G Sridhar

A computational model for transient temperature rise in a dye laser gain medium pumped by a copper vapor laser

Spectrally stable dye lasers play an important role in techniques based on high resolution spectroscopy and atomic spectroscopy. The spectral purity of a dye laser is affected when the pump power to it is increased beyond the threshold. When the pump power is increased beyond the threshold, two mode oscillations occur which decrease the spectral purity of the dye laser. The effect of higher pump pulse energies on transient thermal effects has been studied using a computational fluid dynamics (CFD) model and the disturbances to the laser cavity have been studied using commercially available ray tracing software. The change in the cavity length was determined from the CFD model for several dye concentrations and pump powers. The results of the CFD model have been verified by published results and experimental results from our system. Our study shows that in the longitudinally pumped single mode laser change in the cavity length is a more dominant disturbance than thermal blooming. Our model is useful for the design of the dye cell.

A study of the solvent temperature effects in a single longitudinal mode pulsed dye laser

The effect of the dye solution temperature in a single longitudinal mode pulsed dye laser pumped by a copper vapor laser was studied in detail. The study was carried out using a laser wavelength meter. It was experimentally observed that the wavelength tuning of the single mode dye laser with respect to the optical path length was limited to a grating pass band of 2.5 GHz beyond which a second mode appeared, a mode hop occurred and the laser wavelength settled at a new value. We observed cyclic behavior of single to two mode oscillation when the cavity length was changed continuously in one direction. The wavelength jitter band was observed to be ~2.5 pm for two mode oscillation while it was ~0.5 pm for single mode oscillation. By stabilizing the dye solution temperature to a set value of 20 ± 0.15 °C the cyclic behavior was eliminated and only a small drift of 1.4 pm was obtained over more than 30 min of operation. The wavelength change was attributed to variation of the optical path length due to variation of the refractive index with temperature. The cyclic behavior of single mode to two modes was established by applying voltage to the end mirror PZT, which changed the cavity length with a resolution of 8.5 MHz nm−1.

Ultra-Bright Rhodamines with Sulfobutylether-β-Cyclodextrin: A Viable Supramolecular Dye Laser in Aqueous Medium

Although aqueous dye lasers are much sought after, they have been of no practical use, as laser dyes show a strong tendency for aggregation in water, thus diminishing their optical output. Contributing towards this shortcoming, we studied the noncovalent interactions of two prominent laser dyes, namely, rhodamine 6G and rhodamine B, with a water soluble macrocyclic host, sulfobutylether-β-cyclodextrin (SBE7 βCD). Spectral changes in the absorption and fluorescence behavior of dyes in presence of the SBE7 βCD host indicated adequate complex formation between dye and host (K∼104  M-1 ). A combination of various photophysical parameters evaluated from measurements such as Job plot, changes in the fluorescence lifetime/anisotropy values, and favorable thermodynamic parameters from isothermal titration calorimetric measurements adjudicated a 1 : 1 stoichiometric complex formation between dye and SBE7 βCD host. Consequently, SBE7 βCD prevents dye aggregation/adsorption and present rhodamine dyes in their monomeric forms with enhanced fluorescence yield and brightness. These vital parameters were utilized to optimize and demonstrate cost-effective supramolecular broad-band and narrow-band aqueous dye laser systems with improved lasing efficiencies (∼25 % higher for the SBE7 βCD : RhB system and ∼10 % higher for SBE7 βCD : Rh6G system), better beam profile, and enhanced durability compared to the respective dyes in optically matched ethanol solutions.