B. Wilhelmi

Pulses in the femtosecond range from a cw dye ring laser in the colliding pulse mode-locking (CPM) regime with down-chirp

Abstract Pulses in the range of 85–350 fs generated by a cw pumped, passively mode-locked dye ring laser where the counter-propagating pulses from a transient grating in the thin absorber have been found to have a down-chirp. This down-chirp corresponds to a wavelength sweep during the pulse duration of about 1 nm.

Analysis of a mode-locked ring laser: chirped-solitary-pulse solutions

We present measurements on mode-locked ring dye lasers that demonstrate the role of self-phase modulation in the saturable absorber dye. The resulting bandwidth increase plays an essential role in ultrashort pulse generation, because it leads to intracavity pulse compression in the presence of normally dispersive components. The role of various intracavity components (glass, coatings) in intracavity compression is analyzed. As opposed to extracavity compression, measurements of pulse amplitude and phase show that the nonlinear phase modulation can be completely compensated. The interaction of the light pulse with the absorber is analyzed using Maxwell–Bloch equations. Next, we find the steady-state solution for the problem of pulse propagation through an infinite periodic medium containing all the essential intracavity elements (bandwidth-limiting filter, amplifier, absorber, dispersive component). The condition that the solitary pulses be unchirped enables us to determine the optimum intracavity dispersion, which, in agreement with the experimental data, leads to the shortest pulses.

Influence of solvent viscosity on excited state lifetime and fluorescence quantum yield of dye molecules

Abstract A kinetic model of fluorescent molecules, taking into account the action of internal rotation in a viscous medium as well as of S 1 -S 0 conversion, has been treated by solving a Fokker-Planck equation. Under typical conditions the fluorescence intensity is observed to exhibit a simple exponential decay after excitation. The corresponding decay time, being influenced by the rates of internal rotation and internal conversion, is found to be proportional to η α over a rather broad range of solvent viscosity η, where α is a parameter depending on the fluorescent molecule. Results are compared with those of the Forster-Hoffmann theory and with experiments concerning dye solutions.

Time-resolved spectral hole burning

Abstract Dynamic spectral hole burning observed in femtosecond absorption experiments is explained theoretically. The time-dependent broadening of the holes is shown to be related to the finite correlation time of the dephasing of the electronic transition.

Self phase modulation in a femtosecond pulse amplifier with subsequent compression

The pulses from a colliding-pulse mode-locked dye laser (100 fs, 20 pJ) are amplified to 0.2 mJ and self phase modulated in an excimer laser pumped dye amplifier. Suitable chirp compensation leads to nearly bandwidth-limited pulses of about 50 fs duration.

Measurement of kinetic processes in photoexcited stilbene solutions

Abstract The kinetics of photophysical processes has been measured in stilbene solutions in the temperature range between −40°C and 20°C. The population of the S 1 level excited by two-photon absorption (TPA) and of secondary populated levels has been investigated using a probe beam method. It was found an energy barrier Δ E = 5 × 10 2 cm −1 of the thermically activated transition S 1 → 1′. The rate parameter of this transition is determined to be k −1 11′ , ≈ 2 ps at very high temperatures.

Photon antibunching in resonance fluorescence from impurity atoms in solids

Abstract The experimental conditions under which the intensity correlation function of resonance fluorescence of a single atom in a gas may be observed are briefly discussed. In general they can complicate the direct observation of photon antibunching. A direct observation should be possible in the case of a single impurity atom in a solid state matrix. The corresponding intensity correlation function is given.

Pump-pulse induced chirp production in semiconductors

Nonlinear absorption and refractive index changes in wide-gap semiconductors (CdS, CdSSe, and GaSe) after ps light irradiation are determined with an excite-and-probebeam spectrometer. Based on a simple model pump-pulse induced chirp parameters on a signal pulse of different wavelength are calculated. Possible applications are discussed.

Computer simulation of passive mode-locking of dye lasers with consideration of coherent light-matter interaction

A numerical model of passive mode-locking of dye lasers is presented, which allows the calculation of the steady state pulse parameters without any limitation to pulse energy and duration. The solutions are compared with previous analytical results based on a rate equation treatment (i.e. without considering the phase memory). The pulse evolution and the influence of cavity dumping on the steady state are discussed.

Chirping of femtosecond light pulses passing through a four-level absorber

Abstract The effect of the vibronic relaxation in dyes on the phase modulation of a propagating pulse is calculated. Enhanced chirping in the centre of the pulse can be achieved for suitable position of its carrier frequency with respect to the resonance frequencies of the transitions.