Design of the dye cell of a dye laser to facilitate repetitive operation in the single longitudinal mode

Abstract

A dye cell was designed and fabricated to facilitate high repetition rate single longitudinal mode (SLM) operation with low viscosity solvents such as ethanol. The flow circulation (vortex) in the dye cell was eliminated by reducing the flow cross section from 10 to 5 mm 2 with optimized flow entry. The physical dimension of dye cell is very important for short cavity SLM lasers in terms of keeping the cavity length small. Flow visualization of various geometries in the dye cell was carried out using commercial computational fluid dynamics (CFD) software. It was found that the slit as well as tubular entry to the dye cell of cross section 1 × 10 mm 2 shows flow circulation (a vortex) near the entry to the dye cell. The SLM was obtained from a 10 mm 2 flow cross section dye cell with a high viscosity solvent such as binary solvent (200 cP) or glycerol (1400 cP) with a higher bandwidth. The pulse to pulse fluctuations in the bandwidth and wavelength are generally associated with dye flow instabilities. These flow related instabilities reduced with higher viscosity solvents, which results in an increased bandwidth of the SLM dye laser (by nearly 40%). A specially designed dye cell was fabricated and used for SLM operation at two different pump lasers having different pulse repetition rates ranging from 20 to 6000 Hz. SLM operation was demonstrated for longitudinal pumping of the dye cell with low viscosity solvents. Time averaged SLM line widths of 400 and 175 MHz were obtained with a copper vapor laser (CVL) and Nd:YAG laser, respectively. A single pulse line width of 315 MHz was obtained with a CVL pumped dye laser.

Characterization of dye cells for a high-repetition-rate pulsed dye laser by particle image velocimetry (PIV)

“…The dye cell is a vital component that facilitates the gain to the dye laser cavity [10]. Several types of dye cell geometries, such as converging, diverging, straight, trapezoidal, parallelogram, rectangular, prismatic, curved converging diverging and a cell with convex inner surfaces, have been widely used to obtain higher flow velocities in the dye cell [16][17][18][19][20][21][22][23][24][25][26]. According to the continuity equation the reduction in the cross-sectional area of the flow channel results in higher flow velocities at the expense of the static pressure.…”

“…It has been reported that the higher flow velocity in the dye cell results in self-heating due to wall friction [7]. A thoughtful design of the dye cell flow channel, and suitable selection of active volume and pump power levels, will help to resolve these problems for operation of the dye laser at high repetition rate [16]. To study the several flow-related parameters for a dye laser beam of reasonably good quality, we have developed a computational model to avoid extensive, time-consuming experimental studies for obtaining a suitable dye flow channel.…”

“…To study the several flow-related parameters for a dye laser beam of reasonably good quality, we have developed a computational model to avoid extensive, time-consuming experimental studies for obtaining a suitable dye flow channel. We have computationally evaluated the designs of flow channel for a dye cell that are suitable for a pulsed dye laser in a general-purpose computational fluid dynamics (CFD) code and the details of the CFD model have been reported earlier [7,16,27]. In CFD the equations governing the flow and their interaction between fluid and flow channel have been solved numerically.…”

“…In CFD the equations governing the flow and their interaction between fluid and flow channel have been solved numerically. Several dye cell flow geometries, such as rectangular, converging-diverging and converging-straightdiverging, with different types of flow entry and flow exit, and different cross-sectional areas and flow channel lengths, were studied and optimized using the CFD model [16,27]. These dye cells have been used in high-repetition-rate pulsed dye lasers and the results were published elsewhere [2,27,28].…”

“…A high flow velocity in the dye cell removes the heated volume and also extracts photodegraded products from the active region [30][31][32]. It has been reported that the flow geometry, flow entry to the cell and flow cross-sectional area of the rectangular dye cell are important parameters for eliminating flow circulations [16]. Two types of dye cells, namely type I and type II, have been fabricated based on our computational results [27].…”