The project “Extreme Light Sources and Applications” (ELSA) is aimed at establishing in the Lobachevsky State University of Nizhny Novgorod a world-class laser physics laboratory supervised by Prof. G. Mourou and at wide-range studies on the generation of light fields with extremely high (up to 5-10 petawatt) peak power, with extremely short duration of about 100 attoseconds, and in the terahertz frequency range that is extremely complicated for mastering.

ELSA-laboratory comprises two parts: XT-lab dealing with the physics of attosecond and terahertz generation and MP-lab dedicated to creation and use of petawatt laser sources. In common, XT and MP laboratories include three experimental complexes: multipetawatt, attosecond, and terahertz.

Multipetawatt laser complex

The MP part of the ELSA lab is a terminal unit of the multipetawatt laser complex, which has been constructed together with IAP RAS in the special radiation-protected experimental room in IAP RAS. The laser complex is based on the technique of optical parametric chirped pulse amplification and contains three-cascades of amplification in DKDP crystals with the total gain more than 10¹¹. The first two cascades are pumped by the second harmonic radiation of the Nd:YLF laser, and the terminal cascade with the 10x10 cm² aperture, by the second harmonic of the Nd:glass laser with the energy of about 180 J, pulse duration around 1 ns. In the petawatt regime, the pulse, generated at the wavelength of 910 nm, has ~45 fs duration and ~25 J energy with near diffraction-limited laser beam divergence, which ensures the intensity at tight focusing up to 10²² W/cm². To achieve the multipetawatt regime, we have increased the pump energy for the terminal stage, constructed a new telescope system for better spatial pump-signal matching in the nonlinear crystal, and assembled a new four-grating high-throughput optical vacuum compressor. The complex is now operating in the testing regime. The laser radiation parameters such as pulse duration and the spatial profile are under optimization for laser-plasma interaction experiments. The modernization of the target vacuum chamber for the laser beams with increased aperture has been accomplished. The new target chamber which is optimal for the experiments with solid targets has been designed and is now in a final stage of assembling. A high-precision solid-target positioning system in vacuum has been designed and produced. A technique of flat matrix target alignment by use of a ccd-camera with microscopic lens and three alignment apertures at the target mount, which provides submicron accuracy in execution laser-plasma interaction experiments, has been developed.

Complex for attosecond studies

The attosecond complex was constructed in a special experimental room of 60 m² area with low-vibration environment. The room was electromagnetically shielded and equipped with specially designed ventilation and conditioning system for controlling the temperature and humidity. The system provides the temperature stability in the room with an accuracy of 0.5 C, which is necessary for normal performance of the key component of the lab – the femtosecond laser system with carrier-to-envelope phase stabilization FemtoPower Pro CEP3 (FEMTOLASERS, Austria). The design of the experimental setup for attosecond generation purposes was elaborated. The equipment that comprises the beamline, such as vacuum chambers with pumps and automation electronics, gas dosing equipment, time-of-flight spectrometer, microchannel plate detector, CCD cameras etc, was purchased and installed.

Complex for terahertz studies

The complex has been created on the basis of the terahertz spectrometer already existed at the General Physics Department of the University. The key component of the complex is the femtosecond laser Tsunami with the pump laser Millennia V (Spectra Physics). The MPA-50 laser amplifier (CDP Systems, Russia) provides 100-fs pulses with 1 mJ energy at the wavelength of 800 nm that can be parametrically converted to any wavelength in the range from 200 to 11000 nm by the parametric amplifier.

In 2012, a new experimental room of 40 m² area was assigned to the XT lab by the University for developing new methods of terahertz spectroscopy and imaging in application to biomedical diagnostics, introscopy of pieces of art, nondestructive inspection of pharmaceuticals, and to security purposes. The room was equipped with terahertz spectrometer Tera K15 (Menlo Systems, Germany).

Among the main results of the research conducted on the experimental complex for terahertz studies in 2011-2012, the most remarkable are record optical-to-terahertz conversion efficiencies obtained using original structures with a thin layer of an electro-optic material (LiNbO₃) sandwiched between a reflecting substrate and a Si-prism outcoupler. Pumping such a sandwich structure by amplified laser pulses of tens-of-microjoule energy we achieved a world record efficiency of 0.25% [S.B. Bodrov et al., Appl. Phys. Lett. 100, 201114 (2012)]. For nonamplified pump pulses of nanojoule energy, we achieved a record efficicency of 0.008% [M.I. Bakunov et al., Appl. Phys. Lett. 101, 151102 (2012)].