Biophysical aspects of effects of laser radiation on living systems: I. Effect on laboratory animals

It is shown that, taking into account tendencies in the development of new laser technologies, the study of the effect of laser light on humans and animals is a topical and important ecological problem. The results of studies of the effect of coherent (laser) and partially coherent radiations on the organism of white rats are presented. The results obtained for this model can be extrapolated to humans. Biotesting was performed using the methods of high-spatial-resolution Doppler diagnostics and analysis of the contrast of laser speckles. It is found that the time coherence of light does not affect the cerebral blood flow and does not cause reliable changes in the blood microcirculation in the cutaneous covering. It is also reliably shown that neither monochromatic nor quasi-monochromatic laser radiations change the stability of living systems. It is demonstrated that laser sources in new video technologies have no effect on the blood microcirculation in individual organs.     

Hyperfine coherence in the presence of spontaneous photon scattering

The coherence of a hyperfine-state superposition of a trapped 9Be+ ion in the presence of off-resonant light is studied experimentally. It is shown that Rayleigh elastic scattering of photons that does not change state populations also does not affect coherence. We observe coherence times that exceed the average scattering time of 19 photons which is determined from measured Stark shifts. This result implies that, with sufficient control over its parameters, laser light can be used to manipulate hyperfine-state superpositions with very little decoherence.     

Influence of chaotic pump radiation with finite bandwidth on the intensity correlation of resonance fluorescence radiation

It is shown that the bandwidth of chaotic pump radiation can strongly influence the behavior of the intensity correlation of resonance fluorescence in contrast to a laser pump. This different behavior arises from the different higher order coherence properties of chaotic and laser light with the same bandwidth.     

On the origin of laser coherence

It is shown that the light created in the process of the “emission of many photons by many atoms”, as treated recently by Ernst and Stehle, has extreme coherence properties. In particular, it leads to spatial interference effects between radiation from two distinct sources of this type. Under certain conditions this interference even can become optimal in the sense that the intensity minima vanish. Furthermore, in the sense of the definition of Glauber, the light field produced in this process is practically coherent to the ordern～N, whereN is the the number of emitted photons. One arrives at a natural and simple interpretation of two-laser interference experiments of Magyar and Mandel, and Pfleegor and Mandel, if one assumes that the mentioned process constitutes the primary creation mechanism of laser light. It is shown that and how the physically important features of laser activity can be understood on the base of this assumption.     

A geometric analysis of the probe volume in a dual beam laser Doppler velocimeter

The probe volume of the dual beam laser Doppler velocimeter is analyzed from a geometrical standpoint. The volume is graphically reconstructed and the existence of the characteristic dual beam laser Doppler velocimeter fringes is demonstrated. The fringes are analyzed and are shown to be composed of moving tubes or pockets of coherent radiation. The composition of the light is analyzed and the extent of the coherence of the laser radiation within the light pockets is considered. The scattered light from the tubes is analyzed and the coherence enhancement of the fringe structure is shown. This information is used in an attempt to resolve the controversy as to whether the dual beam laser Doppler velocimeter is governed by a fringe counting phenomena or by a beating phenomena of light from two sources of coherent radiation of different frequencies.     

Investigation of amplified spontaneous X-ray laser radiation using the equation for the transverse correlation function of the field

A physical model, based on the solution of the quasi-optics equation for the transverse correlation function (TCF) of the field amplitude, is developed for investigating the brightness, angular divergence, and spatial coherence of the amplified spontaneous emission in a laboratory X-ray laser. The model takes account of the spontaneous source of radiation, diffraction, regular refraction, regular amplification taking account of saturation, nonresonance absorption, scattering by small-scale fluctuations of the electron density and the gain, and scattering by random hose-like deviations of the extended plasma medium of the X-ray laser. It is established that the TCF method makes it possible to obtain the final result much more quickly than the basic Monte Carlo method for the parabolic equation for the field amplitude. As a result of the statistical linearization of the equation for the transverse correlation function in the presence of gain saturation, this method overestimates the absolute values of the average intensity of the amplified spontaneous radiation, but the maximum overestimation does not exceed 10%. It is found that fluctuations of the optical parameters of the medium of the X-ray laser degrade the quality of the amplified spontaneous radiation beam, and they are the analog of the nonresonance absorption from the standpoint of the effect on the brightness of the laser and therefore decrease the observed gain. For the characteristic conditions of an X-ray laser with a quasistationary generation scheme, the contribution of small-scale gain fluctuations and random hose-like deviations of the plasma filament of the laser to the scattering of the amplified spontaneous radiation is much smaller than the contribution of small-scale density fluctuations. Calculations of the amplified spontaneous radiation in an X-ray laser, which is produced by unilateral irradiation of a curved target and possesses an asymmetric plasma electron density profile in the gain zone, are performed. It is shown that in the gain saturation regime the coherence length and the coherent power of the amplified spontaneous radiation can be substantially increased, realizing in the gain zone a convex electron density profile instead of a typical concave profile. It is found that this improvement of the coherence occurs only under conditions such that the characteristic depth of the small-scale density fluctuations does not exceed several percent of the typical regular values of the density in the gain zone.     

Effect of laser radiation on living systems: Role of light coherence

The influence of spatial and temporal coherence, as well as speckle dynamics, on animal organisms is studied in detail. Our theoretical and experimental studies reveal no biophysical evidence of the influence of light coherence on living systems at any level, as well as no specific effects caused by laser radiation. The effects of laser therapy used for treatment of a wide range of diseases of humans require further detailed investigation and possibly a revision of the existing concept.     

Scaling law and polarization of second harmonic emission from laser generated plasma

Measurements are described of the intensity and polarization of the second harmonic emission from a plasma generated by 1.054 μm, 35 ps laser pulses at oblique incidence. It is shown that the measured scaling cannot be explained by a simple power law and that at high intensities the degree of polarization of the second harmonic radiation does not depend on the polarization of the incident laser light.     

Filtering of light fluctuations by multiple second harmonic generation

It is shown that the level of both quantum and classical light fluctuations can be considerably decreased by multiple second harmonic generation in thin nonlinear plates, when filtering out the generated second harmonic radiation behind each plate. As for the application, a second harmonic plate is proposed to be placed in the laser resonator in order to improve statistical and coherence properties of the lasing mode.     

Ponderomotive action of light in the problem of multiple scattering of light in a randomly inhomogeneous medium

The time correlation function of light reflected diffusely from a semi-infinite randomly inhomogeneous medium is calculated with allowance for the acceleration of the scatterers in the field of the laser beam incident on the medium. An analytical expression is found for the characteristic coherence time due to the ponderomotive action of light. It is shown that even with laser radiation power densities of the order of 1–10 W laser-acceleration effects substantially alter the character of the time autocorrelation function of the scattered light and must be taken into account in theoretical calculations. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 9, 611–615 (10 May 1998)     

半导体光放大光纤环形激光器的偏振混沌与相干性

研究了基于半导体光放大器(SOA)的光纤环形激光器的偏振混沌光的特性及其相干性。实验采集激光器的输出功率和偏振度,得到了基于半导体光放大器的光纤环形激光器的输出从自发辐射到受激辐射、再到偏振态混沌激光辐射的演化过程。利用马赫-曾德尔(M-Z)干涉仪验证了混沌激光的相干性,并发现混沌干涉只有零级。测量不同光程差时干涉仪的输出功率,计算相应的干涉条纹可见度,进一步算得混沌激光的相干时间约为40 ps。这一结果与根据光谱计算的该混沌激光的相干时间43 ps基本一致。实验还测得该混沌激光的相干性与半导体光放大器的电流无关。并指出了混沌激光相干应用于低相干光源探测领域的灵敏度和分辨力优势。     

A unified treatment of real-time ULM correlators

Many studies on an optical ULM correlator have been carried out by various workers. Different types of correlation are usually produced, depending not only on the combinations of signals to be processed but also on the optical and electrical filters used in the detecting stage. This paper investigates the effects of these conditions on the performance of the optical ULM correlator in some detail on the basis of a unified analysis. It is also shown, by considering in the course of this analysis the propagation of a spatial coherence function, that the coherence property of light used for the illumination does not affect the correlation-output signal. Some experiments are performed concerned with the effect of spatial coherence, binary or intensity correlation and the linear response for correlation in the ULM correlator.     

Lasers for ICF with a Controllable Function of Mutual Coherence of Radiation

The current status of laser thermonuclear fusion research in the leading world scientific centers is characterized by the development of superhigh-power multi-channel laser facilities of megajoule pulse-energy level. The development of such laser installations operating in the pulse-repetition mode with a large number of laser beams, which are necessary for high-symmetry irradiation of a spherical thermonuclear target, is an extremely difficult physical and engineering problem. The concept of a special laser with a controllable function of mutual coherence of radiation is proposed. The studies performed demonstrate that a laser based on such a principle has a number of advantages as compared to the conventional schemes of lasers. In particular, the optical scheme of the laser is significantly simplified, and the cost of the output-energy unit is reduced by several times. The influence of radiation coherence on the homogeneity of the thermonuclear target irradiation is analyzed. The feasibility of suppressing the small-scale self-focusing without application of spatial filtration is shown. A module of the laser facility has been triggered to check the validity of the principles proposed for constructing a laser driver for power stations, and the first experimental results are reported. The possibility of controlling the coherence of laser beams used in ICF experiments without violation of the laser--target system matching is demonstrated, as well as controlling the distribution of the laser radiation intensity in the lens focus.     

Visibility interference fringes optimization on a single beam in the case of partially polarized and partially coherent light

We analyze the optimal visibility one can obtain in interference experiments with partially polarized light when one acts on only one of the two interfering beams. This is a practical situation that can appear when one does not want to modify or attenuate one of the beams, such as in homodyne detection. It is shown that the optimal configuration usually does not correspond to light with the same degrees of polarization for the two interfering beams. We also demonstrate that a simple interpretation can be obtained with the recently introduced normalized mutual coherence matrix.     

Effect of coherence of generating radiations on optical parametric up conversion

The effect of the coherence properties of pumping and input radiations on parametric up conversion (PUC) is treated in this paper. It is shown here that the PUC depends essentially upon the coherence properties of the pumping radiation whilst it is hardly affected by the coherence properties of the input radiation. It has been found that for chaotic (Gaussian) pumping radiation with an extremely high degree of coherence the total conversion efficiency is one half of that for coherent (Poisson) pumping radiation, whilst for chaotic pumping radiation with a very low degree of coherence the PUC is much more effective. The influence of the coherence properties of pumping radiation upon the PUC is explained by the intermodal correlation effects in the nonlinear interaction.     

Effect of polarization and coherence of low-intensity optical radiation on fish embryos

  We have shown that brief exposure of sturgeon embryos (fertilized roe) in the organogenesis stage to low-intensity radiation in the visible region of the spectrum can have a long-term effect on embryonic and post-embryonic development of the fish, detectable 50 days after the irradiation procedure. The biological effects (size-weight characteristics and hardiness parameters of the fish relative to unfavorable habitat conditions) induced by linearly polarized emission from a monochromatic laser source (helium-neon laser, λ = 632.8 nm, Δλ ≈ 0.02 nm) and a quasi-monochromatic light-emitting diode (LED) source (maximum in emission spectrum λ = 631 nm, Δ λ = 15 nm) are practically the same. Going to broadband linearly polarized radiation (λ = 420–800 nm) is accompanied by a decrease in the biological effect. From the results of studies of the effect on embryos from linearly polarized and unpolarized radiation from an LED source and also the effect of linearly polarized, circularly polarized, and unpolarized radiation from a helium-neon laser, we concluded that the type of polarization is of critical importance in realization of the biological effect of radiation. In this case, the maximum stimulating effect (on the size×weight characteristics and the hardiness parameters for juvenile fish) is observed on exposure to linearly polarized radiation; the photobiological effect induced in the same dose range by light with natural polarization (i.e., unpolarized) is significantly less pronounced; the stimulating effect of circularly polarized radiation occupies an intermediate position. Based on the presented data and also on data obtained previously, we conclude that among the resonant and nonresonant photophysical processes (orientational effect of light, effect of gradient forces, dipole-dipole interactions, thermooptic processes) capable of inducing photobiological effects dependent on such laser-specific characteristics as polarization and coherence, the determining influence in the processes studied in this work comes from the orientational effect of light and dipole×dipole interactions. And the orientational effect can appear for anisotropic media with liquid-crystal type ordering (especially domains in membranes and multiple-enzyme complexes) both under conditions when there is no resonant absorption and for weakly absorbing structures, and can initiate a change in their conformations and accordingly their functional characteristics. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 843–858, November–December, 2008.     

Role of phase fluctuation and dephasing in the enhancing continuous variable entanglement of a two-photon coherent beat laser

A steady state analysis of the nonclassical features and statistical properties of the cavity radiation of a two-photon coherent beat laser is presented. Results show that the degree of two-mode squeezing, detectable entanglement and intensity of the cavity radiation can increase with the deviation of the phase fluctuations of the laser employed in preparing the atoms, but decrease with the increasing rate at which the induced coherence superposition decays. Although it is found that varying the phase fluctuations and dephasing can lead to modification in the quantum features and statistical properties of the radiation, it does not alter the similarity in the nature of the degree of entanglement detectable by the criteria following from Duan-Giedke-Cirac-Zoller and logarithmic negativity in a perceivable manner. Since the intensity and quantum features can be readily enhanced, this system is expected to be a viable source of a strong robust entangled (squeezed) light under various conditions. Moreover, comparison of the mean number of photon pairs with intensity difference shows that the chance of inciting a two-photon process can be enhanced by changing the rate of dephasing and phase fluctuations.     

Nonclassical effects in a two-photon laser

The steady state quantum statistical properties of light in a two-mode two-photon laser are presented. It is shown that the second-order coherence functions violate a classical inequality.     

Features of the motion of particles suspended in liquid under an applied field

It is experimentally shown that a tenfold-hundredfold increase in the effective diffusion coefficient along the direction perpendicular to an applied electric field takes place in various emulsions and suspensions. It is caused by electrophoretic motion of particles. In inverse emulsions and many suspensions, only a certain fraction of dispersed material is contained in particles whose average radius is determined by the dynamic light scattering method. It is shown that the average coherence time of light scattered by silicon particle suspensions at a constant laser power depends on the beamdiameter. This means that semiconductor particles are characterized by strong nonlinearity.     

Quantum statistical properties of one-atom lasers

Properties of a laser formed by a high-Q cavity and a single incoherently excited atom are studied on the basis of analytical solutions obtained for the quasi-probability P-function. Expressions for the boundaries separating various operating regimes of a one-atom laser (below threshold, above threshold, and self-quenching) are found. It is shown that lasing without inversion and lasing with the decay rate of the excited state exceeding the pump intensity are possible in the system. The degree of coherence of laser radiation is studied.