N. Stelmakh

Highly attenuating external cavity for picosecond-tunable pulse generation from gain/Q-switched laser diodes

The authors analyze in detail the behavior of gain/Q-switched Fabry-Perot laser diodes coupled to a highly attenuating, selective external cavity. Radical differences are shown as compared to the case of strong external feedback used in mode locking. A strong analogy with the case of pulsed lasers with a small quasi-monochromatic injection signal is indicated. Strong chirping is observed in single-mode emission, leading to tunable picosecond pulses after compression. Experiments are carried out on two types of devices. Picosecond pulses with very high tunability (40 nm) and repetition rates (>10 GHz) are obtained from 1.3- mu m gain-switched laser diodes, the minimum pulsewidth being 2.5 ps. >

Nonlinear chirp compensation in high-power broad-spectrum pulses from single-stripe mode-locked laser diodes

We report on the generation of ultra-short high-energy pulses from extended-cavity mode-locked laser diodes by using single-stripe AlGaAs laser devices of long cavity length (1 and 2 mm). The pulse energy is shown to increase with the laser diode length while the spectral width of emitted pulses is decreased in the same time. Record pulse energies of /spl ap/50 pJ are obtained from 2 mm long lasers and super-broad mode-locked spectra of /spl ap/20 mm are achieved with 1 mm long lasers. Strongly nonlinear chirps are always observed in the case of mode-locked pulses whose spectral width exceeds 10 mm. After quadratic chirp compensation, 160 fs pulses are obtained with peak power larger than 100 W. These performances are believed to be the best ever reported for mode-locked single-stripe laser diodes without external amplification. >

Phase-amplitude coupling factor of single-mode gain-switched InGaAsP laser diodes

The phase amplitude coupling factor ( alpha -factor) of gain-switched InGaAsP laser diodes is deduced from chirp measurements. A tunable laser scheme makes it possible to obtain the wavelength dependence of alpha over approximately 40 nm. The alpha -values are found to be higher than those deduced from spontaneous emission spectra below threshold. It is shown that the difference is explained by the dependence of alpha with carrier density. Time-resolved measurements of spontaneous emission during pulse buildup reveal that the carrier density at maximum can be 1.5 times higher than the threshold carrier density. Experimental evolutions of alpha are well reproduced by calculations.<<ETX>>

Measurement of pulse build-up in passively mode-locked laser diodes

We present a detailed analysis of mode-locking process in a passively mode locked AlGaAs laser emitting pulses as short as /spl tilde/450 fs. Measurements of pulse build-up time, laser gain modulation, pulse duration and group velocity dispersion are reported.

Gain-switched laser diode seeded diode-pumped regenerative amplifier for microjoule picosecond tunable UV pulses

Summary form only given. Injection seeding of ultrashort semiconductor lasers into solid-state amplifiers is a simple way to reduce the size of femtosecond or picosecond high-energy laser systems. We present for the first time a very compact system combining a picosecond laser diode with a diode pumped regenerative amplifier capable of generating tunable microjoule UV pulses by frequency conversion. The system used an indirectly diode-pumped Ti:sapphire laser amplifier.

Trains of 250 fs pulses at sub-intrinsic-cavity roundtrip intervals from chirped mode-locked laser diodes

To our knowledge, fine periodical evolutions of the pulse structure with the length of the external cavity have never been reported in short-pulse mode-locked extended-cavity laser diodes. In this communication, we demonstrate a strong inter-dependence between the external and intrinsic cavity lengths in these mode-locked laser systems when an external chirp compensation is used. We found that the length of the external cavity (l/sub e/) must be equal to a multiple of the intrinsic laser diode cavity length (l/sub i/) to produce standard pulse structures with one sub-pulse per intrinsic cavity roundtrip time. Similarly, the external cavity length must be equal to (m+1/n)*l/sub i/, with m being an integer, to obtain n sub-pulses per intrinsic cavity roundtrip time. In our experiments, we observed pronounced pulse structures for n up to 8. This latter value corresponds to the generation of /spl sim/250 fs pulse trains with a pulse repetition rate of /spl sim/300 GHz and a total energy /spl sim/20-30 pJ.

Nonlinear chirp compensation in high-power (>100 W) broad spectrum (/spl sim/20 nm) pulses from mode-locked AlGaAs lasers

In this paper, we show that very broad pulse spectra (20 nm) can be effectively obtained by active/hybrid mode-locking of long-stripe (1 mm) high-power AlGaAs laser diodes, the spectral widths corresponding in principle to sub-100 fs pulses in the transform-limit situation. A novel technique is presented in order to analyze chirp non-linearities (i.e, high-order dispersion effects) in the laser pulses. Second- and third-order dispersion compensation is realized with an external compressor, leading to 160 fs pulses after compression with peak powers in excess of 100 W.

Facteur de couplage phase-amplitude des diodes lasers avec absorbant saturable

RésuméLe facteur de couplage phase-amplitude (facteur α) est ľun des paramètres fondamentaux des lasers à semiconducteurs. Les auteurs montrent qu’il est possible ďévaluer ce facteur par des mesures de spectroscopic résolue en temps en régime impulsionnel. Des expériences sont menées sur des lasers GaAs rendus monomode par injection et dont le ruban actif inclut des sections ďabsorption saturable réalisées par implantation ionique. Les auteurs montrent que la dérive de fréquence mesurée en cours ďimpulsion est proportionnelle à ľénergie ďimpulsion et qu’aux plus grandes énergies sa valeur représente près de quatre intermodes de cavité laser. De façon correspondante, les valeurs trouvées pour α peuvent être cinq fois plus grandes que celles rapportées jusqu’ à présent dans la littérature. Ces valeurs élevées sont confirmées par des expériences de compression ďimpulsion. Plusieurs mécanismes pour interpréter ces nouveaux résultats sont proposés.AbstractThe phase-amplitude coupling factor (α-factor) is one of the fundamental parameters of semiconductor lasers. We show that this factor can be evaluated by time-resolved spectroscopic measurements in pulsed regime. Experiments are carried out with injectionseeded single-mode GaAs lasers whose active stripe includes regions of saturable absorption made by ion implantation. We show that the measured pulse downchirp is proportional to pulse energy. The downchirp amplitude is found to approach four laser cavity intermode spacings at the highest energies. Correspondingly, the ±-values can be five times higher than those reported to date in litterature. High a-values are confirmed in pulse compression experiments. Several mechanisms are proposed to interprete these new results.