Excitation Of Active Medium Research Articles

Finite-element analysis of lasing modes within photonic random media

We investigated several types of random lasing modes against frequency and the excitation of active medium. Random lasing occurring from multiple light scatterings and the interference effect of the scattered light has various complex lasing states in disordered structures, in which light waves are localized in various forms. Modes of random lasing are generally classified into localized, extended and transition modes based on their localization types. Numerical methods are used for analysing such complex phenomena. In this paper, a finite-element method is used to investigate the relationship among lasing modes, frequency and population inversion density of active medium for random lasing. Light amplification defined as the ratio of radiative powers between excited and non-excited states of the active medium is computed by changing both the frequency and the population inversion density of the active medium, which is modelled by the negative imaginary part of relative permittivity. The distributions of random lasing modes is strongly influenced by the lasing frequency. We also found that the localized modes that are strongly confined lasing modes in disordered structures do not appear in the frequency ranges in which mean free paths are approximately equal to the half-wavelength.

Frequency shifting of sub-100 fs laser pulses by stimulated Raman scattering in a capillary filled with pressurized gas

The technique of Raman conversion of sub-100 fs laser pulses based on excitation of active medium by two orthogonally polarized pulses has been developed for Raman lasers with a glass capillary. 52 fs Stokes pulse at the wavelength of 1200 nm has been generated by stimulated Raman scattering of 48 fs Ti:sapphire laser pulse at the wavelength of 800 nm in hydrogen. 13% energy conversion efficiency has been achieved at pulse repetition rate up to 2 kHz.

Study of an electric-discharge molecular fluorine VUV laser

The effect of the discharge voltage, composition and pressure of the He—F2 gas mixture on the output radiation parameters of a VUV F2 laser is studied. It is shown that reaction of dissociative attachment of electrons to fluorine molecules plays a significant role in the process of active medium excitation. The condition for choosing the optimal mixture composition is determined. The use of a pump generator with multistage magnetic compression of high-voltage pulses and preionisation system with a barrier discharge at the surface of a ceramic tube ensures a high homogeneity of the gas discharge (without cathode spots). A small-size 2.5-mJ F2 laser (with an active volume of ∼9 cm3) with a pulse repetition rate of up to 1 kHz operating on a He—F2 mixture at a pressure of up to 3500 mbar is developed.

Development of excitation system for a large-area high-pressure CO2-amplifier

Abstract The paper discusses the problem of developing superatmospheric pressure CO2-amplifiers intended to amplify picosecond light pulses. The advantages of the systems for active medium excitation by a soft X-ray preionized self-sustained discharge are demonstrated. The characteristics of the CO2-amplifier with a 5 cm interelectrode gap and a gaseous medium pressure up to 5 atm are presented.

Mode theory of an axially symmetric laser with a gradient profile of active medium

Results are presented of a rigorous mode theory for a laser with gradient profile of active medium excitation density. The method used to solve the eigenvalue problem is based on Maxwell's wave equation and on impedance boundary conditions of the resonance type at the open resonator ends. The case considered refers to a a laser resonator equipped with plane parallel circular mirrors of finite size. The rigorous solution of the eigenvalue problem is obtained for a bounded parabolic profile of the active medium. The transcendental eigenvalue equation is investigated and distributions of the active resonator eigenfunctions are found. The asymptotic behaviour of the rigorous solutions is investigated. A multilayers approximation method is used to solve the eigenvalue problem when the active medium has an arbitrary excitation density profile.

A104 エキシマレーザの放電部衝撃波の可視化

Experimental study on shock waves in a high repitation rate excimer laser has been carried out. In a high repitation rate excimer laser. shock waves in subsonic loop are induced by the active medium excitation by means of pulse discharge. Shock waves in He gas by a pulse discharge are visualized by schlieren method using a scale discharge section model, CCD camera, stroboscope, and digital image memory which used to take photographer. Shock waves from anode surface, cathode surface. discharge region, and pin sparks for preionization are observed. Shock waves reflect at anode and cathode surfaces alternately for several times. Shock waves from dischrage region travel through channel.