A. Dienes

Astigmatically compensated cavities for CW dye lasers

An analysis is given of folded 3-mirror laser resonators with an internal cell set at Brewsters angle. A method is described to compensate the astigmatic distortions introduced by both the internal mirror and the cell. This compensation is achieved for a specific relation between cell thickness and folding angle. It allows the formation of a tight intracavity focus as required in applications such as CW dye lasers. A discussion is given of the mode characteristics of compensated cavities and of the limitation on beam concentration set by the thickness of the Brewster cell.

Passive mode locking of the cw dye laser

Passive mode locking of a cw Rhodamine 6G laser is reported. A stable continuous output of picosecond pulses has been achieved. Correlation measurements using second‐harmonic generation (SHG) have determined the pulses to be as short as 1.5 psec. The pulses are transform limited and are wavelength tunable over the range 5900–6100 A.

SINGLE PASS GAIN OF EXCIPLEX 4‐MU AND RHODAMINE 6G DYE LASER AMPLIFIERS

Single pass gain has been measured in N2 laser pumped exciplex 4‐Methylumbelliferone (4‐MU) and rhodamine 6G dye lasers using a technique developed by Silfvast and Deech for high‐gain pulsed metal vapor lasers. The gain is measured by comparing the intensities of amplified spontaneous emission in single and double cell lengths with the maximum unsaturated single‐pass gain being limited by the saturation of the spontaneous emission. Maximum unsaturated gains on the order of 20 dB/cm were measured for both dyes. The gain was found to vary linearly with pump power. The technique was also used to measure the variation of gain with wavelength for a given pump power. The maximum gain for exciplex 4‐MU occurred at the fluorescence peak, whereas for rhodamine 6G it was shifted to a longer wavelength due to ground‐state reabsorption. By fitting the measured gain versus wavelength to the theory, it was possible to deduce the fractional excited singlet population in the rhodamine 6G solution.

NEAR uv TO YELLOW TUNABLE LASER EMISSION FROM AN ORGANIC DYE

Tunable laser emission from 3850 to 5740 A has been observed from three solvate forms of 4‐Methylumbelliferone. The three distinct lasing forms basic, neutral, and acid, with tuning ranges of 1070, 720, and 1150 A, respectively, were obtained by adjusting the solvent pH. A tuning range of 1760 A (from 3910 to 5670 A) has been obtained in a critically adjusted, slightly acidic solution. The various chemical structures responsible for the broad tuning have been identified. Evidence that the acid form lases from an exciplex (excited complex) state is presented.

Rapid photobleaching of organic laser dyes in continuously operated devices

Rapid bleaching of Rhodamine 6G and several other dyes has been observed in capillary-guide liquid lasers longitudinally pumped at \lambda = 5145 A. This bleaching appears to be permanent and is shown to present a severe limitation to the operation of nonflowing continuously excited dye lasers. The rate of bleaching has been measured under a variety of conditions and is found to vary linearly with pump power, independent of geometry.

A Mode‐Locked cw Dye Laser

The operation of a mode‐locked cw dye laser is described. A stable output of repetitive 55‐psec pulses has been obtained with an acousto‐optic loss modulator in the dye‐laser cavity. Pulse widths have been determined by autocorrelation measurements using second harmonic generation in ADP.

EVIDENCE FOR EXCIPLEX LASER ACTION IN COUMARIN DYES BY MEASUREMENTS OF STIMULATED FLUORESCENCE

Experiments have been performed that measure the time dependence of stimulated fluorescence from acidified solutions of 4‐methylumbelliferone and 7‐hydroxycoumarin. The results show that laser action takes place from excited state complexes. It was found that exciplex emission is delayed after the neutral molecule emission. The delay gives a measure of the exciplex formation time. The measured dependence of exciplex formation time on hydrogen ion concentration, temperature, and pumping power was found to agree qualitatively with a simple model. Evidence for multiple exciplex formation is also presented.

High-efficiency tunable CW dye laser

An output power of 1 W is reported from a tunable CW dye laser pumped by 3.5 W of argon laser radiation. The nearly 30 percent conversion efficiency is achieved by using a very low-loss folded 3-mirror cavity and by pumping through a Brewster-angle dispersing prism.

An intracavity-pumped CW dye laser

Abstract A new type of cw dye laser in which the dye cell is placed inside an argon laser cavity is described. Both the dye and the argon laser pumping radiation oscillate inside the same optical cavity. The organic dye used was rhodamine 6-G with either water or methanol as solvent, and the pumping radiation was the standing wave of the 4880 A line in the argon laser. This cw dye laser design has the features of automatically aligning the dye laser to the pumping radiation as well as reducing thermal problems. Output powers as high as 35 mW have been obtained with 750 mW pumping power.

HOLOGRAM WAVELENGTH SELECTOR FOR DYE LASERS

A new type of wavelength selector for dye lasers is proposed. It consists of a holographically produced dielectric grating which is backed by a reflecting layer. Gratings of 2300, 3300, and 3700 lines/mm were recorded in dichromated gelatine and tested in an exciplex umbelliferone laser tuning from 3910 to 5670 A.