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.
In the paper, authors present an example of a simple and cost effective system of electric power supply by means of optical fiber. In many cases of physical measurements, it is very important to avoid excessive distortion to measured quantity. One of this is measurement of electromagnetic field of radio frequency. This is of concern in both, far- and near field examination. RF field measurement can be performed by direct measurement of the field at a point of interest or by measurement of the field scattered by a dedicated probe. One of the most important properties of this method is its low influence to the field under test. The full advantage of the system can be taken when the probe can be powered and controlled be means of optical fiber.
A servomechanism for identification of the CO2 laser lines, and searching desired laser signatures is elaborated. The laser signature is used as a standard for calibration of the servomechanism. Algorithms for process automation are find. The system can be used in servo-loop mechanisms for stabilization of the laser operation to a chosen emission line. The method can be expanded using different isotopes of carbon, and/or oxygen molecules in the laser medium. Some applications of the method are suggested.
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.
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.
It has been shown, that a single line operation of the CO2 laser can be easier sustained by careful choosing the laser resonator length. Selection of the right resonator length allows obtaining very sophisticated signatures.
Results of the investigations of pulsed CO2 laser plasma are presented. Theoretical calculations of temperature and pressure changes and their influence on laser tuning during the pulse evolution have been experimentally proven. The laser slab-waveguide structure equipped with an unstable resonator has been used in the experiment.
The qualitative and quantitative description of the laser tuning effect during a pulse forming has been described. The mechanism of the line hopping in the CO laser has been presented. A simple arrangement enabled observing the pulse evolution of all oscillating spectral transitions contributing in the total shape of the output pulse. As shown in the experiment, the jumps from line to line over the pulse duration give the sequence of lines, which is the subsequence of the static laser signature. Thus, the changes of the refractive index can be estimated by setting the static signature against the line hopping during the pulse operation of the laser. On the other hand, the changes of the refractive index during the pulse evolution have been measured directly with a Mach-Zehnder interferometer. The experiment has been performed on the slab-waveguide laser with an unstable positive branch optical resonator. The experiment allowed observing the dynamic evolution of the pulse in time and spectrum. The method of the investigations allows estimating the changes of a pressure and temperature during the pulse evolution, and can explain the effect of bulges observed at the output pulse shape.
The overview of spectral properties of the CO2 laser radiation in modern RF excited waveguide, multi-waveguide, and slab-waveguide laser structures is given. Spectral phenomena in lasers operated in a pulse regime are also demonstrated. The influence of specific spectral features of the CO2 laser on designing the high-brightness and spectrally pure laser devices is shown.
Each mode inside a rectangular slab-waveguide laser consists of four quasi plane waves propagating at small angles to its axis and inducing specific grating ofthe refractive index in the slab medium. Multimode operation of such laser is a superposition of single modes. Each mode can be spatially separated into two high quality lobes with M2 parameter near l . When geometry ofthe slab is controlled, high stability of a mode pattern can be obtained. This effect is particularly strong when extra single mode selection (for example Talbot filtering) is applied. The experimental evidences were performed on a RF excited CO2 slab-waveguide laser.
The analysis of pump geometry presented in this work allowed to determine optimal conditions of excitations of diode pumped solid state lasers for oscillation of quasi-Gaussian TEM00 mode. There appears the existence of weak transverse mode structure. The heterodyne analysis for two kinds of laser: Nd:YAG and Nd:YVO4 was performed. We found the strong mode competition effect decreasing long- term frequency stability of the lasers. The offset frequency stability between two Nd:YVO4 lasers for short averaging time is 10-10. Using offset frequency feedback loop, stability of the level of 300kHz has been obtained.
Results of investigations of RF excited CO2 waveguide lasers in pulse regime are described. The shapes of the output pulses monitored and simulated for the different operation conditions are shown. The characteristics of the power levels are presented. Some aspects of spectral properties of the laser output radiation in pulse regime are given.
The construction of 875 mm long transversally rf excited carbon-dioxide waveguide laser is presented. We show the results of the laser operating in single EH11 waveguide mode for the rectangular aperture of the laser channel equal to 1.7 multiplied by 4 mm.
The new generation of slab waveguide molecular lasers requires new resonators ensuring high extraction of output powers and high beam quality. In this paper we describe a few configuration of laser resonators which seem to be quite attractive for these requirements.
The heterodyne detection of two laser beams offset in frequency is considered. The paper includes all optimization procedures to maximize beat signal in herterodyne experiments of two laser beams shifted in frequency by acousto-optic Bragg cell.