Mingxia Xu

Non-critical phase-matching conditions for fourth harmonic generation of DKDP crystal

The non-critical phase matching (PM) conditions of deuterated dihydrogen phosphate (DKDP) crystal are investigated in this paper for fourth harmonic generation (FHG) of Nd:YAG crystal and Nd:glass lasers, which include exterior angle deviation, deuterium content and PM temperature. DKDP crystals of different deuterium content were grown from aqueous solutions and cut for type-I non-critical phase-matching with the direction at 90° to the crystal Z axis (θ = 90°) and at 45° to the crystal X axis (Ф = 45°). The samples are measured for FHG at 1064 nm and 1053 nm, respectively. The deuterium content of DKDP crystal that supports non-critical phase-matching for FHG experiments is confirmed by measuring the relationship of deuterium content and phase-matching angle. Additionally, the non-critical phase matching temperature is also examined.

Effect of supersaturation on hillock of directional Growth of KDP crystals

KDP single crystals were grown in aqueous solution by using “point seeds” with a defined crystallographic direction of 59° to the Z axis. When hillock slopes on the (100) face of KDP crystals were measured within the supersaturation (σ) range of 0 < σ ≤ 0.06, the slope of hillocks with hollow cores depended nonlinearly on supersaturation. Below σ = 0.02, the hillock slope depended on supersaturation, but when σ was ≥ 0.02, the hillock slope increased more gradually and was less dependent on supersaturation. Hollow funnel-shaped growth dislocation on the (100) face of KDP crystals was observed at σ = 0.04, characterized by large holes with micro-steps and step bunching inside, the formation of which were analyzed. The result verified that the reversed growth appears to occur within hollow channels found on growth hillocks.

Refractive indices in the whole transmission range of partially deuterated KDP crystals

Refractive indices of partially deuterated potassium dihydrogen phosphate (DKDP) crystals with 55%, 70% and 80% deuterium contents were measured by auto-collimation method at 293 K between 0.254 to 1.529 μm. Dependence of refractive indices of DKDP on deuterium content show different trend in the infrared region as in uv-visible region. Dependence of n2 (the square of refractive index) on the mole fraction of deuterium shows a difference between pure KDP and partially deuterated KDP. The Sellmeier equations were obtained by the least square method. The non-critical phase matching angles calculated from the fitted formula were in good agreement with laser experiment results, by which the reliability of these Sellmeier equations was confirmed.

The rapid growth of ADP single crystal

Ammonium dihydrogen phosphate (NH4HPO4, ADP) crystal can be used to generate second, third and fourth harmonics. In this paper, the growth characteristics of ADP and the differences between the growth solubility and structures of potassium dihydrogen phosphate (KDP) and ADP crystal are discussed in detail. Ex situ atomic force microscopy (AFM) was applied to explore the growth morphology of ADP crystal at different supersaturation values. A series of ADP crystals were grown, and the transmission spectra of ADP crystals across the whole transmission region were measured. Laser-induced damage threshold (LDT) was measured, and was found to be higher than the average value of LDT of KDP and 70% deuterated DKDP crystals.

Noncritical phase matching fourth harmonic generation properties of KD 2 PO 4 crystals

Noncritical phase matching (NCPM) fourth-harmonic-generation (FHG) experiments were conducted on different deuterium content DKDP crystals by adjusting crystal temperature to generate 266 nm deep UV laser. Specially, near room temperature NCPM is realized in extremely high deuterium content DKDP crystal at 38.6 °C, which is the lowest temperature to the best of our knowledge. NCPM temperature of DKDP crystals in 60-100% deuterium content range and 1050-1070 nm wavelength range are determined by a linear relationship according to the experimental and calculated results. Angular tuning properties are independent with deuterium content in medium and higher deuterium content DKDP crystals. All of these results will provide good references for future FHG applications of 1 μm laser with DKDP crystals.

Growth and electro‐elastic properties of K(H1−xDx)2PO4 single crystals

A series of K(H1−xDx)2PO4 crystals were grown from deuterated aqueous solution by using a point-seed rapid-growth method. The elastic, piezoelectric and dielectric constants of these crystals were determined using the resonance technique and impedance analysis, respectively. The elastic compliance constant s11 measured in this experiment is larger than that in previous experiments, and the reliability of the results presented herein has been verified. These results show that, with increasing content of deuterium, s11, s44, s66, d36, e36 and k36 are gradually increased, whereas s12, s13, s33, d14, e14 and k14 have no demonstrable variation. The reasons for the composition dependence of these constants were analyzed based on the variation of the crystal structures resolved by single-crystal X-ray diffraction.

Diabetes mellitus affects the biomechanical function of the callus and the expression of TGF-beta1 and BMP2 in an early stage of fracture healing

Transforming growth factor beta 1 (TGF-β1) and bone morphogenetic protein-2 (BMP-2) are important regulators of bone repair and regeneration. In this study, we examined whether TGF-β1 and BMP-2 expressions were delayed during bone healing in type 1 diabetes mellitus. Tibial fractures were created in 95 diabetic and 95 control adult male Wistar rats of 10 weeks of age. At 1, 2, 3, 4, and 5 weeks after fracture induction, five rats were sacrificed from each group. The expressions of TGF-β1 and BMP2 in the fractured tibias were measured by immunohistochemistry and quantitative reverse-transcription polymerase chain reaction, weekly for the first 5 weeks post-fracture. Mechanical parameters (bending rigidity, torsional rigidity, destruction torque) of the healing bones were also assessed at 3, 4, and 5 weeks post-fracture, after the rats were sacrificed. The bending rigidity, torsional rigidity and destruction torque of the two groups increased continuously during the healing process. The diabetes group had lower mean values for bending rigidity, torsional rigidity and destruction torque compared with the control group (P<0.05). TGF-β1 and BMP-2 expression were significantly lower (P<0.05) in the control group than in the diabetes group at postoperative weeks 1, 2, and 3. Peak levels of TGF-β1 and BMP-2 expression were delayed by 1 week in the diabetes group compared with the control group. Our results demonstrate that there was a delayed recovery in the biomechanical function of the fractured bones in diabetic rats. This delay may be associated with a delayed expression of the growth factors TGF-β1 and BMP-2.

Rapid growth of a large size, highly deuterated DKDP crystal and its efficient noncritical phase matching fourth-harmonic-generation of a Nd:YAG laser

A high quality, large size (100 × 105 × 96 mm3) deuterated potassium dihydrogen phosphate (DKDP) crystal with high deuterium content was successfully grown by the rapid growth method. A noncritical phase matching (NCPM) fourth-harmonic-generation (FHG) of Nd:YAG laser (1064 nm) was realized at 39.7 °C or so. The smallest full width at half maximum (FWHM) of angular acceptance for the longest crystal sample (20 mm) is 33.5 mrad, which is 10 times larger than the value of critically PM of a KDP crystal. The FHG conversion efficiency increases with the crystal length and reaches 64% for the 20 mm long crystal. As we have known, this is the highest FHG conversion efficiency of a 1064 nm laser with a repetition rate of 10 Hz in low drive conditions.

New annealing method to improve KD2PO4 crystal quality: learning from high temperature phase transition

The existence of a high temperature phase transition in KD2PO4 was confirmed by thermal analysis, dielectric analysis and Raman spectroscopy. The results showed that KD2PO4 presented only one high temperature phase transition at about Ttr = 430 K, which is much lower than the thermal decomposition temperature. The absence of Raman shift attributable to the dehydration product indicated that the HTPT had nothing to do with thermal decomposition. The structural change during the HTPT was discussed. The strong similarity between the HT-phase and tetragonal phase decreases the temperature of the HTPT in the KD2PO4 crystal. The hydrogen–deuterium exchange can be suppressed under a protective ambient environment, which helps improve the annealing temperature. A new annealing method was developed by using silicone oil as a protective ambient environment under higher temperature up to 403 K, thus improving the quality of KD2PO4 crystals.

Study on the properties of the DKDP crystal with different deuterium content

In this paper, DKDP crystals with deuterium content of 55%, 65% and 70% were grown by the traditional temperature-reduction method. The property including lattice constant, transmittance spectra, Raman spectra, conoscopic image, and laser damage threshold (LDT) were measured. The results showed that with increasing the degrees of deuteration for DKDP crystals, the value of lattice parameter a (b) increases and the transmittance also increases in the range of 350-1800 nm while the laser damage threshold (LDT) decrease. For DKDP crystals, the spectra of Raman scattering split into two parts and the peak intensity of the totally symmetric PO4 vibration decrease compared with that of KDP crystals. The homogeneity of the DKDP crystals has not obvious difference.