Determination of fraction of molecules excited by laser IR radiation

To explain the observed excitation by laser IR radiation of moderate intensity (I = 1?10 MW/cm²) of the many rotational states (much greater than $\text{Ed}{}_{\mathrm{<mtext>01</mtext>}}\text{2}\text{hcB}$) it is suggested that mixing of the ground state components of the common symmetry type (“N-mixing”) take place. Estimation of the fraction of molecules excited by multiphoton processes is in satisfactory agreement with an experiment.     

Polarization characteristics of stimulated emission of organic molecules when excited by intense XeCl laser radiation

We study the influence of the molecular structure, medium, and exciting-radiation parameters on the polarization, energy, and spectral characteristics of the emission of laser-active media based on the dicarboxylic derivative of p-terphenyl, rhodamine 101, and phenalemine 512. We found that the polarization of the stimulated emission of molecules when strongly excited under the conditions studied significantly depends on their structure, the pumping mode, the intensity and polarization of the exciting radiation, the shape and dimensions of the excited volume, and the phase state of the medium.     

Raman spectroscopy of infrared multiple-photon excited molecules

The method of spectroscopy of spontaneous Raman scattering (RS) with time resolution has been applied for the first time to diagnose the process of multiphoton ir molecular excitation (MPE). Some aspects of RS diagnostics of MPE processes are being analyzed. It has been shown experimentally on SF₆ and CF₃I molecules that it is possible to study such important characteristics of excitation process as the fraction of molecules involved in the process of excitation, vibrational energy distribution of molecules, stochastization of inner molecular energy.     

Dynamics of photoprocesses induced by femtosecond infrared radiation in free molecules and clusters of iron pentacarbonyl

The dynamics of photoprocesses induced by femtosecond infrared radiation in free Fe(CO)₅ molecules and their clusters owing to the resonant excitation of vibrations of CO bonds in the 5-μm range has been studied. The technique of infrared excitation and photoionization probing (λ = 400 nm) by femtosecond pulses has been used in combination with time-of-flight mass spectrometry. It has been found that an infrared pulse selectively excites vibrations of CO bonds in free molecules, which results in a decrease in the yield of the Fe(CO)₅⁺ molecular ion. Subsequent relaxation processes have been analyzed and the results have been interpreted. The time of the energy transfer from excited vibrations to other vibrations of the molecule owing to intramolecular relaxation has been measured. The dynamics of dissociation of [Fe(CO)₅]_n clusters irradiated by femtosecond infrared radiation has been studied. The time dependence of the yield of free molecules has been measured under different infrared laser excitation conditions. We have proposed a model that well describes the results of the experiment and makes it possible, in particular, to calculate the profile of variation of the temperature of clusters within the “evaporation ensemble” concept. The intramolecular and intracluster vibrational relaxation rates in [Fe(CO)₅]_n clusters have been estimated.     

Dissociation of vibrationally excited heteronuclear molecules by an intense infrared field

Results of numerical simulations of the vibrational-rotational dynamics of a molecular system in the field of an intense infrared laser pulse are presented. The cases of quasi-monochromatic and ultrashort laser action on the nuclear subsystem are considered. The influence of the coherent repopulation of vibrationally excited molecular states on photodissociation and the peculiarities of photodissociation under the action of an ultrashort laser pulse are discussed. The results obtained for quasi-monochromatic laser action are interpreted in terms of interference stabilization.     

On the influence of dopant ions on blue emission in kgw crystal excited by infrared laser radiation

The role of doping by Nd³⁺ and Tm³⁺ ions in the generation of blue emission in a KGW crystal excited by infrared radiation has been analyzed. Experimental measurements of the emission characteristics and theoretical results of modeling emission spectra of the doping ions are compared. A qualitative difference is shown between the calculated Tm³⁺ luminescence spectrum and that observed in the experiment. Data on branching ratios of luminescence from the ²P_1/2 level of the Nd³⁺ ions suggest a low emission efficiency from this multiplet in the blue spectral region.     

Saturation in the absorption of infrared radiation by gas molecules

A semiclassical method is employed to calculate the absorption coefficient and the spectral-intensity distribution for the absorption of high-intensity radiation in an isotropic gaseous medium in the case of a nonmonochromatic field.The author is indebted to V. E. Zuev for his interest in the investigation and to V. S. Smirnov for valuable comments.     

Emission spectrum of concentrated dye solutions excited by high-power laser radiation

Emission spectra of concentrated (~10¹⁸–10¹⁹ cm^–3) ethanol solutions of Rhodamine C excited by high-power (~10²⁵–10²⁶ cm^–2s^–1) laser radiation were measured. The emission spectrum consists of two narrow bands (with half-widths of ~200–300 cm^–1). The long-wavelength band was interpreted as cooperative spontaneous emission, and the short-wavelength band was assigned to the amplified spontaneous emission. The ratio of their intensities depends on the dye concentration and the pump power density. The ratio of band intensities is assumed to be determined by the dephasing rate of excited molecules responsible for cooperative spontaneous emission.     

序列脉冲激光中的原子共振辐射

本文详细研究了序列脉冲激光与二能级原子共振作用的Bloch方程的解。在此基础上,结合数值计算,求出了序列脉冲作用下二能级原子的共振辐射谱;并得出如下结论:对满足K_1/K=1的原子(如仅受自然展宽的气体原子),序列脉冲差不多等效于一单色激光场;而对满足K_1/K(?)=1的原子(比如一些固体原子)序列脉冲场中边频成份也表现出较强的作用,辐射谱呈现出多边峰现象。     

Pressure-sensitive blackbody point radiation induced by infrared diode laser irradiation

Ultrabroadband radiation from Yb(2)O(3) at ambient and low air pressures was investigated under the excitation of a 980 nm diode laser. The radiation was confirmed to be blackbody radiation, and it is sensitive to environmental air pressure in the way that the integrated radiation intensity decreases linearly with increasing air pressure. An ideal gas model may be employed to interpret the linear dependence. The pressure-sensitive radiation characteristic provides a potential method for noncontact measurement of air pressure with high accuracy.     

The effects of infrared radiation on trapped electrons in excited ZnS-phosphors

By means of rise curves the number of traped electrons in ZnS-phosphors can be determined. The effect of infrared irradiation added simultaneously to UV excitation is that of quenching; in addition the number of occupied traps (n _t) is found to be considerably reduced; approximately in the same ratio as the reduction of light. Since the free electron concentration (n) is also quenched by the addition of infrared to ultraviolet, there is some difficulty with the relationship: Light=constant ×n×n _t.     

Čerenkov radiation excited by an ultrashort laser pulse with oblique amplitude front

We develop the theory of generation of terahertz ?erenkov radiation in a homogeneous nonlinear optical crystal if the amplitude and phase fronts of the excitation pulse do not coincide. It is shown that in the case of the nonlinear optical interaction, the use of laser pulses with oblique amplitude front makes it possible to increase the efficiency of generation of terahertz radiation. In contrast to the case where the amplitude and wave fronts coincide, radiation propagates in a strictly determined direction specified by the amplitude-front plane. It is established that the maximum generation efficiency is reached if the angle of inclination of the amplitude front coincides with that of the terahertz-radiation wave vector.     

Isotopically selective dissociation of CCl4 molecules by NH3 laser radiation

The voltage-current characteristics of a UV preionised CO₂ laser operating at pressures ?13 atmospheres have been investigated and the quasi-steady glow and breakdown fields measured. The discharge resistivity has been found to be a function of the applied excitation field and a simple model has been developed to explain the results obtained.