High Repetition Rate Dye Laser Research Articles

A study of flow characteristics of a high repetition rate dye laser gain medium

The gain medium of a high repetition rate liquid dye laser is made to flow at a sufficiently high velocity through the dye cell in order to minimize the thermal inhomogeneity. In this paper, temperature contours as a function of distance from the pump beam entrance dye cell window wall at various flow velocities in the laminar and turbulent region of gain medium flow were evaluated using computational fluid dynamics (CFD). Appreciable temperature gradients subsist at low Reynolds numbers due to inefficient heat transfer from the gain medium. However, at high Reynolds numbers >6000, the substantial effects of local density turbulent fluctuations degrade the optical quality of the gain medium. These computational studies were used to elucidate the characteristics of observed spectral fluctuations of a dye laser as a function of the Reynolds number.

Studies on gain medium inhomogeneity and spectral fluctuations coupled with a high repetition rate dye laser

Gain medium inhomogeneity is inevitable in a high repetition rate dye laser. In this paper, gain medium inhomogeneity coupled with a high repetition rate dye laser and their influences on the spectral fluctuations are investigated. The wavelength fluctuates within ±0.025 nm while the bandwidth fluctuates within ±1.108 GHz by reducing the flow Reynolds number from 1012 to 221 in the laminar region of flow. The wavelength fluctuations increase from 0.0110 to 0.0200 nm while the bandwidth fluctuations increase from 0.296 to 0.509 GHz by increasing the Reynolds number from 5645 to 6774 in the turbulent region. The heat deposition as a function of distance from the window wall in the gain medium and heat transfer coefficients as a function of Reynolds numbers in laminar and turbulent flow were estimated. Enlargement of the turbulent attribute (through a laminar sub-layer and buffer region) in the gain medium as a function of the Reynolds number was used to illustrate the observed spectral fluctuation trends of the dye laser.

High repetition rate dye laser spectral fluctuations through dye cells

High repetition rate dye lasers have inevitable spectral fluctuations. In this paper, investigation of wavelength and bandwidth fluctuations of a narrow bandwidth high repetition rate dye laser through notable dye cells have been carried out. The concave–convex, pinched and convex-plano geometries along with conventional planar dye cell has brought into participation for the spectral characterization. A diagnostic tool based on Fabry-Perot etalon along with composite image generation and analysis software was used to investigate spectral properties of the dye laser. Among the dye cells investigated for the high repetition rate dye laser, convex-plano duct of the dye cell demonstrated minimum wavelength and bandwidth fluctuations. This is most likely due to the stabilizing characteristics of the flow by the convex surface of the convex-plano dye cell, which reduces the boundary layers thicknesses, as compared to the other geometries.

Spectral fluctuations of a high repetition rate dye laser through a flowing gain medium

In this paper, wavelength and bandwidth fluctuations of a Rhodamine 6G dye laser, transversely pumped by CVL, through a flowing gain medium are investigated. The gain medium mass flow rates were varied in the range 1–6 l min−1 (LPM). Analysis of the wavelength and bandwidth fluctuations of the dye laser was carried out using a high resolution Fabry–Perot etalon based setup and composite images generated from spectral profiles. The wavelength varied within 0.0290, 0.0240, 0.0200, 0.0120, 0.0110 and 0.0200 nm while the bandwidth was within 1.340, 0.912, 0.679, 0.301, 0.296 and 0.509 GHz at flow rates of 1.0, 2.0, 3.0, 4.0, 5.0 and 6.0 LPM, respectively. The minimum fluctuations, which depend on the experimental conditions, were observed at ∼5 LPM. Spectral fluctuations at particular flow rates depend mainly on the microscopic fluctuations in the temperature and flow velocity inside the boundary layers.

Studies on thermo-optic characteristics of a high repetition rate dye laser

In this paper, an investigation on the thermo-optic characteristics of dye solution of a high repetition rate narrow spectral width dye laser has been carried out. The dye laser characteristics such as spectral width, wavelength, average optical power, pulse width and beam divergence are studied for dye solution bulk temperature alteration in 23–35°C range. The dye gain medium temperature was altered through the additional heat supplied to the gain medium. The dye solution temperature at the dye cell was monitored through a PC based temperature data acquisition system. It was observed that there is no appreciable change in the spectral width; however, the dye laser wavelength is shifted by 0.0567nm, in the temperature range investigated. The dye laser average power was decreased by nearly 36% for an increase of 12°C dye solution temperature, above the cavity/room temperature. The dye laser pulse width slightly increases, whereas area under the pulse width decreased from 8850 to 7650 counts in the 23–35°C temperature range. The dye laser horizontal beam divergence increased from 6 to 8.5mrad, while the vertical beam divergence from 1.2 to 1.5mrad, for the increase of temperature by 12°C. Apart from these statistical transforms, fluctuations of the characteristics parameter increased with the rising dye solution bulk temperature.

Design, modeling, and performance evaluation of a novel dye cell for a high repetition rate dye laser

In this paper, a new dye cell for transverse pumping was designed, modeled, and its performance in a narrow spectral width dispersive resonator, pumped by a high repetition rate copper vapor laser, was investigated. The scheme essentially involves the profiling of the cubical glass and stainless steel cylindrical surface such that convex-plano contour be present near the optical pumping region. The design is an amalgamation of straight and curved periphery to enhance the dye solution flow stabilities near the dye laser axis. A computational fluid dynamics analysis of the liquid flow through this dye cell has been carried out. The dye laser outputs such as optical average power, spectral width and wavelength stability, tuning range, pulse shape, through this new dye cell was evaluated. The dye laser average power about 30 mW was fairly steady over the observation period of more than an hour. The dye laser short-term (1 min) spectral width was within 0.824 ± 0.075 GHz, while, in a long-term, more than an hour, drifted by about 180 MHz. The dye laser wavelength in short-term fluctuates within ±0.0065 nm whereas in a long-term, more than an hour, drifted by about 0.0105 nm. The dye laser tuning range was 10 nm with a sub GHz spectral width operation. The pulse shape of the dye laser follows the pump laser pulse profile. Thus, the dye laser has demonstrated fairly long-term stability, without the use of either low expansion material or close loop control on the output.

Study of a new dye cell for a high repetition rate dye laser

In this paper, performance of a transversely pumped high repetition rate narrow spectral width tunable dye laser, which makes use of a very simple dye cell, has been investigated. The dye cell is made of a single piece glass tube, which is free from edges and additional holder for windows as generally used in dye cells. The scheme essentially involves the pinching of glass tube in such a way that smooth profile for liquid flow exists near the optical pumping region. This ensures the minimization of dye solution flow induced instabilities near the dye laser axis. The performance of this dye cell was evaluated by using it in a dye laser system having narrow linewidth dispersive resonator, pumped by a high repetition rate copper vapor laser, by means of the Fabry–Perot interferometer setup. The dye laser spectral stability was within ±5% over the observation period of 75min. The efficiency of the dye laser with uncoated optics was reasonably good. The output power of dye laser was also fairly steady over the observation period of more than an hour.

An experimental study and theoretical analysis of the mode characteristics of a narrow line-width, pulsed dye laser oscillator at different pump powers

This paper presents an experimental study and theoretical analysis on the effect of pump power on the divergence, pointing, line-width and wavelength stability of a narrow line-width, high repetition rate dye laser oscillator. The dye laser oscillator, based on the hybrid multiple-prism grazing-incidence grating cavity, was pumped by copper vapor laser (CVL). The dye laser mode characteristics were studied at CVL average pump powers of 2, 4 and 8 W. The single pulse dye laser divergence/pointing stability was studied by far-field intensity distributions. The line-width and wavelength stability were studied using a high resolution wave-meter. The experimental results were theoretically analyzed in terms of dye laser mode structure drift induced by beam pointing instability, beam divergence and thermally induced optical path length fluctuation. A comprehensive theoretical treatment on pointing stability of dye laser beam and its influence in the dye laser wavelength stability is presented. The theoretical and experimental trends were found to be in good agreement.

Molecular Encapsulation of Fluorescent Dyes Affords Efficient Narrow‐band Dye Laser Operation in Water

A water-based narrow-band high-efficiency dye laser was designed by means of a supramolecular host-guest chemical approach. The lasing characteristics of rhodamine B and sulforhodamine B (Kiton Red S) dyes in aqueous solution with the macrocyclic host cucurbit[7]uril (CB7) as additive were investigated in a narrow-band dye laser setup. Significant improvements in both photostability and thermo-optical properties of the aqueous CB7-complexed dye systems were observed as compared to the uncomplexed dyes in ethanol solution. The tuning curves for the new dye-CB7-water systems were constructed by measuring the laser output at different wavelengths, which showed similar peak efficiencies and red-shifted gains compared to the ethanolic solutions of the dyes, while dye laser operation revealed comparable pump threshold energies and slope efficiencies. The combined results render the dye-CB7-water system an attractive active medium for high-repetition rate dye laser operation.

On the microstructure of thermal and fluid flow field in a lasing medium of a high repetition rate dye laser

A high repetition rate, tunable dye laser suffers from thermal and flow field-induced inhomogeneity inside the laser-active zone of the dye solution, and shows a significant disparity in the spectral characteristics. The thermo–optical distortion developed in the lasing medium of dye solution, under high repetition rate pumping, perturbs the dynamics of the medium. The microstructures of the flow field in the hydrodynamic boundary layer, which are responsible for heat transfer, optical path length modulation, and divergence of the seeding radiation, transform the output characteristics of dye laser. The structure function, which represents the intensity of flow velocity fluctuations, and the eddy diffusivity of fluid flow help in design and development of a high-power tunable dye laser.

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.

The spectral measurement of a high repetition rate tunable dye laser output using Fabry–Perot fringe

We present the measurement of spectral distribution of a high repetition rate dye laser by deriving explicit relationship of the parameters with ring diameter of the Fabry–Perot fringe pattern. The output characteristics and its variation has been represented by generating a composite picture of a single line scan across the ring diameter of the Fabry–Perot fringe, captured through CCD camera and frame grabber card.

Transverse flow flashlamp pumped dye laser

A high repetition rate dye laser utilizing transverse flow and linear, close-coupled flashlamps has been built. Measurements and performance figures including average power, bandwidth, beam divergence, and solvent mixtures will be discussed.

Transverse flow flashlamp pumped dye laser

A high repetition rate dye laser utilizing transverse flow and linear, close-coupled flashlamps hasbeen built. Measurements and performance figures including average power, bandwidth, beam divergence, and solvent mixtures will be discussed.