A. V. Balakin

Enhancement of second-harmonic generation with femtosecond laser pulses near the photonic band edge for different polarizations of incident light

We present experimental evidence of enhancement of second-harmonic generation as a result of an increase of the fundamental-field energy density within a multilayer structure near the photonic band edge.

Experimental observation of the interference of three- and five-wave mixing processes into the signal of second harmonic generation in bacteriorhodopsin solution

Abstract The second harmonic (SH) generation with a Ti:sapphire femtosecond laser system in a randomly oriented suspension of finely fragmented purple membranes of Halobacterium halobium has been studied experimentally. The existence of two interfering contributions to the SH signal due to second- and fourth-order nonlinear processes has been established. The phase and the value of the fourth-order electronic susceptibility (hyperpolarizability) relative to the second-order ones have been determined. The analysis of the experimental data shows the existence of a coherent contribution into the SH signal.

Experimental observation of the interference of three-and five-wave mixing processes in optical second harmonic generation in a solution of bacteriorhodopsin

The generation of a femptosecond second harmonic in a bacterior-hodopsin solution is investigated. It is shown that the behavior of the harmonic can be explained by the coherent interference of several contributions from three-and five-wave mixing processes (χ(2) and χ(4)). The magnitude and phase of the fourth-order electronic susceptibility χ(4) of the medium with respect to χ(2) are determined.

Polarization characteristics of the “forbidden” second optical harmonic of femtosecond laser pulses in a bacteriorhodopsin solution

The generation of the second harmonic of femtosecond laser pulses in a bacteriorhodopsin solution has been experimentally studied for various wavelengths and polarization states of radiation at the fundamental frequency. The polarization properties of the effect are analyzed under various experimental conditions. The nature and properties of the signal are treated as the manifestation of a superposition of nonlinear optical effects of various orders (the second and the fourth). The second-order effects can have both an electric-dipole and a magnetic-dipole or electric-quadrupole character. In analyzing fourth-order processes, besides the direct electric-dipole contribution, the possibility of the participation of cascade processes at second-and third-order nonlinearities is also allowed.

Femtosecond optical pulse compression in a one-dimensional thin photonic crystal

The effect of femtosecond laser pulse compression is discovered, described, and experimentally studied for a one-dimensional 4.8-μm-thick photonic crystal.

Amplification of the generation of the sum-frequency signal in multilayer periodic structures at the edges of the Bragg band gap

A new property of a one-dimensional periodic structure — amplification of the sum-frequency signal arising under the simultaneous action of two laser pulses on this structure with radiation frequencies corresponding to the edges of the fixed Bragg band gap — is experimentally observed and described.

Terahertz emission during interaction of ultrashort laser pulses with gas cluster beam

We present the results of experimental study of terahertz (THz) generation in gas cluster beam excited by intense femtosecond laser pulses. Cluster beam was produced by partial condensation of pure Ar and mixtures CF2Cl2+He, Ar+He during their expansion through a conical nozzle into vacuum. There were used two excitation schemes in our experiments: single color and two color (fundamental frequency mixed with its second harmonic). We have studied how THz signal scales with various control parameters such as laser pulse duration, gas backing pressure and laser pulse energy. Simultaneously we measured intensity of X-Ray emission which originates from laser-cluster interaction. We found that in a single color scheme energy of THz pulses from Ar cluster beam strongly decreases in the region of minimum laser pulse duration while X-Ray power is maximal under these conditions. Both in single- and two color excitation regimes THz signal demonstrated growth without saturation with increasing of optical pulse energy up to its peak value of 25 mJ.

Spectral dependence of the excitation of the “forbidden” second optical harmonic in an aqueous suspension of purple membranes by femtosecond laser pulses under electronic resonance conditions

The spectral dependence of the efficiency of generation of the forbidden (in the electric-dipole approximation) second harmonic (FSH) and its energy on the energy of the excitation pulses is investigated experimentally in a highly disperse suspension of purple membranes containing bacteriorhodopsin (BR) under excitation by femtosecond laser pulses into the single-photon absorption band of BR. The experimental data for the case of resonance excitation attest to an interference character of the interaction of optical nonlinearities of different orders in the process leading to the formation of the FSH signal.

Terahertz reflectometry for the corneal tissue hydration sensing

The cornea is one of the most important external structure of the human eye. Its transparency is an important factor for visual function and depends on the tissue hydration. For cornea hydration sensing we use terahertz reflectometer based on difference frequency generation of a pair of continuous semiconductor lasers. Spectral sensitive measurements are obtained by fine frequency tuning of terahertz source.

Application of Amplified Femtosecond Ytterbium Fiber Laser for the THz Time-Domain Spectroscopy

We report the application of a newly developed femtosecond fiber laser for the THz time-domain spectroscopy. Ytterbium doped fiber was used for generation of laser pulses at wavelength 1.06 mum with the further amplification. The use of novel SESAM (semiconductor saturable absorber mirror) device made it possible to get pulse duration less than 200 fs on the 3 average power up to 1 W at the 50 MHz pulse repetition rate. We analyze the nonlinear and semiconductor devices optimal for the generation and electro optical detection of THz pulses in the time-domain systems based on the femtosecond ytterbium fiber laser.