Barium Nitrate Crystal Research Articles

Development of new real-time phase-shift interferometry for the investigation of crystal growth kinetics

A new technique of real-time phase-shift interferometry was developed for precise in situ observation and measurement of crystal growth. The new signal processor employs an “intelligent” phase unwrapping technique and enables the three-dimensional surface profile of a crystal to be obtained in real time even in the case that a two-dimensional phase distribution profile becomes discontinuous in the conventional signal processor due to dust or small crystals adsorbed on the crystal surface. This interferometry was applied to surface observation of a barium nitrate crystal growing from an aqueous solution.

Investigation of the line broadening of an SRS-active vibration in a barium nitrate crystal by two-photon Raman amplification spectroscopy

An investigation was made of the spectral characteristics of an SRS-active mode in a barium nitrate crystal by the method of two-photon Raman amplification. At room temperature the width of this vibrational mode was 0.6 cm-1. The experimental temperature dependence of the linewidth was analysed within the framework of a theory of multiphonon relaxation.

Vibrational dynamic of the Raman-active mode in barium nitrate crystal

The relaxation time, 1047 cm−1, of the Raman-active mode in barium nitrate crystal has been measured as a function of temperature by a time-resolved coherent anti-Stokes probe scattering technique. The temperature dependence is consistent with the combination of two relaxation mechanisms involving four and six phonons that are dominant at low and high temperatures, respectively. It was found that the Raman mode has a rather long decay time, resulting in attractive stimulated Raman scattering features of barium nitrate crystal.

Study of a〈001〉 and a〈110〉 screw dislocations viewed end-on in crystal Ba(NO3)2 by birefringence topography

The screw dislocations with Burgers vector a〈001〉 and a〈110〉 in Ba(NO3)2 crystals have been studied by birefringence topography. In combination with the results obtained previously [C.-Z. Ge, N.-B. Ming, K. Tsukamoto, K. Maiwa, and I. Sunagawa, J. Appl. Phys. 69, 7556 (1991); C.-Z. Ge, H.-W. Wang, and N.-B. Ming, ibid. 74, 139 (1993)], it has been shown that not only a〈111〉, but also a〈110〉 screw dislocations viewed end-on are visible; however, a〈100〉 screw dislocation viewed end-on are always invisible in barium nitrate crystals. The intensity distributions and extinction rules of birefringence images of a〈110〉 screw dislocation viewed end-on are determined both experimentally and theoretically.

In situ study of surface phenomena by real time phase shift interferometry

Real time phase shift interferometry is applied to the observation of a growing crystal surface. Detailed profiles of a growth hillock, such as local vibrations of slopes and height differences of growth steps, are clearly distinguished on a barium nitrate crystal, together with measurements of growth rate at each location. It was found that the height difference of 0.92 nm was directly detectable in this interferometry, indicating that the present method is a few ten times more sensitive than conventional two-beam interferometry, applicable to in situ study, such as Michelson interferometry. It was found that: (1) Step spacing gradually increases as a step approaches the edge of a crystal, which is inferred from the non-uniformity of surface supersaturation. (2) The observation of fluctuation of the growth rate under a constant condition was analyzed as due to the unequal separation of neighboring dislocations which produce the pertubation of steps.

Stimulated Raman scattering of the beam from a copper-vapor laser in a barium nitrate crystal

Conversion of the beam from a copper-vapor laser through stimulated Raman scattering in a barium nitrate crystal has been achieved for the first time. A conversion efficiency of 32% was achieved at stimulated-Raman-scattering power of 600 mW at the wavelength 539.4 nm, and 18% at a stimulated-Raman power of 300 mW at the wavelength 615.4 nm. Experiments confirm that it is possible to eliminate the thermally induced depolarization of the radiation in a certain orientation of the crystal. Ten lines in the UV spectrum with power levels ranging from 1 to 80 mW have been achieved through parametric summation of the stimulated-Raman radiation with the beam from the copper-vapor laser in KDP and DKDP crystals.

Stimulated Raman scattering of picosecond pulses in barium nitrate crystals

Stimulated Raman Scattering (SRS) of picosecond pulses was investigated in Ba(NO 3) 2 crystals. The results are in good agreement with transient SRS theory. First and second Stokes conversion efficiencies were measured to be 25% and 5%, respectively.

Stimulated Raman scattering in a Ba(NO3)2crystal and subsequent amplification in an LiF:F2−crystal

An investigation demonstrated the feasibility of amplification of a weak seed Stokes radiation generated by concurrent and counterpropagating stimulated Raman scattering in a barium nitrate crystal. The subsequent amplification took place in a crystal of LiF containing color centers, which made it possible to achieve a high efficiency of conversion of the pump energy into the energy of the Stokes radiation without focusing the pump beam.

Nonstationary growth of the cubic faces of a barium nitrate crystal

Significant variations of the dislocation hillock steepness of the {100} faces of Ba(NO3)2 crystals have been found. They are supposed to be due to crawling of helicoidal dislocations in the source of growing. As a consequence, the source activity and the values of normal and tangential velocities of movement of the hillock slopes change periodically. The latter is associated with the formation of higher macrosteps on a steeper slope. A slow change in the hillock shape anisotropy has been noted, which is accounted for by the effect of impurities in the solution. All these phenomena lead to nonstationary growth of a face, trapping of solution inclusions and deterioration of the crystal internal structure.

Activities of spiral growth hillocks on the (111) faces of barium nitrate crystals growing in an aqueous solution

In situ measurements of normal growth rates R, slopes p, and step advancing rates v = R / p of the spiral growth hillocks generated from two types of dislocations, screw (b = [111]) and mixed (b = 〈110〉), were made on the (111) faces of Ba(NO3)2 crystals growing from an aqueous solution at different flow velocity, u. These two types of dislocations were identified also in situ by stress birefringence microscopy. It was found that: (1) The growth hillocks originated from the screw dislocations grow faster than those from the mixed dislocations, and the tendency is more pronounced as u increases (Rs/Rm = 1.3 when u = 40 cm/s). (2) As u increases, the step advancing rates become equal for the two types, in spite of the difference of step heights (hs/hm = 1.5). (3) The growth hillocks generated from the screw dislocations are steeper under any growth conditions than those from the mixed dislocations. It was also demonstrated that the dislocations outcropped near the periphery of a growing face were twice more active as growth centres than those at the centre of the face, due to the higher supersaturation along the periphery of the face. It is concluded that the direct integration model explains the result on the step movement better than the surface diffusion model. It is also concluded that the increase of the interstep spacing and therefore the edge free energy of steps are not proportional to the increase of the step height.

Observation of screw and mixed dislocations in barium nitrate crystals by means of birefringence and x-ray topography

Dislocations in barium nitrate crystals grown from an aqueous solution were investigated by means of polarizing microscopy and X-ray topography. A perfect one-to-one correlation between dislocation images observed by X-ray topography and polarizing microscopy was confirmed. X-ray topographic observations showed that three types of dislocations can be observed in a (111) growth sector of a barium nitrate crystal: edge dislocations with b = 〈 110〉 , mixed dislocations with b = 〈110〉 and screw dislocations with b = [111]. It was established that these three types of dislocations can be imaged and clearly distinguished by polarizing microscopy.

Role of buoyancy driven convection in aqueous solution growth; A case study of Ba(NO3)2 crystal

Using Schlieren technique and Mach-Zehnder interferometry, the diffusion boundary layer and buoyancy driven convection around a growing barium nitrate crystal from the aqueous solution were visualized and their effect upon the growth kinetics of crystals was investigated in relation to the bulk supersaturation. It was demonstrated that buoyancy driven convection plumes behaved differently depending on the bulk supersaturation, and that their behavior gave a definitive effect upon the growth rates.

Growth induced lattice defects in Ba(NO 3) 2 crystals

Combined X-ray topographic and surface microtopographic studies were made on barium nitrate crystals grown from the aqueous solution at known supersaturations on etched and unetched seeds. The following relations were confirmed: (1) Inclusions trapped on the etched seed surface act as sites for both generating new dislocations and inhibiting the propagation of seed dislocations. (2) Higher supersaturation leads to the generation of helical dislocations even at room temperature, and development of wider planar defects. (3) Dislocations change their directions when supersaturation is changed. (4) One-to-one correlation was established between the summits of growth pyramids and outcrops of dislocations with screw components. However, not all screw dislocations outcropped on the growing surface are active as growth centres. As supersaturation increases, the number of dislocations active as growth centres diminishes.

Generation of radiation in a resonator under conditions of stimulated Raman scattering in Ba(NO3)2, NaNO3, and CaCO3crystals

A study was made of the generation of Stokes radiation in plane-plane and unstable telescopic resonators under conditions of stimulated Raman scattering in calcite, barium nitrate, and sodium nitrate crystals. The regimes of effective operation of such Raman lasers were determined. It was shown that the efficiency of conversion of the energy of the pump radiation into the energy of the first Stokes component could be increased by ensuring repetitive passage of the pump along a crystal. It was found that the generation of the second Stokes component became weaker under the conditions of pumping of a crystal in an unstable telescopic resonator by a beam opposite to the Stokes radiation leaving the resonator. Measurements were made of the spatial and angular characteristics of the output radiation. In the case of pulsed generation of radiation in a plane-plane resonator it was possible to reduce the angular divergence by the use of a correcting positive (converging) lens.

In situ observation of the surface of barium nitrate crystals growing in supersaturated solution.

In situ observation of the surface of barium nitrate crystals growing in supersaturated solution.

Stimulated emission and amplification of radiation under conditions of stimulated Raman scattering in crystals

An experimental study was made of the generation of Stokes radiation in focused beams under conditions of stimulated Raman scattering (STRS) in calcite and barium nitrate crystals. A high efficiency (~0.8) of conversion of the pump energy into the Stokes radiation energy was achieved for the opposed STRS and it was found that this was due to four-photon parametric processes. The quality of wavefront reversal of spatially homogeneous and inhomogeneous beams was determined in a wide range of energies and divergences of the pump radiation and also in a wide range of the focal lengths of the lenses employed in the process. Further amplification of radiation was achieved in an STRS amplifier made of barium nitrate and operating in the intensity averaging regime. Under saturation conditions the efficiency of conversion of the pump energy into the Stokes radiation energy was ~0.8 and the small-signal gain was ~ 1.3 × 103.

Stacking fault formation due to the presence of liquid inclusions in barium nitrate crystals

Liquid inclusions on the cubic and octahedral faces of barium nitrate crystals show different formation mechanisms. Using X-ray diffraction topographs, we have established that the defects which appear on the inclusions in octahedral sectors are of two kinds: dislocations having large size Burgers vectors formed by the association of several coplanar 〈110〉 vectors and stacking faults created by the glide of a {111} plane, when the macrosteps which border the inclusion are parallel to the three other {111} planes. The nature of the glide vectors have been analysed and interpreted in terms of the atomic structure. The images on the section and traverse topographs have been compared.