The THz-radiation power from bulk InAs irradiated with femtosecond optical pulses is significantly enhanced and reaches 650 μW in a 1.7-T magnetic field with 1.5-W excitation power. The THz-radiation power is related almost quadratically both to the magnetic field and excitation laser power. We have also found that the power of the THz-radiation from an InAs sample in a magnetic field is over one order of magnitude higher than that from GaAs. Additionally, a dramatic change of ellipticity is observed, and the spectra of the horizontal and vertical polarization components are found to differ.

A 2 in. diam single crystal of lithium tetraborate (Li2B4O7) was successfully grown by the Czochralski method. The crystal was free from macrodefects and had a dislocation density as low as 100/cm2. It had an excellent homogeneity of the refractive index and a wide transparency down to 170 nm. The optical damage threshold was 40 GW/cm2. Second-harmonic generation and sum frequency generation were investigated in association with the generation of the fourth and fifth harmonics of a Q-switched Nd:YAG laser. The conversion efficiency of the second-harmonic generation from the green (532 nm) light was 20%.

We have demonstrated a new scheme for generating intense far-infrared or THz radiation pulses synchronously with near-infrared pulses using a saturable Bragg reflector placed inside a mode-locked laser cavity. With this newly proposed simple scheme, THz radiation which peaked at around 0.66 THz, with an average power of 2–3 nW is directly generated synchronously with femtosecond near-infrared optical pulses.

The THz radiation spectrum from InAs in a magnetic field irradiated with femtosecond pulses can be controlled by varying the excitation pulse width and chirp direction of the excitation pulse. A longer excitation pulse width produces lower-frequency THz radiation. Also, positively chirped pulse excitation will generate higher power and higher frequency THz radiation.