandium gallium garnet activated with chromium and neodymium ions (GSGG:Cr3+: Nd3+). When the pump energy was 7.3 J per pulse, the output energy in the free-running regime was 255 mJ, i.e., the absolute efficiency was 3.5%. At the maximum pulse repetition frequency (20 Hz), which was limited by the nature of the power supply unit, the average output power was 5 W when the pump power was 145 W. The differential efficiency was 4.5%, which was 2.4 times higher than for an YAG:Nd3+ crystal operated under similar conditions. The diameter of the GSGG active element was 5 mm and its length was 50 mm. The differential efficiency in the Q-switched regime was 3% when the pump energy was in the range 3–7 J.

Method for self-consistent calculation of the energy parameters of optically pumped solid-state lasers

A method and software were developed for self-consistent calculation of the energy parameters of solid-state lasers of arbitrary geometry pumped optically by sources with various metal and nonmetal gas fillings. Calculations were made for the free-running regime. It was found that the gain is distributed inhomogeneously over the cross section of the active element. Laser radiation transfer was modeled in three-dimensions by a discrete-ray method. Numerical investigations carried out with the aim of testing the mathematical model gave results in satisfactory agreement with the experimental data.

Intracavity spectroscopy utilizing lasers based on $F^-_2$ color centers in LiF crystals

A description is given of an intracavity spectroscopic system based on a laser utilizing F2- color centers in a crystal of LiF and operating in the free-running regime emitting at wavelengths in the range 1.1–1.25 μ. The color-center laser was pumped by a neodymium laser. The absorption spectra of water vapor, methane, and ammonia were recorded.