Wayne S. Pelouch

Ti:sapphire-pumped high repetition rate femtosecond optical parametric oscillator

A broadly tunable femtosecond optical parametric oscillator (OPO) based on KTiOPO(4) that is externally pumped by a self-mode-locked Ti:sapphire laser is described. Continuous tuning is demonstrated from 1.22 to 1.37 microm in the signal branch and from 1.82 to 2.15 microm in the idler branch by using one set of OPO optics. The potential tuning range of the OPO is from 1.0 to 2.75 microm and requires three sets of mirrors and two crystals. Without prisms in the OPO cavity, 340 mW (475 mW) of chirped-pulse power is generated in the signal (idler) branch for 2.5 W of pump power. The total conversion efficiency as measured by the pump depletion is 55%. With prisms in the cavity, pulses of 135 fs are generated, which can be shortened to 75 fs by increasing the output coupling.

Recent advances of the Ti:sapphire-pumped high-repetition-rate femtosecond optical parametric oscillator

The details concerning the resonator configuration, crystal parameters, and operating characteristics of high-repetition-rate and high-average-power broadly tunable femtosecond optical parametric oscillators are reviewed and discussed in some detail. We also report new results on an intracavity-doubled optical parametric oscillator with tunability from 580 to 657 nm in the visible and the first, to our knowledge, high-repetition-rate femtosecond optical parametric oscillator with the new nonlinear-optical crystal In:KTiOAsO4, which can potentially tune to 5.3 μm.

Self-starting mode-locked ring-cavity Ti:sapphire laser

A self-mode-locked ring-cavity Ti:sapphire laser is described that is self-starting within milliseconds and completely unperturbed by the self-starting mechanism while mode locked. This technique makes use of a position-modulated mirror in an external cavity in which the cavity length and alignment are noncritical. Other benefits of the ring cavity over the linear cavity configuration are described.

Femtosecond optical parametric oscillators

The recent development of femtosecond optical parametric oscillators has extended the wavelength range over which ultrafast lasers are available (visible to 3.5 micrometers has been demonstrated). The options in cavity configurations, phase matching, and nonlinear optical crystals used with a Ti:sapphire pump laser are discussed. Results of an OPO using the nonlinear crystal KTiOAs4, which is potentially tunable to 5 micrometers , are presented.

Investigation of hot-carrier relaxation in quantum well and bulk GaAs at high carrier densities

An investigation of the hot carrier relaxation in GaAs/(AlGa)As quantum wells and bulk GaAs in the high carrier density limit is presented. Using a time-resolved luminescence up-conversion technique with <or=80 fs temporal resolution, carrier temperatures are measured in the 100 fs to 2 ns range. The results show that hot carrier cooling in quantum wells becomes significantly slower than in the bulk for carrier densities greater than 2*1018 cm-3.

Hot-carrier relaxation in quantum well and bulk GaAs at high carrier densities: femtoseconds to nanoseconds

An investigation of hot carrier relaxation in GaAs/AlxGa1-xAs multiple quantum wells and bulk GaAs in the high carrier density limit is presented. Two techniques have been employed: luminescence upconversion with < 80 fs temporal resolution has been used to cover the range from 100 fs to 100 ps, and time-correlated single-photon counting to cover the range from 100 ps to 2 ns. Electron temperatures as a function of time were determined from the slope of the high energy tail of the time-resolved photoluminescence spectra. Our results show that hot electron cooling rates in the quantum wells begin to become significantly slower than that in the bulk when the photogenerated carrier density is above a critical value of approximately 2 X 1018 cm-3; the difference in cooling rates increases rapidly with increasing carrier density. The time constant characterizing the power loss of hot carriers is also determined and discussed. A comparison is made with previous publications to resolve the confusion concerning the difference in cooling rates between quasi-2D and 3D systems.

Extending the frequency range of femtosecond lasers

The development of a Ti:sapphire-based femtosecond system capable of producing high repetition rate and high power output that is tunable from the near-ultraviolet to the mid- infrared is reported. This is achieved using the nonlinear optical processes of optical parametric oscillation and second-harmonic generation that results in sub-100 fs pulses and hundreds of mW of power across the full tuning range.