Improving fourth harmonic generation performance by elevating the operation temperature of ADP crystal.

In current inertial confinement fusion (ICF) facilities, potassium dihydrogen phosphate (KH2PO4, KDP) type crystals are the only nonlinear optical (NLO) materials that can satisfy the aperture requirement of the ICF laser driver. Ammonium dihydrogen phosphate (NH4H2PO4, ADP) crystal is a typical isomer of KDP crystal, with a large nonlinear optical coefficient, high ultraviolet transmittance, and large growth sizes, which is an important deep ultraviolet (UV) NLO material. In this paper, we investigated the effect of ADP temperature on its fourth-harmonic-generation (FHG) performance. When the temperature of the ADP crystal was elevated to 48.9 °C, the 90° phase-matched FHG of the 1064 nm laser was realized. Compared with the 79° phase-matched FHG at room temperature (23.0 °C), the output energy at 266 nm, conversion efficiency, angular acceptance, and laser-induced damage threshold (LIDT) increased 113%, 71%, 623%, 19.6%, respectively. It shows that elevating ADP temperature is an efficient method to improve its deep UV frequency conversion properties, which may also be available to other NLO crystals. This discovery provides a very valuable technology for the future development of UV, deep UV lasers in ICF facilities.

High performance 1.9†µm passively Q-switched bulk laser with germanene as a saturable absorber.

Germanene is an analog of graphene, and its independent novel low-bending honeycomb structure gives outstanding advantages such as environmental stability and significant low-frequency optical absorbance. In this paper, the few-layer germanene was successfully prepared by the liquid phase exfoliation method. The saturable absorption characteristics of germanene in the infrared waveband were detected by the open-aperture Z-scan method. With germanene as a saturable absorber, a high-performance passively Q-switched bulk laser was realized at 1.9 µm. The shortest pulse width of 60.5 ns was obtained from continuous-wave pumping, corresponding to a single pulse energy of 6.7 µJ and peak power of 110 W. By utilizing the pulse pumping style with a repletion rate of 10 Hz, the single pulse energy and peak power increased to 45.8 µJ and 328 W, respectively, which exceeded all two-dimensional SA materials reported before. This research manifests that germanene is an excellent SA material for mid-infrared solid-state lasers.

Spontaneous Raman spectra analysis and efficient nanosecond pulse Raman laser of a BaTeW2O9 crystal.

In this Letter, the spontaneous Raman spectra of a novel, to the best of our knowledge, crystal α-BaTeW2O9 (α-BTW) are characterized and analyzed. The relative Raman gain coefficient of the α-BTW crystal is calculated to be 0.84 times that of YVO4. With a 35-mm-long crystal, the first-order Raman laser of α-BTW operating at 1178 nm is realized. The simple external resonator setup is employed in the first-order Raman laser of α-BTW. The pump source is a lamp-pumped electric-optical Q switched Nd:YAG laser amplifier system operating at 1064 nm with a pulse width of 10 ns. The Raman laser exhibits a threshold of 14.7 MW/cm2. In our experiments, a maximum pulse energy of 21.5 mJ is obtained with an optical-to-optical conversion efficiency and slope efficiency of 43.6%, 57.9%, respectively. Due to its high laser damage threshold, relative high Raman gain coefficient, and excellent thermal properties, the α-BTW crystal is a potential Raman material.

Growth, Optical, and Spectroscopic Properties of Pure and Nd3+-Doped GdSr3(PO4)3 Crystals with Disordered Structure.

Disordered crystals have attracted immense attention for the generation of ultrashort laser pulses due to their good thermomechanical characteristics and wide emission bandwidths. In this work, a Gd-based orthophosphate crystal, GdSr3(PO4)3, (GSP), and a Nd3+-doped GdSr3(PO4)3 crystal, (Nd:GSP), were obtained by the Czochralski method. The crystal structure, optical properties, electronic band structure, laser damage threshold, and hardness of the GSP crystal were comprehensively investigated. It exhibited a disordered structure due to the random distribution of Sr and Gd atoms in the same Wyckoff site, which caused inhomogeneous spectral broadening. Additionally, it exhibited a short UV absorption cutoff edge (<200 nm), a large band gap (5.81 eV), and a high laser damage threshold (∼1850 MW/cm2). The spectral properties and Judd-Ofelt calculations of the Nd:GSP crystals were analyzed. A wide absorption band at 803 nm, with a full width at half-maximum value of 20 nm, makes the Nd:GSP crystal suitable for the efficient pumping of AlGaAs laser diodes. Sub-100-fs pulses could be supported by its 25 nm emission bandwidth. Hence, the GSP crystal could be a promising disordered crystal laser matrix.