The laser pulse from a rf waveguide CO2 laser

The behaviour of a rf-excited waveguide CO₂ laser in the pulse regime is studied experimentally. The specific time sections of the pulse have been defined and described in detail. The output pulse evolution versus input power, pressure of the laser mixture, output coupling, repetition frequency and pulse width has been investigated. The spectral content of the pulse has been analysed. A model explaining the effect of laser tuning during the pulse duration is given. The ultrahigh pulse (UHP), defined as the pulse for which the bulge effect occurs, is predicted. Received: 22 October 2002 / Revised version: 13 January 2003 / Published online: 26 March 2003 RID="*" ID="*"Corresponding author. Fax: +48-71/3203-189, E-mail: eda@zr.ita.pwr.wroc.pl     

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.     

Control of transverse mode pattern in a helium-neon laser using the cat’s eye cavity

This paper introduces an innovative method to control and select transverse mode pattern in a He-Ne laser. The cat’s eye cavity is established by using a cat’s eye reflector as the reflecting mirror. Laser transverse mode pattern varies continuously when the distance between the convex lens and the concave mirror is changed, which form the cat’s eye reflector. By Newton-Cotes method, the numerical solution of two-dimensional diffraction integral equation in the cat’s eye cavity is obtained, the laser operating modes under various parameters are analyzed, and the eigenvalue η_mn and diffraction power loss corresponding with every transverse mode are calculated. The parameters assuring fundamental transverse mode output are figured out, which match the experiment results well. Therefore, a new convenient real-time means for the control and selection of the laser transverse mode is realized.     

Pulsed waveguide CO laser operating at room temperature

A pulsed waveguide CO laser operating at room temperature is described. Experimental results of the laser output power variation with discharge parameters and its spectral distribution are given and discussed. In contrast to other CO lasers the best performance has been obtained without diluent gases. A small amount of oxygen added to the CO laser gas enhances the output energy and prevents carbon deposition at the walls of the waveguide channel. So far a laser pulse energy of 40 J has been obtained at an efficiency of 0.4%. Possible ways to increase the laser output energy are discussed.     

Measurement of rotational temperature in CO2 waveguide laser medium

A small-signal gain in CO₂ waveguide laser medium has been measured on rotational-vibrational transitions in the P-branch of the (0, 0, 1)-(0, 2⁰, 0) band. It has been found that the rotational temperature is well defined in the waveguide laser system where high excitation power is injected and a large amount of energy is flowing through vibrational, rotational, and translational degrees of freedom. The rotational temperature is slightly higher than the translational temperature.     

Measurement of far-infrared laser frequencies generated by optically pumped N 2 H4 and N2D4

A three-laser heterodyne system has been used to measure the frequencies of four previously observed far-infrared laser emissions generated by optically pumping either hydrazine (N₂H₄) or its fully deuterated isotope (N₂D₄) with a continuous-wave carbon dioxide laser. These newly measured frequencies have fractional uncertainties of ± 2 × 10⁻⁷ and correspond to laser wavelengths ranging from 63.9 to 158.4 μm. This work represents the first measurement of a N₂D₄ laser frequency.     

Determination of an optimal five-gas combination in a sealed-off CO<Subscript>2</Subscript> laser

For obtaining the maximal output power, five lasing gas mixtures (CO₂, N₂, He, Xe and H₂) in a sealed-off CO₂ laser are optimized by applying a genetic algorithm and solving CO₂ laser kinetics equations. A comparison of numerical simulations shows that the optimal pressures of CO₂ and N₂ are 1.15 Torr and 7.32 Torr, respectively. Accordingly, the maximum laser power of 124 W is obtained by utilizing the optimal gas combination and an optimized resonator with a length of 1.2 m. Received: 14 August 2002 / Published online: 22 January 2003 The project supported by Zhejiang Provincial Natural Science Foundation of China (No. 602098). RID="*" ID="*"Corresponding author. Fax: +86-571/8832-0369, E-mail: chengch@mail.hz.zj.cn     

The mechanism of the CW sodium-vapor/hydrogen laser

Measurements have been carried out to gain information on the mechanism of the cw 9 m sodium-vapor/hydrogen laser [2]. Observations were carried out on the laser excited with both cw and pulsed discharges and the low-power gain of various gas mixtures was measured using tunable diode lasers. The laser was found to oscillate with mixtures of sodium vapor with H₂, D₂ and HD, but with no other gas. On substituting D₂ for H₂ a more than three-fold increase in laser gain was observed. The results showed that most of the processes used to explain lasing action in other metal-vapor lasers were not applicable to the present case. It was concluded that the primary process which leads to the production of the population inversion involves differential quenching of the laser levels by molecular hydrogen, with the lower 3D level being quenched more efficiently than the upper 4P level. Measurements carried out on the calcium/hydrogen laser [21] with D₂ supported these conclusions.     

Single mode oscillation of TEA CO2 laser with an interference resonator

An effective single-longitudinal mode (SLM) pulse TEA CO₂ laser operation was demonstrated using a Michelson’s type resonator with a tilting Fabry-Perot etalon. A modified numerical model of the interference resonator was investigated for designing the laser. The experimentally measured values were found to have good agreement with the numerical model. A pulse width of about 90 ns and the maximum pulse energy of about 300 mJ were achieved at 10.59 μm in SLM and TEM₀₀ mode. The reliability of producing SLM pulses was 100% and there was no damage on the etalon. By turning the interference resonator, the SLM output was tuned 44 lines of the CO₂ spectrum.     

Copper-vapour laser with silver additive

Results of experimental investigation of a pure elemental copper-vapour laser with silver additive are reported. Average output power as well laser output pulse energy increased by up to 10% with the additive. A possible mechanism of additive influence on laser output parameters is discussed.     

Misalignment sensitivity of the cat’s eye cavity He-Ne laser

A concave mirror and a cat’s eye reflector acting as a resonator mirror form the cat’s eye cavity. Misalignment sensitivities of the cat’s eye cavity and conventional resonator are both analyzed in geometric method and matrix optics with misalignment sensitivity parameter. Valuable conclusions are drawn: in full-external He-Ne laser, cat’s eye cavity can improve the laser stability up to about 60 times better than the conventional one; diffraction loss introduced by the misalignment of the cat’s eye cavity attributes to the straight-line displacement vertical to the laser bore of the cat’s eye reflector; and with the convex lens center of the cat’s eye reflector secured immobile, the ultra-stable and adjustment-free cat’s eye cavity He-Ne laser is obtained. The analysis matches the experiment results very well. Cavities with three kinds of dimension errors are also calculated. This paper could be used as theoretic foundation for the design and application of cat’s eye cavity lasers.     

Cesium vapor laser with transverse pumping by multiple laser diode arrays

We have demonstrated a Cs vapor laser that utilizes fifteen laser diode arrays for transverse pumping of the gain medium. A maximum output power of 28 W was achieved with a total optical to optical efficiency of 14% and a slope efficiency of 15%. Transverse pumping allows scaling of such a laser system to a higher power level by simple increasing of the gain medium volume and the number of pump sources.     

Q-switch of a continuously pumped CO2 laser with a scanning coupled-cavity Michelson mirror

We report on the possibility of Q-switching a continuously pumped CO₂ laser using a scanning Michelson interferometer as an end mirror, instead of the habitual well-known strategies. This method, in addition to its simplicity, produces free tail relaxation pulses having duration of about 1.3 μs, which is comparable to what can be obtained when using a saturable absorber. A pulse repetition frequency as high as 90 kHz is obtained.     

Theoretical and experimental investigation of a waveguide CO2 laser with radio-frequency excitation

A comprehensive experimental and theoretical study of the optimization of a continuous-wave radiofrequency (rf) excited CO₂ waveguide laser is presented. The numerical simulation includes the modelling of the gas-discharge plasma parameters like the plasma impedance and energy deposition, the laser kinetics and finally the influence of the resonator feedback on the lasing process. Along with this theoretical study, an extensive experimental research program enabled us to optimize the laser performance of the CO₂ waveguide laser. As a result, a total output power of 42 W and a specific output power of 1.1 W/cm were obtained.     

New FIR laser lines from CD3OD optically pumped by a CO2 waveguide laser

In this work we report new FIR laser lines from CD₃OD optically pumped by a CO₂ waveguide laser. The wide tunability of this laser (290 MHz) makes it possible to pump absorption lines with large frequency offset relative to the CO₂ laser line center, which are not possible by using conventional CO₂ lasers. As a consequence 19 new laser lines have been discovered, ranging from 38.0 m to 455.2 m in wavelength. For all lines, precise frequency offset measurements between the CO₂ line center and the center of the absorber CD₃OD line were performed using the transferred Lamb-dip technique. We also present direct Doppler-free offset measurements of infrared absorption, obtained within the FIR laser cavity itself, using optoacoustic detection.Work supported by FAPESP, CNPq, FAP-Brasil and CNR-Italy     

Efficient generation of FIR radiation by optical pumping of D2 18O

In this paper we show that D₂ ¹⁸O vapour, optically pumped with a continuously tunable high pressure CO₂ laser, is an excellent source for far infrared radiation. Both high photon conversion coefficients and broad Raman gain regions were found for a large number of new laser transitions spread over the frequency range from 25 cm^–1 to 240 cm^–1. We demonstrate that these Raman gain regions can be used to generate far infrared laser pulses with high intensity and durations of about 100 ps.     

Relationship between coherence length and output power of a multi-longitudinal-mode Ar+ laser

The relationship between the temporal coherence (i.e., the coherence length) and the output power of a multi-longitudinal-mode Ar⁺ laser operated near the threshold current is studied. The experimental measurements show that the coherence length is a hyperbola as a function of the output power. A simple model of the multimode equal-amplitude power spectrum is employed in the theoretical analysis. Good agreement between theory and experiment is obtained. It is shown that for a multi-longitudinal-mode Ar⁺ laser, the product of coherence length and the output power is almost a constant. Mailing address: Department of Physics, Suzhou University, Suzhou, Jiangsu 215006, People's Republic of China     

Mode selection in an unstable-resonator TEA CO2 laser by injection from a waveguide laser

The effect of injecting radiation from a cw waveguide CO₂ laser into a TEA laser through a hole in one mirror of its unstable resonator has been studied experimentally. High-power single longitudinal mode operation of the TEA laser is achieved over a wide but finite range of injection frequencies, the frequency of the single-mode pulse being that of the TEA laser cavity mode lying closest to the injected frequency. Although a simple theoretical model shows good qualitative agreement with observations it underestimates the range of injection frequencies which result in single-mode pulses unless a fast chirping of the cavity mode frequency is postulated.     

Output power optimisation of slab-waveguide laser with Gaussian output mirror

We present an approximate analysis of the nonlinear operation of the hollow slab-waveguide laser with Gaussian reflectivity profile output mirror, including gain saturation and longitudinal as well as transverse field distribution of the laser mode. The model presented is general and can be applied to the study of arbitrary configuration of the slab-waveguide laser. In particular, the laser characteristics obtained reveal the influence of the position of the output mirror and the Gaussian mirror parameter on the power efficiency of the laser system. Received: 6 January 2000 / Published online: 8 November 2000     

Intensity resonances in a double-mode HeNe/CH4 laser with synchronized modes

4 gas laser with an intracavity absorbing cell is studied experimentally and theoretically at a modulation frequency approximately equal to the intermode beat frequency. It is revealed that in the vicinity of the absorption-line centre the intensity of every mode for certain system parameters displays resonance structures narrower than the homogeneous line width of the absorption line. This occurs when the range of mode synchronization is near the absorption-line centre and its size is less than the homogeneous width of the absorption line. Received: 29 February 1996/Revised version: 4 February 1997