Terahertz (THz) radiation is generated efficiently from a bulk InAs mirror with a shallow incidence angle inside the cavity of a femtosecond, mode-locked Ti:sapphire laser self-started by a strained saturable Bragg reflector. A magnetic field is also applied to the InAs mirror to enhance THz radiation.

We demonstrate a new configuration for intracavity generation of THz radiation. A magnetic-field-biased saturable Bragg reflector (SBR) located inside the femtosecond laser cavity is the emitter, while a strained saturable Bragg reflector (SSBR) achieves self-started mode-locking without focusing. The calibrated power of the emitted THz radiation is estimated to be approximately 45 nW with a peak frequency at 0.72 THz and width of approximately 0.7 THz under a 0.88 T magnetic field. The quadratic dependence of THz-radiation power by the SBR on the magnetic field is also observed for the first time.

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A strained saturable Bragg reflector (SSBR) for passive mode-locking of Ti:sapphire lasers was investigated by the frequency resolved optical gating (FROG) technique. Incident pulses of several wavelengths and with zero, positive, or negative chirp were employed. A considerable pulse shortening near the excitonic resonance of the strained quantum well was observed and attributed to anomalous dispersion due to resonance absorption. On the long wavelength side of exciton resonance, however, the chirp of the reflected pulse showed a weak wavelength dependence attributed to the material dispersion of SSBR in pulse broadening was obtained.