New stable tunable solid-state dye laser in the red

A red perylene derivative was impregnated into a composite silica-gel glass, and characterized as a dye laser material. The absorption spectrum in the range 480 - 600 nm belongs to the S ₀ - S₁ electronic transition, with a structure reflecting the perylene skeletal vibrations, of typical energy 1100 - 1200 cm^-1. An additional peak between 400 and 460 nm belongs to the S₀ - S₂ transition. The fluorescence exhibits a mirror image relative to the S₀ - S₁ absorption, with a Stokes shift of about 40 nm for the 0 - 0 transition. Laser tunability was obtained in the range 605 - 630 nm using a frequency-doubled Nd:YAG laser for pumping (λ = 532 nm). This wavelength range is important for medical applications, such as photodynamic therapy of some cancer tumors. Maximum laser efficiency of approximately 2.5% was obtained at 617 nm. Maximum output was approximately 0.36 mJ/pulse at a repetition rate of 10 Hz. Minimum laser threshold obtained was 0.45 mJ/pulse. The medium losses are attributed to an excited-state singlet-singlet absorption, with an upper limit cross-section of approximately 2.5 × 10^-16 cm². The laser output was stable over more than approximately 500,000 pulses, under excitation with the green line of a copper vapor laser (510 nm), of energy density approximately 40 mJ/cm² per pulse. Good prospects exist for a considerable enhancement in laser output efficiency.