Wave Dye Lasers

In all these configurations the active zone consists of the dye solution streaming in a laminar flow of about 0.5 t1 mm thickness in a free jet which is formed through a carefully designed polished nozzle. 

At flow velocities of 10 m/s the time of flight for the dye molecules through the focus of the pump laser (about 10/xm) is about 10 s. During this short period the intersystem crossing rate cannot build up a large triplet concentration, and the triplet losses are therefore small. 

For free-running dye jets the viscosity of the liquid solvent must be sufficiently large to ensure the laminar flow necessary for a high optical quality of the gain zone. Most jet-stream dye lasers use ethylene glycol or propylene glycol as solvents. Since these alcohols decrease the quantum efficiency of several dyes and also do not have optimum thermal properties, the use of water-based dye solutions with viscosity-raising additives can improve the power efficiency and frequency stability of jet stream CW dye lasers [5.179]. Output powers of more than 30 W have been reported for CW dye lasers [5.180]. 

The threshold pump power depends on the size of the pump focus and on the resonator losses, and varies between 1 mW and several Watts. The size of the pump focus should be adapted to the beam waist in the dye-laser resonator (mode matching). If it is too small, less dye molecules are pumped and the maximum output power is smaller. If it is too large, the inversion for transverse modes exceeds threshold and the dye laser oscillates on several transverse modes. Under optimum conditions pump efficiencies (dye-laser output/pump-power input) up to r = 35% have been achieved, yielding dye output powers of 2 W for only 8 W pump power. 

Coarse wavelength tuning can be accomplished with a birefringent filter (Lyot filter, see Sect.4.8) that consists of three birefringent plates with thicknesses d, q d, Q2d (q, q2 being integers), placed under the Brewster angle inside the dye laser resonator (Fig. 5.93). Contrary to the Lyot filter discussed in Sect.4.8, no polarizers are necessary here because the many Brewster faces inside the resonator already define the direction of the polarization vector which lies in the plane of Fig.5.93. 

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T. Elsasser, M.C. Nuss, Femtosecond pulses in the mid-infrared generated by downconver-sion of a travelling-wave dye laser. Opt. Lett. 16, 411 (1991)... 

Continuous-wave dye lasers have also been the basis in experimental investigations for the cure of cancer (Fig. 21). In this work, termed photodynamic therapy, the patient with a tumor is first injected with a drug (hermato-... 

M. Pinard, M. Leduc, G. Trenec, C.G. Aminoff, F Laloc Efficient single mode operation of a standing wave dye laser. Appl. Phys. 19, 399 (1978)... 

F. P. Schafer Principles of Dye Laser Operation. -B. B. Snavely Continuous-Wave Dye Lasers. -C V. Shank, E. P. Ippen Mode-Locking of Dye Lasers. -K.H. Drexhage SiniciUTQm6 Properties of Laser Dyes. - T. W. Hansch Applications of Dye Lasers. - FP Schafer Progress in Dye Lasers September 1973 till March 1977. 

Yarborough, J. M. A cw [continuous wave] dye laser emission spanning the visible spectrum. Appl. Phys. Lett. 1974,24,629-630. 

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