Elementary processes in cells after light absorption do not depend on the degree of polarization: implications for the mechanisms of laser phototherapy.

Objective: The objective of this work was to evaluate the importance of the degree of light polarization in stimulation of cellular metabolism.

Background Data: Although the possible role of polarization's effects on the mechanisms of laser phototherapy is sometimes discussed in the literature, there are still no clear answers.

Material And Methods: A model system (HeLa cell suspension) was used in which the lengths of light scattering (l sc) and absorption (l a) were much larger than the thickness of the irradiated layer (L = 3 mm).

Scanning near-field optical microscope based on a double resonant fibre probe montage and equipped with time-gated photon detection.

We discuss scanning near-field optical microscope based on original double resonant montage of a fibre probe onto the tuning fork and proprietary electronics capable of fast and precise measurements of the resonant frequency and the quality factor of sensor dithering. Special emphasis is given on the pulsed excitation/gated detection of optical signal. This option as well as the possibility of fast scanning facilitates a lot the problem of single fluorescence centres detection.

Shear force distance control in a scanning near-field optical microscope: in resonance excitation of the fiber probe versus out of resonance excitation.

The experimental results of the direct measurement of the absolute value of interaction force between the fiber probe of a scanning near-field optical microscope (SNOM) operated in shear force mode and a sample, which were performed using combined SNOM-atomic force microscope setup, are discussed for the out-of-resonance fiber probe excitation mode. We demonstrate that the value of the tapping component of the total force for this mode at typical dither amplitudes is of the order of 10 nN and thus is quite comparable with the value of this force for in resonance fiber probe excitation mode. It is also shown that for all modes this force component is essentially smaller than the usually neglected static attraction force, which is of the order of 200 nN.

Radiative cycle with stimulated emission from atoms and ions in an astrophysical plasma.

We propose that a radiative cycle operates in atoms and ions located in a rarefied gas in the vicinity of a hot star. Besides spontaneous transitions the cycle includes a stimulated transition in one very weak intermediate channel. This radiative "bottleneck" creates a population inversion, which for an appropriate column density results in amplification and stimulated radiation in the weak transition.

Analysis of fiber probes of scanning near-field optical microscope by field emission microscopy.

It is shown that field emission microscopy and related methods can be used to analyze the metal coated fiber tips, which nowadays are the most frequently used sensor for the scanning near-field optical microscopy (SNOM). Metal free and thus non field-emitting aperture for the light transmission on the tip apex can be directly seen and its parameters can be measured, which is very important for the interpretation of SNOM data.

Resonance-enhanced two-photon ionization of ions by Lyman alpha radiation in gaseous nebulae.

One of the mysteries of nebulae in the vicinity of bright stars is the appearance of bright emission spectral lines of ions, which imply fairly high excitation temperatures. We suggest that an ion formation mechanism, based on resonance-enhanced two-photon ionization (RETPI) by intense H Lyman alpha radiation (wavelength of 1215 angstroms) trapped inside optically thick nebulae, can produce these spectral lines. The rate of such an ionization process is high enough for rarefied gaseous media where the recombination rate of the ions formed can be 10(-6) to 10(-8) per second for an electron density of 10(3) to 10(5) per cubic centimeter in the nebula.

Shear force distance control in near-field optical microscopy: experimental evidence of the frictional probe-sample interaction.

The properties of the probe-surface contact for a near-field optical microscope driven in the shear force mode have been studied applying lateral amplitudes of the probing fiber tip larger than 15 nm. Electric current measurements between a conductive tip and a conductive sample reveal a pulsed current behavior at the very beginning of the approach curve. In the upper part of the approach curve it turns to the quasiconstant current.

Time-resolved optoacoustic measurement of absorption of light by inhomogeneous media.

A method for measuring the absorption of light with optically turbid media is considered. The method is based on the registration of the temporal shape (leading-edge slope) of the developing optoacoustic signal in a medium that is absorbing a short laser pulse. Results of experiments with a Nd:YAG laser (10 ns) demonstrate the effectiveness of the method for both homogeneous and inhomogeneous optical media.

Two different mechanisms of low-intensity laser photobiological effects on Escherichia coli.

Bacterial suspensions in a phosphate buffer were irradiated at wavelengths lambda of 632.8, 1066 and 1286 nm, incubated in Hottinguer broth for 60 min and assayed for viability by the standard surface-plating technique. The difference between the number of viable cells in the irradiated culture and the control was termed growth stimulation.

Studies of acoustical and shock waves in the pulsed laser ablation of biotissue.

Quantitative studies are conducted into the absolute pressure values of the acoustical and shock waves generated and propagating in a biotissue under pulsed (tau p = 50 ns) UV (lambda = 308 nm) laser irradiation (below and above the ablation threshold). Powerful (several hundreds of bars in pressure) high-frequency (f approximately 10(7) Hz) acoustic compression and rarefaction pulses are found to be generated in the biotissue. The amplitudes and profiles of the acoustic pulses developing in atherosclerotic human aorta tissues and an aqueous CuCl2 solution under laser irradiation are investigated as a function of the laser pulse energy fluence.

He-Ne laser irradiation of single identified neurons.

Silent (LPa2 and LPa3) and spontaneously active (V3, V5, V17) neurons of subesophageal ganglia of Helix pomatia were irradiated via a 125-mm fiber probe with a 10-mW He-Ne laser (lambda = 632.8 nm), and the rate of membrane depolarization, duration of latent period, and probability of spike activity were measured as the functions of light intensity. It was found that silent neurons can not be activated by He-Ne laser irradiation.

Comparison of the effects of visible femtosecond laser pulses and continuous wave laser radiation of low average intensity on the clonogenicity of Escherichia coli.

To evaluate the contribution of local pulsed heating of light-absorbing microregions to biochemical activity, irradiation of Escherichia coli was carried out using femtosecond laser pulses (lambda = 620 nm, tau p = 3 x 10(-13) S, fp = 0.5 Hz, Ep = 1.1 x 10(-3) J cm-2, Iav = 5.

Laser detection of the rare isotope (3)He at concentrations as low as 10(-9).

The method of collinear laser photoionization of atoms in a modulated fast beam is used to detect the rare isotope (3)He, with high-repetition-rate lasers being applied to improve the detection sensitivity. The method has made it possible to detect (3)He at relative abundances as low as 10(-9).

Laser ablation of atherosclerotic blood vessel tissue under various irradiation conditions.

A quantitative analysis is presented of the destruction of normal wall and atherosclerotic plaque areas of blood vessels by laser radiation. Threshold laser radiant exposure values were measured experimentally in vitro, along with the ablation efficiency for various laser wavelengths and irradiation conditions. Correlations were found between the ablation efficiency and fluence thresholds on the one hand and the optical properties of the blood vessel tissues on the other.

Channeling of atoms in a standing spherical light wave.

One-dimensional localization of sodium atoms in a standing spherical light wave has been observed. The atoms have an oscillatory motion with an amplitude of approximately lambda/10 along the nodes (or loops) of the wave.

Laser biology and medicine.

The substantial repertoire of laser radiation--its coherence, range of intensity and frequency, controlability of focal area and of beam length--has been comprehensively explored in the contexts of micro- and macro-diagnostics of cells, biochemical kinetics, therapy and surgery.

[Is the coherence of low-intensity laser light essential for its effect on biological objects?].

Low-intensity laser light coherence is considered in relation to biological objects under normal physiological conditions. Estimations show that the excitation rate (the rate of coherent states generation) of typical biomolecules in visible range (sigma abs = 10(-17) cm2, I = 10(-3) W/cm2) is 10(12)-10(13) times lower than that of their phase relaxation. It means that the role of coherent interaction processes is negligible.

[Effect of pulse laser UV-radiation on proliferating and resting HeLa tumor cells].

Low-intensity pulse-periodic UV-radiation (lambda = 271.2 nm) within a definite repetition frequency interval (about 10 kHz and 22 kHz) and doses ranging from 0.1 to 10 J/m2 has a selective action on resting HeLa cells.