Operation Of Dye Laser Research Articles

Kinetics of a distributed-feedback laser with a static grating operating in the travelling pump-wave regime

A kinetic investigation was made of the operation of a distributed-feedback dye laser with a static phase grating in the travelling pump-wave regime. It was found that the use of a travelling pump wave makes it possible to implement unidirectional generation of a single ultrashort pulse of duration several times less than in the case of the traditional system of a distributed-feedback laser with lateral pumping.

Experimental study of Velocity Changing Collisions on Coherent Population Trapping in sodium

In this paper a detailed experimental study of Coherent Population Trapping (CPT) effect on sodium induced by a dye-laser operating in a three-mode regime is presented and a detailed analysis of the role of velocity changing collisions is made. These collisions show a very small relaxation effect on the dark resonances which are visible even at high pressures. For the first time we demonstrate the persistence of the ground state coherence to pressures up to one atmosphere for a relatively “heavy” buffer gas like argon. The experimental results have been compared with theory and a very good agreement has been obtained. Preliminary results on the effect of Na-N2 collisions on Coherent Population Trapping are presented.

Narrow linewidth operation of solid state dye laser based on sol–gel silica

Narrow linewidth laser action was achieved in dye-doped sol–gel derived silica slabs. Using a double grating resonator cavity, one grating serving as the beam expander and the other for tuning, laser output with linewidth as narrow as 3.3 GHz was realized for dye-doped sol–gel silica slabs. The output wavelengths were 560 nm, 474 nm and 378 nm respectively for rhodamine 6G-, Coumarin 460-, Exalite 377-doped samples. Oscillatory laser waveform indicative of two or three longitudinal mode lasing was also observed.

Pulse propagation effects in magnetoactive bulk direct-gap semiconductors

Based upon the time-dependent perturbation treatment of coherent radiation-semiconductor resonant interaction, the effect of an externally applied magnetic field on pulse propagation in bulk III-V semiconductors has been investigated analytically. Numerical estimations are made for a sample of InSb crystal duly irradiated by ultrafast infrared dye laser operating in the 3.9–9.4 μm wavelength range. The transmitted intensity profiles manifest the occurrence of pulse chirping and spectral broadening of the input pulse while propagating through the semiconducting crystal under the nonlinear dispersion regime. Although the mechanisms are different, similar characteristics were observed experimentally in atomic rubidium vapour in the presence of a strong magnetic field.

Pulse propagation effects in magnetoactive bulk direct-gap semiconductors

Abstract Based upon the time-dependent perturbation treatment of coherent radiation-semiconductor resonant interaction, the effect of an externally applied magnetic field on pulse propagation in bulk III-V semiconductors has been investigated analytically. Numerical estimations are made for a sample of InSb crystal duly irradiated by ultrafast infrared dye laser operating in the 3.9–9.4 μm wavelength range. The transmitted intensity profiles manifest the occurrence of pulse chirping and spectral broadening of the input pulse while propagating through the semiconducting crystal under the nonlinear dispersion regime. Although the mechanisms are different, similar characteristics were observed experimentally in atomic rubidium vapour in the presence of a strong magnetic field.

Transient pulse propagation and pulse break-up phenomena in III–V semiconductors

The coherent radition-semiconductor interaction model based upon the time-dependent perturbation technique has been employed for the analytical study of transient pulse propagation and pulse break-up in directgap semiconductors. In order to check the validity of our model, we have applied our analysis initially to the Rubidium atomic vapor system duly irradiated with pulsed ruby laser. Numerical estimation of the change in transient transmitted intensity reveals good agreement between the present results and the experimental observations in Rb vapor system. Finally, we have analyzed pulse propagation in an important direct-gap crystal, namely InSb duly irradiated by ultrafast infrared dye laser operating in the 3.9-9.4 μm wavelength range. Pulse break-up and pulse peak shifts can be noticed from the results. The pulse velocity is also found to reduce by at least a factor of 100. These features are analogous to the phenomenon of self-induced transparency where the pulse area theorem is usually employed.

Kinetics of the operation of a distributed-feedback dye laser with nanosecond excitation

An experimental investigation was made of the conditions for the generation of ultrashort pulses in a dye laser with light-induced distributed feedback. Experiments involving excitation of this laser with single-frequency and multifrequency radiation in the form of the second harmonic of an YAG:Nd3+ laser showed that in all these cases the ultrashort pulses were generated in the distributed-feedback laser by excitation of relaxation oscillations of the level populations and self-Q switching of the laser caused by such excitation

Dual-wavelength operation of a self-seeded dye laser oscillator

We demonstrate simultaneous dual-wavelength operation of a self-seeded dye laser. The laser cavity consists of one dye cell, two pairs of grating and tuning mirrors, and two reflecting mirrors. This configuration can be decomposed with two grazing-incidence cavities and a standing-wave cavity. The self-seeded dual-wavelength output beams are collinear and independently tunable. We were able to vary the output powers at the two wavelengths smoothly by changing the cavity length of a master oscillator.

Excited-State Dynamics of CH2CHO (B̃2A‘‘)

State-specific radiative lifetimes and electronic quenching cross sections are reported for four different vibrational modes of CH2CHO (B̃2A‘‘). Ground-state vinoxy radicals are produced by 193-nm excimer laser photolysis of CH3OCHCH2, and pumped to the B̃ state by a tunable dye laser operating between 332 and 348 nm. Fluorescence decay rates are determined in the presence of 12 collision partners: He, Ar, N2, O2, CO, H2, HCl, N2O, CO2, C2H4, CH3OCHCH2, and SF6. The measured electronic quenching cross sections vary from 0.01 to 66.5 Å2. Zero pressure radiative lifetimes are found to vary from 98 ± 10 to 154 ± 18 ns, depending on the vibrational mode. Possible mechanisms for lifetime shortening and collisional quenching are discussed.

Operation of Rhodamine 6G Dye Laser in Water Solution

The ethanolic solution of Rhodamine 6G is used for dye lasers in the atomic vapor laser isotope separation (AVLIS) system. However, the water solution is preferable from the standpoint of easy treatment and safety. In this paper, we systematically investigated the laser efficiency of a Rhodamine 6G dye laser pumped by a frequency-doubled Nd:YAG laser, for various water-based solutions with surface-active agents and alcohols. By adding an appropriate amount of surface-active agent (Triton X or Emulgen) or alcohol (ethanol or propanol), we obtained almost the same level of laser efficiency as in the pure ethanolic solution. The improvement in the laser efficiency with these additives was attained by the deaggregation of nonradiative dimers. It was also confirmed that the water-based solution showed better performance against thermal distortion than the ethanolic solution, and was suitable for copper vapor laser (CVL) pumping.

Experimental transient exudative retinal detachment in the rat.

To establish a new model of exudative retinal detachment in the rat. Photothrombosis was produced in a single retinal vein using direct treatment with a dye laser operating in the yellow wavelength (577 nm). Control eyes received identical laser applications, but treatment was placed alongside the vessel and photothrombosis was not produced. Eyes were examined at intervals during the subsequent week with ophthalmoscopy, photography, fluorescein angiography, and light microscopy. In 13 (41%) of 32 eyes with photothrombosis, bullous retinal detachments developed 1 day after laser treatment, and continued occlusion of the vein was confirmed with fluorescein angiography. Detachments persisted for 2 to 4 days and spontaneously resolved; resolution coincided with restored venous patency at 5 to 7 days. None of the 20 control eyes developed bullous detachments (P < .005). Laser photothrombosis in the rat offers a simple and accessible model of transient exudative retinal detachment without the need for exogenous chromophores.

Dye lasers using tapered optical fibers

A new type of dye laser operating in a single-mode optical fiber has been studied. The gain is produced by surrounding a tapered section of the fiber with laser dye. Interaction of the light in the fiber with the laser dye is achieved through the exposed evanescent field at the taper waist. Low lasing thresholds (25-65 mW) are obtained as a result of the high intensities at the taper waist. These tapered fiber dye lasers combine the advantages of a laser in fiber form with the wide spectral tuning ranges provided by laser dyes. Three experiments, demonstrating low-threshold operation of a grating tuned laser, an all-fiber ring laser, and cw lasing in tapered fiber dye devices, are presented.

Sputtered neutrals mass spectrometry of organic molecules using multiphoton postionization

Multiphoton postionization of sputtered neutral molecules has been investigated by high-resolution time-of-flight mass spectrometry. The desorption of the molecular species is induced by a pulsed 10 keV Ar+-ion beam with primary-ion dose densities below 1013 PI/cm2. For postionization an excimer laser at 193 nm wavelength or a tunable dye laser operating between 240 and 300 nm are used. In systematic investigations fragment patterns and useful yields of the commonly occurring amino acids were investigated. With λ=193 nm nearly all of them could successfully be identified by their (M-45) fragment which corresponds to the loss of the carboxyl group. The photoion yield varied over nearly two orders of magnitude for different amino acids. The aromatic ones could also be postionized at longer wavelengths (260–300 nm). Ion yields and fragment patterns critically depend on energy deposition of both the sputter process and the multiphoton absorption. This can be seen by comparison with gas-phase ionization of evaporated molecules and by the dependence of the ionization signal on the laser power density. In contrast to the postionization of sputtered atoms the ionization of sputtered molecules is not characterized by strong spectral features and only a poor degree of ionization selectivity can be achieved. In general, the results demonstrate that the combination of ion-beam sputtering and multiphoton postionization offers great potential not only in element analysis, but also in surface analysis of organic materials.

TO THE COLORED-LOSS-NOISE DYE-LASER MODEL WITH ADDITIVE NOISE TERM BELOW THRESHOLD

A single-mode colored-loss-noise dye-laser model with additive spontaneous emission noise term is treated by a new version of approximate effective Fokker–Planck equation which is proved to be valid below at and above threshold. Particular attention is paid to the dye-laser operation below threshold, where the additive noise term seems to play irreplaceable role in the context of the above mentioned model, preventing collapsing of the system to the vacuum state.

The effects of multi-mode CW laser-induced perturbations of neon metastable states on optogalvanic phenomena in pre-breakdown discharges

Optogalvanic effects have been induced in the pre-breakdown regime in neon by the use of a CW ring dye laser operating in the wavelength range 550-650 nm. Those effects that arise when the dye laser output is allowed to operate in the multi-mode configuration at a wavelength tuned to a particular neon transition from one of the four 1s to one of the ten 2p energy levels have been investigated. The strong influence of the energetic metastable 1s5 particle has been examined in detail by inducing its transition to the 2p4 level with laser radiation tuned to 594.5 nm. The effect of collisional coupling between the closely spaced 1s levels complicates the interpretation of the observed temporal and spatial changes in the nanoampere pre-breakdown ionization currents following the laser-induced perturbation. The relevant coupled differential equations, relating the particle densities appropriate to the levels of the 1s manifold and the 2p4 state, have been solved. These solutions, in conjunction with an extension of the Molnar treatment for the temporal growth of ionization in the presence of two or more metastable particles, have led to determinations of the diffusion coefficients, the fundamental time constants associated with the diffusion processes, the corresponding quenching parameters linked to the effects of trace impurities, as well as the specific action of the laser radiation. Observations of the variation of the fundamental time constant with laser intensity agree well with theoretical predictions but lead to some unexpected consequences concerning the identity of the unperturbed residue.

Stable Modelocking of a Coupled Cavity Moving Mirror Ring Dye Laser

Abstract We report the stable operation of a new modelocked standing-wave ring dye laser operating with a repetition rate of 250 MHz. Two external cavities are coupled to a bidirectionally operating continuously pumped ring dye laser. When a moving mirror is placed in one of the external cavities, the laser produces pulses 6 ps in duration. The operation is stable with the modelocked pulses arriving in a constant intensity envelope 5 ms in duration at a repetition rate of 90 Hz.

Improvements in the Generation of Quasi-Continuous, Tunable Ultraviolet Excitation for Raman Spectroscopy: Applications to Drug/Nucleotide Interactions

We demonstrate the generation of quasi-continuous ultraviolet excitation at wavelengths shorter than 240 nm using the frequency-doubled output of a synchronously pumped picosecond dye laser operating in the region of 420 nm. Owing to the relatively low peak power but high average power of the system, we obtain high-quality resonance Raman spectra at wavelengths as short as 209 nm. We apply the source to the study of the binding of anticancer drugs to DNA. In particular, we compare the binding of cis-diamminedichloroplatinum (II) (cisplatin) and cis-diammine-1, 1-cyclobutane dicarboxylate platinum (II) (carboplatin) to certain mononucleotides.

Stable, Efficient, Single-mode Operation of a High Repetition Rate Grazing Incidence Dye Laser

Abstract A pulsed, grazing incidence dye laser has been designed to oscillate at a repetition rate of 6·5 kHz in a single, narrow and stable, axial mode with a high excitation conversion efficiency. A single mode efficiency of 12% has been measured in a near diffraction limited beam. No measurable fluctuations of the central laser wavelength or the 100–150 MHz single mode linewidth were observed during an hour of observation. The effect of grating incident angle and dye flow rate on laser operation have been investigated and a correlation has been found between the state of polarization of the dye laser output and the polarization of the pump laser.

Excimer Pumped Dye Mixtures for the Wavelength Region 340–380 nm

Two binary mixtures of ultraviolet laser dyes in p‐dioxane solution are described. The tuning curve of each mixture spans more than 30 nm of useful tuning range in the 340–380 nm wavelength region. Both mixtures are robust with half‐lives comparable to, or in excess of, associated single dye values. These mixtures degrade symmetrically with dye laser operation, making them useful throughout the entire life of the mixture. A simple model for the mixture lasing, based on independent fluorescences of the component dyes, is able to semi‐quantitatively match the tuning curves of the dye mixtures. The results presented should be easily extendable to other dye mixtures.

Synchronous pumping of picosecond dye laser using high efficiency second harmonic generation from optical fibres

The stable operation of a mode-locked dye laser synchronously pumped by the second harmonic of an Nd:YAG laser produced in an Nd codoped germanosilicate optical fiber is reported. The optical fiber preparation technique, which results in a second harmonic conversion efficiency of 2 percent, is described. This optical fiber SHG conversion efficiency is the highest reported to date using a continuous-wave mode-locked laser.