Dye Laser Wavelength Research Articles

Influence of dye gain medium flow on the wavelength jitter and the drift of high repetition rate—Single mode dye lasers

This paper presents the effect of the flow of the dye gain medium on the wavelength jitter (<30 s) and drift (≈10 min) of a single axial mode dye laser pumped by a copper vapor laser (5.5 kHz). The study was carried out using a wave-meter. The dye solution temperature was maintained to within ±0.1 °C to allow the influence of dye flow rate on the wavelength stability. For the investigated dye flow rate, varying from 1.4 to 2.8 lpm (with corresponding Reynolds number varying from 1975 to 3950), the dye laser wavelength jitter reduced from ±0.15 pm (±130 MHz) to ±0.08 pm (±70 MHz) and drift rate reduced from 1.0 to 0. 2 MHz/s. However for flows beyond 1.7 lpm, random fluctuations in dye laser wavelength were observed. The observed behavior was linked to the flow related variation of angular spread and angular drift of the dye laser beam circulating in the cavity. This was revealed by an exhaustive study of the long term (≈10 min) divergence and pointing stability of the single mode dye laser output beams for different dye media flows.

Solid-state dye lasers based on polymethyl methacrylate doped with pyrromethene 650

Solid-state dye samples based on polymethyl methacrylate (PMMA) doped with different concentrations of the dye PM650 were prepared. With SHG of Q-switched Nd:YAG laser (532 nm, ∼15 ns) pumping the samples longitudinally, the fluorescence, lasing spectra and slope efficiencies of the samples were obtained. The highest slope efficiency 27.49% and laser output energy 22.0 mJ was achieved in the sample with a dye concentration of 2.0 × 10−4 mol/L. To our knowledge, the results are the best under the same condition so far. The maxima of output lasing spectrum is about 653.5 nm. Our results have shown that using solid-state samples doped with PM650 can extend the dye laser wavelength to the red.

Analysis of the spectral variation of a dye laser by gain medium inhomogeneity

In this paper, an analysis of spectral variation of a high repetition rate dye laser by an optical inhomogeneity developed inside the gain medium is presented. The passive band-pass, responsible for bandwidth, set (in homogeneous medium) by dispersive optical element in its resonator is modulated by scale length of the inhomogeneity introduced in the gain medium. Inhomogeneities, introduced by temperature in laminar flow (at low Reynolds number) and fractional change in flow-induced scale length (at higher Reynolds number) have an effect on the wavelength of dye laser.

Treatment of molluscum contagiosum with a pulsed dye laser: Pilot study with 19 children

Molluscum contagiosum is a common, self-limiting viral disease of childhood caused by a poxvirus. Often the children themselves and their parents desire treatment for cosmetic reasons or because of pruritus. Laser therapy offers another option to the traditional methods of treatment. 19 children aged between 2 and 13 years (median:6) with molluscum contagiosum were treated in a prospective, non-randomized pilot study with the flashlamp pumped pulsed dye laser (wave length:585 nm, pulse duration 0,45 ms, spot size 7 mm, energy density 6-7 J/cm(2)). All patients tolerated the laser treatment well. In 84.3% one laser treatment led to total remission. In 10.5% a further laser session was necessary and one patient was treated three times to achieve total remission. Treatment of molluscum contagiosum with the flashlamp pulsed dye laser is a safe and efficient treatment modality.

Hypericin and Pulsed Laser Therapy of Squamous Cell Cancer in Vitro

This in vitro study compares continuous wave and pulsed laser light at longer wavelengths for activation of the phototoxic drug hypericin in human cancer cells. Two-photon pulsed laser light now allows high-resolution fluorescent imaging of cancer cells and should provide deeper tissue penetration with near infrared light for improved detection as well as phototoxicity in human tumors. Cultured Seoul National University (SNU)-1 tumor cells from a squamous cell carcinoma (SCC) were incubated with hypericin before photoirradiation at four laser wavelengths. Phototoxicity of hypericin sensitized SCC cells was measured by dimethyl thiazoldiphenyl (MTT) tetrazolium bromide cell viability assays and by confocal fluorescence microscopy via 532-nm and infrared two-photon pulsed laser light. Phototoxic response increased linearly with hypericin dose of 0.1-2 microM, light exposure time of 5-120 sec, and pulsed dye laser wavelengths of 514-593 nm. Light energy delivery for 50% cell phototoxicity (LD50) response was 9 joules at 514 nm, 3 joules at 550 nm, and less than 1 joule at the 593 nm hypericin light absorption maxima. Fluorescence confocal microscopy revealed membrane and perinuclear localization of hypericin in the SNU cells with membrane damage seen after excitation with visible 532 nm continuous wave light or two-photon 700-950 nm picosecond pulsed laser irradiation. Hypericin may be a powerful tumor targetting drug when combined with pulsed laser light in patients with recurrent head and neck SCC.

Fluctuations in near 360° curved and straight channel dye cells for high repetition rate copper vapour laser pumped dye laser

A study of wavelength and bandwidth fluctuations of a rhodamine 6G dye laser, transversely pumped by high repetition rate copper vapour laser, using a near 360° curved and a straight duct dye cell, is presented. The axial modes, which are indistinguishable in the straight duct cell, are clearly distinguishable in the curved duct cell dye laser. The curved duct dye cell has smaller fluctuations in wavelength and bandwidth as compared with the straight dye cell.

Resolution enhancement of pHe+ atomic line profiles measured with a pulsed dye laser and a Fizeau wavelength meter.

A Fizeau wavelength meter was used to compensate for fluctuations in the longitudinal mode structure and wavelength of a pulsed dye laser. The average laser linewidth was effectively narrowed by selection of laser pulses with a single longitudinal mode. These techniques were recently employed to measure some atomic transition wavelengths in pHe+ to fractional precisions greater than 1 part in 10(7). The wavelengths were absolutely calibrated against iodine or tellurium lines by absorption spectroscopy or against neon or argon lines by optogalvanic spectroscopy.

Absolute wavelength calibration of pulsed lasers by use of machine vision

We developed a new absolute wavelength calibration system that uses machine vision for measurement of low-repetition-rate, short-pulse-duration (10-Hz, 5-ns) tunable lasers. Weak fluorescence from an iodine cell was measured by use of machine vision as a spatially gated integrator, and a pulsed dye-laser wavelength was calibrated with an accuracy of +/-0.005 nm , which is precise enough for differential absorption lidar application.

A Computerized System for Controlling the Wavelength of a High-Power Dye Laser

A system for the rotation of a dispersive laser element with a stepper motor is described. The motor is controlled by a personal computer that can be located at a distance of more than 20 m from the motor. The stepper control unit is connected to the computer interface board by a twin line. The system ensures highly reliable operation under conditions of intense electromagnetic noises from the laser power supply system due to the use of noise-suppressing differential transmission lines and optoelectronic isolators.

LiAr, LiKr and LiXe excimers: Photochemical formation of the $\mathsf3^{2}\Sigma^{+} $ - $\mathsf1^{2}\Sigma ^{+}$ bands

We investigated the photochemical formation of lithium-rare-gas excimers in the 3\(\) state through the reaction of Li2(2(C)\(\)) and the ground-state rare-gas atom. Lithium-rare-gas vapor mixture was prepared in the heat-pipe oven. We populated the 2(C)\(\)state of the Li2 molecule using the XeCl excimer laser wavelength at 308 nm or the PTP dye laser wavelength at about 335 nm. The 3\(\)-1\(\) transitions were observed with peaks at 414, 420 and 435 nm for LiAr, LiKr and LiXe, respectively. We estimated thermally averaged rate constants for these photochemical reactions, which are \(\)cm3s-1 for LiAr, \(\)cm3s-1 for LiKr and \(\)cm3s-1 for LiXe. Ab initio potential-energy curves and transition dipole moments for LiKr were calculated applying the SCF MRDCI method. Available data for the LiAr and LiKr excimers are presented, including potential-energy curves, electronic transition dipole moments, and spectroscopic constants. Possible photochemical formation of these molecules in the excited states is discussed. We performed the quantum-mechanical spectral simulations of the LiAr and LiKr 3\(\)-1\(\) transitions, using ab initio potential-energy curves.

Dye laser pumped, continuous-wave KTP optical parametric oscillators

(KTP) optical parametric oscillators (OPOs) with pump and idler resonant cavities. With a linear two-mirror cavity the pump power at threshold was 70 mW. The single-frequency signal and idler output wavelengths were tuned in the range of 1025 to 1040 nm and 1250 to 1380 nm by tuning the dye laser in the range of 565 to 588 nm. With a dual three-mirror cavity the threshold was 135 mW. Pumped by 500 mW of 578 nm radiation the 1040 nm single-frequency signal wave output power was 84 mW. Power and frequency stable operation with a spectral bandwidth of less than 9 MHz was obtained by piezo-electrically locking the length of the pump resonant cavity to the dye laser wavelength. Similar performance was achieved by placing the idler resonant OPO inside the resonator of the dye laser. With this system power stable and single-frequency operation was achieved with a spectral bandwidth of less than 11 MHz for the idler wave.

The pulsed dye laser--possibilities and limits

The pulsed dye laser (wavelength 585 nm, pulse duration 0.3-0.45 ms) is very effective in the treatment of port-wine stains, beginning hemangiomas, telangiectasias, spider nevi, xanthelasma and red hypertrophic scarring. It is the laser of choice in the therapy of young patients with port-wine stains. The pulsed dye laser is limited by its relatively superficial penetration into the skin with a maximum of 1.5 mm.

Effect of pulsed dye-laser wavelength stabilization on spectral overlap in atmospheric NO fluorescence studies

We introduce an inexpensive application of a Fabry-Perot etalon to control long-term UV-laser line drift in atmospheric NO laser-induced fluorescence (LIF) measurements by monitoring the visible fundamental of a pulsed dye laser. A linear image sensor captures the interference pattern, and the dye grating can be adjusted to maintain a fixed wavelength through an interface with labview software. Results indicate that the laser wavelength can be fixed to an accuracy of +/-0.0001 nm in the dye fundamental and +/-0.00003 nm in the UV beam. Hence the average error in the LIF signal owing to fluctuations in spectral overlap between the laser and the NO absorption transition decreases from ~5 to ~0.05%, which results in improved measurement accuracy.

Gain measurements in binary and ternary dye mixture solutions under nitrogen laser excitation

Energy transfer studies in the case of binary [Coumarin 485 (C485) + Rhodamine 610 perchlorate (Rh 610)] and ternary [C440 + C485 + Rh610 perchlorate] dye mixture solutions in ethanol have been made and discussed through optical gain characteristics at various acceptor concentrations and pump powers of the N 2-laser. In case of binary mixtures, we observe that the optical gain of the acceptor dye (Rh610) improves and the threshold power required for lasing action decreases when donor dye (C485) is added. The concentration dependence of peak gain and peak lasing wavelength of the energy transfer dye laser (ETDL) has been studied. The results have also been compared with the optical gain characteristics of these dyes in single component solutions. The energy transfer rate constants ( K F , the Förster type non-radiative and K R , the radiative rate constants) and critical transfer radius ( R o ) have been calculated using a Stern-Volmer analysis of the pump power dependence of the gain. From the experimental results, we find that the dominant mechanism responsible for efficient excitation transfer in this bimixture is of a radiative nature. Further, the gain equation for a ternary dye mixture has been derived using the transfer rate constants for two different possible bimixtures; C440 + C485 and C485 + Rh610, which is helpful in obtaining the optimum concentration to be used in the ternary mixture for higher gains.

Optimal parameters for laser treatment of leg telangiectasia.

The optimal parameters for treatment of leg telangiectasia with a pulsed laser are investigated. The Monte Carlo method is used to calculate the light penetration and absorption in the epidermis, dermis, and the ectatic blood vessel. Calculations are made for different diameters and depths of the vessel in the dermis. In addition, the oxygen saturation of the blood vessel, the laser beam diameter, and the laser irradiation profile is varied. It is found that for vessels with diameters between 0.3 mm and 0.5 mm wavelengths about 600 nm are optimal to achieve selective photothermolysis for the considered damage model. It is also shown that an elliptical laser beam area has advantages compared to a circular beam area for treatment of leg telangiectasia. We recommend the treatment of leg telangiectasia with dye laser wavelengths longer than the normally used 577 nm and 585 nm.

Laser-induced excitation and dispersed fluorescence spectra of the ethoxy radical

Extensive laser excitation and dispersed fluorescence spectra of the ethoxy radical have been recorded in a supersonic jet expansion. Neon transitions have been used to calibrate both the wavelength of the excitation dye laser and the optical multichannel analyser system used to record the wavelength-resolved emission spectra. Both the excitation and dispersed spectra are characterized by prominent progressions involving the C - O stretch vibrational mode. Seven vibrational frequencies for the excited electronic state and eight for the ground state have been assigned. To the best of our knowledge, 10 of these 15 assigned frequencies are reported here for the first time. Vibrational and anharmonic constants for the C - O stretch mode have been determined via least-squares fits for the X state and the B state .

Photoacoustic analysis of stimulated emission in pulsed dye lasers

Stimulated emission in pulsed dye lasers was characterized in several experimental conditions by analyzing the changes in the acoustic signals generated in a dye solution, with the dye laser cavity either active or inhibited (i.e., by blocking the optical path or misaligning of the optical components). Pump energy threshold, optimum dye concentration, tuning range and maximum-emission wavelength of a rhodamine 6G dye laser were measured by this method. An approximate model for the photoacoustic signal generation consistent with the experiments is presented.

A wavemeter for measuring changes in wavelength of pulsed dye lasers

The performance of a simple wavemeter for measuring changes in wavelength of a pulsed dye laser is described. Details of optics and electronic circuitary used, along with the algorithm for wavelength measurement, are given. Using this instrument wavelength changes of a dye laser could be measured, as well as introduced through a user interface, with an accuracy of 1 ppm.

Laser optogalvanic wavelength calibration with a commercial hollow cathode iron-neon discharge lamp

351 optogalvanic transitions have been observed in the 337–598 nm wavelength region using an iron-neon hollow cathode discharge lamp and a pulsed tunable dye laser. 223 of these have been identified as transitions associated with neon energy levels. These optogalvanic transitions have allowed, in conjunction with interference fringes recorded concomitantly with an etalon, the calibration of the dye laser wavelength with 0.3 cm -1 accuracy.

Rainbow-enhanced forward glory from fused-silica spheres

A tertiary rainbow enchances the forward glory scattering from a fused-silica sphere because of its refractive index m ≍ 1.465. The scattered light contains a strong cross-polarized component and varies rapidly in brightness with changes in m. In experiments m is varied by the use of a range of argon and dye laser wavelengths. The forward cross-polarized scattering is found to be in agreement with Mie theory calculations. A reflective coating on small areas around the equator and polar caps of the sphere increases the forward scattering by a factor of ~ 180.