Plastic deformation as nature of femtosecond laser writing in YAG crystal.

Longitudinal inhomogeneity of tracks inscribed in a YAG crystal and the statistics of nonlinear transmittance of the writing beam is studied under conditions of direct femtosecond laser writing in non-thermal mode. Nonlinear transmittance fluctuations inherent in the laser writing were discovered, and their correlation with track inhomogeneity is established. A model of femtosecond laser writing in crystals is built that includes three modes of plastic deformation in the laser impact zone. The modification threshold of the femtosecond direct laser writing is identified with reaching yield stress.

Laser-induced cavities with a controllable shape in nanoporous glass.

The formation of birefringent structures inside nanoporous glass by femtosecond laser pulses was investigated. The laser-modified region is shown to be a cavity whose shape depends on the number of pulses. The shape of the void cross section varied from circle to ellipse when increasing the number of pulses from one to three. A layer of non-porous dense glass was revealed around the cavity. The cross section of this layer is nearly circular, regardless of the cavity shape and number of pulses in the investigated range. The mechanism of elongated cavity formation based on aniostropic light scattering on the spherical cavity is proposed.

Ultrafast laser-induced nanogratings in sodium germanate glasses.

We report ultrafast laser inscription of nanogratings possessing form birefringence in binary sodium germanate glasses in a wide range of Na2O content from 3 to 22 mol.%. A minimal number of laser pulses required to induce noticeable form birefringence is shown to grow exponentially with Na2O content in glass. Atomic force microscopy showed similarity of their periodical structure and period value to those in the nanogratings formed in fused silica. A sharp pulse duration threshold below which laser pulses do not induce nanogratings in the studied glasses has been revealed. Formation of a nanograting in 22Na2O·78GeO2 at the studied conditions is accompanied by crystallization of a surrounding submicron layer and partial crystallization inside the nanograting with precipitation of Na2Ge4O9 crystals.

Direct femtosecond laser-induced formation of CdS quantum dots inside silicate glass.

We report the one-step precipitation of CdS quantum dots in the volume of CdS-doped silicate glass under the focused femtosecond laser beam without additional heat treatment of glass. Femtosecond direct laser writing leads to the annular distribution of the precipitated CdS quantum dots in laser-written domain optical properties of which could be tuned by laser beam parameters. Increasing the laser pulse number to 103 significantly enhances luminescence intensity in the domains, while further increasing up to 106 pulses leads to luminescence quenching. A possible scenario for the formation and distribution of quantum dots is proposed.

3-bit writing of information in nanoporous glass by a single sub-microsecond burst of femtosecond pulses.

We have found that a single sub-microsecond burst of femtosecond laser pulses produces a sub-micrometer cavity possessing the homogeneous birefringence with slow-axis orientation perpendicular to polarization of the laser beam in high-silicate nanoporous glass. Retardance and the root mean square of slow-axis orientation are investigated in dependence on the energy and the number of pulses in the burst. A burst of just three pulses with 98 ns inter-pulse intervals has been shown to induce homogeneous birefringence, and a burst of four pulses has provided birefringence with retardance of 35 nm, which is sufficient for reliable readout of the information recorded with multilevel encoding in slow-axis orientation. A text file has been recorded and read out in an array of birefringent cavities, each carrying 3 bits of information. The sub-microsecond burst of femtosecond pulses paves the way for a multiple increase of the rate of digital information recording with multilevel encoding in glass.

[Liquid crystal thermography in the diagnosis of acute appendicitis, cholecystitis and pancreatitis]. / Termografiia zhidkimi kristallami v diagnostike ostrykh appenditsita, kholetsistita i pankreatita.

The authors have shown the diagnostic value of the coloured liquid crystal thermography on the basis of a comparative investigation of the data of clinical and thermographic studies, operation findings and histological studies in 223 patients with acute appendicitis, cholecystitis, pancreatitis and other diseases of organs of the abdominal cavity. The method is recommended for wide use in clinical practice.