Sergey I. Chizhikov

Adaptive acousto-optic technique for femtosecond laser pulse shaping

We discuss the theoretical and experimental investigation of acousto-optic dispersive tunable filters, based on quasi-collinear geometry of light-sound interaction in a tellurium dioxide single crystal. The geometry uses the effect of strong acoustic anisotropy in the paratellurite as well as peculiarities of acoustic wave reflections at the free boundary of the crystal. A mathematical concept for determination of optical, electrical, and constructional parameters of the filters is developed. Different experimental acousto-optic filters intended for femtosecond pulse shaping are designed and tested. Preliminary experiments are performed in a subpetawatt optical parametric chirped pulse amplification laser system. The experimental data conform completely with the predicted data.

Acousto-optical adaptive correction of a chirped laser pulse spectral profile in a Nd-phosphate glass regenerative amplifier

We present results of experimental research carried out with the help of an acousto-optical light dispersive delay line (LDDL) on spectral correction of chirped laser pulses in a Nd-doped phosphate glass regenerative amplifier (RA) characterized by high gain (G 4 10 7 ). The spectral resolution of the LDDL was equal to 1:1 cm 1 at a diffraction efficiency greater than 80%. The use of the LDDL made it possible to implement operating conditions of the RA under which the duration of the output chirped pulse did not shorten in comparison with the duration of the input one, which meant that the width of the spectral emission could be preserved. (Some figures may appear in colour only in the online journal)

Acousto-optical imaging spectropolarimetric devices: new opportunities and developments

We report design and prototype performance of an acousto-optical imaging spectropolarimeter aimed for the 2.5 m telescope at Caucasian Mountain Observatory of Lomonosov Moscow State University. Special geometry of the acousto-optical interaction provides two diffracted beams polarized along the slow and the fast axes of the crystal. The optical system of the spectrometer consisting of plane and elliptical mirrors delivers the images of the object with two orthogonal polarizations to a single CCD matrix, increasing the focal ratio of the telescope.

Anisotropic diffraction of bulk acoustic wave beams in lithium niobate.

The formalism of planar diffraction tensor was applied to the analysis of anisotropy of bulk acoustic wave diffraction and to build a full map of anisotropic diffractional coefficients for three bulk acoustic wave modes propagating in lithium niobate. For arbitrary propagation direction the diffractional coefficients derived allow estimation of ultrasonic beam divergence in far-field. Analysis of obtained data revealed that the maxima of acousto-optic figure of merit for anisotropic diffraction in the YZ plane correspond to moderate diffractional spreading of the beams exceeding isotropic diffraction 2-3 times.

Anisotropic diffraction of acoustic waves in crystals used in acousto-optic dispersive delay lines

Acoustooptic (AO) light dispersive delay lines (LDDL) are widely used in high-power ultrashort laser pulse amplification chains for pulse shaping. The geometry of AO interaction of LDDL is determined mainly by the acoustic beam propagation and photoelastic properties of the crystal. Propagation of bulk acoustic wave (BAW) beams depends on acoustic anisotropy of the crystal and is characterized by the planar tensor of diffraction, which can be considered as an extension of anisotropy parameter for 3D-space. Two nonzero eigenvalues of the tensor are compared for pure shear BAWs propagating in the symmetry planes of TeO2 and LiNbO3. The found combinations of BAW characteristics, including high velocity, low diffraction, and sufficiently large acousto-optic figure of merit, make lithium niobate more preferable for application in LDDL with rapid scan repetition frequency up to 100 kHz compared to TeO2.

Acousto-optical systems for the images spectra analysis

Two different acousto-optical tunable filter based imagers for acquisition the spectral data of optical objects are described. The first imaging spectrometer is intended mostly for astronomical observations and studying the planets and emission objects: planetary nebulae and Seyfert galaxies. The spectrometer is based on the tunable TeO2 acousto-optical filter that combines simultaneously both high spatial resolution and high spectral resolution. The acousto-optical filter with a 13 Å pass band at wavelength 6328 Å operates in the wavelength range 6300-11000 Å. The spatial resolution of the spectrometer is about 1 angular sec. The geometry of acousto-optical interaction as well as design peculiarities of the acousto-optical filter is discussed. The astronomical observations were performed at the Crimea laboratory of Sternberg Astronomical Institute. The telescope was 600 mm f/12.5 Cassegraine Zeiss-600. Series of spectral images of the planetary nebulae NGC 7027 in the vicinity of the 6563 Å Hα and 6586 Α N [II]emitting lines are obtained. The performed measurements of the rapid spectral variability of Hαemission line in the nuclear of the Seyfert galaxy NGC 4151 (redshift Z=0.003) are also discussed. In this paper we describe also the laboratory visible - to - near infrared acousto-optical spectral imager. TeO2 based acousto-optical filter with 15Å pass band and tuning wavelength range 6000 - 1400 Å is used in this imager. Image - forming optics, RF electronics and factors influencing on the image quality is discussed.

Acousto-optical delay lines for femtosecond pulse shaping based on crystal materials with strong acoustic anisotropy

The femtosecond pulse quality in a laser system is determined by a non-compensated high-order dispersion and spectral deformation of the amplifier. A dispersive device that modifies the spectral amplitude and phase of the femtosecond pulse should be used to improve the duration of the compressed pulse and suppress the prepulses. The application of acousto-optical dispersive delay lines is considered. Different modifications of delay lines are compared and the types of devices used to shape femtosecond pulses are discussed. Several experimental dispersive delay lines were fabricated and investigated.

High-performance lithium niobate quasi-collinear acousto-optic filter

Quasi-collinear type of acousto-optic (AO) diffraction by bulk acoustic waves (BAW) is widely used for high-resolution tunable optical filters and dispersive delay lines for ultrashort laser pulse shaping. Most often, quasi-collinear paratellurite (TeO2) AO filters are used due to high AO figure of merit of this material (V. Molchanov et al. Quant. Electron. 39:353, 2009). Lithium niobate (LN, LiNbO3) collinear filters along Y-axis are known to provide a better spectral resolution or a shorter response time. A demand for higher spectral performance of AO filters is caused by progress in ultrafast laser technology and adaptive spectroscopy. The performance of a LN filter can be improved using quasicollinear diffraction. We aimed at design of a quasi-collinear AO filter in LN with maximum diffraction efficiency.

Interaction between femtosecond radiation and sound in a light dispersive delay lines using effect of strong elastic anisotropy

Femtosecond optical amplifiers typically have high nonlinear spectral dispersion breaking relationships of the spectral phases of femtosecond pulse. It is necessary to use some additional dispersive device for controlling of spectral amplitude and phases of amplified laser pulses. We discuss the investigation of light dispersive delay lines based on the light-sound interaction in crystals. The light dispersive delay lines geometry uses the effect of strong elastic, photoelastic and optic anisotropy in the TeO2 single crystal. Different experimental delay lines were designed and tested. The problem of femtosecond laser beam angular chirp compensation was solved also. The experiments were performed at the OPCPA femtosecond laser system.