The relations between range of operation and aperture of laser weapon system were investigated, taking into account diffraction and technical limitations as beam quality, accuracy of point tracking, technical quality of optical train, etc. As a result for the medium ranges of 1 - 2 km we restricted the analysis to apertures not wider than 150 mm and the optical system without adaptive optics. To choose the best laser beam shape, the minimization of aperture losses and thermooptical effects inside optics as well as the effective width of laser beam in far field should be taken into account. We have analyzed theoretically such a problem for the group of a few most interesting from that point of view profiles including for reference two limiting cases of Gaussian beam and ‘top hat’ profile. We have found that the most promising is the SuperGaussian profile of index p = 2 for which the surfaces of beam shaper elements can be manufactured in the acceptable cost-effective way and beam quality does not decrease noticeably. Further, we have investigated the thermo-optic effects on the far field parameters of Gaussian and ‘top hat’ beams to determine the influence of absorption in optical elements on beam quality degradation. The simplified formulae were derived for beam quality measures (parameter M2 and Strehl ratio) which enables to estimate the influence of absorption losses on degradation of beam quality.
We demonstrate partially athermal Nd:YAG transmitter. Laser generates pulses with energy of 55 mJ with duration of 15 ns. It corresponds to 3.7 MW of pulse peak power. The full-angle beam divergence is 2.5 mrad. 18% of pulse energy stability is maintained over temperature range of 20-36°C.
Several schemes of side-pumping by novel, high brightness, 2D laser diode stacks were analyzed. The three most promising schemes were chosen, for which the optical set-ups have been designed, manufactured and preliminary characterized. The special, robust, compact cavity with high tolerances to misalignments, mechanical disturbances and shocks was designed. The analysis of temperature sensitivity of pump unit and laser was performed. In preliminary characterization 180 mJ of output energy with 2-mrad full divergence angle (parameter M2 ~ 5) in free running mode for 0.8-J of incident pump energy was demonstrated in such a compact cavity with 80% transmission of integrated output coupler. The main drawbacks in such design found in preliminary experiments are: low threshold of self-lasing due to high gain density and inhomogeneities in transverse beam profile. The strategy of mitigation of these drawbacks was discussed.
V:YAG saturable absorber, developed mainly for 1.3 μm lasers Q-switching, was used as a passive Q-switch for the 1.03 μm Yb-doped YAG (10% Yb/Y, 3mm long) and LuAG (15% Yb/Lu, 1mm long) lasers. Longitudinally diode pumped gain medium together with the V:YAG crystal were placed inside the 22mm long hemispherical laser cavity. For Yb-doped crystal excitation fibre-coupled (fibre core diameter 100 μm) laser diode (max power amplitude 20W, emission wavelength 968 nm) was used. The laser diode was operating in a pulsed regime (repetition rate 10 Hz, pumping pulse width 2 ms) to reduce parasitic thermal effects inside the gain medium. Stable Q-switching was obtained for laser output coupler reflectivity 70% and V:YAG initial transmission 70% at Yb laser emission wavelength. For the both tested active media the parameters of the generated giant pulses were similar. Pulses with duration of 2.5 ns (FWHM), energy about 0.3 mJ, and peak power up to 120kW were generated. The maximal Q-switched pulses repetition rate inside the single pumping pulse was 6.6 kHz in case of Yb:YAG and 8.6 kHz in case of Yb:LuAG. The beam transversal profile was close to the fundamental Gaussian mode. The output was partially polarized.
A single and double-bounce grazing-incidence Nd:YVO4 laser is presented. The output pulse energy of ~20 mJ with slope efficiency reaching up to 24.5% was achieved. The beam quality parameter M2 was 1.25.
To homogenize inversion profiles and mitigate thermo-optic effects in high-power, end-pumped lasers the optimal spatial profile of pump beam should be close to ‘top-hat’ one, whereas typical pumping beams have Gaussian-like profiles. The aim of work was to examine feasibility of laser beam transformation with the use of a beam shaper consisted of a pair of aspheric refractive elements. Two beam shapers (with magnification m = 0.4, 0.8 respectively) for transformation of Gaussian profile to Super-Gaussian were designed and fabricated applying Magneto-Rheological Finishing technology. Both elements were experimentally verified for diffraction limited and partially coherent laser beams. The analytical model based on Fourier transform plane wave decomposition was applied for verification of experiments and to determine the performance of fabricated elements.
Passively Q-switched, closed-loop, self-adaptive resonator with a Nd:YAG as an active medium is presented. For maximal pump energy of 840 mJ Q-switched generation provided 5 pulse series with total energy of 120 mJ. Single pulse width was 24 ns. The beam quality parameter M2 was 1.6. Four-wave mixing and linear resonators were compared.
We report on free-running operation in a side-pumped Yb:YAG slab laser. For maximum available pump pulse energy of
850 mJ at 967.7 nm delivered by a 2D laser diode stack with fast-axis-collimation, the output pulses with energy of 150
mJ at 1.03 μm were obtained. The laser system operated in room temperature providing a slope efficiency of 26.9%. The
performance of the laser is described.
The novel scheme of self-adaptive, closed-loop resonator of diode-side-pumped Nd:YAG slab laser was presented. The
dynamic holography principle was exploited to spatial cleaning of the laser mode. The phase conjugate mirror was
created inside the gain medium as a result of four-wave mixing of resonator standing waves intersecting at a small angle.
The output beam was extracted from the cavity as a 1-st diffraction order of laser mode interacting with the dynamic gain
gratings created inside active medium. The near diffraction limited (parameter M2=1.2) output beam with 250 mJ of
energy at repetition rate up to 25 Hz in free running regime was achieved. Any spectral narrowing effects were not
The development of high energy and high power lasers based on solid state technology is mostly limited by thermal effects that occur inside the laser cavity under high heat loads and intensities. The thermo-optical effects emerging inside cavity mirrors, output couplers and windows can significantly degrade beam quality of such lasers. The knowledge on transient thermal effects occurring inside bulk laser elements exposed on laser intensities of several dozens of kW/cm2 is of special interest for some specific applications (e.g. heat capacity lasers). The goal of this paper were theoretical analysis and experimental verification of these effects. Tips for best materials choice for cavity mirrors, laser windows and output couplers were shown. Simple theoretical thermo-optical model was presented. The special laboratory setup allowing simultaneous registration of thermo-optical effects applying shearing interferometer and wavefront sensor (Shack-Hartmann test) was elaborated. The non-stationary and stationary thermo-optical effects emerging inside tested mirrors can be observed, be measured and resolved as result of surface absorption in coating layers and volume absorption in the material. The resolution of measurements: less than 0.1 K and thermally induced optical power of about 0.1 D were demonstrated.
The most important limitations in development of high energy and high power lasers based on solid state technology are
thermal effects occurring under high intensity and high heat loads. The thermo-optical effects occurring inside output
couplers, folding mirrors, output windows can significantly diminish the beam quality of high power lasers and therefore
have to be investigated. The knowledge on transient thermal effects occurring inside bulk laser elements exposed on
laser intensities of several dozens of kW/cm2 is of special interest for some specific applications (e.g. heat capacity
lasers). The aims of work were theoretical analysis of those effects occurring inside the laser mirrors and its experimental
verification. The hints for choice of the best materials (from the point of view of thermal limitations) for laser windows
and output couplers were pointed out. The special laboratory setup enabling simultaneous registration of thermo-optical
effects applying shearing interferometry and wavefront sensing by means of Shack-Hartmann test was worked out. The
transient as well as averaged in time thermal-optical effects occurring inside the volume of examined element as a result
of surface absorption in the coatings and bulk absorption in the material can be resolved and measured. The resolution of
measurements: less than 0.1 K temperature difference and thermally induced optical power of about 0.1 D were
An efficient high-peak-power Ho:YAG hybrid laser resonantly pumped by a 20 W linearly polarized Tm:fiber laser
at the wavelength of 1908 nm was developed. At room temperature a maximum continuous output power of 10.7 W
with a slope efficiency of over 55% with respect to the incident pump power was achieved. In Q-switching regime
an acousto-optic modulators were applied. The research was conducted for normal and Brewster's angle Q-switches
respectively. In CW pumping regime the repetition rate was changed from 500 Hz to 5000 Hz. For the best case, for
5 kHz repetition rate, pulses of 1.6 mJ energy and 123 kW peak-power were achieved at the wavelength of 2090.2 nm
with an M2 ≈ 1.6.
The aim of work is to develop efficient theoretical model enabling analysis and optimization of Q-switched quasi-threelevel
lasers. The model consists of two parts: pumping part and Q-switched part, which can be separated in a case of
active Q-switching regime. For the pumping of quasi-three-level gain medium the semi-analytical model was developed,
enabling the calculations for average occupation of upper laser level for given pump power and pump duration, spatial
pump beam profile, length and dopant level of gain medium. Moreover, ground-state-depletion, up-conversion parasitic
relaxation and temperature effects were considered in the model. The new approach for optimization of CW regime of
quasi-three-level lasers was developed for Q-switched lasers operating with high repetition rates. Moreover, for long
pump durations comparable to laser upper level lifetimes, the optimization procedure based on Lagrange multiplier
technique was developed. The simple analytical formulae for effective pump duration needed to achieve the quasistationary
inversion for given pump power density and up-conversion parameter were derived. The model enables the
optimization of gain medium length and absorbance, average pump area and out-coupling losses for wide class of quasithree-
The aims of paper were theoretical analysis of thermo-optic effects occurring inside laser elements under high heat load
and its experimental verification for two particular cases: dichroic window and Nd:YAG ceramics disk. Transient
thermal effects in dichroic mirrors and ceramic gain media were modeled applying COMSOL Multiphysics software and
verified experimentally. Moreover, thermally induced distortions, thermally induced stresses and birefringence were
calculated for gain elements of rod and disk shapes applying analytical, stationary model based on linear thermoelasticity
theory. The 100-mm diameter dichroic mirrors made of BK7 and fused silica and gain disks made of Nd:YAG
ceramics of 15-mm diameter and 3-mm thickness were prepared for experimental verification of the theoretical models.
The special laboratory set-up enabling simultaneous registration of thermally induced birefringence and wavefront
distortions was worked out. We have investigated the thermo-optical effects for different heat densities in range of
0.1 kW/cm2 up to 50 kW/cm2 changing the pump power , beam diameter or duty cycle. The experiments were carried
out in lasing and non lasing conditions. The new method of measurement of heat conversion efficiency and absorption in
mirrors based on threshold shearing interferometry was proposed and verified for dichroic mirror and ceramic Nd:YAG