Discharge CO Laser Research Articles

Pulsed RF Excitation Inductive Discharge CO2 Laser with the Radiation Energy of 1 J and High Efficiency

Pulsed RF Excitation Inductive Discharge CO2 Laser with the Radiation Energy of 1 J and High Efficiency

Cryogenic slab RF discharge CO laser with hybrid waveguide-unstable resonators

Dependences of a cryogenic slab radio-frequency discharge CO laser output power on a distance between mirrors of a hybrid negative-branch waveguide-unstable resonator were experimentally studied. The maximum output power was observed at the resonator length longer than the one calculated by taking into account the mirrors radii of curvature. Optimization of the resonator length made it possible to get the output power increase up to 20%–25%. The results obtained can be used for designing not only slab laser systems with hybrid waveguide-unstable resonators, but also for high-power lasers with full-sized negative-branch unstable ones.

FREQUENCY CONVERSION OF RADIO-FREQUENCY ELECTRIC DISCHARGE SLAB CO AND CO2 LASERS INTO THE SPECTRAL RANGE OF ~ 2—20 μm (Review)

A review of researches that both initiated and provided development of a hybrid IR laser system based on conversion of Q-switched radio-frequency discharge slab CO and CO2 lasers in various nonlinear crystals is presented. The broadband laser system developed operates in the spectral range from ~2 to ~20 μm due to generation of emission on difference and sum frequencies in these crystals.

Double-range (λ = 2.6–2.9 and 4.9–6.0 μm) slab RF discharge CO laser system with intracavity frequency conversion in temperature-controlled ZnGeP2 crystal

Temperature phase-matching tuning in a ZnGeP2 nonlinear crystal under intracavity CO laser sum-frequency generation (SFG) was for the first time carried out. This slab RF discharge CO laser with the intracavity frequency conversion simultaneously operated within two wavelength ranges of ∼ 2.6–2.9 and ∼ 4.9–6.0 μm. The SFG conversion efficiency was up to 2.9 ± 0.1%. The crystal heating from the room temperature up to 115 °C resulted in the SFG spectrum shifting towards the short-wavelength range and in the spectrum width and the number of SFG lines decrease.

Multifunctional compact dual band repetitively pulsed slab RF discharge CO laser with average output power up to 40 W

A new repetitively pulsed cryogenically cooled slab RF discharge CO laser running in both fundamental and first-overtone bands without its active medium forced replacement with average output power three times as much as that of previous models was developed. Compared to our previous installations, the output power was increased due to using gold-coated copper electrodes of ∼ 1.5 times larger surface area. The fundamental band free-running lasing was obtained within the spectral range of 5.06–5.92 μm with average output up to ∼ 40 W. Under Q-switching the laser operated in the spectral range of 4.95–7.0 μm with pulsed peak power up to 4.5 kW. The first-overtone band lasing was observed in the spectral range of 2.6–3.05 μm with maximum average power of ∼ 6 W.

Frequency-selective Q-switched repetitively pulsed slab RF-discharge carbon monoxide laser

Q-switched cryogenically cooled slab RF discharge CO laser operating in multi-line mode, single-line mode with a diffraction grating, and also with frequency selection by special spectral filters situated both outside and inside the laser cavity was experimentally studied. Characteristics of CO lasing on individual ro-vibrational spectral lines produced by this laser with various cavities under the same active medium and pump parameters were compared. Application of output couplers with a relatively narrow spectral band of high transmittance compared to the non-selective CO laser range of operation, but with high reflection in the rest of the range, was effective for obtaining narrow-band multiline lasing. For selection of the long-wave part of Q-switched CO laser spectrum, which was needed for frequency conversion into the long-wave mid-IR when mixing with CO2 laser emission, application of a broadband spectral filter with a very low reflection coefficient in the spectral range where lasing was necessary to be suppressed (sort of a step function) proved to be efficient being installed outside the laser cavity.

Slab RF-discharge carbon dioxide laser with active mode-locking

Mode-locking with an acousto-optic modulator was for the first time demonstrated for a repetitively pulsed (150 Hz) slab RF discharge CO2 laser. The mode-locked CO2 laser emitted trains of 5.5 ns pulses following with 27.25 MHz repetition rate. Mode-locking also affected the laser pulses envelope in respect to free-runing mode. The numerical estimation of the laser system scalability indicated an opportunity to develop a very compact CO2 laser emitting sub-nanosecond pulses.

Dynamics of frequency-selective operation of a CO laser tunable in a wide spectral range

This paper presents a computational/theoretical analysis of the generation of a single pulse by a frequency-selective electron-beam sustained discharge CO laser. The calculations have been performed using a theoretical model in which the entire set of VV exchange processes involving CO molecules at high vibrational levels is taken into full account. We present calculated pulse shapes for a wide range of transitions, including transitions between high vibrational levels, and examine the possibility of raising the laser output intensity by optimising the density and composition of the gain medium.

Cryogenically cooled CW electric discharge CO laser operated with CO2 laser mixture

We report lasing on multiple wavelengths in the 5 µm region from a non-selective CW-CO laser cavity utilizing the CO2 laser gas mixture when its gain length was maintained at LN2 temperature. The inversion obtained in the CO medium formed by the dissociation of CO2 gas in the discharge made this possible. The findings are significant as the handling of the toxic CO gas that is conventionally employed in the generation of wavelength in the 5 µm region has been dispensed with. A maximum CW output power of 8 W was obtained at an electro-optic efficiency of 8%. The cascading lasing transitions have been identified and matched with known transitions available in the literature.

Residual-stress-induced helical long period fiber gratings for sensing applications.

We demonstrate a high-efficiency grating fabrication system, which can be used to inscribe a high-quality helical long period fiber grating (HLPFG) on single-mode fiber by means of hydrogen-oxygen flame. Such the HLPFG can be produced in enormous quantities with a uniform grating parameters and good reproducibility of grating inscription. Possible mechanisms for refractive index modulation in the HLPFG can be attributed to residual stress concentration by solidifying the periodic twisting stress under a fused status of optical fiber. Moreover, the HLPFG exhibits an excellence performance of high temperature sensing with a high sensitivity of ~132.8 pm/°C and a measuring range from room temperature to 900 °C. Comparing to the traditional LPFG fabricated by CO2 laser or arc discharge technique, the HLPFG has a low the bending and tensile strain sensitivity of 1.94 nm/(1/m) and 1.41 pm/με, respectively. So the proposed HLPFG could have a great potential in special applications as optical high-temperature sensors.

Q-switched repetitively pulsed cryogenic slab RF discharge CO laser with active medium comprising air

Q-switched repetitively pulsed cryogenic slab RF discharge CO laser output characteristics (its spectrum, peak power and pulse duration) were studied for various active medium compositions and pump pulse energies. It was found that small addition of N2 increased output peak power at the same other parameters. The highest peak power of this CO laser facility ~ 4 kW was obtained for gas mixture CO:O2:N2:He with O2:N2 concentration ratio 1:4 as about in the atmospheric air. It was shown that the atmospheric air as the active gas mixture component can be applied instead of pure nitrogen and oxygen without the laser peak power loss.

Theoretical investigation of the regenerative amplification of ultrashort pulses in a high-pressure transverse electric CO2 laser.

We have developed a theoretical model for the regenerative amplification of ultrashort mid-infrared radiation in high-pressure transverse electric discharge CO2 lasers. This model is based on counter-propagating wave equations that are combined with Boltzmann equation, six-temperature, and circuit-coupled kinetic models. For the first time to our knowledge, the effect of spontaneous emission is taken into account. The model describes noise behavior, contrast ratio, and self-lasing of amplified spontaneous emission. The proposed scheme allows the attainment of a few-picosecond pulse with GW-level peak power and contrast ratio on the order of 106 in the 9μm range.

Sum frequency generation under conversion of Q-switched cryogenic slab RF discharge CO laser radiation in ZnGeP2

For the first time broadband sum frequency generation in ZnGeP2 crystal has been accomplished with a compact cryogenic slab RF discharge CO laser. The spectrum of the CO laser operating in a repetitively pulsed multiline Q-switching mode consisted of ~90 emission lines in the wavelength range of 4.95–6.60 µm. Internal sum frequency generation efficiency was reached up to 8.2%. The resulted spectrum contained ~200 spectral lines in the wavelength range of 2.5–3.2 µm.

Q-switched slab RF discharge CO laser

A compact repetitively pulsed cryogenically cooled slab RF discharge CO laser with double path V-type laser resonator equipped with external Q-switching system based on rotating mirror was developed and studied. The laser produced mid-IR (λ ~ 5–7 µm) radiation pulses of ~1 ÷ 2 µs duration (FWHM), peak power up to ~3 kW, and pulse repetition rate up to 130 Hz. Averaged output laser power reached 0.5 W, the laser spectrum consisted of ~80 laser lines with individual peak power up to 80 W.

Diagnostics of Low Temperature Plasma by CO Laser Radiation (5.0-7.5 μm)

A review of the work conducted in Gas Lasers Laboratory of P.N. Lebedev Physical Institute of the Russian Academy of Sciences and devoted to a research of the diagnostic of dynamics of small-signal gain, temperature and population of vibrational levels in the CO-containing gas mixtures excited by pulsed electron-beam sustained discharge is presented. With the help of laser probing techniques the nonlinear Zeeman splitting of the NO lines in a strong magnetic field was also investigated. The studies of gain of the train of nanosecond pulses allowed us to estimate the intensity of the gain saturation of the active medium of the pulsed electron-beam sustained discharge CO laser.

Amplification of a train of nanosecond pulses from a frequency-selective CO laser by an electric discharge CO laser amplifier

The output characteristics of an electric discharge CO laser amplifier with an input in the form of a nanosecond (ns) pulse train of wavelength-selective CO laser emission (λ = 5.28 μm) were calculated. The input pulse train characteristics were assigned on the basis of experimental data. The calculated multiplication factor of the first 200 pulses in the laser amplifier is in good agreement with the experimental data. It is shown theoretically that at conditions under study, both the individual pulse shapes and multiplication factor of a train composed of 200 pulses are sensitive to magnitudes of rotational relaxation rates for populations of involved rotational–vibrational energy levels of a CO molecule. It is shown theoretically that the output characteristics of the laser amplifier are not sensitive to the variation of the radial profile of the axisymmetric input laser beam. It is predicted that experimental study on amplification of a separate short pulse will allow evaluation of the rotational relaxation rate with better accuracy.

Plasma-chemical processes in the active medium of a CO laser

The concentrations of plasma-chemical products (C, O, CO2, C2, and C3O2) were measured under conditions typical of the active medium of an electrical discharge CO laser. The dependence of the concentration of C3O2 molecules on the experimental conditions was studied. A reaction scheme responsible for the concentration of C3O2 molecules formed in the discharge was proposed.

Effect of misalignments on phase-locking in a large area discharge CO2 laser

The line deviations and angle deviations of the injected beam at the resonator mirrors in the large area discharge CO2 laser (LADCL) are changed when the output mirror and the phase-locking mirror (PLM) are misaligned. The equiphase surfaces excited by the injected beam are different in the laser resonator and the effect of phase-locking will be influenced. It is shown that the misalignment of PLM is the main cause of phase-locking range reduction. The misalignment of the output mirror will mainly result in the deviation of the output beam, and the misalignment of the PLM will mainly cause decrease of the light intensity. And the maximum misaligned angle should not exceed 20s in order to obtain the ideal effect of phase-locking. The calculated results can provide references for studying deeply the misalignment of LADCL.

Misalignment analysis of combination-cylinder discharge CO(2) laser.

The axes of a laser resonator will deviate away from the initial places when the combination-cylinder discharge CO2 laser (CCDCL) is misaligned. The new cavity axes are established through using the misaligned augmented matrixes. The influences of the misalignments on the properties of the laser beams are studied in detail, such as the line deviations and angle deviations of oscillation beams in CCDCL, the near- and far-field distribution of output beams, the diffraction loss and output power, and the beam quality factor. It is shown that the influences of the misalignments on the above properties of the laser beams are obvious when the misaligned angle of the laser resonator exceeds 30s. The studied results can afford references for the design of a CCDCL.

An optically pumped carbon monoxide laser operating at elevated temperatures

A flowing gas, optically pumped, CO laser has been designed and built. The laser has been made to operate on the fundamental (≈5 μm) infrared bands of the CO vibrational states. The laser is powered by absorption of continuous wave radiation from an electric-discharge-excited CO laser. With this system, the kinetics of the establishment and maintenance of strong population inversions in CO at temperatures above 300 K is studied, independently of the complications of the electron impact processes and of other chemical channels which are present in electric discharge CO lasers. Lasing is obtained at temperatures up to 450 K, well above the cryogenic operating temperatures of conventional electric discharge CO lasers. The vibrational population distribution in the optically pumped laser is measured and the laser output power is determined as a function of the system operating parameters. Laser power conversion factors up to 14% have been observed. An optically pumped CO laser kinetic model is used to analyze the experimental results, providing insight into the details of secondary lasing kinetics.