The experiment is performed on a three-mirror laser resonator. The injection is arranged in two ways: by a feedback from the movable third mirror, and by chopping the running back laser beam when the third mirror is stable.
The paper describes the results of investigations of optical phenomena on an RF excited slab-waveguide CO2 laser. The
experiments are performed in two optical arrangements: two-mirror resonator and three-mirror one. The main purpose of
the experiments is to check possibilities to observe the optical phenomena using a microphone. The laser plasma is
modulated with a self-mixing signal in the three-mirror resonator. The response of the microphone is observed and
analyzed. Detection of the laser signature phenomenon with the microphone is experimentally considered. The
experiments are done at cw regime of the laser. The investigations are performed at pulse operation of the laser, as well.
The response of the microphone is analyzed. It is checked how the laser pulse is reconstructed at a profile of the
microphone signal. The output laser pulse with a mapped laser signature in the laser pulse profile is compared to the
microphone signal shape. The presence of the laser signature at the acoustic signal is investigated.
The paper gives an algorithm for elaboration of the RF excited slab-waveguide CO2 laser working on one chosen emission line in a pulse regime. The solution of the problem bases on an RF transversal excitation in a slab-waveguide laser structure and laser signature phenomenon. The structure gives a homogeneous distribution of the excited laser plasma along the electrodes. The plasma in the structure is stable and reproducible from the pulse to pulse comparing to conventional tube lasers, and particularly to flow dynamic lasers. On the other hand, the applied unstable kind optical resonator produces a single-mode operation by definition. It suppresses higher modes in the laser cavity. The only problem are parasitic "hooting modes" created along the waveguide direction - between electrodes. But usually they do not bring too much perturbations to a spectral contents of the laser output radiation. The problem of the one-color operation of the laser can be solved by careful selection of the laser signature. The paper shows the results of the experiments, and gives the methodology to design the CO2 laser in a pulse regime operating on one chosen emission line. Controlled two-color and multi-color pulsed operations are also considered. The results can be applied to design lasers for the trace gas analysis around of 10 or 9 μm or other spectral devices. It can be also applied for material processing of the media sensitive for the wavelength of the laser radiation.
Results of the investigations on an RF pulsed excited CO2 laser plasma are given in the paper. A slab-waveguide configuration of the laser is used. An unstable positive branch resonator structure is applied to ensure a single-mode operation of the laser. The configuration of the laser system guaranties a spectral purity of the laser output radiation, and makes the investigations clear. As known, a pulse excitation introduces dramatic perturbations of the laser plasma pressure, and temperature. The density of the laser gas mixture, or in other words, the refractive index is changed during the input pulse developing, as a consequence. The laser radiation frequency is changed in time of the laser pulse duration. Sometimes it is a parasitic effect, when a single-frequency laser operation is required. The aim of the work is to give a clear picture of the laser plasma behavior caused by a pulse excitation of the laser medium. The results obtained gives a possibility to elaborate the method of a laser frequency control in a pulsed regime.
The paper presents studies on influence of the gas laser cavity shape on an acoustic wave created in the cavity. Results of investigations on an RF excited CO2 slab-waveguide laser are shown. As is demonstrated, rapid changes of a laser plasma pressure appear in the laser gas mixture as a consequence of the pulsed RF discharge in the laser. The pressure variations create an acoustic wave propagated in the laser chamber, and involve changes of the refractive index of an excited plasma. As a result, the frequency of the optical wave emitted by the laser changes - a "line hoppings" effect appears. In the case of the slab-waveguide laser an acoustic wave propagates in a closed space - the laser reservoir, that is a special kind of an acoustic resonator. As known, a material from which cavity is made, a shape of the walls and their mutual position are significant for a wave propagation. In the experiment, the walls of the chamber are made of aluminum, so it is a very reflecting area. More, the walls are parallel that is an advantageous condition for creating standing waves. The aluminum wedges were used in the experiment to change the geometry of the reservoir. The influence of pulse duration time on the acoustic signal is investigated.
Thermodynamic and optical parameters of the CO2 slab-waveguide pulsed laser are given. The methodology of the investigations is based on a known Gladstone-Dale formula, linking the refractive index of the fluid, density (or pressure), and temperature of the medium.
An acoustic wave changes, by definition, the pressure of the gas medium. The power delivered to the pulsed gas laser changes the pressure (and temperature) of the laser medium. The monitoring of the acoustic wave in the laser cavity, taken as a specific acoustic resonator, can be an easy measure of the local changes of the laser gas pressure. The changes of the pressure involve changes of the laser gas density, and changes of the refractive index, as a consequence. It leads to a frequency tuning of the laser optical resonator. In the case of the CO2 laser a rotational line hopping phenomenon is observed as a result. In other words, a single frequency operation of the RF excited CO2 laser with a pulsed plasma is problematic. The main goal of the experiment is to give a picture of the laser plasma behavior during the pulsed excitation of the CO2 laser medium.
A pulsed excitation of the laser plasma in gas lasers creates an acoustic wave in the laser reservoir. It changes thermodynamic parameters of the laser plasma in the laser cavity like pressure, and temperature, as well, and consequently it changes the density of the laser plasma, or, in other words, the refractive index of the laser medium. Tuning laser frequency during the pulse developing is observed as a result. The measurements of the pressure, temperature, and refractive index changes in an RF pulsed excited CO2 slab-waveguide laser are purposes of the work. The pressure changes are measured with calibrated microphones situated close to the laser plasma. The temperature changes are calculated via measured refractive index characteristics, and simple formulas linking the refractive index with the gas density. The picture of the acoustic wave propagation in the laser cavity is presented. The obtained results give the picture of the laser plasma behavior during the pulsed excitation. It leads to a single frequency pulsed laser operation design.