Guochun Zhang

Growth and optical properties of a new nonlinear Na 3 La 9 O 3 (BO 3 ) 8 crystal

New nonlinear crystals Na(3)La(9)O(3)(BO(3))(8) (abbreviated as NLBO) with desired morphologies, high quality and weight exceeding 40g have been grown along different directions, such as [001], [110], and [100], by top-seeded solution growth(TSSG) method. The refractive indices were accurately measured over the full transmission range, and the second-order nonlinear optical coefficients were determined by the Maker fringe technique. The optimal phase-matching (PM) conditions and the corresponding effective nonlinear coefficient were calculated for second harmonic generation (SHG) at different wavelengths. In order to confirm the correctness of our calculation, we also performed the SHG experiments under 1064 and 800 nm pumping, respectively. In addition, we directly compared the SHG performance of NLBO with that of LBO under the same experimental conditions with the 1064 nm pumping source. As the results, a conversion efficiency of 58.3% at 532 nm was obtained for NLBO, and whereas only 21.5% was obtained for LBO, indicating that NLBO is a highly attractive nonlinear material for frequency conversion of pulses into the visible and ultraviolet.

Optical properties of BaBPO 5 crystals

Large single crystals of BaBPO5 have been grown with Li4P2O7 as the flux by the top-seeded solution growth method. The crystal is chemically stable and easily polished and absolutely insensitive to moisture. The obtained BaBPO5 crystals are bounded by a combination of well-developed {1 0 1¯ 1} rhombohedron and {1 0 1¯ 0} hexagonal prism faces. The crystal is found to be transparent from 180 to 3300 nm. The refractive indices were measured with the minimum-deviation method and fitted to the Sellmeier equations. The nonlinear optical coefficient d11 of BaBPO5 measured by the Maker fringes technique is 0.49d36 (KDP).

Widely tunable and monochromatic terahertz difference frequency generation with organic crystal 2-(3-(4-hydroxystyryl)-5,5-dime-thylcyclohex-2-enylidene) malononitrile

We report an experimental study on widely tunable terahertz (THz) wave difference frequency generation (DFG) with hydrogen-bonded crystals 2-(3-(4-hydroxystyryl)-5,5-dime-thylcyclohex-2-enylidene) malononitrile (OH1). The organic crystals were pumped by a ∼1.3 μm double-pass KTiOPO4 optical parametric oscillator. A tuning range of 0.02–20 THz was achieved. OH1 crystals offer a long effective interaction length (also high output) for the generation below 3 THz, owing to the low absorption and favorable phase-matching. The highest energy of 507 nJ/pulse was generated at 1.92 THz with a 1.89-mm-thick crystal. Comprehensive explanations were provided, on the basis of theoretical calculations. Cascading phenomenon during the DFG process was demonstrated. The photon conversion efficiency could reach 2.9%.

Raman spectroscopy and density functional theory analyses of the melt structure in a Li2B4O7 crystal growth system

Melt structure, a fundamental and challenging subject for borate crystal growth, has not been solved for many years. In this paper, a new method has been employed to study the Li2B4O7 melt structure. High-temperature Raman spectroscopy has been used to investigate the structural evolvement from a Li2B4O7 crystal to a Li2B4O7 melt. Based on the investigation, a model was proposed to describe the Li2B4O7 melt. The melt is made up of polymer-like boron–oxygen chains; the minimal repeated unit is the B4O6O22− (O = bridging oxygen) group which is formed by a B3O4O2− six-membered ring and a BOO2− triangle linked by a bridging oxygen atom. DFT calculations have verified the melt structure and provided accurate assignments for the vibrational bands present in the Li2B4O7 melt Raman spectrum.

K6Li3Sc2B15O30: A new nonlinear optical crystal with a short absorption edge

A new non-centrosymmetric rare-earth borate K6Li3Sc2B15O30 has been synthesized by solid-state reaction technique, and a transparent crystal with dimensions of 28 × 28 × 8 mm3 was successfully obtained with a K2O–Li2O–B2O3–LiF flux by the top-seeded solution growth method. Single crystal X-ray diffraction results show that it crystallizes in the space group R32 (No. 155). In the structure of K6Li3Sc2B15O30, B5O10 groups are bridged by discrete ScO6 octahedra, giving rise to columns packed side-by-side in a rhombic motif along the c-axis to form a three-dimensional framework with one-dimensional tunnels along the a- and b-axes. K6Li3Sc2B15O30 is nonhygroscopic, and melts incongruently at 838 °C. The transmittance spectrum of K6Li3Sc2B15O30 exhibits a short UV absorption edge at 190 nm. Second harmonic generation (SHG) tests on powder samples reveal that K6Li3Sc2B15O30 possesses an SHG effect close to that of KDP.

Synthesis, crystal growth, and second-order nonlinear optical properties of new configurationally locked polyene derivatives

Five new crystals based on configurationally locked polyene (CLP) structure are synthesized. This series of crystals all consists of a π-conjugated hexatriene bridge between the dicyanomethylidene electron acceptor and the electron donors with strong hyperpolarization. In particular, the acentric 2-(3-(4-phenylstyryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile (PSDCM) exhibits a large powder second-harmonic generation intensity about 0.3 times that of OH1 (a commonly used CLP nonlinear optical crystal), and the mechanism is elucidated by first-principle studies. Single-crystal X-ray diffraction and diffuse reflectance spectroscopy are performed and the thermal properties in PSDCM are characterized.

A 7.81 W 355 nm ultraviolet picosecond laser using La2CaB10O19 as a nonlinear optical crystal

We demonstrate high-power 355 nm ultraviolet (UV) picosecond (ps) laser using a type I phase-matching nonlinear optical crystal of La(2)CaB(10)O(19) (LCB), which possesses the characteristic of non-hygroscopicity. The high-power third harmonic generation was successfully achieved from two types of 1064 nm ps fundamental lasers. The maximum output power of 7.81 W of 355 nm UV laser was obtained with a pump of 35.2 W 1064 nm ps laser (80 MHz repetition rate, 10 ps pulse width) with optical conversion efficiency of 22.2%. The experimental results show that the LCB crystal is a promising candidate for generating high-power UV laser.

High-Power Ultraviolet 278 nm Laser from Fourth-Harmonic Generation of a Nd:YAG Laser in CsB 3 O 5

We demonstrate a high-power UV 278 nm laser by fourth-harmonic generation (FHG) of a 1112 nm Nd:YAG laser in a nonlinear optical (NLO) crystal CsB3O5 (CBO) for the first time, to our best knowledge. A 30 W level diode-pumped Q-switched Nd:YAG laser at 1112 nm with beam quality factor M2=1.2 was used as the fundamental light source at a pulse width of 500 ns. With an LiB3O5 crystal, the 1112 nm laser was first frequency-doubled to 556 nm with an average output power of 13.5 W. It was then frequency doubled again in a CBO crystal to obtain the FHG output at 278 nm. The maximum average output power of the 278 nm laser is up to 1.5 W. The results demonstrated that CBO crystal is a promising NLO material for UV high-power lasers below 300 nm.

355nm laser generation based on Na 3 La 9 O 3 (BO 3 ) 8 crystal

Na3La9O3(BO3)8 (NLBO) single crystals with size up to 35 × 20 × 15 mm3 have been grown by the top-seeded solution growth (TSSG) method. The phase-matching (PM) conditions and the effective nonlinear coefficients were fully calculated for third-harmonic generation (THG) at different wavelengths. The THG experiments for NLBO crystals were performed for the first time. A 355 nm UV light output of 1.9 mW was successfully obtained under a picosecond Nd:YAG laser. Through the calculations of effective nonlinear coefficients, we believe that the output power and conversion efficiency will further increase if the high optical quality NLBO samples can be utilized.

Growth and characterization of CsB3O5 crystals without scattering centers

CsB3O5 (CBO) single crystals without scattering centers have been successfully grown from the Cs2O–B2O3–MoO3 ternary system by the top-seeded solution growth method. The suitable region for CBO crystal growth was investigated by growth experiments, viscosity and volatility measurements, which confirmed that the optimal molar ratio of Cs2O:B2O3:MoO3 was 2:3:2.5. By carefully controlling growth parameters, including the temperature gradient in the axis, rotation rate, cooling rate, and seed direction, a free of scattering centers CBO crystal with dimensions up to 29 × 31 × 47 mm3 has been obtained. The grown CBO crystals possess high optical quality. The full-width at half-maximum (FWHM) of the rocking curve is 0.0057°, and the optical homogeneity is at the level of 10−6 cm−1. The optical absorption at the critical wavelengths of 1064 and 532 nm was measured to be 200 and 60 ppm cm−1, respectively. The laser-induced damage threshold (LIDT) at λ = 1.064 nm and τ = 5.0 ns is about 4.50 GW cm−2. Moreover, a high-power 278 nm ultraviolet (UV) laser through fourth harmonic generation (FOHG) of a diode-pumped 1112 nm Nd:YAG laser has been demonstrated in CBO crystal for the first time.