Temporal synchronization of independently tunable single longitudinal mode hybrid CO2 lasers

We report a quantitative study of temporal synchronization of two independently tunable, single longitudinal mode, hybrid CO₂ lasers, sharing a common high pressure section. The theoretical estimates for the dependence of the laser pulse build up time on the cw section pressure are in satisfactory agreement with the experimental results. Further, we show that temporal synchronization over a larger frequency range with no significant degradation of peak power or longitudinal mode selection is possible, by utilising the cw section gain length and cavity Q as additional control parameters.     

A high-power transverse-flow cw CO2 laser-output and small-signal gain measurements

A high-power CO₂ laser for investigations on materials processing is described. Measurements of the output characteristics of the laser are discussed on the basis of an adequate model.     

Automatic alignment of a high-power CO2 laser resonator

An on-line, electronic feedback approach for automatic alignment of a laser resonator is described. A measure of the resonator alignment error is derived by partitioning a 1% sample of the laser output into quadrants, and using standard electronic circuits to compare the average power present in each quadrant. A motorized X — Y alignment system is then used to implement the alignment changes required to maintain optimum output quality from the laser. The system is shown capable of stabilizing the output power in each quadrant of the beam to within about 2% of the optimum level.     

Waveguide CO2 lasers on sequence-band transitions

Two waveguide CO₂ lasers, a quartz waveguide and an alumina waveguide, have been studied on the 00°2–[10°l,02°1]_I,II sequence bands. The use of an intra-cavity hot CO₂ cell, which is a part of the waveguide, suppresses the regular-band transitions. The quartz waveguide laser has a total of 58 lines lasing on both the 9.4 µm and 10.4 µ,m sequence bands. The alumina waveguide laser has 36 lines lasing on the 10.4 µm sequence band and twice the output power of the quartz waveguide laser, whereas lasing on the 9.4 µm sequence band is difficult. The lasers can be operated on the selected single line without line jumping problem. The frequency tuning range of the strong lines is limited by the free spectral range of the cavity.     

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.     

Efficient low-voltage operation of a reverse-biased autoprepulse XeCl laser

An improved version of the auto-prepulse excitation scheme for long-pulse operation of the XeCl excimer laser is reported. A pulsed reverse bias on the small peaking capacitance allows efficient (1.7%) operation at 100 mJ output level with a charge voltage limited to 5–7 kV. Analogies and differences with other long-pulse operation schemes are also discussed.     

Independently controllable multiline emission from a TEA CO2 laser

Spatial separation of wavelengths in a CO₂-laser resonator helps to avoid competitions. We have achieved this by means of a nearly concentric resonator with a grating or prism in its center. Thus, we demonstrated independent multiline emission with a variety of output spectra. The temporal sequence of the lines was conveniently controlled by varying their losses.     

CO laser stabilization using the optogalvanic Lamb-dip

Frequency stabilization of the CO laser using a CO lamb-dip is achieved in the range from 5.0–6.3 m. The CO saturation signal is obtained from a low-pressure discharge in absorption and is detected using optogalvanic, detection. The frequency stability and reproducibility has been verified to be better than 100 kHz; this is an improvement of more than one order of magnitude compared with locking techniques using CO laser gain profiles.Alexander von Humboldt Awardee from National Bureau of Standards, Boulder, Colorado, USA     

Kinetic study of a short-pulse electron-beam pumped Kr/F2 laser amplifier medium at very low pressure operation

A numerical investigation has been performed for very low pressure (200 Torr) buffer-free KrF laser-amplifier medium pumped by a short pulse (10 ns FWHM) electron beam with low excitation rate operation (200 kW/cm³). The small-signal-gain coefficient (g ₀) and absorption coefficient () have been estimated for this new operational mode. The formation and quenching processes are also discussed kinetically.     

Two-color TEA CO2 laser oscillation on the lines of regular and hot bands

Based on the separation of two orthogonally-polarized waves simultaneous, efficient lasing on an arbitrary pair of lines of regular 00⁰1-10⁰0(02⁰) and hot 01¹1-11¹0 bands in the TEA CO₂ laser has been obtained. The possibility of controlling energy, spectral, and temporal radiation parameters of the two-wavelength regime over a wide range is shown experimentally.     

Radio frequency excited waveguide CO2 lasers on sequence-band transitions

2 lasers based on either a quartz or an alumina waveguide were studied on the 00°2 - [10°1,02°1]_I,II sequence bands. A compact multisegment RF excitation with capacitive coupling was used for pumping the gain section of the laser waveguide. The use of a separate intracavity hot CO₂ waveguide suppresses the regular-band transitions. The quartz waveguide laser has a total of 62 lines lasing on both the 9.4 and 10.4 μm sequence bands. The alumina waveguide laser has 40 lines lasing on the 10.4 μm sequence band. These lasers can be either pulsed or continuous-wave (CW) operated on the selected line without a line jumping problem. Received: 29 September 1997/Revised version: 2 December 1997     

Gain dynamics of the 4.3 μm CO2 laser

A detailed study of the gain dynamics of the pulsed, optically pumped 4.3 m CO₂ laser is described. Small-signal gain coefficients as high as 14%/cm are measured in a 4.3 m amplifier using low-power pulses from a 4.3 m probe laser. The measurements are compared with a rate-equation model and good quantitative agreement is obtained. The model, which uses no adjustable parameters, is described in detail. Gain is studied as a function of optical pumping power, gas mixture, gas pressure and discharge excitation of the 4.3 m amplifier. Optimization of the gain is discussed.     

Tunable and high-energy Q-switched operation of an alexandrite slave ring laser

Narrow bandwith tunable Q-switched operation of an alexandrite oscillator was used for injection-locking of a high-energy alexandrite slave ring laser. Pulses with up to 600 mJ in energy over a 600 cm^–1 tuning range were obtained.     

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.     

Pulse shortening to 25 ps in a cw mode-locked Nd: YAG laser by introducing an intracavity etalon

The gain spectrumG(v) of a cw mode-locked Nd:YAG laser is flattened by a properly designed intracavity etalon. The increase in amplification bandwidth allows the generation of very stable trains of pulses shorter than that of standard systems. A reduction of the pulse width from 70 to 25 ps is observed by incorporating a BK 7 platelet of 420 m thickness in the resonator. The properties of the laser are investigated as a function of the thickness and the orientation angle of the etalon. The laser performance is found to be considerably influenced by the fact that the Nd³⁺ laser transition at 1.064 m consists of a line doublet.     

Detailed vibrational population distributions in a CO2 laser discharge as measured with a tunable diode laser

A tunable diode laser (TDL) operating in the 2150–2350 cm^–1 wavenumber region is used to probe a conventional cw CO₂ laser discharge. Absorption lines in more than 25 different vibrational bands are observed, enabling us to determine absolute vibrational populations inall levels of concern to the dynamics of the 10 m CO₂ laser. Levels in thev ₃ mode of CO₂ as high as 00°9 are monitored, and it is found that anharmonic effects play a significant role in the populations of such levels. Thev ₁ andv ₂ mode populations are also investigated in detail, and it is found that these modes are strongly coupled and maintain a common vibrational temperature under all discharge conditions. The use of a TDL is shown to be a powerful technique for investigating the dynamics of infrared molecular lasers.This work was supported in part by the National Science and Engineering Research Council, Canada     

Comparative performances of stable-and unstable-resonator TEA CO2 lasers with cw injection

The performances of stable- and unstable-resonator TEA CO₂ lasers with cw injection are experimentally compared. Two types of measurements are reported. First, locking band-widths are measured for a wide range of cw injected powers. It is shown that 5-s 1-J single longitudinal mode pulses can be obtained with unstable resonator lasers for injected powers as low as 200 nW. Second, heterodyne measurements of the intrapulse TEA laser frequency are presented. The use of unstable resonators is experimentally proven to be the most efficient way to achieve reproducible high-power chirpless single-mode pulses at 10m.This work has been supported by Direction des Recherches et Etudes Techniques     

A study of the electron quenching of excimers in a KrF* laser excited by a coaxial electron beam

Measurements of the output energy, the optical pulse length and the build-up time of the laser pulse, obtained with a coaxially e-beam pumped KrF^* laser, were performed varying the total gas fill pressure, the F₂ content and the e-beam current from 1–5 bar, 0.1–0.8% and 13.3–26.6 kA, respectively. The maximum specific extraction energy amounts to 64 J/l. The large range of measurements, especially at low F₂ concentrations, reveals the necessity to extend the kinetics of the F₂ chain in the usual computer model. With the introduction of electron quenching of KrF^* and ArF^* by dissociative attachment the predictions are also for low F₂ concentration in agreement with experiments.     

A high power high energy pure N2 laser in the first and second positive systems

Simultaneous high energy lasing in the N₂ first and second positive systems is reported. 20.5 mJ (1.5 MW) UV and 5 mJ (0.4 MW) IR laser pulses were produced in pure N₂. The design is open and easy to improve.     

Highly efficient synchronous amplification of a picosecond dye laser at a kHz repetition rate

A short pulse, high energy, high repetition rate dye amplifier with superior conversion efficiency is reported. The dye amplifier is composed of three single-pass dye cells, longitudinally pumped by a frequency doubled 1 kHz Nd: YLF regenerative amplifier. The dye amplifier yields 3.5 ps, 150 J pulses at 595 nm, corresponding to a 12% conversion efficiency. The ASE is 1% or less, and the transverse mode quality is near-Gaussian.In absentia from the Department of Chemistry, Princeton University, Princeton, NJ 08544, USA