DF Laser Research Articles

Study on beam quality of DF laser with inner cavity unstable resonator

Study on beam quality of DF laser with inner cavity unstable resonator

Lasing and luminescence characteristics of Fe:CdTe single crystal at room temperature

A technology for obtaining high-quality single-crystal active elements for a Fe:CdTe laser was described, which includes growing a single crystal from a melt using a modified vertical gradient freeze method followed by high-temperature treatment to remove free charge carriers. The room-temperature lasing and luminescence characteristics of a Fe:CdTe single crystal with a Fe2+ ions concentration of 6.1 × 1018 cm−3 were studied. The upper laser level lifetime, the output energy and a slope efficiency with respect to absorbed energy of the Fe:CdTe laser excited by the Fe:ZnSe laser were 340 ns, 13.5 mJ and 32%, respectively. The lasing spectrum of the Fe:CdTe laser with a nonselective cavity was located within the range 5.63–6.02 μm. It was noted the possibility to control the lasing spectrum by changing the pump laser spectrum (shifting the Fe:ZnSe laser spectrum to the short- or long-wavelength region by changing the quality factor of the cavity). Ways are discussed for further increasing the output energy of a Fe:CdTe laser at room temperature of the active element, in particular, by using a nonchain electric-discharge DF laser for pumping.

DF laser pumped single-crystal Fe:CdTe laser operating at room temperature

The operation at room temperature of a single-crystal Fe:CdTe laser excited by a nonchain electric-discharge DF laser was studied. The output energy of 29 mJ was obtained with a slope efficiency in terms of absorbed energy of 30%. The development of transverse parasitic oscillation at large pump spot sizes on the crystal surface limited the laser output energy. The laser with a nonselective cavity operated in the range of 5.3–5.9 μm; the total width of the generation spectrum was about 600 nm. Comparison of the Fe:CdTe generation spectra, obtained by pumping the crystal with DF and Fe:ZnSe lasers, confirmed the shift of the generation spectrum to the long wavelength region with increasing pump wavelengths. The maximum generation wavelength of the Fe:CdTe laser with a nonselective resonator excited by the Fe:ZnSe laser was 6.02 μm with a total width of the generation spectrum of about 370 nm. Ways are discussed for further increasing the room-temperature output energy of a Fe:CdTe laser.

Investigation of the Beam Quality of a Compact Non-Chain Pulsed DF Laser with a Confocal Positive Branch Unstable Resonator

The results of detailed studies on the beam quality of a non-chain pulsed electric discharged DF laser based on a compact inner cavity confocal positive branch unstable resonator were presented herein. The theoretical and experimental divergence angles for magnification M = 1.65, 1.85, 2.05, and 2.25 were calculated according to Fraunhofer diffraction and measured by the method of calibrated apertures. The smallest divergence of θ = 0.66 mrad was obtained with M = 2.25 in our experiment, which is 1.95 times the theoretical value. The corresponding far-field energy density at 10 km distance from the laser exit was 82.8 mJ/m2. The beam quality and energy density were increased by 11 and 91 times, respectively, compared with a similar stable resonator in our lab.

Dual-frequency Doppler velocimeter based on delay interferometric optical phase-locking

We present a dual-frequency laser Doppler velocimeter (DF-LDV) relying on a DF laser source (DFLS) generated by optical phase-locking two individual lasers to a common unbalanced Mach-Zehnder interferometer, which allows achieving high stability regardless of the DF separation of the lasers. This DFLS is evaluated using an optical frequency comb, testifying to the generation of DFLS with large DF separation up to terahertz with flexible tunability and high stability. Demonstration of DF-LDV using the DFLS of ${\sim}1.024\; {\rm THz}$ separation has achieved $1.62 \times {10^{- 2}}$ mm/s velocity resolution even for a slow velocity of $1.8\; {\rm mm}/{\rm s}$ in a mere 5 s acquisition time, confirming the high resolution and efficient speckle noise suppression enabled by the proposed DF-LDV. Featuring high precision, flexibility, and robustness, this method is particularly attractive from the practical point of view.

Planar multifrequency mid-IR microwave-pumped lasers

The characteristics of planar repetitively pulsed diffusion-cooled HF, DF, HF – DF, Xe, and HF – DF – Xe(Kr) lasers pumped by a microwave discharge (2.45 GHz) are studied depending on the pump pulse duration (10 – 40 μs) and repletion rate (50 – 400 Hz), as well as on the composition and pressure of the working gas mixture (30 – 200 Torr) at low (to 0.6 L s−1) gas flow rates. It is demonstrated for the first time that a HF – DF – Xe gas-discharge laser may simultaneously operate as a HF – DF chemical molecular laser and a recombination laser based on xenon atom transitions and generate broadband (octave) radiation in the range 2.0 – 4.2 μm with an average output power of 43 mW and an efficiency of 0.9 %. With substitution of xenon for krypton, lasing in a HF – DF – Kr laser is obtained at wavelengths of 2.52 – 4.15 μm. Lasing in a HF – DF laser was achieved simultaneously in two spectral regions (2.7 – 2.9 and 3.6 – 4.2 μm) with an output power of ∼50 mW. It is found that a decrease in the pump pulse duration with a simultaneous increase in the pulse repletion rate for retaining the average energy deposition leads to an increase in the average output power and efficiency of the laser. At low pulse repetition rates (50 – 100 Hz) and a low gas mixture flow rate, helium buffer gas can be effectively substituted for neon. Operation of the Xe laser was achieved in the spectral range 2.03 – 3.65 μm with an average output power of 580 Mw at a pump pulse duration of 20 μs, a pulse repetition rate to 10 kHz, and a maximum efficiency of 55 %. The obtained experimental results demonstrate the possibility of creating broadband HF – DF – Xe lasers emitting in the frequency range 2 – 4 μm with a desired ratio of intensities in different spectral ranges.

Economical generation regime of a supersonic continuous-wave chemical DF laser

We have performed experimental and computer-aided theoretical studies of the effect of the dilution degree ψ2 of a secondary fuel (deuterium) by an inert gas (helium) on the output characteristics of a supersonic cw chemical DF laser with a flat nozzle array, constructed in accordance with the nozzle – nozzle reagent mixing scheme. It is shown that an increase in the dilution degree in the range of 0 ⩽ ψ2 ⩽ 20 leads to a monotonous increase in the lasing zone length (a decrease in the radiation load on the resonator mirrors) and a drop in the laser specific energy output. With an increase in the optical path length (a decrease in the threshold gain), the sensitivity of the laser energy characteristics to the dilution degree decreases. Consequently, for a high-power DF laser (with a long nozzle array) with partial replacement of expensive deuterium with cheaper helium, a potential possibility for the implementation of an economical generation regime with acceptable specific energy output is achieved. The conditions for the implementation of this regime are identified.

Repetitively pulsed non-chain DF laser with pulse repetition frequency up to 50 Hz

The design and performance of a closed cycle repetitively pulsed non-chain DF laser based on self-initiated volume discharge is presented. In order to effectively solve the problem of large volume uniform glow discharge in non-chain pulsed DF laser, a voltage doubling reverse circuit in the Fitch generator was used. The working mechanism and effects of the voltage doubling circuit was analyzed theoretically according to closed loop equation of RLC circuit, and the results were in good agreement with the experiment. The performance of non-chain DF laser operating in both single pulse mode and repetitive mode was researched. A maximum output energy of 3.65 J and a technical efficiency of 3.12% were recorded in single pulse mode. A laser power of 150 W was obtained at the repetition rate of 50 Hz, the amplitude difference of laser pulse was better than + 8%, and the laser pulse width was about 135 ns.

氮稀释剂连续波DF激光器输出光谱分析

氮稀释剂连续波DF激光器输出光谱分析

冷气流引射式小型DF激光器紧凑度分析

冷气流引射式小型DF激光器紧凑度分析

非链式DF激光器非稳腔数值仿真与实验

非链式DF激光器非稳腔数值仿真与实验

非链式脉冲DF激光器放电生成物处理技术

非链式脉冲DF激光器放电生成物处理技术

非链式DF激光器非稳腔数值仿真与实验

非链式DF激光器非稳腔数值仿真与实验

Analysis of the possibility of designing more compact DF lasers driven by combustion of preheated fuels

We report a theoretical calculation of the processes proceeding in the combustor of combustion-driven cw DF/HF chemical lasers with different mixtures of fuels preheated to high temperatures. Calculation results demonstrate a great effect of the preheating temperature on the yield of F atoms and strongest deactivator, on the primary dilution ratio and on the estimated specific power. When fuels are preheated to about , the specific power is improved by about 74.2 %, and the total mass of the fuel is reduced by about 43 %, which makes it possible to realise a more compact and efficient design of combustion-driven cw DF/HF chemical lasers at elevated combustor pressures. Fuel preheating can facilitate the development of chemical lasers and high-power lasers based not only on airborne and space-borne platforms, but also on mobile ground-based platforms.

Divergence and polarisation of radiation of a wide-aperture chemical DF laser with an unstable resonator

Influence of a plane-parallel plate, placed inside an unstable resonator and entirely overlapping the beam cross section, on the polarisation and divergence of wide-aperture DF-laser radiation is studied at various angles of plate inclination to the resonator axis. It is shown that the plate inside a resonator has no effect on the radiation divergence and only requires a corresponding shift of a convex mirror in order to keep the resonator confocal. A noticeable change in the radiation polarisation has been observed only at angles of plate inclination greater than ; at angles of above the radiation becomes actually linearly polarised.

Forecast of intense near- and mid-IR laser radiation propagation along slant atmospheric paths

The effectiveness of the use of intense radiation from different near- and mid-IR laser sources propagating along high-altitude slant optical paths is numerically estimated on the basis of the optical model of the Earth’s atmosphere developed by the authors. Different laser sources, including chemical oxygeniodine laser (COIL), chain chemical DF laser, and carbon-monoxide (CO) laser are considered with different optical weather conditions taking into account linear and nonlinear optical effects. A COIL source is shown to be the most preferable in terms of the total laser power transmitted along a path, because of weak atmospheric attenuation and minimal effects of nonlinear factors. In addition, this laser source shows the best performance in terms of the mean radiation intensity at a receiver. Among chemical multiwavelength lasers, DF lasers lead in terms of the power transfer function.

Non-chain pulsed DF laser with an average power of the order of 100 W

The design and performance of a closed-cycle repetitively pulsed DF laser are described. The Fitch circuit and thyratron switch are introduced to realize self-sustained volume discharge in SF6–D2 mixtures. The influences of gas parameters and charging voltage on output characteristics of non-chain pulsed DF laser are experimentally investigated. In order to improve the laser power stability over a long period of working time, zeolites with different apertures are used to scrub out the de-excitation particles produced in electric discharge. An average output power of the order of 100 W was obtained at an operating repetition rate of 50 Hz, with amplitude difference in laser pulses <8 %. And under the action of micropore alkaline zeolites, the average power fell by 20 % after the laser continuing working 100 s at repetition frequency of 50 Hz.

Discharge processes of UV pre-ionized electric-discharge pulsed DF laser

The discharge processes of ultraviolet (UV) pre-ionized electric-discharge pulsed DF laser operating with a SF6–D2 gas mixture are studied. A mathematical model based on continuity equation of electrons and Kirchhoff equations for discharge circuit is established to describe the discharge processes. Voltage and current waveforms of main discharge and voltage waveforms of pre-ionization are solved numerically utilizing the model. The calculations correctly display some physical processes, such as the delay time between pre-ionization and main discharge, breakdown of the main electrode and self-sustained volume discharge (SSVD). The results of theory are consistent with the experiments, which are performed in our non-chain pulsed DF laser. Then the delay inductance and peak capacitance are researched to analyze their influences on discharge processes, and the circuit parameters of DF laser are given which is useful to improve the discharge stability.

Gas-dynamic perturbations in an electric-discharge repetitively pulsed DF laser and the role of He in their suppression

The gas-dynamic perturbations in a repetitively pulsed DF laser are studied using a Michelson interferometer. Based on the analysis of experimental data obtained in two experimental sets (working medium without buffer gas and with up to 90 % of He), it is concluded that such phenomena as isentropic expansion of a thermal plug, gas heating by shock waves and resonance acoustic waves do not considerably decrease the upper limit of the pulse repetition rate below a value determined by the time of the thermal plug flush out of the discharge gap. It is suggested that this decrease for a DF laser with the working mixture is caused by the development of overheat instability due to an increased energy deposition into the near-electrode regions and to the formation of electrode shock waves. Addition of He to the active media of the DF laser changes the discharge structure and improves its homogeneity over the discharge gape cross section, thus eliminating the reason for the development of this instability. A signification dilution of the active medium of a DF laser with helium up to the atmospheric pressure allowed us to achieve the limiting discharge initiation frequencies with the active medium replacement ratio .

High-power pulse repetitive HF(DF) laser with a solid-state pump generator

Operation of a repetitively pulsed electric-discharge HF(DF) laser with an all-solid-state pump generator based on FID switches is demonstrated. The energy stored in the pump generator capacitors was at an open-circuit voltage of and a discharge pulse repetition rate of . The specific energy extractions were 3.8 and for the HF and DF lasers, respectively. The possibilities of improving the output laser characteristics are discussed.