Theoretical investigation of amplified spontaneous emission with picosecond light pulses in dye solutions

The amplified spontaneous emission in dye solutions excited with intense picosecond light pulses is studied theoretically. A multi-level model is applied to take into account the effects of the various dye parameters such as ground-state absorption, stimulated emission, excited-state absorption, reabsorption and relaxations from populated excited levels. The influence of the pump laser duration and intensity and of the dye concentration and sample length is investigated. Optimum situations are derived for the generation of intense picosecond light pulses at new frequencies by amplified spontaneous emission. On the other hand, conditions are found where amplification of spontaneous emission may be neglected. The analysis allows the determination of unknown dye parameters by comparing the calculations with the experiment.     

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.     

Direct Generation of Tunable UV Picosecond Laser Pulses Using Spectrotemporal Selection

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Nd:YAP laser pulse compression by three-stage transient stimulated Brillouin and Raman scattering

There is a continuous effort to generate stable, powerful picosecond laser pulses for application in spectroscopy, nonlinear optics and parametric light generation, as well. One of the possible methods is the compression of longer nanosecond laser pulses by stimulated Brillouin and stimulated Raman scattering. The advantages of such a technique, in comparison to the used mode locked picosecond lasers, are as follows: the absence of the active and/or passive mode lockers used to generate a train of picosecond pulses, and the absence of a fast electrooptical shutter used to select a single pulse from a train of pulses. The application of stimulated Brillouin and stimulated Raman scattering permits to generate picosecond pulses in the wavelength regions not covered by mode locked lasers. Of special interest is the wavelength region of 0·8 m, which may be amplified by the attractive Titanium Sapphire lasers. In this paper we are summarizing our results in theoretical modelling and in real generation of picosecond pulses by means of cascaded stimulated Brillouin and Raman scattering. The models of scattering processes have been investigated. The stable generation of 5, 7, 3 picosecond pulses have been optimized for the wavelengths of 0·8, 0·64 and 0·54 m, respectively. In all these cases, the pulses exhibited the far field pattern close to Gaussian, with the pulse energy ranging from 0·2 to 1 mJ.     

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.     

Determination of the shape and duration of picosecond light pulses by bleaching of dyes

A new method is developed to measure the shape and duration of picosecond light pulses in a single shot. A pump and probe technique in a dye sample is applied. Single picosecond light pulses at different frequencies were analysed with various absorbers. Asymmetric pulse shapes with leading edges steeper than the trailing edges were observed.     

Amplification of fluorescence using collinear picosecond optical parametric amplification at degeneracy

We demonstrate the output characteristic of broadband parametric amplification of incoherent light pulses in a 355-nm pumped degenerate picosecond optical parametric amplification with either saturated or unsaturated amplification.The optical parametric amplifier is seeded by the fluorescence generated in a solution of pyridine-1 dye in ethanol.With the saturated amplification,we can obtain high energy incoherent light pulses,whose full width at half maximum bandwidth varies from 16 nm to 53 nm for the different phase matching angles near degeneracy.Moreover,the unsaturated bandwidth of the amplified pulses fits well to the calculated result at degeneracy.Selecting s-polarized fluorescence with a Glan-Taylor prism,the maximum bandwidth of the amplified fluorescence is found to be 59 nm for a purely s-polarized seed.The maximum output energy is 0.67 mJ for the optical parametric amplifier.By using an optical filter and compressor,the generated high energy incoherent light has great potential as the incoherent pump,signal or idler wave of a parametric down-conversion process,so that a wave with a high degree of coherence can be generated from an incoherent pump light.     

Intrapulse thermally induced wavelength shift in a distributed feedback dye laser

It is shown that when a distributed feedback dye laser is used to generate a train of picosecond pulses, the narrow lines observed in the spectrum are not longitudinal modes, but are due to the intrapulse refractive index changes caused by the heating effect of the pumping pulse.     

Picosecond pulses from passively mode-locked dye lasers

Successive stages of the development of ultrashort pulses in passively mode-locked dye lasers are studied. It is numerically shown that the initial fluctuations evolve into a picosecond pulse which retains its magnitude and particular shape and moves slower than the speed of light.     

Spectrally Adjustable Picosecond Dye Laser Pulses Generated with Nanosecond Nitrogen Lasers

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Simple generation of 400–700 nm picosecond dye laser pulses with nanosecond laser pumping

New results in the experimental study of the spectro-temporal selection (STS) method to produce picosecond dye laser pulses are presented. Adjustability of the picosecond pulse wavelength, possibility of extension of the STS method to different dyes and to UV pump wavelength, stability of the output pulse duration and intensity, and the concentration effect on pulse duration, are reported for the first time. From these results, production of high power picosecond (50–100 ps) dye laser pulses spectrally adjustable between 400 and 700 nm is obtained with a standard nanosecond pump laser, in a compact and simple device.     

Pulse properties of a synchronously mode-locked,cavity dumped,picosecond dye laser system

A synchronously mode-locked, cavity-dumped picosecond dye laser is described. The structure and intensity of the picosecond pulses measured under different conditions are reported. It was found that the structure of the pulses from the synchronously pumped dye laser depends critically on the length of the Ar⁺ laser pulses. At the shortest Ar⁺ laser pulses of about 70 ps the dye pulses are as short as 1.1 ps. With Ar⁺ laser pulses of 200 ps the dye laser pulses contains a broad satellite pulse which contains a large fraction of the total intensity. When a cavity dumper is added to the system one gets dye laser pulses 15–20 ps long with a substructure, which indicates incomplete mode-locking. Well mode-locked 1.5–2.0 ps pulses were obtained in the red part of the dye laser action spectrum, i.e. 620–650 nm for R6G, 595–608 nm for R 110 and 657–662 nm for RB, respectively. Addition of mode-locking dyes also improved the pulse quality at some wavelengths.     

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.     

A time-compensated spectral filter for transform-limited tunable picosecond pulse generation from spectro-temporal-selection dye lasers

Diffraction and transform-limited picosecond tunable pulses are generated from Spectro-temporal-Selection (STS) dye lasers by using a new extra-cavity filter. This filter is based on a grazing-incident grating and arranged in the configuration of a folded dispersive delay line. Thus, it provides both high spectral selectivity and controllable temporal compensation for elimination of pulse broadening. Direct production of diffraction- and transform-limited picosecond dye laser (10 µJ, 50 ps) pulses spectrally adjustable between 398 and 702 nm is demonstrated in a compact device, with 8 ns pump pulses from a nanosecond nitrogen laser.     

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.     

Observation of twin-beam-type quantum correlation in optical fiber

We report generation of pulsed twin beams of light through optical parametric amplification in a fiber Sagnac loop. By pumping the Sagnac loop with picosecond pulses at a wavelength near the zero-dispersion wavelength of the fiber, we achieve phase-matched nondegenerate four-wave mixing with gain. For a gain of 2.2, the intensity noises of the amplified signal and the generated idler (conjugate) pulses are found to be correlated by 5.0 dB, and the subtracted noise drops below the shot-noise limit by 1.1 dB (2.6 dB when corrected for losses). We have investigated the gain dependence of the quantum-noise reduction as well as of the intensity noises of the amplified signal and idler pulses. As the gain increases, we observe the onset of excess noise on the idler pulses.     

利用较完善模型研究半导体光放大器对皮秒光脉冲的放大

提出了一个描述半导体光放大器（SLA）对皮秒脉冲的放大这一物理过程的较为完善的物理模型，并数值分析了光脉冲经SLA放大后的上升时间和下降时间.结果表明：随着SLA偏置电流的增大，上升时间将缩短而下降时间将延长；输入脉冲的大峰值功率将加速上升时间的缩短和下降时间的延长；增益压缩对脉宽为几个皮秒的输入脉冲的上升时间和下降时间有明显的影响，而对脉宽为几十皮秒的输入脉冲可近似认为没有影响；增益非对称和漂移强烈影响上升和下降时间. 关键词： 半导体光放大器 皮秒光脉冲 上升和下降时间     

Generation and applications of passively mode-locked picosecond light pulses

A model concerning the generation of picosecond light pulses in solid state lasers is compared with existing experimental observations. The quality of selected single pulses and their favourable properties for investigations with ultrashort light pulses are discussed. Extensive physical applications of picosecond light pulses are reviewed. Emphasis is given to quantitative investigations of non-linear optics and of ultrafast relaxation processes in condensed matter.     

Rapid scanning autocorrelator for measurements of picosecond laser pulses

A rapid scanning autocorrelation interferometer for measurements of picosecond laser pulses is described which uses a rotating prism as scanning device in one arm of the interferometer to permit continuous display of autocorrelation traces at audio frequencies on an oscilloscope. Scan widths of more than 500 ps with high linearity can be achieved. Autocorrelation measurements of picosecond pulses from a synchronously pumped mode-locked dye laser are presented.     

Picosecond pulse generation and detection in the wavelength range 1200–1600 nm

Optical pulses of 1.5–5 ps duration tunable in the wavelength range 1200–1600 nm are generated by difference-frequency mixing mode-locked dye laser pulses in a lithium iodate crystal. The IR pulses are detected with picosecond resolution after transmission through long lengths of optical fibre, allowing the study of linear and nonlinear pulse propagation.