Time-resolved inline digital holography was validated during study of nonlinear optical properties of graphene microparticles on the sample glass. A set of probe pulse inline digital holograms were recorded and compared with numerically simulated data.

A difference in the dependences of the THz radiation energy on the pump pulse duration in cases of single pulse and double pulse excitation of various liquids is revealed experimentally and justified by the numerical simulation. The possibility of reaching optical-to-terahertz conversion efficiency up to 0.1 % is demonstrated under optimal conditions.

Abstract We present the excited-state dynamics and optical properties of Fe- and Nd-diffusion doped zinc selenide polycrystals with different concentration measured by pump-probe spectroscopy in the visible and NIR range (400-1000 nm). The introduction of dopants allows one to control the optical properties of samples, which then can be used to create effective optoelectronic components for wide spectral ranges.

AbstractA modified Z-scan method for determining the nonlinear refractive index of colloidal quantum dots in the near-IR spectral range in the resonant excitation mode is proposed. It is demonstrated that the thermal effects related to heating of the solution due to strong light absorption can be mitigated by reducing the probing pulse repetition rate. The nonlinear refractive index of colloidal lead sulfide quantum dots is found to be on the order of 10^–16 cm^2/W.

We investigate the possibilities of the time-resolved inline digital holography to study local optical nonlinear properties. Proposed approach includes the registration, processing and simulation of the diffraction patterns and enables to distinguish local nonlinear responses.

In this paper we present results of experimental study of two-photon absorption (2PA) induced in electro-optical crystals ZnTe and ZnSe by intensive optical radiation in 450– 950 nm wavelength range. These crystals are of interest due to common usage in THz systems. Femtosecond pump-probe spectroscopy with the supercontinuum source helps to induce and detect different types of non-linear processes such as 2PA and to estimate nonlinear part of refractive index.

We present experimental measurement and numerical simulation of terahertz radiation generation with respect to the duration of optical excitation pulse and the thickness of the water jet.

A modified Z-scan method for determining the nonlinear refractive index of colloidal quantum dots in the near-IR spectral range in the resonant excitation mode is proposed. It is demonstrated that the thermal effects related to heating of the solution due to strong light absorption can be mitigated by reducing the probing pulse repetition rate. The nonlinear refractive index of colloidal lead sulfide quantum dots is found to be on the order of 10–16 cm2/W.

Recent works demonstrated that digital time-resolved holography is the prospective approach to study nonlinear light-matter interaction processes. In this Letter, we present a straightforward inline holographic approach for studying degenerate phase modulation induced by an inclined collimated pump beam in the isotropic sample. The method is based on a minimization of the difference between experimentally acquired data and simulated inline holograms obtained from a numerical model of pump-probe interaction in optical nonlinear media. A sophisticated experimental data processing algorithm is implemented to provide high sensitivity and a signal-to-noise ratio eligible for soft interaction with a collimated pump beam. The integral phase shift determined by our method can be used to estimate the nonlinear refractive index and the relaxation time for material with a low damage threshold. We validated our approach for the case of soda-lime and BK7 glasses.

A modification of the Z-scan technique for measuring nonlinear refractive index n2 in the terahertz spectral region is proposed. Measurements are made at a broadband terahertz radiation intensity of 0.8 × 109 W cm−2. Coefficient n2 = 2.5 × 10−11 cm2 W−1 is estimated for semiconductor crystalline ZnSe.

Исследование пропускания легированного железом селенида цинка в терагерцовом диапазоне частот

A method of ultrafast wireless information transmission using spectrum-sliced supercontinuum (SC) along the THz frequency range is presented in this letter. The THz spectrum-sliced SC was formed by femtosecond optical pulses doubled in a Michelson interferometer before being input onto a MgO:LiNbO 3 -THz generator. Two THz pulses generated by femtosecond pulses within a MgO:LiNbO 3 -crystal provided the spectrum-sliced SC in the spectral domain, which was recorded by an electro-optical detection system. The transmission rate in this method is determined by the bandwidth of the THz spectrum, the number of spectral lines in the SC, and the pulse repetition rate. We have demonstrated an SC containing 31 spectral lines with 23-GHz spacing within the range from 0.04 to 0.75 THz. The signal with encoded information was successfully transmitted over 2.4 m in free-space.

We present the results of our experimental investigation of the transmission of plates of zinc-selenide crystal doped with iron at a level of 0.23 mass % in the terahertz-frequency range and compare them with the transmission of undoped samples. We show that the presence of iron impurities in a zinc-selenide sample makes the medium more transparent in the frequency range from 0.35 to 0.5 THz. The transmission of a doped sample in this range increases to 20% compared to pure ZnSe. This result can be used in the future to create efficient devices for controlling terahertz radiation.

In this work, we considered mixtures of ethanol and water in the form of jets as samples for THz generation based on laser-induced filamentation. The dependence of the output energy of terahertz radiation on the concentration of ethanol in water was experimentally studied. It is shown that the energy grows linearly, which can be explained by an increase in the ionization energy due to the linear replacement of low-efficient charge carriers (water) with highly-efficient (ethanol). The dependence of the THz generation on the optical angle of incidence on the mixture jets was also demonstrated. The results of this study can be further used to create universal source of terahertz radiation.

Experimental and numerical modeling techniques demonstrated the possibilities of the spectral-time encoding and decoding for time division multiplexing sequence of femtosecond subpulses with a repetition rate of up to 6.4 THz. The sequence was formed as a result of the interference of two phase-modulated pulses. We report the limits of the application of the developed method of controlling formed sequence at the spectral-temporal coding.

This paper reflects the results of the research on the character of the dependence of the non-Faraday rotation of the femtosecond stimulated photon echo polarization plane on the time interval between the second and third exciting pulses, discretely varying from 180 to 900 fs in increments 180 fs. The time interval between the first and second pulses was equal to zero. The echo signal was formed at room temperature on exciton states localized on the surface defects of a thin three-layer textured ZnO/Si(P)/Si(B) film in the presence of a homogeneous magnetic field of 0.25 mT applied longitudinally to the optical excitation axis. The qualitative coincidence of the investigated dependence with the theoretical prediction of the investigated effect for gaseous medium is shown.

We report the measurement of the intensity-dependent refractive index m of ZnSe crystal at THz frequencies. We used a modified Z-scan method with an intense THz beam of maximum intensity 0.8×10 9 W/cm 2 . We measured an extremely large m value of the order of 10 -11 cm 2 /W, which is significantly larger than the m value of ZnSe in the near infrared.

Dependences of the decay of stimulated photon echoes excited in thin textured p- and n-type zinc oxide and silicon films characterized by different sizes of crystal fibers are studied. Two characters of recombination were revealed for localized excitons on crystal lattice defects, presented in the studied dependences in the form of fast and slow decay components.

Recently, great progress has been made in the generation of high-intensity terahertz (THz) radiation, which has led to the opportunity to explore non-linear processes in the THz frequency range [1]. A key parameter characterizing the nonlinear response of a material is the non-linear refractive index, denoted as n2. It has been predicted theoretically [2] that the THz nonlinear response of crystals is extremely large as a consequence of a strong vibrational contribution. An indirect assessment of n2 for lithium niobate at THz frequencies was reported in [3], leading to a value of approximately 10cm/W. We find that n2 = 4.0 × 10сm/W, which is approximately 3 orders of magnitude larger that the value 2.4×10 cm/W in the NIR spectral range [4]. The present paper is devoted to theoretical analysis and a direct experimental measurement of n2 for crystalline ZnSe in the THz spectral range. In this paper, we also consider the special aspects of self-action of single-cycle waves in media with given nonlinearities. It is shown that self-focusing efficiency in transparent dispersive medium decreases when the number of oscillations in input radiation is decreased for few-cycle paraxial waves with the same maximum electric field and transverse size, i.e., with the same ratio of the radiation power to the critical self-focusing power.