We report THz transmission and reflection properties of an ultrafast optically excited highly resistive silicon wafer. Amplified Ti:Sapphire femtosecond laser pulses at 800 nm were used to create fluence-dependent carrier density on the front surface of the wafer which modifies the dielectric properties at the THz frequencies. Time-resolved experiments in the optical pump-THz probe configuration were conducted in which THz pulses reflected off from the surface at 0° and 45° angles of incidence make it possible to measure the pump-fluence dependent ultrafast evolution of the reflection and transmission coefficients in 0.5-6 THz range. An analytical model, where both the Drude contributions from the photo-excited electrons and holes account for the change of the dielectric constant of the photo-excited silicon, has been used to evaluate the THz reflection and transmission coefficients at steady state. Thus obtained results match well with the experimental results and demonstrate an all-optical means to convert a silicon wafer into an ultrafast, tunable and broadband neutral density filter or reflector in the THz frequency range.

We present a gigahertz (GHz)-repetition-rate optical parametric oscillator (OPO) pumped by an electro-optic (EO) comb at 1.03 µm, delivering sub-picosecond signal pulses across 1.5-1.7 µm from a MgO-doped periodically poled LiNbO 3 crystal. Using a pump power of 5 W at 14.2 GHz repetition rate, 378 mW of signal power is obtained at 1.52 µm from a subharmonic cavity, corresponding to a signal extraction efficiency of 7.6%. By cascading a Mach-Zehnder modulator, the pump pulse repetition rate can be divided by any integer number from 1 to 14, allowing the OPO to operate with flexible repetition rate from 1 to 14.2 GHz. Besides, a strategy leading to quasi-continuous repetition rate tunability of the OPO is also discussed.

We designed an all-normal dispersion ytterbium rod-type fiber laser oscillator delivering picosecond pulses which are continuously tunable both in central wavelength and pulse duration. This system delivers self-mode-locked pulses with an average power up to 25 W. At a repetition rate of 78 MHz, it yields picosecond laser pulses, of which the central wavelength and pulse duration can be tuned between 1010 nm - 1060 nm and 4.5 ps - 1.8 ps, respectively. The tunability is obtained by adjusting the position and the width of a slit which acts as a spectral bandwidth filter, placed close to the center of a 4f-folded zero dispersion line inserted in the laser cavity. This oscillator delivers nearly Fourier limited pulses with at most a 1.2 time-bandwidth product. A numerical model accounts well for the behavior of this all-normal dispersion fiber oscillator.

Given their interest in multiple, most notably in spectroscopy, high-speed optical sampling, optical frequency comb, super-continuum generation, and others, high repetition rate (HRR) femtosecond lasers have attracted a lot of attention in the last decade. In rare-earth-doped fiber, the HRR can be achieved by controlling the nonlinear polarization rotation in long and heavily doped erbium or ytterbium fibers. However, it is usually difficult to tune the central wavelength of oscillators by providing pulses at an HRR. Further extension in the IR can be achieved through pumping an optical parametric oscillator (OPO) by amplifying the output of an HRR laser system. Compared with SHG and SFG, OPOs generate pulses that can be tuned on a broad spectral range, with limited pulse-to-pulse energy fluctuations and almost a TEM00 beam profile. Hence, one of the simplest and efficient ways to generate tunable HRR femtosecond pulses on a broad spectral range is to pump an OPO with a high-power laser oscillator, where one can adjust the PRR. We perform an experiment using an ytterbium rod-type fiber that provides more than 4.5W output power and tens of nJ per pulses, in which the PRR is controlled by nonlinear polarization rotation. The pulses delivered by this laser are further used to pump an OPO. The OPO is shown to work without any further adjustments. The femtosecond signal pulse delivered by this singly resonant OPO is tunable from 1450nm to 1700nm.