The N2-laser pumped distributed feedback dye laser is a new type of picosecond light source. A rate equation model describing the ultrashort pulse formation is presented. The temporal behavior of the distributed feedback dye laser predicted by the model has been compared with experimental results obtained with a streak camera system. The observed good agreement allows application of the theoretical model for the engineering of an inexpensive picosecond laser

Ultrashort pulse generation by distributed feedback dye lasers. I

The design and operation characteristics of a low-Q cavity dye laser chain pumped by a single laser (seeded Nd:YAG) for generating high-power tunable subpicosecond pulses are presented. Two low-Q short dye cavities in cascade pumped well above threshold followed by extracavity pulse shaping in a highly saturated absorber and amplifiers lead to stable generation of single 500-fs pulses, i.e., a pulse-shortening factor > 104 (from a smooth 6-ns pump pulse). Output pulse energies of 500 μJ (1-GW peak power) are produced from 40-mJ pump energy and used to generate high-power tunable subpicosecond pulses from 450 to 700 nm by supercontinuum generation, spectral selection, and amplification in dye amplifiers pumped by the same Nd:YAG laser. The spectral and time processes involved in these pulse-shortening methods are discussed with a rate-equation model.

Generation of tunable subpicosecond pulses using low-Q dye cavities.

Injection control of a tunable Ti:sapphire laser using a narrow-bandwidth pulsed dye laser operating at a wavelength removed from the peak of the Ti:sapphire-laser gain curve is reported. The free-running Ti:sapphire laser had broadband laser emission from 750 to 790 nm. Injection at 727 nm resulted in essentially complete energy extraction at that wavelength in a 2.5-pm bandwidth matching the injection source.

Pulsed injection control of a titanium-doped sapphire laser.

The nanosecond pulses of a dye laser oscillator based on the excited-state intramolecular proton-transfer reaction (IPT) of salicylamide and 2′-hydroxylphenyl benzimidazole dyes have been studied as a function of several experimental parameters. To explain the operation of this laser a numerical four-level kinetic model was developed until the lasing properties of these dyes, in the presence of a variable oxygen concentration and pumped with a double pulse technique, could be reproduced. This was possible only by assuming that the efficiency of the laser is controlled by the absorption cross-section of a transient state with a lifetime in the nanosecond-picosecond range, which was tentatively identified as a ground state tautomeric species.

Experimental test of a four-level kinetic model for excited-state intramolecular proton transfer dye lasers

Molecules undergoing excited-state intramolecular proton transfer often show transient absorption after pulsed optical excitation, due to the tautomeric form in the singlet ground state. This absorption may be used to suppress, after a short time, the laser action of dyes emitting in the transient absorption band. The method is designed for high photochemical stability. Lasing from PBBO, pumped 10 times above threshold by an excimer pumped PTP dye laser, was suppressed after 3.3ns by the addition of 2-(2′-hydroxyphenyl)-benzoxazole, which absorbed 30% of the pump energy. At higher concentrations, intense and stable 80ps PBBO laser pulses were obtained. The pulse evolution is simulated by model calculations. A hypothetical super-dye, consisting of chemically linked laser- and absorber-moities, is also discussed. Here Forster energy transfer should result in particularly efficient laser pulse shortening.

Dye-laser pulse shortening by transient absorption following excited-state intramolecular proton transfer

The model of a homogeneously broadened laser with pulsed excitation is considered. We compute solutions of coupled non-linear differential rate equations describing the spectral properties of the emission as a function of time. It is shown that the use of appropriately space averaged quantities allows one to take into account gain saturation effects. Injected, Fabry-Perot etalon tuned and broad-band oscillator emissions are studied. Spectro-temporal evolution of the laser emission which occurs in all cases is the main result of the computations and fully supports, as expected, the previously derived analytical equations. In addition it is shown that the basic phenomenon of spectral evolution implies the existence of an "ultimate wavelength" of the emission. How to predict the optimum and limits of injection locking is discussed in terms of a "delocking time."

Y. Meyer

Papers

Spectral properties of pulsed dye lasers