Disk Active Elements Research Articles

Suppression of thermally induced lensing in composite disk active elements by shaping a heat-removing plate

We propose an original method of suppressing thermally induced beam distortions in composite active elements of disk geometry. The main idea of the method is to use a heatsink of special geometry to provide heat removal from the active element only in the pump area. In this way, the heat flows and temperature gradients in the thick active element, and, as a consequence, thermally induced distortions are reduced. The wavefront distortions, temperature, and gain in the composite element mounted in a profiled heatsink have been simulated numerically and measured in experiment. A 2.5-fold reduction of thermally induced lensing compared to a flat heatsink was demonstrated in the experiment at the same small signal gain.

Multipass cryogenic Yb:Y2O3 ceramic disk amplifier

The features of laser radiation amplification in Yb:Y2O3 ceramic disk active elements have been studied. The first multipass disk pulse-periodic amplifier with a cryogenically cooled Yb:Y2O3 ceramic active element has been created. Its average output power is 15.8 W at a pulse repetition rate of 11.5 kHz, pulse duration 0.5 ns, and spectral width 1.2 nm. The results obtained demonstrate the potential of broadband radiation amplification with subsequent compression to the subpicosecond range of pulse durations.

Thin-disk laser with multipass unstable ring resonator

We propose a scheme of a ring unstable resonator with multipass geometry, which allows overcoming the problem of low gain of a disk active element. The original design of the laser resonator enables power scaling using a larger pump aperture of the active element, maintaining good beam quality. The developed resonator operates with a disk Yb:YAG active element and output beam quality M2=2 at 2.5 magnification, which agrees well with the results of modeling.

Disk laser heads based on Yb : YAG for multikilowatt average power lasers

The main factors affecting the cooling efficiency of Yb : YAG disk active elements have been investigated, and key technologies for designing disk lasers with high average power and efficiency have been developed. The main parameters of a disk active element operating in the cw regime are optimised using numerical calculation. Disk laser heads are fabricated based on calculations and developed technologies, and lasing with optical efficiency up to 50 % is demonstrated. An average power at the kilowatt level is obtained in a cavity with two laser heads, and a possibility of its further increasing is demonstrated.

Formation of a spatial laser-beam profile in a channel of high-power neodymium facilities

A system for one-dimensional spatial profiling of a laser beam is suggested, capable of compensating for the spatial laser-beam distortions that arise due to a nonuniform gain distribution over the aperture in the amplifying channel of high-power Nd : glass lasers with wide-aperture stages on disk active elements. The principle of operation, the approach to calculation of the key element parameters, and calculation and experimental results of studying the formation of spatial profiles of the laser beam intensity at the output from the system in question are described. Possible applications of the system both in single-beam and multi-beam optical schemes are considered.

Effect of nonuniform heating of the active disk on characteristics of the solid-state laser cavity

Generation characteristics of the neodymium laser with disk active element and diodepumped active medium were studied. It was shown that lasing occurs at a cavity length significantly exceeding the focal length of the thermal lens induced in the active element. Bending radii of the active disk surface were determined depending on the absorbed pump power. The cavity calculation performed taking into account the active disk surface bending showed that the negative lens formed by such bending of the surface and a laser mirror deposited on it efficiently compensates for the positive thermal lens, thus expanding the stability region of the disk laser cavity.

Limiting thermal regimes of active disk elements under steady-state pumping and two-dimensional temperature distribution inside the disk

An analytic expression describing the stationary two-dimensional axially symmetric temperature distribution in a disk active element (AE) is derived upon pumping the entire disk whose thickness is 0.01 cm ≤ h ≤ 0.3 cm and the diameter-to-thickness ratio is 1 ≤ d/h ≤ 100. Thermomechanical stresses are calculated. It is shown that from the point of view of the disk damage, the tangential stress on the disk side face constitutes the major threat. For different scaling parameters x =d/h, the limiting lasing powers Plas are estimated in multimode approximation, which can be obtainedusing a disk AE in the case of end and side cooling for different heat exchange coefficients a (by the example of an Nd : YAG crystal). It is found that the side cooling can decrease Plas in some situations. The priority regions are established in the space of the parameters h, x, and a which, while increasing the pump intensity, are accompanied by one of the three events violating the normal operation of the laser: deterioration of spectral and luminescent AE parameters due to heating, malfunctioning of the cooling regime, or thermomechanical damage of the disk. It is shown that an increase in thescaling parameter x smoothes the radial temperature profile and the thermoelastic stress distribution profile.

Distributions of temperature and thermoelastic stresses in a thin disk active element with an arbitrary optical density

Stationary distributions of temperature and thermoelastic stresses (thermal tensions) are obtained in an active disk element with an arbitrary optical density upon a double-pass pumping. It is shown that the temperature distribution is determined by the sum of three terms: two exponential and a linear one, the exponential terms being preserved with changing the boundary conditions while the linear term producing no thermal tensions changes. It is found that thermal tensions decrease with increasing the absorption coefficient both for the constant thickness of the disk and for the constant optical density. The assessed values of the temperature are calculated during the local heating of a thin disk when the diameter of the pumped region is comparable with the disk thickness.

Temperature distribution in disk active elements of lasers with longitudinal diode pumping

Experimental and computational data for determination of temperature profile in the region of crystalline laser disk pumping are presented. The analytical relations obtained link the values of temperature, pumping spot radius, and disk thickness and allow optimization of these parameters in the choice of laser construction. Good agreement between computational and experimental results is demonstrated on an example of an Nd:YVO4 crystal disk active element.

Accuracy of Active Element Manufacturing and Regulation of Optical Component Positions in Amplification Channel of Power Laser System

Wavefront quality of large-aperture output beams in high power Nd:glass laser systems depends to a great extent on the accuracy of manufacturing and processing of slab active elements. In a ray tracing approach the detailed analysis of this dependence has been carried out for a four-pass amplification channel of Luch facility. We have analyzed the relations coupling the positions of the point of the best focusing (BFP) and focal spot dimensions with the quality of disk active element surfaces. The obtained results allowed us to elaborate recommendations for designing laser-system amplification channels including optical amplifiers and spatial filters.

Solid-state laser with semiconductor pumping of a disk active element and aspherical optics

A compact solid-state laser with aspherical optics and a thin-disk active element is proposed. This laser is pumped from the base side by radiation from an array of semiconductor lasers. A resonator mirror, a diode laser array, an active element, and a cooling system are combined in the same device. The use of a hybrid stable—unstable resonator in this laser makes it possible to weaken the diffraction scattering of a focused laser beam and increase the power density at the focus. The proposed configuration can be used in the construction of high-power wide-aperture lasers of minimal weight and size.

Thermal strains in active elements of color-center lasers. I. Theory

Analytic calculations are made of thermal strains in disk, cylindrical, and rectangular active elements made of KCl, LiF, and CaF2 crystals, used in color-center lasers. Expressions are obtained for the thermooptic characteristics and calculations are made of their numerical values.

Neodymium-glass disk laser amplifier with an immersion medium

A description is given of a laser amplifier with a disk active element made of GLS2 (40 x 40 x 220 mm dimensions). This amplifier is filled with thionyl chloride (n=1.53, absorption coefficient k<10/sup -3/ cm/sup -1/ at lambda=1.06 ..mu..). The single-pass inactive losses, per 1 cm length of the active medium, are 4.3 x 10/sup -3/ cm/sup -1/. The results are reported of measurements of the small-signal gain and of the gain obtained at pump energy densities up to 25 J/cm/sup 3/.

Investigation of a periodically operated disk active element

An investigation was made of the influence of the inactive losses and resonator deformation on the energy characteristics of the output radiation of a neodymium glass laser. Stresses in a disk active element, causing considerable depolarization of the output radiation under periodic operation conditions, were studied.