W. Rudolph

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.

Multilayer dielectric mirrors generated chirp in femtosecond dye-ringlasers

Abstract The phase modulation arising from multilayer dielectric laser mirrors of a fs-dye-ringlaser has been calculated and measured by the determination of an equivalent intracavity path length in glass. The main source for phase modulation in our laser system seems to be the saturable absorber.

Influence of transient absorber gratings on the pulse parameters of passively mode‐locked cw dye ring lasers

A theoretical explanation of the experimental results obtained by the method of colliding pulse mode locking (CPM) is given. It is shown that, compared to other passive methods, the coherent interaction of the counter‐running pulses in the thin absorber yields considerably shorter pulses with a more favorable stability region. Deviations from an amplifier position being symmetric with respect to the amplification of the counter‐running pulses lead to different energies of the pulses and to a strong decrease of the stability range of the CPM.

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.

Combined self-phase modulation and amplification of femtosecond light pulses

The influence of depletable amplification, group velocity dispersion and self-phase modulation due to Kerr-type nonlinearity on pulse shaping in femtosecond pulse amplification has been calculated. With gain depletion which is typical for the last stage of multi-stage amplifiers, spectral broadening occurs which, under certain conditions, can be utilized for pulse compression. This spectral broadening as well as a predicted spectral shift is compared with experimental results.

Femtosecond solitary waves in the presence of resonant absorption

Abstract The McCall and Hahn solution of the self-induced transparency is examined in the presence of host dispersion and nonlinearity. The first-order correction to the slowly varying envelope approximation as well as the third order dispersion contribute to a chirped steady pulse.

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.

Formation of frequency chirp in ultrashort light pulses passing through saturable absorbers

Abstract The distortion of modulus and phase of the slowly varying envelope of ultrashort laser pulses in passing through absorbing samples has been calculated. With off-resonance excitation phase modulation, and in particular a frequency chirp arise, which originate from phase memory and saturation of the absorber.

Pulses from an Ar+-laser in the colliding pulse mode locking regime

Abstract The pulse emission from an Ar + -laser passively mode locked by the dye Rh 6G is investigated. Autocorrelation and cross correlation measurements show that a two pulse regime where the pulses interact coherently in the absorber is most favourable with respect to small pulse widths and stability.