A frequency-doubled pulsed chemical oxygen-iodine laser

The intracavity second-harmonic generation of pulsed chemical oxygen-iodine laser radiation was investigated. A pulsed chemical oxygen-iodine laser with a maximum output energy of 6.14 mJ was used. The second-harmonic output of 0.5 mJ was demonstrated using a lithium iodate crystal. The conversion efficiency of 8% was limited by intracavity losses. Numerical simulation predicts that a conversion efficiency of 75% can be obtained with 1% intracavity losses.     

High-pressure subsonic mode operation of chemical oxygen-iodine laser

A new regime of chemical oxygen-iodine laser (COIL), high-pressure subsonic mode operation, was demonstrated using a jet-type singlet oxygen generator (SOG). The laser output power of 342 W with chemical efficiency of 20.9% was obtained at the Cl₂ flow rate of 18 mmol/s and the operating pressure of 6.4 Torr in the laser cavity. The specific energy was 3.1 J/l which was four times higher than our supersonic device, and was comparable to the highest value for the supersonic regime. The experimental results were in good agreement with the numerical simulation results. Received: 26 February 1999 / Revised version: 13 July 1999 / Published online: 30 November 1999     

Experiment and modeling of a small-scale,supersonic chemical oxygen-iodine laser

We report on detailed experiment and modeling of a small-scale, supersonic chemical oxygen-iodine laser. The laser has a 5 cm long active medium and utilizes a simple sparger-type O₂(¹ ) chemical generator and a medium-size pumping system. A grid nozzle is used for iodine injection and supersonic expansion. 25 W of cw laser emission at 1.315 µm are obtained in the present experiments. The small size and the simple structure of the laser system and its stable operation for long times make it a convenient tool for studying parameters important for high-power supersonic iodine lasers and for comparison to model calculations. The lasing power is studied as a function of the molar flow rates of the various reagents, and conditions are found for optimal operation. Good agreement is found between the experimental results and calculations based on a simple one-dimensional semi-empirical model, previously developed in our laboratory and modified in the present work. The model is used to predict optimal values for parameters affecting the laser performance that are difficult to examine in the present experimental system.     

Lasing performance of a chemical oxygen iodine laser (COIL) with advanced ejector-nozzle banks

Experimental results have demonstrated that the use of ejector-nozzle concepts can allow to achieve simultaneously high chemical efficiency and high pressure recovery in a chemical oxygen iodine laser. The estimated small-signal gain of the gain medium generated by these nozzle banks was from 0.5 to 0.8 %/cm. In laser experiments with all nozzle banks (NB-1–NB-5), Pitot pressures of the order of 80 Torr and Mach numbers of ∼2 in the cavity-mixing chamber have been achieved. The geometry of a given ejector-nozzle bank and gas-flow conditions affect the power extraction and chemical efficiency. The main factors for high efficiency and high power are small mixing scale, high area for the oxygen flow, dilution of chlorine by helium, and the arrangement of nozzles. A chemical efficiency of 25% at a power level of ∼900 W was obtained for NB-1 having the smallest mixing scale, parallel injection of all flows, and dilution of oxygen by helium. The highest power of ∼1.2 kW with a chemical efficiency of 19.5% and 160 W/cm² of specific output power was achieved with NB-5 having the largest area for the oxygen flow and dilution of oxygen by helium. Received: 7 October 2002 / Accepted: 20 January 2003 / Published online: 28 May 2003 RID="*" ID="*"Corresponding author. Fax: +7-8462/355-600, E-mail: nikolaev@fian.smr.ru     

Efficient second-harmonic generation in Tl3AsSe3 using focussed CO2 laser radiation

The nonlinear material Tl₃AsSe₃ was used to convert pulsed 10.6 m laser radiation into the second harmonic. The laser beam was tightly focussed, and an energy conversion efficiency of 57% was obtained, which is the highest reported to date in the mid-IR.     

Chemically pumped O2(a-X) laser

A theoretical and experimental study was conducted aimed at achieving laser oscillation in the (a-X) electronic transition of oxygen molecules. Although this transition is highly forbidden by rigorous selection rules, it may nevertheless concede stimulated emission, if the population inversion is high enough. The idea is based on a recently developed apparatus, namely, a porous pipe type high-pressure chemical singlet oxygen generator. A numerical model which describes the characteristics of this generator was developed to estimate the population inversion and small-signal gain achievable in a laser cavity using this source. The calculations showed that the small-signal gain ought to be sufficient to achieve laser oscillation. Preliminary experiments were conducted, but lasing was not yet observed. It is shown that the scattering losses caused by water droplet aerosols are mainly responsible for preventing our system from laser oscillation.     

Novel concept of electric discharge oxygen-iodine laser

A novel concept of discharge oxygen-iodine laser (DOIL) is presented. The supersonic DOIL includes a discharge singlet oxygen generator (DSOG) and discharge atomic iodine generator (DAIG). The operation of DSOG is based on a fast mixing of hybrid argon plasma jet of DC electric arc and RF discharge with a neutral molecular oxygen stream. The goal of our effort is achievement of DOIL oscillations by this new discharge technique, which should provide the singlet oxygen yields exceeding 30% at the total pressures higher than 10 torr. The DAIG operation is based on a cw/pulse RF discharge dissociation of iodine donors directly inside a laser iodine injector. This method substitutes the classic dissociation of molecular iodine by energy of singlet oxygen, which saves its energy for laser generation and so can increase the laser efficiency. The laser power could be thus enhanced by up to 25% if this method is employed in a chemical oxygen-iodine laser (COIL) operation, and even 3 times in DOIL without increase in the iodine laser pumping by singlet oxygen.     

Intracavity second-harmonic generation of 1.06 μm in GdCa4O(BO3)3 crystals

The characteristics of intracavity second-harmonic generation (SHG) at 1.06 μm in GdCa₄O(BO₃)₃ (GdCOB) crystals cut for different type I phase-matching (PM) directions of (θ,φ)=(66.8°, 132.3°); (19.4°, 0°); (90°, 46°) have been investigated. It was found that the intracavity SHG was significantly efficient in the PM direction of (66.8°, 132.3°), and that the intrinsic lower effective nonlinear coefficient (d_eff) was responsible for the less-efficient SHG in the other two directions. A maximum CW SHG output power of 2.81 W was obtained with an optical conversion efficiency of 18.7%, while the corresponding effective intracavity SHG efficiency was determined to be 41.3%. The intracavity SHG efficiency of GdCOB has been found to reach two-thirds of that obtained with type II phase-matching KTiOPO₄ (KTP). Received: 26 April 2000 / Revised version: 3 July 2000 / Published online: 5 October 2000     

43 W picosecond laser and second-harmonic generation experiment

Combining the advantages of diode-end-pumped Nd: YVO₄ and diode-side-pumped Nd: YAG amplifiers, a high average power and high beam quality picosecond laser is designed. The system delivers a picosecond laser with average power of 43.4 W and good beam quality of M² < 1.7. By focusing the high power picosecond laser in LBO crystal, 532 nm green laser with maximal power of 20.8 W is generated and the conversion efficiency of second-harmonic generation reaches 56.4% when 17.7 W green laser obtained from the fundamental frequency laser with power of 31.4 W and beam quality of M² < 1.25.     

Dynamics and correlated performance of a photo-triggered discharge-pumped HF laser using SF6 with hydrogen or ethane

3 , has been performed in Ne/SF₆/H₂ and Ne/SF₆/C₂H₆ mixtures. Parameters involved have been the storage line capacitance and the circuit inductance, the capacitors charging voltage, the RH-molecule type and partial pressure, and the X-ray dose for the preionization. High laser performance has been achieved with C₂H₆: an output energy up to 3 J corresponding to a specific energy of 9.6 J/l at an efficiency of 4.7%, which strengthens the advantage of the photo-triggering technique to energize high-power HF lasers. However the optimum performance achieved with H₂, 5.75 J/l and 3.5%, are lower. It is shown, through a time-resolved study of the electrical discharge and spatial dynamics correlated to laser power and energy measurements, that discharge instabilities are responsible for the poor laser performance of the mixture with H₂. These instabilities, which lead to arc development, are characteristics of the discharge in Ne/SF₆. It is demonstrated for the first time that addition of a heavy hydrocarbon, such as C₂H₆, to that mixture induces the discharge stabilization so that the laser emission arises in a homogeneous active medium. This effect allows us to achieve better laser performance than with H₂. Received: 17 March 1998/Revised version: 13 July 1998     

A frequency doubled chemical oxygen iodine laser

The output of a chemical oxygen iodine laser (=1.315 m) has been frequency doubled at an overall conversion efficiency of 1%. A lithium iodate (LiIO₃) crystal was used in an intracavity doubling scheme. This represents the first time visible laser light has been obtained, solely from a chemical source.To whom the correspondence should be addressed.     

Development of the Chemical Oxygen-Iodine Laser (COIL) with chemical generation of atomic iodine

This article addresses the development of a Chemical Oxygen-Iodine Laser (COIL) with alternative chemical ways of generating atomic iodine. Injection of atomic iodine as opposed to molecular iodine has the potential to improve the COIL efficiency. This paper describes two chemical methods for generating iodine atoms based on the gas phase reactions of hydrogen/deuterium iodide with fluorine or chlorine atoms, which are also produced chemically. Simplified one-dimensional gas dynamic modeling that describes the stream-wise profiles of species concentrations within both reaction systems is used to gain a theoretical understanding of both reaction systems under COIL conditions. The modeling results are used for the design of an experimental device and the interpretation of experimental data. The first experimental investigation studies the production of iodine atoms produced from reactions of Cl with HI. Atomic iodine yields of 70–100% in nitrogen are obtained, and the gain on the I(² P _1/2)–I(² P _3/2) transition in a flow of singlet oxygen is measured. Received: 7 October 2002 / Accepted: 8 February 2003 / Published online: 28 May 2003 RID="*" ID="*"Corresponding author. Fax: +420-2/8689-0527, E-mail: kodym@fzu.cz     

Small signal gain measurements in a small scale HF overtone laser

The overtone gain medium of a small-scale HF overtone laser was probed using a sub-Doppler tunable diode laser. Two-dimensional spatially resolved small signal gain and temperature maps were generated for several ro-vibrational transitions in the HF (v=2→v=0) overtone band. Our results compare well with previous measurements of the overtone gain in a similar HF laser device. Received: 7 October 2002 / Accepted: 20 January 2003 / Published online: 28 May 2003 RID="*" ID="*"Corresponding author. Fax: +1-505/846-4807, E-mail: kevin.hewett@kirtland.af.mil     

Theoretical study of a new energy extraction scheme of a chemically pumped pulsed iodine laser amplifier

A new energy extraction scheme of a chemically pumped pulsed large-scale iodine laser based on a high-pressure pulsed singlet oxygen generator is proposed. In previous investigations only low-pressure oxygen generators have been considered. Since they require a high iodine density for an efficient amplifier operation, the lifetime of the stored energy is correspondingly small and thus only small-sized iodine amplifiers appear to be technically feasible. We found, however, that when the singlet oxygen is generated at high-pressure, the iodine density required can be considerably reduced so that the lifetime of the stored energy becomes sufficiently long to fill up large amplifier cells. A numerical model is developed and the extractable energy is theoretically estimated. It is shown that 0.2J/1·pass can be extracted when an input pulse of 20 ns duration (FWHM) and 1 J/cm² fluence is fed into the amplifying medium.     

Generation of 2.1 W Continuous Wave Blue Light by Intracavity Doubling of a Diode-End-Pumped Nd：YAG Laser in a 30 mm LBO

A folded four-mirror cavity with a composite Nd：YAG rod is optimized to obtain high efficient cw 473nm blue output. The laser could operate stably in the region of the thermal-lens focal length from 20mm to 70mm. LBO is used for intracavity frequency doubling of the 946nm transition of Nd：YAG and the optimum LBO length is investigated. A maximum output power of 2.1 Win the blue spectral range at 473nm is achieved with 30-mm-long LBO, corresponding to an optical conversion efficiency of 9.1%.     

Subpicosecond UV pulse generation for a multiterawatt KrF laser

A 180-fs UV pulse has been generated based on a hybrid synchronously pumped mode-locked dye laser for a multiterawatt KrF laser system. The pulse width was measured by the single shot autocorrelation technique with the three-photon fluorescence of the XeF C-A transition. The pulse width broadening due to dispersive media was investigated. The results show that the observed pulse width broadening from 210 fs to 390 fs through the entire system is explained mostly by the linear dispersion of the optical elements for near-transform-limited input pulses.     

41 mW high average power picosecond 177.3 nm laser by second-harmonic generation in KBBF

We report on the generation of high average power, high repetition rate, and picosecond (ps) deep-ultraviolet (DUV) 177.3 nm laser. The DUV laser is produced by second-harmonic generation of a frequency-tripled mode-locked Nd: YVO₄ laser (<15 ps, 80 MHz) with KBBF nonlinear crystal. The influence of different fundamental beam diameters on DUV output power and KBBF-SHG conversion efficiency are investigated. Under the 355 nm pump power of 7.5 W with beam diameter of 145 μm, 41 mW DUV output at 177.3 nm is obtained. To our knowledge, this is the highest average power for the 177.3 nm laser. Our results provide a power scaling by three times with respect to previous best works.     

Intracavity second-harmonic and sum-frequency generation with a laser-diode-pumped multitransition-oscillation LiNdP4O12 laser

Efficient simultaneous intracavity second-harmonic and sum-frequency generation that is free from irregular large amplitude fluctuations (the so-called green problem) is achieved with a laser-diode-pumped LiNdP(4) O(12) (LNP) laser with a type II phase-matching KTiOPO(4) crystal. Observed frequency-mixing operations result from the simultaneous single-frequency oscillations on different transitions that arise from the wide fluorescence linewidth in a stoichiometric LNP laser that possesses inherently high Nd concentrations. Sum-frequency generation has been shown to arise from the interaction of oscillating longitudinal modes that belong to different transitions. A promising application to coherent terahertz-wave radiation by use of photomixers is proposed.     

Frequency Characteristics of the Satureted Gain in Nonequilibrium Gas Flow and Doppler-Broadened Chemical Laser Amplifiers

We present "convection-nonequilibrium cross relaxation" model for a gas flow and chemical lasers, Teh experessions of the saturated gain spectrum are obtained for the two-type flow models with layer or turbulent flow mixture respectively. The numerical results show that the gain profile of a saturated amplifier with Doppler-broadening is a mixture of inhomogeneous and homogeneous profiles     

High-power continuous-wave diode-end-pumped intracavity-frequency-doubled Nd:GdVO4/LBO red laser

A high-power continuous-wave (CW) diode-end-pumped intracavity-frequency-doubled red laser is reported here. The laser consists of a 0.3 at.% Nd:GdVO₄ crystal as laser gain medium, a type II non-critical phase-matched (NCPM) LBO crystal or a type I critical phase-matched (CPM) LBO crystal as frequency-doubler, and a three-mirror-folded cavity. At incident pump power of about 41 W, maximum output powers of 3.8 W and 3 W at 671 nm are obtained with corresponding optical-to-optical conversion efficiency of 9.3% and 7.5%, respectively. During half an hour, the instability of the red beam is less than 3% at output of 3 W.