Versatile OSCAT time-domain THz spectrometer.

We report on a compact and versatile time-domain spectrometer operating in the THz spectral region from 0.2 to 2.5 THz based on ultrafast Yb:CALGO laser and photo-conductive antennas. The spectrometer operates with the optical sampling by cavity tuning (OSCAT) method based on laser repetition rate tuning, which allows at the same time the implementation of a delay-time modulation scheme. The whole characterization of the instrument is presented and compared to the classical THz time-domain spectroscopy implementation. THz spectroscopic measurements on a 520-µm thick GaAs wafer substrate together with water vapor absorption measurements are also reported to further validate the instrument capabilities.

Femtosecond Mamyshev fiber oscillator started by a passively Q-switched microchip laser.

A femtosecond Mamyshev fiber oscillator in normal dispersion mode at 1 µm was started reliably and safely by an inexpensive diode-pumped passively Q-switched monolithic microchip laser emitting 300-ps pulses. Four-wave mixing spectral broadening is shown to play a pivotal role in starting the Mamyshev oscillator, owing to the random short and intense temporal fluctuations allowed by its ∼10-nm bandwidth. Systematic studies of the starting dynamics show that a success rate of 100% of the attempts is achieved with modest seed energy, as low as ∼30 nJ from the sub-nanosecond laser, corresponding to ∼100 pJ for the total four-wave mixing signal required to start the oscillation.

Low-noise Yb:CALGO optical frequency comb.

We report on a compact optical frequency comb, operating in the wavelength range from 670 to 1500 nm, based on diode-pumped low-noise femtosecond Yb:CALGO amplified laser system. Both the carrier-envelope offset and repetition rate are phase-locked to reference synthesizers. A full characterization of the frequency comb, in terms of frequency stability, phase noise analysis, and optical beating against a single-frequency non-planar ring oscillator Nd:YAG laser, is presented, showing the excellent properties of the Yb:CALGO comb.

Multi-watt amplification in a birefringent Yb:LiLuF4 single crystal fiber grown by micro-pulling-down.

We present, to the best of our knowledge, the first demonstration of a single crystal fiber solid-state amplifier based on a birefringent Yb3+-doped thin crystal grown by the micro-pulling-down method. We measured a small signal gain >30 in a four-passes Yb:LiLuF4 amplifier pumping with a 120-W maximum power fiber-coupled laser diode. At an absorbed pump power of 80 W, a maximum output power of 8.4 W was obtained seeding the 42-mm-long, 2%Yb3+-doped single crystal fiber sample with 0.8 W at 1021 nm. Even at the maximum incident pump power, the amplified laser beam polarization and spatial quality were excellent (M2=1.15×1.06).

Laser investigation of Yb:YLF crystals fabricated with the micro-pulling-down technique.

Fiber rods of 10% doped Yb:YLF were fabricated with the micro-pulling-down technique and characterized. The crystal a axis was oriented along the rod length, allowing polarized emission with the largest cross section available in the c direction. Laser experiments showed that these fiber samples perform similarly to crystals grown by the standard Czochralski method. Intrinsic slope efficiency of ∼50% was measured in both cases, with small comparable intracavity losses, proving the good quality of the fiber material.

High-brightness 2.4-W continuous-wave Nd:GdVO4 laser at 670 nm.

We report on a diode-pumped 1.3-microm Nd:GdVO4 cw laser, intracavity doubled for highly efficient generation of red light. We obtained as much as 2.4 W of power at 670 nm (corresponding to 26% optical-to-optical efficiency) in a nearly TEM00 mode and with small amplitude noise. To the best of our knowledge, these results represent the highest performance at this wavelength for cw solid-state lasers.