Flow and thermal characteristics of high Reynolds number (2800–17000) dye cell: simulation and experiment

Abstract

This paper presents computational and experimental studies on wavelength/frequency fluctuation characteristics of high pulse repetition rate (PRR: 18 kHz) dye laser pumped by frequency doubled Nd:YAG laser (532 nm). The temperature gradient in the dye solution is found to be responsible for wavelength fluctuations of the dye laser at low flow rates (2800 < < 5600).

Study of output power of very high pulse repetition rate (18 kHz) dye laser pumped by frequency doubled diode pumped Nd: YAG laser (λ~ 532 nm)

“…Figure 10 gives the variation of + l in the region of 0-100 μm from the wall. + l does not exist in this region for 2 LPM flow rate due to a large thickness of the laminar sub-layer and turbulence Reynolds number e R T < 1 [12]. + l values are small < + l ( 1) at 4 LPM but + l attains a significantly high value ( + l max > 1.5) if the flow rate is beyond 6 LPM.…”

“…Each eddy of a particular size of a turbulent flow can be considered to be homogeneous in refractive index [30]. The continuous distribution of eddy sizes from the largest eddy size (l) to the smallest eddy size (η) [12] in the moving dye solution leads to a distribution of refractive indices following an inverse power law of the physical size of eddies [30]. The variation in the refractive index (n) in the gain medium produces optical inhomogeneity and is related to the cross section of losses (σ in ) by the following relationship [31]:…”

“…Reference [12] introduces a new fluid flow parameter, dimensionless eddy size + l , which is proportional to Δn n / . Therefore, equation ( 5) can also be written as:…”

“…It is well known Laser Phys. 25 (2015) 055001 that turbulent flow is chaotic and the eddy size at one particular point cannot be estimated at a particular time but the range of eddy sizes is fairly fixed at a point and the same can be calculated [12]. Therefore, magnitude of the dimensionless eddy size at a point correlates the chaotic nature of turbulent flow with a predictable loss of output power.…”

“…The line-width of a dye laser is a strong function of wavelength fluctuations of the dye laser produced during the interaction of the pump beam with the flowing dye solution [9][10][11]. The wavelength fluctuation has been discussed in [12].…”