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A prototype of a direct-current photoinjector (DC) with an electron energy of up to 400 keV is being developed at JINR for future electron accelerators (electron-positron colliders and free-electron lasers). This article describes the injector, one distinctive feature of which is the use of the transmission photocathode operation mode. A unique laser system is implemented on the photoinjector. The system makes it possible to synchronize the repetition rate and the phase of the laser pulses (of 10 ps duration, 262 nm wavelength, and 1.85 μJ energy) with the frequency of the accelerator RF system. The first experimental results of a DC photoinjector are presented and further plans for the development of the installation are discussed. more...

A new self-propagating high-temperature synthesis (SHS) technique for production of yttrium oxide nanopowders, doped with rare-earth ions, from metal acetatonitrates was developed. The synthesized powders were used for preparing transparent ceramic samples by microwave sintering. Optical properties (transmittance, absorption, scattering, refraction) of Yb0.1(Y, La)1.9O3 ceramics depending on the content of lanthanum oxide, have been investigated. For the first time lasing at 1030 nm in Yb0.1Y1.7La0.2O3 ceramics, prepared by these methods, has been attained. more...

Ellipsoidal laser pulses with central wavelength of 1030 nm and duration of 40 ps were obtained. It is expected that after conversion into the fourth harmonic this will reduce appreciably emittance of the electron beam, injected by the laser. more...

We use a PW-class PEARL facility to study fast electron beam generation during high intensity laser pulse interaction with a supersonic gas jet. We show that electron beams with several hundreds of MeV and relatively large charges, of hundreds of pC and more, can be effectively produced without any guiding structures. PIC simulations also confirm the obtained experimental data and provide optimized conditions of laser–plasma interaction for high-charged beam production. more...

In this paper, we describe adaptive compensation of thermal lens in a Faraday isolator using a DKDP crystal. Thermal lens measurements were made with a modification of the conventional Hartmann sensor – a 2D scanning Hartmann sensor. Our experiments showed that a DKDP crystal does not influence the isolation ratio of Faraday isolator and efficiently compensates for thermal lens. The negative effect produced by the thermal lens is estimated as the amount of power losses from the original beam mode (Gaussian mode in our experiments). Without compensation the losses were measured to be about 25% for 45 W radiation power and were compensated to less than 0.5% by a negative thermal lens in a 5.5 mm-thick DKDP crystal. Numerical extrapolation of experimental data to a higher power range has shown that for the powers up to 150 W, power losses can be made less than 5%. more...

In this paper, we present a new interference scheme with transverse shift of beams for remote monitoring of parameters of optical elements. The results of studying the measurement accuracy are given and the main noise sources of the presented scheme are considered. The advantages of this scheme are the high accuracy (the experimentally realized accuracy is higher than λ/3000, where λ is the wavelength of the sounding radiation), high speed allowing us to study nonstationary processes, and selectivity ensuring the study of a given surface by using other optical elements of the scheme. more...

Two methods of compensation of thermal lensing in high-power terbium gallium garnet (TGG) Faraday isolators have been investigated in detail: compensation by means of an ordinary negative lens and compensation using FK51 Schott glass possessing a negative dn/dT. Key thermooptic constants for TGG crystals and FK51 glass were measured. We find that the contribution of the photoelastic effect to the total thermal lens cannot be neglected for either TGG or FK51. We define a figure of merit for compensating glass and show that for FK51, an ordinary negative lens with an optimal focus is more efficient, but requires physical repositioning of the lens for different laser powers. In contrast, the use of FK51 as a compensating element is passive and works at any laser power, but is less effective than simple telescopic compensation. The efficiency of adaptive compensation can be considerably enhanced by using a compensating glass with figure of merit more than 50, a crystal with natural birefringence or gel. more...

We study experimentally the possibility of using the recombination continuum (RC) emitted by a nonequilibrium plasma of the positive column (PC) of a Cs–Xe discharge for real-time imaging of the spatial distribution of microwave intensity. A uniform plane slab of dense plasma of the PC of a Cs–Xe discharge with aperture 10×8 cm2 was used for the imaging. A continuous-wave (CW) magnetron was the microwave source with frequency 35.4 GHz and power up to 20 W. We measured the dependence of the RC intensity on the intensity of the microwaves incident on the plasma. Spatial distributions of the microwave intensity for a microwave beam and the H01 mode of a circular waveguide were imaged. The results of these experiments show that spatial distributions of microwave intensity measured using RC agree well with the distributions obtained using other methods. A temporal resolution of 10 μs was demonstrated and an energy-flux sensitivity of about 4·10-5 J/cm2 was achieved in the microwave-imaging experiments. more...

In this paper we discuss laser wake field acceleration experiments made at the PEtawatt pARametric Laser (PEARL). Using free 2mm and 5 mm gas jet without preplasma we generated electron beam with energy up to 260 MeV. The charge of quasimonoenergetic beams achieved 300 pC, angular divergence 0.2 degree. The special attention is paid for diagnostics which is adapted for low repetition rate systems with low output parameters stability. more...

In this paper we discuss laser weak field acceleration experiments made at the PEtawatt pARametric Laser (PEARL). Using free 2 mm gas jet without preplasma we generated electron beam with energy up to 200 MeV, angular divergence 0.2 degree, and charge 10 pC. The special attention is paid for diagnostics which is adapted for low repetition rate systems with low output parameters stability. more...

Thermal effects in optical mediums became more and more important in applied optics because of quick and steady grow of average power of modern lasers. Radiation power is so high that phase distortions caused by thermal lensing effects became important for achieving lasers resonators stability. In this paper we discuss interesting experimental results for YLF crystal: high anisotropy and high astigmatism of thermal lens in acutted YLF rods. The first effect is more or less predictable because YLF is uniaxial crystal. But high astigmatism of thermal lense is unexpected and is not explained in literature so far. Astigmatism is so high that phase distortions profile for perpendicular directions can change its sign [1–3]. Unfortunately in most papers the reason of thermal lens astigmatism is not discussed. At some papers there is a try to explain this by thermal conductivity anisotropy and as a result - non-symmetric temperature distribution but this effect is unable to change the sign of the lens. more...

In struggle for record average and peak power of laser radiation it was found out that many characteristics before used materials don't answer increasing inquiries. There was a problem of searching new alternative materials. One of such materials can be a ceramic. For lasers with high average and peak power a polycrystalline ceramics offers well-known advantages: large aperture like in glass, high thermal conductivity like in single crystals, higher than in single crystal thermal shock parameter, possible control of spectroscopic characteristics and low cost. Recently, 67kW CW ceramics laser was reported. At such power the important role is played by the thermal effects which studying in ceramics becomes actual. In this paper, we present a theoretical model of thermal effects in laser ceramics and their experimental confirmation. more...

Large-aperture Faraday isolators with compensation of thermally induced polarization and phase distortions of highpower laser radiation have been studied experimentally. The degree of isolation is considerably increased up to 24-26 dB at 10-750 W power for one Faraday isolator and up to 42 dB at 10-200 W power for another Faraday isolator and is limited by the quality of TGG crystals. Phase distortions are also considerably reduced. more...

An optical system that comprises two devices for remote measurements, a broadband optical interferometer and a scanning Hartmann sensor, is described. The results of simultaneous measurements with both devices and the results of numerical modeling of sample surface heating are presented. more...

In this paper we describe adaptive compensation of thermal lens in a Faraday isolator using a DKDP crystal. Thermal lens measurements were made with a modification of the Hartmann sensor -a 2D scanning Hartmann sensor. This device proved to be convenient and adequate for thermal lens measurements. Our experiments showed that a DKDP crystal does not influence the isolation ratio of Faraday isolator and efficiently compensates thermal lens. The negative effect produced by the thermal lens is estimated as the quantity of power losses from the original beam mode (Gaussian mode in our experiments). Without compensation the losses were measured to be about 5% for 50W of radiation power and were compensated to less than 1% by a negative thermal lens in a few millimeters thick DKDP crystal. Numerical extrapolation of experimental data to a higher powers range showed that for the power up to 200W, power losses can be made less than 5%.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only. more...

Positive thermal lens in optical element (Faraday isolator in our case) produced by absorption of high power radiation was experimentally compensated with negative thermal lens in DKDP sample self-adaptive to different radiation powers. more...

We developed a scanning Hartmann sensor and an interferometer detector for precision measurements of thermal effects in samples in vacuum are developed. The simultaneous use of these methods allowed us to distinguish contributions of different thermal effects. Besides we discussed active thermal correction of thermally induced wawefront distortions by means of ancillary heating using CO2 laser irradiation. more...

Two methods of compensation of thermal lensing in high wer terbium gallium garnet (TGG) Faraday isolators have been investigated in detail: compensation by means of an ordinary negative lens and compensation using FK51 Schott glass possessing a negative dn/dT. Key thermo-optic constants for TGG crystals and FK51 glass were measured. We find that the contribution of the photo-elastic effect to the total thermal lens cannot be neglected either for TGG or for FK51. We define a figure of merit for compensating glass and show that for FK51, an ordinary negative lens with an optimal focus is more efficient, but requires physical repositioning of the lens for different laser powers. In contrast, the use of FK51 as a compensating element is passive and works at any laser power, but is less effective than simple telescopic compensation. The efficiency of adaptive compensation can be considerably enhanced by using a compensating glass with figure of merit more than 50, a crystal with natural birefringence or gel. more...

Two methods of reduction of thermal lens in Faraday isolators were theoretically and experimentally investigated and compared: compensation by means of an ordinary negative lens and compensation by means of a glass inducing negative thermal lens when heated. more...

Investigations of thermal effects caused by absorption of laser radiation in Faraday isolators and Faraday mirrors are becoming more important. A most promising medium for Faraday devices in the wavelength range of 600-1200 nm is the terbium gallium garnet (TGG) crystal. In order to measure its thermo-optic constants (which are unknown) we used a scanning Hartmann sensor technique. This technique can easily and inexpensively measure wavefront distortions induced by optical elements to within 2nm. more...

Thermal lens measurements were made by means of a high-accuracy phase shift interferometer that combines a lambda/1000 sensitivity and 10 microm transverse resolution. The effect of random small-scale modulation in thermally induced phase distortion predicted earlier was proved experimentally. The statistical parameters of modulation were measured depending on heating power for two different ceramic samples. The experimental data agree well with results of numerical simulation. more...

Faraday isolators play a key role in the operation of large-scale gravitational-wave detectors. Second-generation gravitational-wave interferometers such as the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Advanced Virgo will use high-average-power cw lasers (up to 200 W) requiring specially designed Faraday isolators that are immune to the effects resulting from the laser beam absorption–degraded isolation ratio, thermal lensing, and thermally induced beam steering. In this paper, we present a comprehensive study of Faraday isolators designed specifically for high-performance operation in high-power gravitational-wave interferometers. more...

An original laser system for implementation at DESY PITZ photoinjector to generate profiled UV optical pulses with energies exceeding 2 μJ with 28 ps pulse duration was designed and constructed.

The cross-correlator described below excels in its high speed (>1500cm/s) and high amplitude of the diagnostic channel delay. Such characteristics allow the cross-correlator to scan pulses inside 300-microsecond long pulse trains, repeated with the frequency of 10Hz. more...

Summary form only given. The European X-ray Free Electron Laser (XFEL) is being built at DESY in Hamburg. Its ultrashort X-ray flashes with extremely high peak and average brilliance are expected to allow unprecedented experiments with atomic resolution on femtosecond time scales. The Photo Injector test facility at DESY, Location Zeuthen (PITZ) is responsible for the developing of the electron source for the XFEL. The laser driven RF gun has to fulfill very challenging specifications on electron source performance for linac based FELs, namely it should provide electron bunches with high bunch charge (~1 nC) and extremely low transverse emittance ( more...