Auto-prepulse operation of a long-pulse XeCl laser

A standard corona preionized XeCl laser prototype has been excited by a very simple L-C circuit consisting of a large storage capacitance charged at relatively low voltage (12 kV) and discharged via a switch on the electrodes, tightly coupled with the peaking capacitors. The resulting overvoltage following the switch closure behaves as an effective and automatic prepulse, providing a homogeneous discharge lasting up to 400 ns. Energy output levels of the order of 150 mJ at 1.4% overall efficiency have been achieved.     

Two-photon dissociation of HgBr2 as passive mode locking mechanism of a long-pulse XeCl excimer laser

Results are presented related to the use of two-photon dissociation of HgBr₂ molecular vapor as a non-linear fast-opening passive mode locker of a long-pulse XeCl laser. A dye solution, with or without scatterers, is also examined for comparison. Pulses with durations below our resolution limit of 400 ps and with a modulation better than 90% are reported. The low threshold, the non-destruction and the broadband absorption causing photodissociation make this molecule useful for laser pulse compression and decoupling for many lasers in the ultraviolet region. Received: 22 April 2002 / Revised version: 2 July 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +30-2810/394201, E-mail: efthim@physics.uoc.gr     

Four-branch oscillation from a dual-polarization cavity CO2 laser

We report here for the first time multiline oscillation of a cw-CO₂ laser on all the four branches 10P, 10R, 9P, and 9R where all laser wavelengths share a common gain medium. The 9R, 9P and 10R branch lines lased at the expense of the high-gain 10P branch lines for which the cavity offered very high transmission losses. The 10P(20) line was made to lase by constructing another cavity with orthogonal polarization, thereby easing the strong competition between this line and the relatively low-gain 9R, 9P and 10R branch lines within the gain medium which is common to both cavities.     

Two-wavelength operation of a tunable KrF excimer laser — A promising technique for combustion diagnostics

A KrF excimer laser was operated on two independently tunable lines. This was achieved by a double-resonator configuration with two gratings. Tuning range and gain competition were investigated. The narrow line width (<1 cm^–1) and the independent tunability make this laser ideal for simultaneous spectroscopic detection of two species and temperature measurements in combustion processes.     

Effective and simplified hybrid TEA laser design and operation

A compact hybrid TEA CO₂ laser has been developed which, when operated with the low pressure section well below oscillation threshold, demonstrates that little cw gain is necessary to ensure single longitudinal mode (SLM) output pulses with peak power, energy and pulse shape approaching those of normal multi-mode operation. This has allowed reliable SLM operation to be obtained with a very short, wide bore rf-excited low-pressure section, making feasible simple single-mode, large-aperture TEA lasers with high peak powers and energies.     

Theoretical and experimental investigation of a quenched cavity laser with saturable absorber

Received: 14 April 1997/Revised version: 11 August 1997     

A novel picosecond distributed feedback dye laser arrangement for excimer laser pumping

A distributed feedback dye laser arrangement is described which can generate pulses at the subharmonic wavelengths of the main excimer laser lines (308 nm, 248 nm, 193 nm, etc.). The laser can be pumped with broadband lasers, such as the XeCl^* laserpumped dye laser with competing cavities. The laser is designed to be used as a part of a femtosecond, terawatt excimer laser system.     

Astigmatically compensated cw dye laser resonators using lenses

The compensation of the astigmatism of Brewster-angled dye cells can be performed with lenses as well as with spherical mirrors. The advantages of cw dye laser resonators using lenses lie in the linear configuration of the optics and the convenient adjustability of astigmatism compensation. An output efficiency of 30% already at 1.6W pumping power has been observed. In addition, ring laser resonators with lenses have been investigated and they delivered up to 400 mW single mode power in travelling wave operation at less than 2 W pumping power.     

Tunable dual-wavelength operation of an external cavity semiconductor laser

Tunable dual-wavelength operation of a laser diode has been achieved using a dual-period holographic element. The holographic element was positioned in Littrow configuration in an external cavity. The design of this holographic element was based on the superposition of a constant-period grating and a variable-period grating on the same location in a photoresist. We observed simultaneous emission at two wavelengths from a visible semiconductor laser operated with this holographic element. The spectral separation of the dual-wavelength output was varied from 0.76 to 6.27 nm by a simple translation of the holographic element.     

Output and picosecond amplification characteristics of an efficient and high-power discharge excimer laser

Improvements in output pulse energy and efficiency of a conventional capacitor-transfer-type discharge excimer laser with automatic preionization have been achieved by extending the discharge volume and resulting moderate pumping of the active medium. The discharge laser produces a pulse energy of more than 1 J for XeCl, KrF, and ArF lasers in square beams of about 2×2 cm², and the maximum overall efficiency observed is 2.9% for XeCl, 3.2% for KrF and 1.8% for ArF. The laser device has been involved in a picosecond ( 32 ps) XeCl laser amplification system, and was operated as an amplifier at a repetitive frequency of 10 Hz. Saturation fluence for XeCl laser was measured to be 1.4 mJ/cm², and the picosecond pulse energy of 40 mJ was extracted from the amplifier.On leave from Ebara Corp., 6-6-7, Ginza, Chuo-ku, Tokyo 104, JapanOn leave from Mitsubishi Heavy Industries, LTD., 4-6-22, Kan-on shinmachi, Nishi-ku, Hiroshima 733, Japan     

A new blue-green XeF (C→A) excimer laser amplifier concept

The feasibility of using the electrically excited XeF(C»A) excimer medium as an efficient wideband amplifier in the blue-green region of the spectrum has been investigated. Calculations show that for an intense blue-green optical flux input the amplification characteristics of XeF(C»A) improve, as a result of both bleaching of the pump induced absorbers and by additional production of XeF(C) level population. The removal of one of the major absorbing species, Xe^** in the XeF (C»A) laser mixture by means of a pulsed ruby laser probe beam has been demonstrated.     

Direct generation of sub-nanosecond pulses in a high-pressure miniature excimer laser

Direct generation of subnanosecond pulses in a 9.0 cm discharge-length high-pressure XeCl laser is reported. The shortest pulse obtained was 670 ps (FWHM) with an energy of 1.2 mJ corresponding to 1.8 MW peak power.     

Determination of the unsaturated losses and of the saturation intensity in the KrCl excimer laser

The unsaturated losses , and the saturation intensityI _s, were measured in an uv-preionized KrCl laser for optimized He and Ne based laser gas mixtures. The measurements were made as a function of the specific power loading and of the total pressure of the laser mixtures. Higher values for andI _s were found for the Ne-based laser mixture than for the He-based mixture. At 45 kV charging voltage and at 355 kPa of total pressure we measured =0.053 cm^–1 andI _s =9.4MW/cm² for the Ne based mixture, and =0.035 cm^–1 andI _s =5.1MW/cm² for the He based mixture.     

20 ps pulse generation by an excimer laser pumped double self-Q-switched distributed feedback dye laser

The behaviour of an excimer-laser-pumped distributed feedback dye laser (ELP DFDL) using a mixture of saturable absorber and laser dye as an active medium was studied. In a DFDL self-Q-switching occurs because of the population inversion dependence of the feedback. If the DFDL contains absorber saturation of the absorption by the leading edge of the created laser pulse also causes Q-switching. As a result of this double self-Q-switching, mixing a saturable absorber into the laser dye, the laser pulses become shorter and more stable. This was demonstrated experimentally. Mixing Rhodamine B into the dye solution of a Coumarin 153 ELP DFDL, a six-fold reduction in the pulse duration and a more than two-fold reduction in the pulse energy instability were observed. The experimental results were in good qualitative agreement with the predictions of a simple rate equation model.     

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.     

High-pressure behaviour of an X-ray preionized discharge pumped XeCl laser

The output characteristics are described of an X-ray preionized discharge pumped XeCl laser, fed by a low-impedance pulse forming line (PFL), at pressures up to 12 bar. The influence of a multichannel rail gap placed between the PFL and the laser head on the output energy was studied. We found an increase of output energy with increasing pressure up to 8 bar. At higher pressures a saturation behaviour was found. The maximum output energy per unit volume was 6.5 J/l.     

Excimers and excimer lasers

The development of excimers and excimer lasers are reviewed. The excimers of the noble gases (Xe ₂ ^* , Kr ₂ ^* , Ar ₂ ^* ) and of the noble gas halides (e.g. KrF, XeCl) which, respectively, radiate in the vacuum ultra-violet and ultra-violet regions of the spectrum are described in terms of their structure, spectroscopy and formation kinetics and the methods of pumping, operational characteristics and applications of the lasers are discussed.     

Three-level operation of a diode-bar-pumped Yb:S-FAP laser

We present an all solid-state Yb:S-FAP laser system running on the three-level laser transition at 985 nm. The pump source was a high fill-factor laser diode bar, with the output reformatted using a two-mirror beamshaping system to produce a rectangular pump beam that focused to a square spot. A nearly on-axis multipassing system was used to obtain four pump passes through a 1.6 mm Yb:S-FAP laser crystal. Gain-switched three-level laser output was achieved with an efficiency of 4.3% with respect to incident pump power. Electro-optic Q-switching produced 0.12 mJ pulses for a pump pulse energy of 11 mJ. Intra-cavity second-harmonic generation yielded a maximum pulse energy at 492.5 nm of 12 μJ.     

Gain and saturation measurements in a discharge excited F2 laser using an oscillator amplifier configuration

The small-signal gain coefficient and the saturation intensity of a F₂ pulsed discharge molecular laser at 157 nm have been measured using two discharge devices in an oscillator-amplifier configuration. The small signal gain coefficient was measured to be 5.2±0.4% cm^–1 at 3 atm total pressure and 1.5 cm electrode spacing and 4.1±0.4% cm^–1 at 2 atm total pressure and 2 cm electrode spacing while the values of the saturation intensity were 5 MW/cm² and 4.6 MW/cm², respectively.     

Active mode locking of a high pressure CW waveguide CO2 laser

In this paper, we report on a new concept for active mode locking of lasers. It has been successfully applied to a cw waveguide CO₂ laser and pulse widths as short as 2 ns have been obtained.