A versatile dye-laser generator-amplifier system for intense,tunable picosecond pulse generation

Passively mode-locked ruby-laser pulses are used to generate nearly diffractionlimited picosecond light pulses in a dye cell by longitudinally amplified spontaneous emission. The output pulses are amplified in three longitudinally pumped dye cells, then spectrally filtered with a grating spectrometer and finally reamplified in a fourth dye amplifier in order to generate intense frequency tunable picosecond light pulses.     

Intense ultrashort pulse generation in a two-photon pumped generator-amplifier system

Intense ultrashort light pulses are generated i) by two-photon induced amplified spontaneous emission in a dye generator cell and ii) by two-photon induced seeding pulse amplification of a picosecond light continuum. The generated signals are amplified in a twophoton pumped dye amplifier. A passively mode-locked Nd: glass laser is used as pump source. Ligh pulses in the spectral region between 565 and 630 nm are generated in the dyes rohodamine B, rhodamine 6G, and PYC.     

Two-photon absorption and emission dynamics of bulk GaAs

Bulk n-type GaAs (dopant silicon) is investigated with picosecond pump pulses of a passively mode-locked Nd:glass laser. The two-photon absorption, the spontaneous emission, and the longitudinal amplified spontaneous emission are measured. The experimental results are compared with computer simulations and relevant material parameters are determined.     

Absorption and Emission Properties of a New Two-photon Absorption Dye

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Absorption and Emission Properties of a New Two-photon Absorption Dye

The emission properties of a newly synthesized organic two-photon absorption dye, trans-4-[p-(N-ethyl-N-ethylamino)-styryl]-N-methyl-pyridinium tetraphenylborate, have been investigated. When pumped by infrared pulses from a picosecond Nd∶YAG laser, the dye exhibits intense upconverted fluorescence and strong superradiance properties. For comparison, the one-photon induced fluorescence and superradiance are also measured. The one- and two-photon excited fluorescent lifetimes are 86 and 64 ps, respectively. The maximum efficiency of the dye is measured to be 1.97% and the upconversion efficiencies at different pump wavelengths have also been investigated by the optical parametric amplifier.     

S0-S n two-photon absorption dynamics of rhodamine dyes

The intensity-dependent transmission of picosecond ruby laser pulses of different duration through methanolic and ethanolic solutions of rhodamine B and rhodamine 6G is analysed. The transmission is affected by S₀-S _n two-photon absorption, by stimulated emission at the pump-laser frequency, by amplified spontaneous emission and by excited-state absorption. Various parameters involving the two-photon absorption dynamics are determined by comparing experiments with numerical simulations.     

Efficient phase-matched third harmonic light generation in hexafluoroisopropanol solutions of a pyrimidonecarbocyanine dye

The phase-matched collinear third harmonic generation of picosecond laser pulses in a 0.0825 molar hexafluoroisopropanol solution of a pyrimidonecarbocyanine dye is studied. The fundamental pulses are generated in a passively mode-locked Nd-phosphate glass laser. The saturation of third harmonic generation at high intensities is investigated. The influences of two-photon absorption, excited-state absorption, and amplified spontaneous emission are discussed. For input peak intensities above 10¹¹ W/cm² a third harmonic energy conversion of about 2×10^–4 is achieved.     

Saturable absorbers with concentration-dependent absorption recovery time

The ground-state bleaching of highly concentrated rhodamine 6G solutions in methanol is studied with intense picosecond light pulses. The ground-state recovery time changes with concentration from about 3.9 ns at low concentration (10^–5 mol/dm³) to about 1 ps at high concentration (0.6 mol/dm³). The shortening of the absorption recovery time is determined by the concentration dependent quenching of theS ₁-state population due to unbound dimers and by the intensity dependent longitudinal and transverse amplified spontaneous emission.     

Experimental and theoretical investigation of tunable picosecond pulse generation in longitudinally pumped dye laser generators and amplifiers

Picosecond pulse generation in longitudinally pumped dye laser generators and amplifiers is studied experimentally and theoretically. Frequency-tunable pulses between 720 and 940 nm are generated with a picosecond ruby laser pump source. The amplification of spontaneous emission and of seeding pulses in the generator and amplifier cells is investigated. Stimulated emission cross-sections and excited-state absorption cross-sections are determined by computer simulations. The coherence properties of the generated radiation are analysed. Resonance Raman contributions are resolved.     

Dispersion of phase response of dye solutions using picosecond excitation

Dispersion of phase response (frequency-dependent light-induced variations of the refractive index) of a solution of bleachable dye 3955 due to variation in the populations of the ground and excited states of molecules is investigated using wavelength-tuned picosecond light pulses. On the wavelengths of the dye absorption band the refractive index increases under bleaching, and in the fluorescence band it decreases, what is in qualitative agreement with the expected picture.     

Effective stimulated emission cross-sections determined by transient fluorescence amplification in a Fabry–Pe´rot resonator

The amplification of fluorescence light of an active medium in a Fabry-Pe′rot resonator, transversely pumped with picosecond pulses, is exploited to determine the effective stimulated emission cross-section spectrum, σem,eff(λ). A theory is presented for the ratio of amplified fluorescence output to spontaneous emission signal (resonator mirrors removed). The detection sensitivity is enhanced by the multi-pass amplification. Its dependence on the output mirror reflectivity and residual ground-state absorption in the emission region is analysed. As an example the effective stimulated emission cross-section spectrum of coumarin 2 in methanol is measured in the wavelength region 435nm to 610nm. This revised version was published online in November 2006 with corrections to the Cover Date.     

Direct Generation of Tunable UV Picosecond Laser Pulses Using Spectrotemporal Selection

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Experimental and theoretical investigation of third-harmonic generation in phase-matched dye solutions

The phase-matched third-harmonic light generation in dye solutions is studied experimentally and theoretically. In the experiments picosecond light pulses of a passive mode-locked Nd-glass laser are converted to the third-harmonic frequency. A third-harmonic conversion efficiency of up to 4×10^–4 was achieved for one of the dyes investigated (1,3,3,1,3,3-hexamethylindocarbocyanine iodide in hexafluoroisopropanol). The theoretical calculations determine the influence of various dye and solvent parameters on the conversion efficiency. The conversion efficiency is found to be limited by excited-state absorption of pump laser light and third-harmonic light from the S₁-state to higher singlet states. The S₁-state is mainly populated by two-photon absorption. Amplified spontaneous emission may reduce the limiting effects of excited-state absorption. Phase changes caused by the non-linear refractive index and the refractive index dispersion within the spectral bandwidth of the laser pulses reduce the conversion efficiency. Under ideal conditions conversion efficiencies up to 10% may be achieved.     

Theory of travelling-wave amplified spontaneous emission

A rate-equation model for describing the travelling-wave amplified spontaneous emission pulses (TWASE) in a transversally excited travelling wave arrangement is given. 6.35 ps long ASE pulses have been obtained by 12 ps long pump pulses. The effect of pump intensity, pump-pulse duration, molecular parameters of the dyes and pump-sweep velocity on the ASE pulses is studied.     

Nonlinear phenomena in chromatophores of photosynthetic bacteria excited by picosecond laser pulses

The contradictions between the fluorescence and difference absorption data on primary processes of photosynthesis have been elucidated taking into account light absorption by the excited states as well as nonlinear processes taking place in the chromatophore samples excited selectively by picosecond light pulses.     

Subnanosecond amplified spontaneous emission pulses by a nitrogen pumped dye laser

Pulses of 100 ps duration and peak power up to 100 kW are obtained with a dye laser pumped by an atmospheric pressure nitrogen laser of 0.5 ns duration. The shortening of the dye laser pulses is attributed to amplified spontaneous emission.     

Theoretical analysis of S1-state lifetime measurements of dyes with picosecond laser pulses

Various methods for the determination of the S₁-state lifetime of dye solutions (laser dyes and modelocking dyes) are analysed. A general model of interaction of laser light with dye molecules is presented and reduced to a dye energy level scheme of six levels. Fluorescence emission, light amplification and absorption recovery techniques are investigated theoretically and their limitations revealed. The determination of the S₁-state lifetime of saturable absorbers by single picosecond pulse bleaching experiments is very thoroughly discussed. The influence of various laser and dye parameters on the bleaching experiments are analysed numerically. The results are compared with isotropic steady state two- and three-level dye models.     

Numerical study of femtosecond travelling-wave amplified spontaneous emission

The generation of pulses from amplified spontaneous emission in dye solutions is studied in the case of femtosecond pump pulses. The effects of ultrafast vibrational relaxation, self-phase modulation and optimum synchronization are discussed.     

S1 singlet excited-state absorption of DODCI

1 excited-state absorption cross-section spectrum of DODCI in ethylene glycol is determined in the wavelength range from 500 nm to 750 nm. The S₁ state is populated by amplified femtosecond dye laser pulses (wavelength 592 nm) and the S₁-state absorption and emission behaviour is probed with a femtosecond light continuum. A general analysis procedure is developed to extract absolute excited-state absorption cross-sections from the measured transmissions. For DODCI in ethylene glycol the wavelength regions of saturable absorption (mode-locking application), reverse saturable absorption (optical limiter application), and effective stimulated emission (laser application) are determined. Received: 25 July 1996     

Nonlinear optical characteristics of polymethine dyes

Nonlinear refraction, nonlinear absorption, and saturated absorption of a number of polymethine dyes are studied and their nonlinear optical parameters are measured by the Z-scan method (λ=1064 nm). Simultaneous occurrence of several nonlinear optical processes in the case of excitation of dye solutions by picosecond pulses is analyzed. Saturated absorption of dye solutions is considered in terms of different models.