Huanchu Chen

Efficient self-frequency doubling of Nd:GdCOB crystal by type-I phase matching out of its principal planes

Abstract We report on the efficient self-frequency doubling of Nd:GdCOB crystal by type-I phase-matching at θ=66.3° and ϕ=134.4°, which is out of its principal planes. A CW output power of 225 mW at 530.5 nm is obtained at an absorbed pump power of 1.56 W with an optical conversion efficiency of 14.4% and an absorbed threshold pump power of 1.8 mW. To our knowledge, this is the highest output power, the highest efficiency and the lowest threshold obtained from a self-frequency-doubled Nd:GdCOB laser to date.

Novel (Zn, Nb)-doped SnO2 varistors

Abstract The effect of ZnO on the Nb-doped SnO 2 varistors was investigated. The grain boundary barrier height (Φ B ) of the varistors were determined by use of Schottky type of conduction mechanism. The grain boundary impedance measurements of the varistors were performed using the impedance spectroscopy technique. It was found that ZnO had a significant effect on the varistor properties of Nb-doped SnO 2 ceramics. An optimal doping composition of 98.95SnO 2 –1.00ZnO–0.05 mol% Nb 2 O 5 with the highest nonlinearity with α =12.3, the highest Φ B =0.73 eV and the largest grain boundary resistance R GB =3.43×10 6 Ω cm was obtained. A defect barrier model was introduced to illustrate the formation of the grain boundary barrier for SnO 2 –ZnO–Nb 2 O 5 ceramic varistors. The key element of this model is that the depletion layers formed at the near-grain-boundary region due to the introduction of defects in the crystal lattice, are responsible for the formation of Schottky type potential barriers at the grain boundaries.

Formation of α-Si3N4 whiskers with addition of NaN3 as catalyst

alpha -Si3N4 whiskers with diameters of about 0.1 mum and length of 3-5 mum were fabricated through combustion synthesis route under very low nitrogen pressure of 0.5-1 MPa. The measured maximum combustion temperature is about 1863 K which is rather lower than the adiabatic temperature (about 4400 K) and the decomposition temperature (about 2170 K) of Si3N4 under atmospheric pressure. The addition of NaN3 catalyst plays a key role in the formation of alpha -Si3N4 whiskers under such low nitrogen pressure

Growth and some properties of undoped and doped (K1 - xNax)0.4(Sr1 - yBay)0.8Nb2O6(KNSBN) single crystals with tungsten-bronze structure

Abstract The typical conditions of Czochralski growth of a new ferroelectric single crystal family of undoped and doped (K 1 - x Na x ) 0.4 (Sr 1 - y Ba y ) 0.8 Nb 2 O 6 (KNSBN) with tungsten-bronze type structure are described. A striation-free single crystal was obtained by proper control of crystal rotation and pulling rate. For growth of large crystals, a proper temperature gradient near the solid-liquid interface should be maintained. The ferroelectric domain structure of a dispoled single crystal with square columns has been successfully observed by SEM technique after chemical etching.

Passively Q-switched self-frequency-doubled Nd 3+ :GdCa 4 O(BO 3 ) 3 laser

The performance of a flash-lamp-pumped self-frequency-doubled Nd3+:GdCa4O(BO3)3 (Nd:GdCOB) laser that is passively Q switched with Cr4+:YAG saturable absorbers is demonstrated. The maximum 0.53-µm pulse energy obtained is 2.6 mJ, and the maximum peak intensity is 15 MW/cm2. The dependence of the pulse characteristics on the orientation of the saturable absorber and on the cavity length is measured. Meanwhile, the transversal distribution of the intracavity photon density is taken into account in the rate equations for an intracavity frequency-doubled passively Q-switched laser, and the solutions are used to account for the behavior of the passively Q-switched Nd:GdCOB laser.

High-performance self-pumped phase conjugator with a multichannel in KNSBN:Cu crystal

A Cu-doped (0.04 wt. %) (K(0.5)Na(0.5))(0.2)(Sr(0.61) Ba(0.39))(0.9)Nb(2)O(6) crystal produced as much as 68% self-pumped phaseconjugate reflectivity at the laser wavelength lambda = 514.5 nm. We also observed some phenomena that helped us to understand the mechanism for the self-pumped phase-conjugate mirror.

The elastic and piezoelectric properties of tungsten bronze ferroelectric crystals (Sr0.7Ba0.3)2NaNb5O15 and (Sr0.3Ba0.7)2NaNb5O15

The elastic and piezoelectric constants of tungsten bronze ferroelectric crystals (Sr0.7Ba0.3)2NaNb5O15 (SBNN70) and (Sr0.3Ba0.7)2NaNb5O15 (SBNN30) are determined by using the ultrasonic and resonance methods. The measured results show that these single crystals have larger dielectric constant and good piezoelectric property compared to other known lead-free perovskite ferroelectric crystals. The measurements show that the SBNN70 has larger dielectric and piezoelectric constants than SBNN30 since the former is near the morphotropic phase boundary composition. Our results confirmed that the SBNN single-crystal system is another good candidate as lead-free piezoelectric and dielectric materials.

Second harmonic generation and self-frequency doubling performance in Nd:GdCa4O(BO3)3 crystal

Abstract Second harmonic generation (SHG) conversion efficiency of Nd:GdCOB crystal is reported. Theoretical calculation has shown that the largest effective nonlinear coefficient is not in the principal plane. The SHG experimental results of samples cut in the phase-matching direction of θ =66.3°, φ =134.4° and θ =90°, φ =46° are presented. The self-frequency doubling laser performance of the two samples is investigated.

Self-pumped phase conjugation of 18°-cut Ce-doped KNSBNcrystal at 632.8 nm

We report the self-pumped phase conjugation of an 18°-cut Ce-doped (KyNa1−y)2m(SrxBa1−x)1−m Nb2O6 crystal at a 632.8-nm He–Ne laser wavelength. A maximum phase-conjugation reflectivity of 84.3% has been measured. In addition, its incident angular response and time response are measured.

Growth and properties of a new TB type photorefractive crystal

This paper is focused on the studies on the new composition of tungsten bronze photorefractive KNSBN:Cu crystals. By changing the A-site occupation of the crystals and doping Cu ions in them, their ferroelectric and photorefractive properties were modified. These new crystals have excellent polarization stabilities and a two-wave coupling gain coefficient as large as 20 cm −1 . The photorefractive sensitivity is of the order of 10 −3 cm 2 /J and the cat-SPPC reflectivity can reach 65% with a response time lower than 10 s.