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Deformable mirrors in adaptive system for high power lasers should have high damage threshold and thermally stabilized surface. The cooling is required for average beam power above 100W. In this paper, the problem of the thermo-stabilizing of the deformable mirrors is studied. Bimorph deformable mirrors (BDM) and stack actuator deformable mirrors (SADM) are considered. For BDMs the active and passive cooling designs have been implemented. In active design, the waffletype cooling system for circulation of the cooling liquid was made inside of the thin substrate. In passive design, the periphery surface is thermally contacted with the condenser which temperature is constant. Such BDMs not damaged at CW power density 20kW/cm2 when the beam fills full surface of the mirror and can be used in powerful solid state ceramic YAG lasers. SADM is most suitable to correct for small-scale and high-speed aberrations. We developed SADM where reflecting substrate is cooled through the actuator bodies. Individual actuators are housed in metal holders and can be replaced if they fail due to electrical breakdown. SADM has the diameter 120 mm and included 121 actuators. The deformation stroke of the actuator was 7μ. The first resonant frequency was 18.5 kHz, which allowed operating in adaptive system in kHz range.

Adaptive system for wavefront correction based on 240-mm bimorph deformable mirror and Shack-Hartmann wavefront sensor is presented. The dynamic characteristics of the deformable mirror and the performance of the wavefront correction in various operating modes of the PEARL facility as well as the features of phase distortion compensation in a single-shot generation regime are studied. An improvement in the quality of focusing that led to an increase in the Strehl ratio to 0.6 is demonstrated.

Stacked-array deformable mirror is one of the most popular tools for correction of wavefront aberrations. We manufactured the stacked-array deformable mirror with small diameter by using piezoceramic combs with few actuators on them. In this case the aperture of mirror will be equal to 30 mm. The stroke of such mirror would be about 5 microns. The thickness of the mirror substrate is 1 mm. Developed deformable mirrors will be suitable for fast adaptive optical systems for optical radiation transferring through turbulent atmosphere tasks.

The article discusses the use of stacked-actuator adaptive mirrors to improve the focusing of laser radiation. The criterion of focusing efficiency is the fraction of the energy of the laser radiation passing through the pinhole located in the focal plane of the focusing lens.

One of the main problems in tasks of laser beam propagation though Earth’s atmosphere is decrease the efficiency of the optic-electronic systems operation due to atmospheric turbulence influence that leads to laser beam’s wavefront distortions. Use of fast adaptive optical system are suggested to solve this problem. It allows to compensate the wavefront distortions, which upper bound of the spectrum is up to 150 Hz, in real time. Owing to the fact that adaptive optical system is discrete (it’s defined by digital camera included in the system), the sampling rate shall be at least 1500 Hz (frames per second).

Bimorph deformable mirror for correction of low-order aberrations of laser radiation was manufactured. Two technologies were used to develop this wavefront corrector: laser engraving technology and ultrasonic welding technology. The mirror has aperture of 10 mm and 13 control electrodes. The thickness of the wavefront corrector is 1 mm. The applied voltages took values in the range from -150 to +200 V. The stroke of the mirror for one electrode was equal to 1 micron (P-V). The first resonant frequency was found at 10.8 kHz. Such mirror can be used in closed-loop adaptive optical system with speed about 1.1 kHz.

Bimorph deformable mirror with 63 electrodes on 20 mm aperture is discussed. Methods of dividing all round electrode into sectors with a square of 2-4 mm2 are described. Results of flat-top beam formation by means of 50 mm bimorph deformable mirror with 48 electrodes and 20 mm miniature bimorph mirror with 27 electrodes are presented.

An adaptive optical system that implements a phase conjugation algorithm designed to compensate for the effect of atmospheric turbulence the propagating laser beam is presented. The system allows compensating for the influence of atmospheric disturbances up to 200 Hz (in terms of sine). To achieve the compensation effect system operates at a frequency of 2000 Hz (in terms of fps - frames per second). Such high performance can be achieved only when using FPGA as the master control element of the system. The results of correction of disturbances obtained by using a heat fan, simulating the turbulence to frequencies of 200 Hz, are presented.

Laser beam shaping technology nowadays requires as small diameter of the adaptive optics as possible. In our lab we usually control for laser radiation by means of bimorph deformable mirrors with a typical size of more than 50 mm. To fit the most of industrial and scientific applications the aperture of the corrector should be reduced because the use of extra optics instead makes the whole optical scheme more complicated and introduces extra distortions. But in a bid to reduce the size of the mirror we should care of the response of the mirror electrodes which obviously should not decrease drastically. Here we present 20 mm bimorph mirror with high density of electrodes which is manufactured using laser engraving technology to divide the electrode on the piezoceramic disc into a large number of the controlled sectors. The ability of laser beam formation by means of this mirror is discussed, the results are compared with the ones obtained using 50 mm bimorph deformable mirror.

As well known, the quality of radiation of laser beam is reduced during propagation along optical trace, because of various reasons (for example, atmospheric turbulence, scattering, thermal fluctuations etc.). We propose small-size deformable mirrors with high spatial resolution of control elements, that will allow to compensate for wavefront aberrations in wide range. Developed wavefront corrector could be used in different scientific areas: free-space communications, destruction of space debris, etc.

In tasks related to free-space communications, a significant role has a turbulent atmosphere which influences lead to a decrease in the efficiency of systems. Since the characteristic turbulence spectrum rarely exceeds 100 Hz for typical paths, it is proposed to use a discrete adaptive optical system with a frequency of 1500 frames per second to reduce the influence of the atmosphere. The structure of the system based on the use of FPGA as a computing device as well as the main results associated with the correction of both static and dynamic components of aberrations are presented.

The article discusses the use of stacked-actuator adaptive mirrors to improve the focusing of laser radiation. The criterion of focusing efficiency is the fraction of the energy of the laser radiation passing through the pinhole located in the focal plane of the focusing lens.

The most important part of any adaptive optical system is a deformable mirror. One of the most widely used type of such mirrors are the bimorph ones. In fact, there is no problem to manufacture a wide aperture bimorph wavefront correctors that perfectly can compensate low-order laser aberrations. But if one needs a tiny deformable mirror to correct for high order aberrations with reasonable amplitude, he usually will use stacked actuator mirror or a MEMS one. In this presentation we suggest the new design and technology of production of a small size bimorph mirrors to be used to correct for atmospheric phase fluctuations. Our mirror has the diameter of 30 mm and 37 control electrodes (mirror with 20 mm and 63 control electrodes is being developed). The resonance frequency of 13.2 kHz is due to its small diameter. At the same time, large number of electrodes allows to reproduce high order aberrations. To manufacture this device two modern technologies are used: ultrasonic welding and laser engraving technology.

In this work, we investigate the efficiency of the use of the bimorph deformable mirror to focusing laser beam in the pinhole. Pinholes of different diameters are used as an instrument for focusing verification. Different algorithms are discussed and analyzed for the investigation of the process of the beam focusing. It is shown that tip-tilt correction is an essential condition for increasing the focusing efficiency.

High-power laser systems are widely used for technological purposes or laser fusion experiments, but also to deliver the energy to some remote places here on the Earth as well as in space. Probably the only instrument to improve the phase structure of the laser beam is to use methods and elements of adaptive optics. The heart of any adaptive optical system is of course the deformable mirror. That is why the research and development of such optical elements continues for many years already. Here we propose a new stacked actuator mirror to be used to correct for not just the turbulent phase fluctuations, but also it should work with high CW power laser beams. Therefore, our mirror is a water-cooled one. Another important feature of this device is that each actuator could be easily substituted in case of failure. The mirror is 120 mm in diameter and has 121 control elements. Main characteristics of a mirror are presented in this work.

As it is well-known, the laser radiation, propagated through different mediums, is affected by wavefront distortions and thus the quality of the radiation is significantly decreased. To compensate for the wavefront aberrations adaptive optics means are used. We developed miniature bimorph mirror with 37 electrodes. To manufacture this type of mirrors two technologies were used. Those are laser engraving technology for drawing electrode grid on the piezoceramic disc, and ultrasonic welding technology to connect wires to the control electrodes. Main parameters of such a deformable mirror were investigated and presented in this paper.

Fast adaptive optical system can be used, for example, for correction of laser beam passed through a strong turbulent atmosphere. The frequency that such a system should operate with to achieve an acceptable level of wavefront correction is about 1 - 1.5 kHz. There are two most popular methods to develop this system: by using a standard PC computer and by using FPGA. This paper presents the advantages and disadvantages of each of these approaches. The results obtained with the use of these systems are presented. Recommendation for achieving higher performance are given.

During propagation of the high-power laser radiation through atmosphere the quality of the beam is significantly reduced due to atmosphere turbulence. For compensation of the wavefront distortions and improving quality of radiation, as a rule, adaptive optics approaches are used. The design and main characteristics of 121-element water-cooled stacked-actuator deformable mirror for this kind of applications is discussed in this paper.

Laser beam focusing (λ = 0.65 μm) through the scattering suspension of polystyrene microspheres in distilled water was investigated. Shack-Hartmann sensor was used to measure the local slopes of the Poynting vector, the CCD camera was used to measure the far-field focal spot’s intensity. Numerical and experimental investigations of focusing efficiency of the two bimorph deformable mirrors with 14 and 48 control channels were performed.

Formation and correction of the given laser beam intensity and phase is an important practical and scientific problem. Semipassive bimorph flexible mirror is one of the most widely used devices for this purpose. But the key disadvantage of these kind of mirrors is their low spatial resolution of the corrected phase. Mainly this problem occurs when one deals with the small aperture wavefront correctors. In this work we present two approaches to overcome this problem – one to use a multilayer bimorph (multimorph) mirrors and another to put higher density of control electrodes and use a special technique (ultrasonic welding) to make the wire connection to these electrodes. Here we also present a numerical model to simulate bimorph correctors, based on a variation approach of the finite elements method.

The transformation of an intensity distribution from Gaussian to a flattop, doughnut, etc. still is a very interesting and important task. And the necessary result could be obtained with the use of adaptive optics that changes the phase of the beam and modifies the shape of the focal spot in the far-field zone. In this paper, we present the flattop and doughnut beam formation result with the use of a bimorph and stacked-actuator deformable mirrors as well as LC phase modulator. The experimental results are also given.

We investigated the ability to focus laser beam (λ = 0.65 nm), propagated through the scattering suspension of polystyrene microspheres in distilled water, by means of two bimorph mirrors. Shack-Hartmann sensor was used to measure the local slopes of the Poynting vector, and the CCD camera was used to measure the intensity of the focal spot in the far-field. Correction efficiency of the two bimorph deformable mirrors — with 14 and 31 control channels — were compared. Numerical and experimental investigation of the focusing improvement of the laser beam propagated through the scattering medium was performed.

Key elements of the fast adaptive optical system (AOS), having correction frequency of 1400 Hz, for atmospheric turbulence compensation, are described in this paper. A water-cooled bimorph deformable mirror with 46 electrodes, as well as stacked actuator deformable mirror with 81 piezoactuators and 2000 Hz Shack-Hartmann wavefront sensor were considered to be used to control the light beam. The parameters of the turbulence at the 1.2 km path of the light propagation were measured and analyzed. The key parameters for such an adaptive system were worked out.

Distortions of the scattered laser beam (λ=0.65μm) were numerically estimated by means of Shack-Hartmann technique and experimentally measured. The ability to focus laser beam, passed through the scattering suspension of polystyrene microspheres in distilled water, using bimorph deformable mirror was investigated both numerically and experimentally. Shack-Hartmann technique was used to measure the local slopes of the Poynting vector, and CCD camera was used to analyze the intensity distribution of the focal spot in the far-field. Bimorph deformable mirror with 14 electrodes was utilized in order to increase the focusing efficiency of the laser beam. The voltages to be applied to the mirror electrodes were calculated using three techniques: LSQ (least squares) fit-error minimization by Shack-Hartmann sensor, Hillclimbing optimization by Shack-Hartmann sensor and Hill-climbing optimization by the far-field CCD camera.

We have fabricated a 410 x 468 mm size deformable mirror with 100 Bimorph piezoceramic actuators for the LFEX laser system at Osaka University. In the case of Bimorph-type deformable mirrors, the mirror surface had to be polished and coated after bonding the piezoceramic actuators to the rear side of the thin mirror substrate. This provides a good surface figure, but the coating temperature for the high-reflection mirror was strictly limited because of the thermal fragility of piezoceramic actuators. The mirror substrate with the actuators was polished, and an ion-assisted multilayer dielectric coating was produced at 60 degrees Celsius with our 80-inch coating chamber. The flatness of the mirror just after coating was 7 μm, and reduced by aging to 3.2 μm when the mirror was assembled. The surface figure of the assembled mirror with 20 piezostack bonded actuators is demonstrated and a laser-induced damage threshold tested with a witness sample is also reported.

In this paper we present recent results of formation of different beam intensity distribution by means of bimorph deformable mirrors. We discuss the results of such formation as well as the problems that one faces on this way. A new method for beam structure modification is suggested based on the use of Shack-Hartmann wavefront sensor with the combination of standard M2 meter. Keywords: Bimorph deformable mirror, laser beam shaping, Shack-Hartmann wavefront sensor, M2 meter 1. INTRODUCTION A uniform beam (or flat-top beam) is a beam with a flat intensity profile over the diameter. Such beam profile is required for different laser applications like laser beam cutting, laser thermal processing, laser fusion. Usually a uniform beam is obtained from Gaussian beam by transforming its intensity or phase profile with some optical elements ± diffractive optics like PI shapers 1 , adaptive mirrors 2,3 , or just a set of certain lenses. The main goal of this work was to find the way how to change the wavefront of the beam in order to convert Gaussian intensity distribution to the uniform one at the focal plane of the focusing system. Our scheme for beam shaping is presented on Fig. 1. Incoming beam reflects from the bimorph deformable mirror and is splitted both to Shack-Hartmann wavefront sensor and CCD camera at the focal plane of the focusing lens. Shack-Hartmann sensor was used as a part of a closed-loop system to get the desired Zernike polynomials coefficients and CCD camera was used both to check the resulting focal spot intensity distribution and to improve the results of the closed-loop based on Shack-Hartmann wavefront sensor with one of gradient methods like hill-climbing

The deformable mirror with the size of 410x468 mm controlled by the bimorph piezoceramic plates and multilayer piezoceramic stacks was developed. The results of the measurements of the response functions of all the actuators and of the surface shape of the deformable mirror are presented in this paper. The study of the mirror with a Fizeau interferometer and a Shack-Hartmann wavefront sensor has shown that it was possible to improve the flatness of the surface down to a residual roughness of 0.033 μm (RMS). The possibility of correction of the aberrations in high power lasers was numerically demonstrated.

Sometimes to improve the performance of industrial or scientific laser technology it is desired to transform an intensity distribution from Gaussian to the flattop. The adjusting of the intensity profile can be implemented by means of adaptive optics. In this paper we present laser beam control with bimorph deformable mirrors. Shack-Hartmann wavefront sensor is used to determine the control signal for the bimorph deformable mirror while focal spot is observed with CCD camera to check the result of beam shaping.

Wide aperture bimorph mirrors for laser beam correction and formation were developed and investigated. Different types of substrates and active piezoceramics materials were considered to fabricate temperature independent shape of the mirror surface and to maximize the sensitivity of the mirror. High reflectivity coatings for different wavelengths were studied.

This paper presents the design of the closed loop adaptive system to measure and correct for the aberrations of CO 2 laser radiation. We considered two wavefront sensors - one sensor is based on commercially available IR camera while the second one – on the so-called thing film sensors. Also we present the design of two bimorph deformable mirrors to be used under high power laser radiation. We discuss both positive and negative attributes of these devices and the possibility to use them in the real laser high-power systems.

Shack-Hartman wavefront sensors are widely used in scientific investigations of wavefronts and also, as a component of the closed-loop adaptive optical system, intended to correct for laser beam aberrations. This paper presents successful application of such type sensors in the laser systems investigations to obtain high quality laser radiation. Results of investigations of wavefronts of modern high power solid-state lasers are given in this paper.

This paper discusses the novel adaptive optical closed loop system with water-cooled bimorph mirror as a wavefront corrector to compensate for the aberrations of high-power CW laser beam. Shack-Hartmann wavefront sensor is used as an element for feedback control. Comparison of phase conjugation and modified hill-climbing technique is shown.

Bimorph mirrors for laser beam correction and formation were developed and investigated. Different types of substrates and active piezoceramics materials were considered to fabricate temperature independent shape of the mirror surface and to maximize the sensitivity of the mirror. High reflectivity coatings for different wavelengths were studied.

Here we investigate closed-loop adaptive optical system to compensate for laser beam aberrations. A bimorph mirror is used as a wavefront corrector and Shack-Hartmann wavefront sensor is an element for feedback control. Comparison of phase conjugation and multi-dither technique is shown.

Here we investigate closed-loop adaptive optical system to compensate for laser beam aberrations. A bimorph mirror is used as a wavefront corrector and Shack-Hartmann wavefront sensor is an element for feedback control. Comparison of phase conjugation and multi-dither technique is shown.

It is very important to analyse phase ingomogenity of high-power laser beam. Usually Shack-Hartmann wavefront sensor or interferometer is used to test both laser beam aberrations and quality of the optical element surface. But we found out that in case of strong distortions the measured aberrations differ from the real ones. To investigate this problem we used bimorph deformable mirror to introduce strong aberrations to the laser beam. The results of our experiments are discussed.

The main disadvantage of contemporary bimorph flexible mirrors is that they used to have rather large aperture. At the same time semipassive bimorph flexible mirror is one of the most widely used devices in various adaptive systems. We present a novel approach of multilayer bimorph (multimorph) mirrors and a numerical model to simulate them, based on a variation approach of the finite elements method in order to reduce the size (diameter) of these wavefront correctors. The multilayer bimorph mirror consists of a substrate and a number of piezoceramic layers. The electrode grid of each layer is determined separately to reproduce low order aberrations. We also present our results in reproduction of the wavefront phase dislocations (vortices) with the help of tiny bimorph mirror.

We present a novel algorithm of bimorph mirror grid determination. Its usability is demonstrated on practical examples of defining electrode grid to form a vortex beam. We briefly describe the developed finite element bimorph mirror model, designed to evaluate an arbitrary electrode response function.

Some peculiarities of the use of adaptive optical elements and the whole system to correct for the aberrations of high power single pulse lasers are discussed in this paper. The examples of the use of adaptive system to correct for the aberrations of some lasers are presented. As a corrector we used bimorph multi electrode deformable mirror while as a sensor - Shack- Hartmann wavefront sensor.

Some peculiarities of the use of adaptive optical elements and the whole system to correct for the aberrations of high power single pulse lasers are discussed in this paper. The examples of the use of adaptive system to correct for the aberrations of some lasers are presented. As a corrector we used bimorph multi electrode deformable mirror while as a sensor - Shack-Hartmann wavefront sensor.

We describe a closed-loop adaptive optical system with bimorph deformable mirror to obtain good focused laser beam. This adaptive system can correct for the wavefront aberrations without any measurements of the wavefront: we use M2-meter as a sensor for the feedback. Closed-loop software allows to measure focal spot with M2-meter and then to calculate voltages to be applied to corrector. The best focal spot can be reached by use of combined method based on genetic and hill-climbing algorithms. We demonstrate the use of such a system with water-cooled bimorph deformable mirror as a wavefront corrector on CW solid state Nd:YAG 1kW CW laser system.

A key element in any adaptive optics system is the deformable mirror used to introduce the conjugate correction. In this paper we will present the results from characterizing a pair of custom 20 element, 38 mm diameter, bimorph deformable mirrors that were specifically designed to provide unusually large stroke to allow correction of significant focus and astigmatism terms in a human fundus adaptive optics imager. Data on the measured correction capability and inherent hysteresis of the mirror shown that the mirrors have 40 μm waves of defocus correction and 20 μm waves of astigmatism correction at 760 nm, with a typical hysteresis at full deflection of 15%. This technology is patented under Patent # 6,331,059 B1.

This paper presents adaptive optical closed loop system with bimorph mirror as a wavefront corrector and Shack-Hartmann wavefront sensor to compensate for the aberrations of the high power lasers. Adaptive system can correct for the low-order aberrations in the real-time -- the frequency of corrected aberrations is less than 25 (30) Hz. The amplitude of such aberrations -- about 7 microns. These parameters are mostly determined by utilized Shack-Hartmann wavefront sensor. Number of corrected aberrations -- up to 30th Zernike polynomial (excluding tip-tilt). We are presenting the results of the use of our adaptive system in several high-power laser systems such as ATLAS, LULI, JAERI and Beijing Institute of Physics.

This paper presents the novel optical closed-loop adaptive system (CLAS) for compensation of the laser beam aberrations and results of its application in high power lasers. A closed-loop adaptive algorithm is developed to control for a continuous-surface deformable bimorph mirror. The control voltages applied to the electrodes reduce the wavefront distortions measured by a Shack-Hartmann wavefront sensor (SHWS). Adaptive system can correct the low-order aberrations with the frequency is about 25 Hz. The amplitude of corrected aberrations is about 10 microns and sensitivity is about 0.08 microns. The examples of the use of such systems to control for radiation of TW Ti:Sa lasers are presented.

This paper discusses the novel adaptive optical closed loop system with bimorph mirror as a wavefront corrector and Shack-Hartmann wavefront sensor to compensate for the aberrations of the laser beam occurred during the distribution of the beam from laser to processed material. Adaptive system can correct for the low-order aberrations in the real-time, the frequency of corrected aberrations is less then 25 (30) Hz. The amplitude of such aberrations, about 7 microns. These parameters are mostly determined by utilized Shack-Hartmann wavefront sensor. Number of corrected aberrations - up to 15th Zernike polynomial (excluding tip-tilt).