Telescopic Resonator Research Articles

LASER CAVITY WITH A GRADUALLY EXPANDING RADIATION BEAM IN THE ACTIVE MEDIUM

Subject and Purpose. Increasing the operational efficiency of laser generators and the amount of their radiated power is an important task in laser development, which can be approached to in a number of alternative ways. The present work has been aimed at increasing the efficiency of energy exchange between the active medium and the laser radiation by way of optimizing the radiated intensity distribution over the entire active volume within the resonant cavity of a novel structure. Methods and Methodology. A model for the process of radiated power amplification in the laser cavity has been considered. Losses within the cavity have been analyzed, as well as possibilities for improving the efficiency of energy transfer from the gain medium to the laser radiation. The importance of optimizing the density of laser radiation in the gain medium is substantiated, and the main problems that might arise clearly identified. The task of increasing the cross-section of the radiation beam being amplified in the active medium has been formulated, and a concept suggested for solving the problem through modification of the telescopic resonator’s optical scheme. Results. A novel configuration has been suggested for the laser resonator, where the radiated beam is expanded in width over two stages of counter propagation. Nonlinear regimes of increasing the beam cross-section in the resonator have been analyzed and recommendations formulated for selecting dimensions of the resonator and geometry of the mirrors, depending on the amount of amplification in the active material. Fragmentation of the output mirror is proposed as a means for feedback optimization, with account of diffraction-caused diver- gence of the radiation. As has been found, field-exciting elements can be placed inside the active medium. Recommendations are developed as for practical application of the scheme proposed in lasers of a variety of frequency ranges. Conclusions. Application of laser resonators of the design considered opens up new possibilities for increasing the efficiency of lasers and their radiated power.

Adjusting and Determining the Direction of the Axis of a Telescopic Resonator

Abstract—A method for adjusting an unstable confocal resonator and determining its axis direction using an angular reflector is proposed. A semiconductor laser was used as an auxiliary laser, which set the direction of the cavity axis. A collimator was used as the device that controls tuning. A corner reflector mounted inside the resonator from the side of the concave mirror made it possible to create the “direct” and “reverse” passages of the beam of the collimator through the resonator. This makes it possible to observe images of the collimator scale in the eyepiece from the “direct” and “return” passages. Fine tuning of the resonator is carried out by combining the centers of the scales, while the axis of the resonator coincides with the axis of the collimator.

Theoretical analysis of a new T-shaped thermo-stable telescopic resonator for sum-frequency beam generation by 1064 and 1319 nm lasers

A new shorter T-shaped thermo-stable telescopic resonator is demonstrated in this Letter. By means of thick lens model, a longer 1064-nm telescope linear cavity is designed and simulated first by analyzing the influence of the distance between every two optical elements on the fundamental mode radius on the end mirror and the system stable zone. On the basis of the parameters analyzed, a shorter telescopic composite laser system is presented for both the 1064 and 1319 nm operating lasers that will be applicable to high-quality yellow laser generation by means of sum-frequency technology.

Analytic model for unstable telescopic resonator with an active medium to a two-dimensional geometrical approximation

The design of an unstable telescopic resonator with an arbitrary configuration of the active medium inside the resonator was evaluated for cases of outcoupling of radiation from a concave mirror or from a convex mirror. The calculation makes it possible to assess routinely the energy parameters of laser systems without using high-performance computers.

Short-pulse, eye-safe Nd:YAG laser using cavity-dumping

A short-pulse 1.444-/spl mu/m laser based on Nd:YAG technology has been demonstrated. The 1.444-/spl mu/m is eye-safe. With the cavity-dump technique, a pulse of 50 m/spl times/ and 14 ns was obtained. The beam quality was excellent with an M/sup 2/ of 1.6 by the use of a telescopic resonator. Silicon-window polarizers were used to suppress the 1.06-/spl mu/m radiation but showed 1.444-/spl mu/m absorption as well.

Space-time extents of optical distortions in the cylindrical active element of a high-power solid-state laser

Results of investigations of the space-time structure of distortions in the glass active element of a high-power solid-state laser with and without cooling of the active element are reported. A possibility is shown and the domains of applicability are determined for correction of spherical distortions by adjustment of a telescopic resonator.

Properties of radiation emitted by an oxygen—iodine chemical laser with an unstable telescopic resonator and an exit mirror with a Gaussian reflectivity profile

A numerical study is reported of the spatial distribution of the radiation emitted by an oxygen—iodine chemical laser with an unstable telescopic resonator and an exit mirror with a Gaussian reflectivity profile. The results show that a resonator of this kind with parameters of practical interest generates a smooth field which fills well the resonator aperture. The field in the far-field zone is concentrated in one peak with a width close to the diffraction limit. The results demonstrate that such a resonator should have a positive influence on the quality of the output radiation also in the case of other gas-flow lasers with a previously established population inversion.

Convex-concave resonator for mode selection in a large-bore laser

A study is reported of transverse mode selection in a convex—concave resonator of a large-bore argon laser. The main resonator parameters are calculated and determined experimentally. It is shown that under certain conditions a resonator of this type has a better selectivity, and is also simpler to construct and more convenient to use, than the traditional telescopic resonators. Single-mode stimulated emission of ultraviolet lines of Ar2+ is reported.

Application of a telescopic resonator to high-power chemical oxygen-iodine lasers

The application of an intraresonator telescope to high-power chemical oxygen-iodine lasers to decrease the output beam divergence is analyzed and demonstrated. A theoretical formula based on the ABCD matrix theory is developed to analyze the characteristics of the telescopic resonator. Calculations are carried out using Galilean type telescopes with magnification factors in the range of two to four, and our high-power chemical oxygen-iodine laser as an analysis model. By locating the telescope at a proper position on the optical axis, the overall telescopic resonator can be conveniently tailored to the hardware of this model laser in a way that the beam divergence and the resonator stability can be improved simultaneously. Experiments are carried out for one of the conditions used in the calculations. Measured divergence angles are in excellent agreement with the theoretical values.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Unstable resonator with a semitransparent exit mirror for a fast-flow CO2laser

A theoretical and experimental investigation was made of an unstable resonator having a semitransparent exit mirror and a magnification close to unity with Fresnel numbers of 5–15 and active medium gains of 0.5–2.4. Numerical modeling was employed in order to find a condition for minimum diffraction losses. Under the conditions of an electric-discharge fast-flow kilowatt CO2 laser, the radiation divergence was improved by roughly a factor of two relative to that for a telescopic resonator without an appreciable reduction in the mode volume and output power.

Laser with a conjugate resonator based on a corner-cube reflector

A resonator system equivalent to a conjugate resonator, is suggested for a YAG:Nd3+ laser: it is based on a corner-cube reflector and utilizes polarization coupling-out of radiation. A comparison is made of the energy and spatial-angular characteristics of the output radiation in the proposed resonator and an unstable telescopic one. It is shown that an equivalent conjugate resonator can be used to generate radiation whose energy and divergence are comparable with the corresponding parameters of the radiation obtained from a telescopic resonator. The proposed resonator is not critically sensitive to misalignment.

Kinetics of angular and spectral characteristics of excimer laser radiation

The three-dimensional transfer equation is used to analyze the divergence of laser radiation from XeCl and KrF excimer lasers with plane–plane and telescopic resonators. Narrowing of the transition line profile in the amplifying medium is discussed.

Use of stimulated scattering in improvement of the spatial characteristics of the radiation emitted by a high-power XeCl laser

An experimental study was made of stimulated Brillouin scattering of wide-band depolarized XeCl laser pulses of 300 ns duration in hexane and in quartz rods. The scattered radiation was used to improve the spatial characteristics of the XeCl laser with an output energy of 30 J and an unstable telescopic resonator. This resulted in a threefold increase in the radiation intensity in the focal spot of the laser beam.

Application of unstable telescopic resonators in generation of low-divergence radiation in a pulsed chemical SF6–H2laser with electron-beam initiation

A study was made of the divergence of the radiation generated using unstable telescopic resonators in a pulsed chemical SF6–H2 laser initiated by a transverse electron beam. The duration of laser radiation pulses was ~ 100 ns. Initiation of the active medium resulted in a strong transverse inhomogeneity. It was possible to use telescopic resonators to ensure that the divergence of the output radiation was reduced to ~ 0.15 mrad, which was close to the diffraction limit (~ 0.05 mrad). The laser radiation energy in the far-field zone was then ~ 0.2 J. The energy efficiency in the formation of the radiation was ~ 20%. Comparison with the same laser, but with a plane–plane resonator showed that the axial density was two orders of magnitude higher and the angular divergence was two orders of magnitude lower.

Spatial and temporal characteristics of the radiation from a high-power XeCl laser with an unstable telescopic resonator

The radiation characteristics of an XeCl laser with a 30-liter active medium were investigated as a function of the magnification of an unstable telescopic resonator. Optimal resonator magnifications minimized the divergence at half the radiation energy (M = 18) and ensured the highest radiation brightness in the far-field zone (M = 8.5). When an unstable telescopic resonator was used, the radiation pulses were modulated in the far-field zone and the modulation period was a multiple of the resonator round-trip time for the radiation. The depth of modulation increased with M. The time of formation of the transverse resonator modes increased as their order became lower and decreased with M for the lowest-order modes. The width of each of the lasing lines due to the 0–1 and 0–2 transitions was 25 pm for M = 8.5.

Conditions for cw lasing in a filled open telescopic resonator

The condition ensuring cw lasing is derived and the normal oscillation modes are found for an unstable telescopic resonator filled with an amplifying medium. The diffraction of light at the mirror edges is allowed for. The problem of the normal oscillations is solved for a resonator with cylindrical mirrors. The selected properties of such resonators are considered.

Influence of thermal deformation of mirrors on the characteristics of an unstable resonator of a gas-discharge CO2laser

A description is given of a procedure used in numerical solution of the self-consistent problem of finding the radiation field and thermoelastic deformations of rectangular mirror sheets in a telescopic resonator of a continuous-flow gas-discharge CO2 laser. The results obtained are compared with the case when the resonator mirrors are undeformed. An analysis is made of the mutual influence of the radiation and thermal distortions of the mirrors, and of the effects of these distortions on the divergence of the output beam of such a laser.

Design of a CO2gasdynamic laser with selective thermal excitation and an unstable resonator

The task of design of an unstable telescopic resonator for a CO2 gasdynamic laser with selective thermal excitation is considered. The laser is described by parabolized Navier–Stokes equations and by equations of propagation of a field in a resonator in the geometric-optics approximation. A study is made of the dependence of the efficiency on the magnification and distance between the mirrors. It is shown that a high (up to 70%) efficiency of an unstable resonator can be expected for a CO2 gasdynamic mixing laser.

Flashlamp-pumped liquid laser with a diffraction-limited beam divergence of 9 × 10−5rad

An output beam having a divergence 0.5E = 9 × 10−5 rad at half-energy and a total beam energy of 0.7 J was obtained from a laser utilizing a solution of rhodamine 6G in ethanol excited by a flashlamp with a transverse discharge of 250-ns duration. An unstable telescopic resonator in the positive branch with a magnification of 3 was used to achieve this divergence, which corresponded to the diffraction limit at the laser exit aperture.

CO2/SF6laser with a three-mirror resonator

A three-mirror resonator was used to reduce the saturation of the absorption in an intracavity cell. Power resonances of 0.3 mW amplitude and 100 kHz wide were observed using an absorption cell of length 0.5 m in a CO2/SF6 laser with a three-mirror telescopic resonator when the pressure of the absorbing gas was 0.1 Pa.