Search

We report the investigation of a repetitively pulsed laser based on a Fe : ZnSe crystal, cooled to a temperature of 195 K by two thermoelectric modules with a maximum cooling power of 34 W. Two pulsed synchronised Er : YAG lasers, operating in the free-lasing regime, are used for pumping. It is shown that the average laser power in a series of short pulses may exceed 20 W. An average power of 3.1 W is attained in the stationary temperature regime. The lasing spectrum is centred at a wavelength of 4.38 μm, and the total divergence angle is 5 mrad.

One-dimensional gratings with a period of are formed on the surfaces of CdSe and ZnSe crystals ablated by two interfering radiation beams of a nanosecond excimer KrF laser. Investigated are the dependences of the shape and depth of gratings on the energy density under irradiation by a single pulse, and on the number of pulses at a given energy density. The maximum grating depth is estimated as of the period. By forming a one-dimensional grating with a period of and a depth of on the CdSe-crystal surface, this surface becomes antireflective at a wavelength of . The surface reflectivity is reduced by 88 %. A possibility of forming two-dimensional gratings having periods of 1 and is demonstrated.

The characteristics of a Fe:ZnSe laser pumped by a single-pulse free-running Er : YAG laser and a repetitively pulsed HF laser are presented. An output energy of 4.9 J is achieved in the case of liquid-nitrogen cooling of the Fe2+:ZnSe active laser element longitudinally pumped by an Er:YAG laser with a pulse duration of 1 ms and an energy up to 15 J. The laser efficiency with respect to the absorbed energy is 47%. The output pulse energy at room temperature is 53 mJ. The decrease in the output energy is explained by a strong temperature dependence of the upper laser level lifetime and by pulsed heating of the active element. The temperature dependence of the upper laser level lifetime is used to determine the pump parameters needed to achieve high pulse energies at room temperature. Stable repetitively-pulsed operation of the Fe2+:ZnSe laser at room temperature with an average power of 2.4 W and a maximum pulse energy of 14 mJ is achieved upon pumping by a 1-s train of 100-ns HF laser pulses with a repetition rate of 200 Hz.

A continuous-wave oscillation is obtained for the first time in a Fe2+:ZnSe laser. The laser wavelength was in the range from 4.04 to 4.08 μm. A liquid-nitrogen-cooled active element was pumped by a Cr2+:CdSe laser at 2.97 μm. The maximum output power of the laser was 160 mW with the 56% slope efficiency. The minimum absorbed pump power threshold was 18 mW. The intrinsic losses in the Fe2+:ZnSe crystal did not exceed 0.024 cm-1 during lasing.

The efficient lasing of a Cr2+:CdSe single crystal pumped by 1.94-μm, 300-μs pulses from a Tm:YAP laser was obtained. The Cr2+:CdSe laser with a nonselective resonator emitted up to 17 mJ at a wavelength of ~2.65 μm with the quantum slope efficiency of 63% with respect to the absorbed pump energy. The absorption coefficient of the Cr2+:CdSe crystal at the laser wavelength did not exceed 0.045 cm-1. By using a resonator with a dispersion prism, the laser wavelength was continuously tuned in the spectral range from 2.26 to 3.61 μm.

A Fe2+:ZnSe laser emitting in the spectral range between 3.77 and 5.05 μm is used for the first time for intracavity laser spectroscopy. The intracavity absorption spectra of methane in the 4.1-μm region are recorded at different instants of lasing (0–80 μs) and the dynamics of spectral holes during lasing is investigated. It is found that an intracavity absorption signal linearly increases with time during lasing in the time range from 0 to 80 μs, which provides the effective absorption length up to 24 km.

The temperature dependence of the efficiency of a laser based on a Fe:ZnSe crystal grown from the vapour phase by the free-growth method is studied in the 85-255-K temperature range. As the temperature was increased, the slope efficiency of the laser with respect to absorbed energy decreased from 43% (at 85 K) down to 9% (at 255 K) and its emission spectrum shifted from 4.0 to 4.17 mu m. Lasing was obtained in a Fe2+:ZnSe crystal cooled with a thermoelectric module down to similar to 220 K. In this case, the slope efficiency of the laser with respect to absorbed energy was 30%. The output energy of the thermoelectrically cooled laser was 142 mJ for the slope efficiency with respect to the incident pump energy equal to 21%.

The growth dynamics of intracavity absorption is studied during recording line absorption spectra by the method of intracavity laser spectroscopy using a pulsed Cr2+:ZnSe laser tunable between 2.1 and 3.1 μm. In the lasing duration range from 0 to 235 μs, an intracavity absorption signal increases linearly with time, providing the effective absorption length of 70km.

The method of intracavity laser spectroscopy using a Co:MgF2 laser is applied to record the absorption spectra from the first excited a1Δg state of gaseous molecular oxygen at the a1Δg → b1Σg+ transition at 1.91 μm. The gas flow from a chemical singlet oxygen generator with a known concentration of singlet oxygen O2 (a1Δg) was supplied to the cavity of the Co:MgF2 laser. The absorption line intensities are measured for five spectral lines of the Q-branch of the 0–0 vibrational band for the a1Δg → b1Σg+ transition. The O2 (b1Σg+ → a1Δg) transition probability calculated from these data was (1.20 ± 0.25) × 10-3 s-1.

The electrical and spectroscopic characteristics of electron-beam-sustained discharge (EBSD) in oxygen and oxygen-containing gas mixtures are studied experimentally under gas pressures up to 100 Torr in a large excitation volume ({approx}18 L). It is shown that the EBSD in pure oxygen and its mixtures with inert gases is unstable and is characterised by a small specific energy contribution. The addition of small amounts ({approx}1%-10%) of carbon monoxide or hydrogen to oxygen or its mixtures with inert gases considerably improves the stability of the discharge, while the specific energy contribution W increases by more then an order of magnitude, achieving {approx}6.5 kJ L{sup -1} atm{sup -1} per molecular component of the gas mixture. A part of the energy supplied to the EBSD is spent to excite vibrational levels of molecular additives. This was demonstrated experimentally by the initiation of a CO laser based on the O{sub 2} : Ar : CO = 1 : 1 : 0.1 mixture. Experimental results on spectroscopy of the excited electronic states O{sub 2}(a{sup 1{Delta}}{sub g}) and O{sub 2}(b{sup 1{Sigma}}{sub g}{sup +}), of oxygen formed in the EBSD are presented. A technique was worked out for measuring the concentration of singlet oxygen in the O{sub 2}(a{supmore » 1{Delta}}{sub g}) state in the afterglow of the pulsed EBSD by comparing with the radiation intensity of singlet oxygen of a given concentration produced in a chemical generator. Preliminary measurements of the singlet-oxygen yield in the EBSD show that its value {approx}3% for W {approx} 1.0 kJ L{sup -1} atm{sup -1} is in agreement with the theoretical estimate. Theoretical calculations performed for W {approx} 6.5 kJ L{sup -1} atm{sup -1} at a fixed temperature show that the singlet-oxygen yield may be {approx}20%, which is higher than the value required to achieve the lasing threshold in an oxygen-iodine laser at room temperature. (laser applications and other topics in quantum electronics)« less

A Cr2+ : ZnSe laser emitting 100-μs pulses tunable in the 2–3-μm region is used for the first time for the highly sensitive detection of absorption spectra by the method of intracavity laser spectroscopy. The intracavity absorption spectra of the atmospheric air were recorded at different instants of lasing in the spectral region from 2.41 to 2.46 μm. An increase in the sensitivity of the laser emission spectrum to intracavity absorption was observed over the entire range of lasing durations studied.

A laser based on a Fe2+:ZnS crystal is demonstrated for the first time. Lasing in this crystal is obtained at room temperature under pumping by 40-ns pulses of an Er:YAG laser at a wavelength of 2.94 nm. The slope efficiency of the Fe2+:ZnS laser with respect to the absorbed pump energy was 32%, and the output energy reached 3.4 mJ. Continuous tuning of the laser wavelength within the range of 3.49 — 4.65 nm was achieved using an intracavity dispersion prism.

The absorption spectrum of singlet oxygen O2(a1 Δg) is detected in a gas phase at the a1 Δg → b1 Σg+ transition by the method of intracavity laser spectroscopy using a broad-band Co : MgF2 laser emitting 200-μs pulses at a wavelength 1.91 μm. In the case of Doppler broadening of absorption lines at room temperature, the sensitivity of detection of O2 (a1 Δg) is ~ (2 — 5) × 1014 cm-3 . It is shown that the gas temperature can be calculated from the dependence of absorption cross sections for individual lines on the rotational quantum number.

It is found that inserting aerosol in a cavity of a multimode (wide-band) Co:MgF2 laser can strongly affect its emission spectrum, provided the typical size of aerosol particles is comparable to the laser wavelength (~2 μm). In the presence of aerosol, intensity spikes are formed in the spectrum at the initial lasing stage, which develop in time. At moments of time ~100 μs, condensation of the spectrum was observed, which manifested itself as a sharp (more than two orders of magnitude) narrowing of the laser emission spectrum down to the value determined by the spectral resolution of a spectrograph (not better than 0.04 cm-1), with an insignificant decrease in the output energy.

The spatial distribution of the scattered-radiation energy during focusing, in atmospheric air, of the fourth-harmonic beam of a pulsed neodymium laser (λ = 264 nm) with an annular cross section was studied experimentally. Shortening of the UV scattered-radiation by a factor of 2 — 5, compared with the duration of the laser pulse, was observed. An interference structure of the scattered radiation, varying with increase in the laser-pulse energy, was recorded. The diffraction rings and bands originating from screens were transformed into analogous diffraction rings and bands from additional screens. This can be accounted for by the scattering of the laser beam on a gas perturbation or on a particle in the caustic. Experiments were performed on the scattering of radiation with λ = 0.63 μm on formations with an abrupt boundary, which confirmed the above hypothesis.

The characteristics of a laser based on a Fe2+:ZnSe single crystal pumped by an electric-discharge HF laser at room temperature are studied. The HF laser beam diameter on the crystal surface was 17 mm. The achieved laser energy was 1.2 J with an efficiency of ~ 25% with respect to the pump energy.

Intracavity spectroscopy, with the aid of a Al2O3:Ti3+ laser, was used to determine the concentrations of H2O and O2 and the temperature of the active medium of an oxygen—iodine laser. When duration of the Al2O3:Ti3+ laser pulses was 120 μs, the sensitivity of the method was 6×1014 and 3×1014 cm-3 for H2O and O2, respectively. The error in the determination of the oxygen concentration in the range 2×1015—1016 cm-3 did not exceed 5% at temperatures 200–500 K and the temperature error did not exceed 25 K.

The lasing characteristics of a Fe:ZnSe single crystal grown from the vapour phase by the free-growth technique using the chemical transport in hydrogen are studied. A Fe2+:ZnSe laser cooled to liquid nitrogen temperature and pumped by 2.9364-μm radiation from an Er:YAG laser produces the 130-mJ output energy with a slope efficiency of 40% in terms of the absorbed energy, which corresponds to a quantum efficiency of 55%. The lasing spectrum in a dispersive resonator can be continuously tuned between 3.77 and 4.40 μm.

We report on the successful growth of single crystals of Fe2+:CdSe by seeded physical vapor transport (SPVT) technique with doping within the growing process and subsequent annealing in Se vapor. Luminescence lifetime measurements, spectroscopic studies of 5E–5T2 transition of Fe2+ in CdSe, and laser experiments were performed. The lifetime of the 5T2 energy level was measured to be 20 ± 5 ns at a room temperature (RT) of 290 K. At liquid nitrogen (LN) temperature, luminescence kinetics displayed a non-exponential decay, which can be fitted to a bi-exponential function with time constants τ 1 = 6 µs and τ 2 = 29 µs. As much as 3.2 mJ of output energy at 5.2 µm with 27% absorbed pump energy slope efficiency of an Fe2+:CdSe laser was achieved at RT under 2.94 µm nanosecond Er:YAG laser pumping. The Fe2+:CdSe laser was tuned from 4.63 to 6.10 µm. Obtained characteristics of Fe2+:CdSe indicate that the crystal can be considered a promising medium for amplification of femtosecond pulses in the middle infrared range up to 6 µm.

We demonstrate a first-of-its-kind efficient amplification of a broadband tunable (from 3.8 to 4.8 µm) mid-IR femtosecond seed pulse generated from a AgGaS2-based optical parametric amplifier pumped by a Cr:forsterite laser in a multi-pass Fe2+:ZnSe amplifier optically pumped by a solid-state nanosecond Cr:Yb:Ho:YSGG laser. A total gain of 2000 for an input seed energy of 40 nJ has been obtained. The magnitude of the output energy reaches 80 µJ at a pulse duration of 200 fs.

The output energy of 10.6 and 3.25 J with a pulse duration of ~1 ms and a crystal temperature of 85 K was achieved in the Fe:ZnSe and Fe:ZnS lasers, respectively. At room temperature, the Fe:ZnSe laser energy was as high as 1.2 J with a pulse duration of 150 ns. A few optical schemas of the Cr:CdSe laser with laser diode pumping were realized.

A numerical analysis is made of the extraction of energy from a mixture of singlet oxygen and atomic iodine by repeated passage of a 10 ns laser pulse through an amplifier 1 m long. Production of atomic iodine by photolysis of the iodides CH3I and CF3I is considered. It is shown that a high degree of energy extraction is possible after a reasonable number of passes (20–40) if CH3I is used, but this requires the absence of chlorine impurities from the mixture. The replacement of CH3I by CF3I considerably reduces the energy extraction efficiency and leads to more stringent requirements in respect of an initiation system.

The lasing characteristics of a Cr2+ : ZnSe crystal grown by the method of free growth on a single-crystal seed using physical transport in helium are studied. The crystal was doped from a vapour phase during its growth. The achieved concentration of dopant Cr2+ ions (5×1018 cm-3) provides the absorption coefficient of 4.5 cm-1 at the maximum of the pump band (1.78 μm). Upon pumping by a pulsed Co : MgF2 laser at 1.67 μm, the slope efficiency equal to 59 % with respect to the absorbed energy was achieved, which corresponds to the quantum efficiency 87 %.

The intracavity absorption spectra of CO2 and H2O in the range 2.03 — 2.05 μm, as well as NH3 and CH4 in the range 2.23 — 2.26 μm, were obtained with the aid of a Co:MgF2 laser. It was found that an intracavity laser spectrometer based on a Co:MgF2 laser emitting for 1 ms can be used to detect many impurity gases in the atmosphere at a concentration level of (1 — 40) × 10-9.

The dynamics of the spectral dips, observed in detection of weak absorption lines by intracavity laser spectroscopy with a Co:MgF2 laser, was investigated. When the pumping rate exceeds the threshold by factors of 2.6 and 1.4, the intracavity absorption increases linearly with increase in the duration of lasing to 0.5 and 1 ms, respectively. A deviation from linearity is observed for longer times. This ensures a sensitivity sufficient for measurement of the line absorption coefficient down to 3 × 10-9 cm-1 in the 1.6 — 2.5 μm spectral range of laser emission.

The operation of a room-temperature, solid-state, Cr-doped CdSe continuous-wave laser is demonstrated. Longitudinal pumping with a continuous-wave diode laser array at 1.94 µm produced a broadband output of 200 mW at 2.6 µm with an incident power slope efficiency of 6.4%.

For the first time, an experimentally measured seed pulse gain of about 2 cm−1 allows possibilities in the scaling power of such a femtosecond laser system in terawatts. The concept of a subterawatt power level hybrid femtosecond mid-IR (4–5 μm) laser system, based on a weak pulse from an optical parametric mid-IR seeder that is amplified in chalcogenide monocrystalline Fe2+:ZnSe, to gain medium has been proposed and designed. The method and approach for optimizing the choice of nonlinear medium, its length, and the required light intensity for the efficient non-linear self-compression of an ultrashort pulse has also been proposed and considered.

A laser on single-crystal ZnSe:Fe2+ was investigated at room temperature. Pumping of the laser was performed by a pulsed electrodischarge HF laser. In experiments, the spot diameter of HF laser radiation incident to the surface of the crystal varied from 5.6 to 17 mm. Generation energy of ~1.2 J was obtained and the efficiency with respect to the energy arriving at the crystal was η in ≈ 25%. The slope efficiency with respect to the energy absorbed in the crystal at large spot dimensions was η slope = 45%.

We report the laser properties of Fe:ZnS in the temperature range from 85 to 186 K. Under pumping by a pulsed free-running 2.94 μm Er:YAG laser, a maximum output energy of 3.25 J at 85 K was produced with 27% optical-to-optical efficiency. The output wavelength was observed to tune with temperatures from 3.60 μm at 85 K to 3.78 μm at 186 K. As the temperature was increased, the absorbed energy slope efficiency decreased from 42.4% at 85 K down to 2.5% at 183 K. With a CaF2 prism, the Fe:ZnS laser could be tuned from 3.44 to 4.19 μm at 85 K.

Absorption spectra of atmospheric carbon dioxide and water vapor are recorded by intracavity laser spectroscopy technique using a broadband Co:MgF 2 laser, tunable over the range from 1.6 to 2.5 μm. Pulsed Co:MgF 2 laser has been operated at room temperature. The dynamics of intracavity absorption was studied for the generation time of 0–100 μs. The observed linear dependence of sensitivity on the generation time demonstrates that Co:MgF 2 laser can be utilized for high sensitivity intracavity laser spectroscopy measurements in the near infrared (IR) region.

A Co : MgF2 crystal laser was pumped with radiation (λ =1.35 μm) from a neodymium glass laser. This resulted in generation of radiation of 1.6 J energy with a quantum efficiency of 67%. The Co : MgF2 crystal could thus be used for efficient conversion of λ =1.3 μm laser beams, such as those from iodine photodissociation and chemical oxygen — iodine lasers.

An intracavity laser spectroscopy method was employed in recording for the first time the absorption spectrum of the NF radical in the vicinity of the b—X transition. Experiments showed that the method could be used successfully in direct measurements of the population difference. When the duration of a dye laser pulse was 1.3 μs, the minimum recorded population difference was 3.5×1015 cm-3. The rate constant for the NF(X) +NF(X) process was determined: it was (5.5 ± 1.5)×10-12 cm3 s-1.

Solid-state cw Cr2+ : ZnSe laser has been used for Doppler-free spectroscopy of lines of the vibrational — rotational v1 + v4 band of methane. Saturated-dispersion resonances on the components of the R(2) line near λ = 2.36 mm are revealed. The parameters of the saturated-dispersion resonance obtained upon cooling intracavity methane cell to a temperature of 77 K confirmed good prospects of developing an optical master oscillator with a high (10-15 - 10-16) short-term frequency stability based on a Cr2+ : ZnSe/CH4 laser.

Lasing in a Cr2+:CdS crystal is demonstrated for the first time. The output power of a Cr2+:CdS laser pumped by a pulsed Tm:YAP laser at 1.94 μm achieved 4 mJ and the slope efficiency with respect to the absorbed pump energy was 39%. The continuous tuning was obtained from 2.2 to 3.3 μm in the laser with a dispersion prism resonator.

Continuous wave lasing in a Cr2+:CdSe crystal is obtained for the first time. The Cr2+:CdSe crystal pumped by a 1.908-μm thulium fibre laser generated 1.07 W at 2.623 μm with the quantum slope efficiency with respect to the absorbed power equal to 60%.

Passive Q-switching of 3-mu m lasers with the help of a Fe2+ : ZnSe single crystal is demonstrated. The 6-mJ, 50-ns giant pulses are obtained from a 2.9364-mu m Er : YAG laser by using this passive Q switch.

We report the results of a study of a pulsed Fe:ZnSe laser for temperatures ranging from 85 to 295 K. With a free-running Er:YAG laser, operating at 2.94 μm, as a pump source, a maximum output energy of 2.1 J at 85 K was produced at a wavelength of 4.1 μm. The optical-to-optical efficiency of the laser was 35% at maximum energy while the maximum absorbed energy slope efficiency was as high as 51%. By operating at 245 K (a temperature which can be easily reached using thermoelectric coolers) we achieved 1.3 J of output energy from an Fe:ZnSe laser, with a slope efficiency of 29% (23% optical-to-optical efficiency). The maximum output energy reached 42 mJ at room temperature (295 K). The temperature dependence of the lifetime of the 5T2 energy level of Fe2+ in ZnSe was studied in the 275–365 K temperature range. The activation energy for nonradiative relaxation was found to be 2235 cm−1.

Radiation from a chemical oxygen — iodine laser was used for the first time to pump a Co : MgF2 crystal laser. The attained differential (slope) efficiency of 40%, corresponding to a quantum efficiency of 62%, demonstrated that a Co : MgF2 crystal can be used for efficient conversion and summation of iodine laser beams.

The intraresonator laser spectroscopy was used in a determination of the absorption spectrum of air in the 5850–5930 A range. This spectrum was compared with the published information obtained by conventional methods using optical paths in the atmosphere amounting to many kilometers. Atmospheric absorption lines of NO2 were observed. The absorption coefficient of water vapor at the center of the 5919.054 A line was determined at a pressure of 150 mm Hg.

A laser utilizing F2+ color centers in an LiF crystal was used in intracavity laser spectroscopy to determine the increase in the temperature of molecular fluorine due to the absorption of energy in the course of its flash photolysis. Measurements were based on the temperature dependences of the absorption coefficients of the individual lines of vibrational–rotational transitions in HF molecules which were present in fluorine as a trace impurity. The degree of dissociation of molecular fluorine was determined.

It was established that organic dye lasers could be used in very-high-sensitivity laser spectroscopy based on the selection of losses in the resonator. A smooth emission spectrum was obtained for rhodamine G and the abosrption spectrum of I2 with an absorption coefficient of ~10–3 cm–1 was recorded in the 16450–17950-cm–1 range.