Wavelength beam combining technology plays an important role in generating high-brightness laser beams at high-power levels. This technology is used for various applications, including military and industrial manufacturing. Recent studies have demonstrated the system using mini-bar diode laser stacks, which offer superior optical performance but suffer from pricey, customized fabrication and possibly intense thermal loads. Hence, we offer a suitable alternative approach by incorporating full-bar diode laser stacks, which are relatively cost-effective, off-the-shelf, and easy to manufacture, making the frameworks more amenable to mass production. However, this framework needs further development due to the higher smile effect in the fullbar stacks. In this work, we experimentally demonstrate this idea with a 213 W output power at a central wavelength of 975 nm. Moreover, although the degradation caused by the smile and thermo-optical effects, its preserved beam quality is most prominent in its availability of applied to couple into a 105 mu m core fiber. This research opens new possibilities for future WBC system design and development using full-bar diode laser stacks.

We study an off-axis terahertz (THz) parametric oscillator and show its superior performance over a conventional THz parametric oscillator. Furthermore, by pumping an off-axis lithium-niobate oscillator with a pulsed Nd:YAG laser having an axial-mode spacing matched to the THz oscillator's mode spacing, we generated an ultra-broad red-shifted frequency comb between 1065 and 1085 nm at the output, which corresponds to a four-octave-spanning THz-frequency comb in the idler spectrum. We also demonstrated a signal-seeded off-axis THz parametric oscillator, which generates 8 nJ narrow-line radiation at 2.1 THz and achieved 46% pump depletion in a 6.5 cm long crystal with only 4 mJ pump energy in a 460 ps pump pulse width. Furthermore, tuning between 3.6 and 4.9 THz for the generated radiation is also demonstrated in this work. (C) 2018 Optical Society of America

A high-energy electro-optically Q-switched Nd:YAG laser at 1064 nm is presented, which can provide the largest output pulse energy of 196 mJ with the pulse duration of 12 ns and the repetition rate up to 30 Hz. The crossed-Porro resonator and zigzag slab gain medium are utilized to increase the misalignment tolerance of resonator up to 2 arcmin and minimize the divergence angle of laser beam to 1.7 mrad. We control the initial population inversion by intra-cavity quasi-CW lasing to limit maximum output pulse energy, and the excess pump energy is used to overcome performance degradation dependence on environmental temperature. As a result, a nearly constant output pulse energy can be obtained over a wide operating temperature range.

Stimulated polariton scattering in lithium niobate is an effective means to generate the THz radiations. All the previously reported THz SPS from LN shows a stand-alone gain peak about 2 THz, resulting from the lowest A 1 -symmetry vibration mode near 250 cm -1 . Generation of THz radiation from lithium niobate with frequencies higher than 2.5 THz has been considered difficult due to sharply increased material absorption. Since lithium niobate is relatively low-cost and high-quality, it is desirable to extend the useful THz radiation bandwidth of LN to higher frequencies. By using the so-called off-axis THz parametric oscillator, we report the discovery of a phase-matched gain peak near 4 THz from lithium niobate. We also demonstrated a signal-seeded lithium-niobate off-axis THz parametric oscillator that generates 1.4 nJ pulse energy at 4 THz with 17.5 mJ pump energy at 1064 nm.

We report highly efficient stimulated polariton scattering near 4 THz with a parametric gain overtaking the well-known one near 1.8-THz in lithium niobate by using an off-axis parametric oscillator resonating the THz wave.

We present a non-collinearly phase matched terahertz parametric oscillator with a 1064-nm laser pumping a y-cut LiNbO3 crystal. An off-axis THz-wave oscillator was demonstrated by utilizing THz guided scheme and total internal reflection.

Lithium niobate is the most popular material for terahertz wave generation via stimulated polariton scattering (SPS), previously known to have a gain peak near 2 THz. Here we report the discovery of another phase-matched gain peak near 4 THz in lithium niobate, which greatly extends the useful gain spectrum of lithium niobate. Despite the relatively high 4 THz absorption in lithium niobate, the 4 THz SPS becomes dominant over the 2 THz one in an intensely pumped short lithium niobate crystal due to less diffraction-induced absorption and mode-area mismatch. We also demonstrate a signal-seeded OTPO that generates 1.4 nJ at 4.2 THz from lithium niobate with 17.5 mJ pump energy.

We report a high-efficiency THz parametric oscillator with the THz wave zigzagging inside a slab lithium niobate crystal. When seeded by a signal wave, the device generates a 40-W peak power at 1.8 THz.

we demonstrate a 40 W peak power terahertz (THz) wave from an off-axis parametric oscillator by pumping a y-cut monolithic lithium niobate slab crystal with a pulsed laser at 1064 nm. This is a demonstration that, for the first time, a THz parametric oscillator resonates a THz wave, having the advantages of compact size, easy alignment, and high efficiency. The experimental results show that the efficiency of such a monolithic parametric oscillator is significantly larger than of a THz parametric generator using the same crystal dimensions.

We report superior terahertz parametric generation from potassium titanyl phosphate (KTP) over congruent-grown lithium niobate (CLN) and lithium tantalate (CLT) in terms of parametric gain and laser damage resistance. Under the same pump and crystal configurations, the signal emerged first from KTP, 5% Mg-doped CLN, CLN, and then finally from CLT. The signal growth rate in KTP was comparable to that in 5%-Mg-doped CLN, but the signal power from KTP reached a much higher value after all the other crystals were damaged by the pump laser. We further demonstrate seeded terahertz parametric amplification in an edge-cut KTP at 5.74 THz. The THz parametric amplifier (TPA) employs a 17-mm long KTP gain crystal, pumped by a passively Q-switched pump laser at 1064 nm and seeded by a continuous-wave diode laser tuned to the signal wavelength at 1086.2 nm. With 5.8-mJ energy in a 520-ps pump pulse and 100-mW seed signal power, we measured 5-W peak-power THz output from the KTP TPA with 22% pump depletion. In comparison, we measured no detectable THz output power from a similar edge-cut CLN TPA under the same pump power, detection scheme, and crystal configuration, when tuning the seed laser wavelength to 1072.2 nm and attempting to generate a radiation at 2.1 THz.

In this work, a high-power and narrow-linewidthed allfiber laser system is demonstrated with diffraction-limited beam quality. In order to suppress stimulated Brillouin Scattering (SBS) in the master oscillator power amplifier (MOPA) system, a 2-tone modulation method is applied to the seeding source. The result shows that the output spectrum linewidth of the fiber laser can be controlled less than 500 MHz with an excellent beam quality of M=1.03 at 200Watt output power. High power fiber laser with a narrow linewidth and an excellent beam quality should be very useful for the power scaling application such as beam combining.

We show superior terahertz parametric generation from potassium titanyl phosphate over lithium niobate and lithium tantalate, and demonstrate seeded terahertz parametric amplification in KTP at 5.7 THz.

Optical parametric mixing is a popular scheme to generate an idler wave at THz frequencies, although the THz wave is often absorbing in the nonlinear optical material. It is widely suggested that the useful material length for co-directional parametric mixing with strong THz-wave absorption is comparable to the THz-wave absorption length in the material. Here we show that, even in the limit of the absorption loss exceeding parametric gain, the THz idler wave can grows monotonically from optical parametric amplification over a much longer distance in a nonlinear optical material until pump depletion. The coherent production of the non-absorbing signal wave can assist the growth of the highly absorbing idler wave. We also show that, for the case of an equal input pump and signal in difference frequency generation, the quick saturation of the THz idler wave predicted from a much simplified and yet popular plane-wave model fails when fast diffraction of the THz wave from the co-propagating optical mixing waves is considered.

In this paper, we report a master-oscillator fiber power amplifier system at 1061 nm by using a 4 m long Yb-doped large mode area (LMA) double-clad fiber as the gain medium. At a repetition rate of 20 kHz and 11 ns pulse width, this amplified laser system emitted average and peak power up to 9.9 W and 43 kW, respectively.

We measured enhanced forward and backward THz-wave difference frequency generations at 1.5 and 0.6 THz, respectively, from a PPLN rectangular waveguide. A theory accounting for large mode mismatch is derived to explain the experimental result.

Some believes that the useful length of THz different frequency generation (DFG) in a highly absorptive material is comparable to the absorption length of the THz wave. We show in theory and experiment that it is only true for backward THz DFG. For forward DFG with strong idler absorption, the THz wave can continue to grow with the length of a DFG crystal.

When the idler absorption loss exceeds parametric gain in THz DFG, the THz wave can still grow monotonically versus crystal length for forward DFG but saturates within a few absorption lengths for backward DFG.

We report a mid-infrared, CW singly resonant optical parametric oscillator (OPO) with a thermally induced waveguide in its gain crystal. We measured a numerical aperture of 0.0062 for the waveguide at 80-W intracavity power at 3.2 microm. This thermal-guiding effect benefits to the stable operation of an OPO and improves the parametric conversion efficiency by more than a factor of two when compared with that without thermal guiding.

We report a CW, watt-level, red, green, and blue (RGB) laser pumped by an economical multimode (1-nm linewidth) Yb-fiber laser at 1.064 mum. A singly resonant optical parametric oscillator at 1.56 mum has two intracavity sum-frequency generators for red and blue laser generation. An extracavity second harmonic generator converts the residual pump power into green laser radiation. At 25-W pump power, the laser generated 3.9, 0.456, and 0.49 W at 633, 532, and 450 nm, respectively. The multimode pump laser offers a large temperature bandwidth for operating the RGB OPO without the need of a precision crystal temperature stabilizer.