Pulses having durations as short as 60 fsec have been directly generated by a self-mode-locked, dispersion-compensated Ti:sapphire laser. By using an extracavity fiber-prism pulse compressor, pulse durations as short as 45 fsec have been obtained.

60-fsec pulse generation from a self-mode-locked Ti:sapphire laser.

The evolution of the theory of mode-locking over the last three and a half decades is reviewed and some of the salient experiments are discussed in the context of the theory. The paper ends with two-cycle pulses of a mode-locked Ti:sapphire laser.

Mode-locking of lasers

The theory of additive pulse mode locking (APM) is developed in closed form under a linearization approximation. The pulse parameters are determined in terms of the gain, the gain dispersion, the group-velocity dispersion, and the self-phase modulation. Stability regimes are established. Various possible configurations of laser systems that can produce APM are presented. Some of them permit single-cavity realizations that may not require interferometric length stabilization circuits. In general, the results are applicable to a wide range of fast saturable absorber mode-locked systems.

Structures for additive pulse mode locking

A theory of noise in mode-locked lasers is developed that applies to additive pulse mode-locked and Kerr lens mode-locked systems. Equations of motion are derived for pulse energy, carrier linewidth, frequency pulling, and timing jitter. The effect of gain fluctuations, mirror vibrations, and index fluctuations are determined. Measurements that can determine all four fluctuation spectra are described. Experimental data in the literature are compared with theory. >

Noise of mode-locked lasers

Over the past 2 decades there has been tremendous advancements in the field of ultrafast carrier dynamics in semiconductors. The driving force behind this movement other than the basic fundamental interest is the direct application of semiconductor devices and the endless need for faster response and faster processing of information. To improve and develop microelectronics devices and address these needs, there must be a basic understanding of the various dynamical processes in the semiconductors which have to be studied in detail. Therefore, the excitation of semiconductors out of their equilibrium and the subsequent relaxation processes with various rates has become a key area of semiconductor research. With the development of lasers that can generate pulses as short as a few femtoseconds the excitation and subsequent probing of semiconductors on an ultrashort timescale have become routine. Processes such as carrier momentum randomization, carrier thermalization, and energy relaxation have been studied in detail using excite-and-probe novel techniques. This article reviews the status of ultrafast carrier and phonon dynamics in semiconductors. Experimental techniques such as excite-and-probe transmission, time-resolved up-conversion luminescence, and pump-probe Raman scattering along with some of the significant experimental findings from probing semiconductors are discussed. Finally, a selfconsistent theoretical model, which correlates the carrier and phonon dynamics in germanium on an ultrashort time scale, is described in detail.

Probing ultrafast carrier and phonon dynamics in semiconductors

Ultrashort pulses are generated in a Ti:Al2O3 laser by using a coupled nonlinear external cavity. The external cavity uses self-phase modulation in an optical fiber to achieve passive mode locking without the need for synchronous pumping or acousto-optic modulation. A stable train of chirped 1.4-psec pulses is generated. After dispersive compensation, pulses as short as 200 fsec are obtained.

Femtosecond passively mode-locked Ti:Al(2)O(3) laser with a nonlinear external cavity.

A diode-pumped Nd:YAG laser is demonstrated by using self-starting additive-pulse mode locking with a nonlinear external cavity. Pulse durations of 1.7 psec are generated at an average output power of 25 mW without the need for active amplitude or phase modulation. Design and scaling issues for this technology are discussed.

Self-starting additive-pulse mode-locked diode-pumped Nd:YAG laser.

The starting dynamics of the additive-pulse mode-locked Ti:Al2O3 laser are investigated. Mode locking develops from mode beating with pulse formation times of several hundred microseconds. A simple model based on additive-pulse mode-locking theory is developed that describes self-starting and pulse evolution.

Starting dynamics of additive-pulse mode locking in the Ti:Al 2 O 3 laser

Additive pulse modelocking provides a powerful technique for passive modelocking a wide variety of solid state lasers. The additive pulse modelocking technique uses a laser coupled with a nonlinear external cavity to produce modelocking by a fast saturable absorber like mechanism without the need for active modulation. Ultrashort pulse generation is demonstrated in Ti:Al2O3, diode pumped Nd:YAG and Nd:YLF.

Ultrashort Pulse Generation with Additive Pulse Modelocking in Solid State Lasers: Ti:Al2O3, Diode Pumped Nd:YAG and Nd:YLF

A novel electric-field correlation technique is presented. By the incorporation of a dispersion-compensating element into the autocorrelator, it is possible to determine both the pulse amplitude and the amount of phase chirp for well-behaved pulses. The technique requires no nonlinear processes or spectral analysis.

J. Goodberlet

Papers

Femtosecond passively mode-locked Ti:Al(2)O(3) laser with a nonlinear external cavity.

Self-starting additive-pulse mode-locked diode-pumped Nd:YAG laser.

Starting dynamics of additive-pulse mode locking in the Ti:Al 2 O 3 laser

Ultrashort Pulse Generation with Additive Pulse Modelocking in Solid State Lasers: Ti:Al2O3, Diode Pumped Nd:YAG and Nd:YLF

ChirP-compensated autocorrelation of optical pulses.