Dynamics of excimer laser ablation of polyimide determined by time-resolved reflectivity

The time-dependent intensity profile of pulsed KrF excimer laser radiation reflected from polyimide is determined over a range of laser fluences, from well below to above the ablation threshold. The reflected laser beam is truncated once the incident laser radiation exceeds a threshold fluence, i.e., truncation depends on the energy per unit area and not on the intensity, analogous to results for the ablation threshold and the etch depth per pulse. The threshold fluence for pulse truncation corresponds to the onset of ablation. The results indicate that the truncation is not due to laser plasma interactions at these fluences. A general mechanism is discussed involving a time dependent index of refraction.     

Polarisation of the IR luminescence of cubic ZnS single crystals

The polarization of the IR luminescence of oriented ZnS crystals has been measured. None of the three main emission bands shows measurable polarization after excitation with polarized or unpolarized light. This result supports centers with symmetryT _d because they do not require any selection rules for the polarization of optical dipole transitions.     

Study of excimer laser induced melting and solidification of Si by time-resolved reflectivity measurements

In this paper we present the interpretation and analysis of time-resolved reflectivity measurements for excimer laser irradiated silicon. A nonequilibrium melting model is used to calculate the temperature distribution in the sample and the position of the solid-liquid interface. Calculations of the reflectivity of the probe beam are performed to obtain time-resolved reflectivity signals from basic principles, independent of the experiments, which can be compared with experimental data to reveal information about dynamics of the heating and cooling process. We propose more accurate methods for the determination of the melting threshold, the melt front position and the reflectivity of the sample for excimer laser light. From model calculations and experimental data we determine the reflectivity of the solid and liquid silicon for ArF excimer laser light.     

Laser excited time-resolved low-temperature luminescence of nucleic acid bases single crystals

The first results on low temperature (80 K) one photon fluorescence of single crystals of nucleic acids bases excited by picosecond light pulses are reported. The excitation to the first absorption band of the crystals was realized by tuning the fundamental frequency of the passive modelocked Nd:YAG laser into UV spectral region. Our spectroscopic measurements confirm previous assumptions about the excimer character of the fluorescence of the crystals. Kinetic parameters of complex fluorescence decays show a strong dependence on the exciting wavelength.     

放电泵浦ArF准分子激光动力学模拟与参数分析

利用一维流体模型研究了放电泵浦ArF准分子激光动力学过程,得到气体放电过程中放电电路的电流电压波形,得到了电子密度、光子密度、电场的时空分布特性,分析了放电参数对激光输出的影响。结果表明,电路参数、工作气压、氟气比例均对激光输出有显著影响,放电电路中的电感值对输出影响较小,参数范围较广,而电路中较小的峰化电容值有利于获得长脉冲输出,气压太大或太小都会使输出能量降低,同样,氟气比例太大或太小也会使输出能量降低。     

Linear photogalvanic current excited in sillenite crystals by femtosecond laser pulses

We observe electric pulses generated in sillenite crystals (Bi₁₂SiO₂₀ and Bi₁₂TiO₂₀) by 100-fs laser pulses at the wavelength of 400 nm (below the band gaps of both crystals). The peak value of the current pulses scales linearly with the intensity of laser pulses up to ∼45 GW/cm². The direction of the induced current depends on the polarization state of the laser pulse. This polarization dependence and features of the current detection via charge accumulation at the sample electrodes allow us to conclude that the electric pulses are generated due to the linear photogalvanic effect.     

An anomalous emission excited near the absorption edge of pyrene crystals

Emission spectra and decay times of the fluorescence excited at the absorption edge region in pyrene crystals were measured. At liquid nitrogen temperature, the fluorescence under the excitation at 390 nm is considered as the excimer emission and its band peak shifts a little to the short wavelength in comparison with that of the excimer emission under the excitation at 360 nm. The emission decay times under the excitation at the 390 nm and 360 nm are about 155 ns and 180 ns, respectively, at liquid nitrogen temperature. The former decay time changes its value abruptly near 127 K. This abrupt change of the decay time may be due to the phase transition in pyrene crystals.     

In situ time-resolved optical measurements of a-Si thin films during excimer laser crystallization

An in situ time-resolved optical reflection and transmission (TRORT) monitoring system combining two He-Ne probe lasers, a digital oscilloscope and three fast photodetectors is developed to investigate the crystallization processes of Si thin films during excimer laser crystallization (ELC). The physical meaning of optical spectra obtained by TRORT measurements has been interpreted in detail. The melt duration and transient phase transformation dynamics of Si thin films can be determined and interpreted immediately. A high efficiency and non-destructive evaluation approach is proposed for determining the grain size of polycrystalline Si after ELC directly and immediacy under appropriate experimental conditions.     

Long pulse ultraviolet laser emissions in an aerodynamically cooled electron-beam excited Ne-NF3 mixture

Long pulse laser action has been achieved at 3378.28 and 3481.96 Å in an electron beam excited supersonic flow. These laser emissions, attributed to NeII transitions, have been obtained when a mixture of Ne and NF₃ at a pressure of 0.2 atm. and aerodynamically cooled to 80 K was excited by a medium intensity electron beam. Laser pulse duration, about 350 ns fwhm for both lines, was only limited by the electron beam pulse length. The second of these laser lines had not been previously reported.     

Tuning ranges of an injection-locked excimer laser

The advantages and the practical limitations of injection locking are discussed. Experimental results for a system working in the regime between ideal injection locking and regenerative amplification are presented.     

Some remarks on photoluminescence of AgCl crystals excited by laser or after deformation

This paper summarizes and analyses our experimental results obtained on photoluminescence of AgCl crystals excited by ruby and u.v. laser in first part, and after and during deformation in second part. The influence of pressure on AgCl photoluminescence is explained by means of a qualitative model based on charged dislocations for both the elastic and plastic regions of the deformation curve.     

Interaction of excited Cr3+ ions in laser crystals

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 56, No. 1, pp. 77–80, January, 1992.     

Excitonic susceptibility of semiconducting crystals influenced by a uniform electric field

Summary The Stahl’s polariton equations for crystals, influenced by a uniform electric field, can be solved by means of an appropriate Green’s function. The Green’s function is calculated for the half-space geometry and the field directed along the z-axis. Using its asymptotic form a formula for the excitonic susceptibility is derived.     

Investigation of the mechanisms of luminescence of ZnS−Ag(Al) single crystals by the method of time-resolved spectroscopy

By the methods of amplitude and time-resolved spectroscopies the mechanisms of luminescence of ZnS−Ag(Al) single crystals differing in dislocation density are studied in pulse laser excitation. Experimental results are analyzed based on the theory of donor—acceptor pairs and the theory of centers surrounded with defect clouds. The data obtained are in agreement with the second theory. Ural State Technical University, 19 Mir Str., Ekaterinburg, 620002, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 6, pp. 857–860, November–December, 1999.