Vladimir S. Syrtsov

Nonlinear rotation of the polarization of the intense femtosecond laser radiation in BaF2

The dependence of the polarization plane rotation angle in the BaF2 crystal on the intensity of the femtosecond laser radiation with 0.62 μm wavelength in the ω = ω + ω − ω process on cubical nonlinearity χ(3) is investigated. An anomalous increase in the efficiency of the cross-polarized radiation generation at I > 2 × 1012 W cm2 is observed for the first time. The 10% efficiency of the orthogonal component generation at the ∼3 × 1012 W cm2 intensity is obtained.

Nonmonotonic Behavior of the Absorption of the Tightly Focused Femtosecond Radiation of a Cr:Forsterite Laser in a Dielectric Due to an Increase in the Number of Photons Involved in the Process

In the tight focusing mode of the femtosecond radiation of a Cr:forsterite laser system in the transparent-dielectric bulk, the nonmonotonic behavior of absorption has been revealed as the laser pulse energy increases. The effect is caused by a change in the number of photons involved in ionization due to an increase in the effective ionization potential.

Non-Linear Polarization Rotation of Intense Femtosecond Radiation in BaF 2 Crystal: Influence of Fifth Order Non-Linearity

Non-linear polarization rotation of femtosecond laser radiation with intensity of the order of 1013 W/cm2 in BaF2 crystal under plasma formation conditions was investigated. Abnormal behavior of cross-polarized wave generation efficiency on laser pulse energy may be explained by influence on the process of polarization anisotropy of fifth order non-linearity.

Plasma channel formation and micromodification of KDP crystal by tightly focused Cr:forsterite femtosecond laser radiation

Experiments on single pulse plasma channel formation in non-linear KDP crystal by tightly focused (NA = 0.47) fundamental and doubled Cr:forsterite laser radiation with energy of 0.1 ÷ 10 μJ and 100 fs pulse duration were carried out. We propose the simple model of non-linear absorption of femtosecond laser radiation in plasma channel. This model allows estimate laser intensity in the channel and plasma parameters.

Plasma channels characteristics dependence on tightly focused femtosecond laser radiation parameters

Tight focusing of femtosecond laser radiation with microjoule pulse energy in non-linear crystal volume (intensity of the order of 10 W/cm2) causes self-focusing, multiphoton ionization of the matter, plasma channel formation, electrons heating, and subsequent micromodification of the structure. The processes threshold, behavior and efficiency strongly depend on such laser pulse parameters as pulse duration, energy and radiation wavelength

Low-operation-voltage electro-optical modulator based on Fe:KNbO3 crystal

Results of low- and high-frequency modulation of laser beam, propagating both in the direction of optical axis and along three crystallographic axes in Fe-doped KNb03 crystal, are presented. It was found, that the high-frequency electro-optical constants of Fe:KNb03 are: r33 = (5353) pm/V, r13 = (21±3) pm/V, and r51 = (88±11) p d V . The difference between high- and low-frequency values is about 20% and this is in good accordance with known data for nominally pure crystal. We found also, that there was no twinning effect in this crystal under the electrical fields up to 2.5 kV/cm. The half-wave voltage was only 800 V at the wavelength of 633 nm in a longitudinal configuration of modulator. We measure also that bandpass of light modulation in Fe:KNb03 is equal to at least 6 MHz. In our experiments we also determined the speed of acoustic waves, created in the crystal by inverse piezoelectric effect, when fast HV electrical pulse is applied to it, these values are vl=(56001100) d s and v2=(6400±100) m/s along Oz and Ox axes correspondingly.

Photorefraction in a KDP crystal induced by femtosecond laser radiation

Femtosecond laser radiation self-channeling and second harmonic generation under plasma formation conditions were investigated. Laser pulses with sub- and microjoule energy were tightly focused into the volume of a KDP crystal, Estimated laser pulse intensity was of the order 1013 W/cm2 in the focal spot exceeding damage and plasma ignition thresholds in the crystal. Threshold of plasma channel formation measured in the experiment corresponds to critical power of self-focusing 1.5f0.1 MW for KDP crystal. Plasma channels with length up to 150 μm were observed in the volume of the KDP crystal. We developed an algorithm allowing estimating electron density and temperature in the plasma channel using experimental dependence of laser energy transmittance through the crystal on incident laser energy. For laser pulse energy 1 μJ estimated electronic density in the plasma channel is of the order of l020 cm-3 (that is about one tenth of the critical plasma density value) and mean electronic temperature is about 3 eV. Free plasma electrons leaded to refraction index increasing by 5 %, extinction coefficient was -25 cm-1. The maximum measured efficiency of second harmonic generation was 1.2 %.