Bi12SiO20 Crystals Research Articles

Quasi-balanced two-wave mixing interferometer for remote ultrasound detection

We present an improved detection scheme for a two-wave mixing interferometer with a Bi12SiO20 crystal. The proposed detection scheme allows quasi-balanced detection of ultrasonic signals whereby electrical disturbances are suppressed. Quasi-balancing is achieved by changing the polarity of the high voltage at the photorefractive crystal, leading to an inversion of the optical interference signal, in combination with inversion of the detector signal using a signal inverter before the data acquisition device. The polarity of the high voltage is changed by utilizing an H-bridge consisting of five high-voltage relays. Microcontrollers are used to synchronize the reversion of the high voltage at the photorefractive crystal and the inversion of the measured signals. We demonstrate remote measurement of ultrasonic waves and shown that electrical disturbances are suppressed using the quasi-balanced mode.

Experimentally obtained values of electric field of an atmospheric pressure plasma jet impinging on a dielectric surface

We report on experimentally obtained values of the electric field magnitude on a dielectric surface induced by an impinging atmospheric pressure plasma jet. The plasma plume was striking the dielectric surface at an angle of 45°, at 5 mm from the surface measured at the axis of the jet. The results were obtained using Pockels technique on a BSO (Bi12SiO20) crystal. A coaxial configuration of the plasma jet was used, operating in a stable mode with one bullet per voltage period, at 30 kHz and amplitude of 2 kV. The electric field was shown to be a function of the gas flow (He, at 300, 500 and 700 SCCM) and the manner in which the discharge spreads over the dielectric surface. The maximum value of 11.6 × 105 V m−1 was obtained at the negative half-period of the discharge current measured at the grounded electrode, at the flow of 300 SCCM. The largest electric field averaged over the area of the spreading of the discharge (3.6 × 105 V m−1) was found in the same conditions.

Digital holographic microscopy with photorefractive sillenite Bi12SiO20 crystals

In this work, we demonstrated by first time that image digital holographic microscopy can be instrumented using photorefractive sillenite Bi12SiO20 (BSO) crystals in diffusion regime as holographic recording medium. The writing–reading holographic process in photorefractive BSO crystal and this holographic reconstructed image is combined to form the image hologram with the second reference beam in CCD plane in the Mach–Zehnder interferometer. The system was tested using a micro scale object and 3D phase image is calculated by performing digital reconstruction using only one hologram.

Speckle photo-electromotive force in Bi12SiO20: Effect of the speckle size

A study of the speckle photo-electromotive force (PEMF) in a photorefractive sensor of amplitudes of micro-oscillations is presented. The experimental behavior of the first harmonic of the photocurrent generated as a function of the average speckle diameter and the oscillation amplitude of the speckle pattern is analyzed for a sensor implemented with a Bi12SiO20 (BSO) crystal. For a given light intensity, a nearly constant value of the maximum amplitude of the first harmonic was experimentally observed for the range of speckle sizes considered. This experimental result and the linear dependence of the vibration amplitude yielding the maximum of the photocurrent as a function of the speckle diameter were appropriately described by the mathematical model considered. Results show the possibility of adequately selecting the speckle size to optimize the output of speckle PEMF-based sensors depending on the oscillation amplitude to be measured.

Adaptive interferometers for sensor applications

We report on simple high-sensitivity interferometric techniques of detecting vibrations and present characteristics of laser vibrometer using Bi12SiO20 crystal. Adaptive interferometer enables efficient conversion of high-frequency phase modulation of speckle-like optical wave reflected from the vibrating object into an output signal with concomitant setting of optimal operation point of the interferometer and suppression of amplitude laser noise.

Energy enhancement in time-reversed ultrasonically encoded optical focusing using a photorefractive polymer

Time-reversed ultrasonically encoded (TRUE) optical focusing achieves light focusing into scattering media beyond one transport mean free path, which is desirable in biomedical optics. However, the focused optical energy needs to be increased for broad applications. Here, we report the use of a photorefractive polymer (PRP) as the phase conjugate mirror in TRUE optical focusing. The PRP boosted the focused optical energy by ~40 times in comparison to the previously used photorefractive Bi12SiO20 crystal. As a result, we successfully imaged absorbing objects embedded in the middle plane of a tissue-mimicking phantom having an optical thickness of 120 scattering mean free paths.

Quasi-nonvolatile storage in Ru-doped Bi_12SiO_20 crystals by two-wavelength holography

Prolonged read-out process of a hologram recorded at near infrared with simultaneous green light exposure is measured in Ru-doped Bi12SiO20 crystal. The experimental results are confirmed by numerical simulations, suggesting two different traps involved in the space-charge transport mechanism. In addition, quasi-permanent holographic recording of image with fast updating speed by using two-wavelength recording is demonstrated.

Growth and characterization of Nd:Bi12SiO20 single crystal

A Nd:Bi12SiO20 crystal was grown by the Czochralski method. The thermal properties of the crystal were systematically studied. The thermal expansion coefficient was measured to be α=11.42×10−6K−1 over the temperature range of 295–775K, and the specific heat and thermal diffusion coefficient were measured to be 0.243Jg−1k−1 and 0.584mm2/s, respectively at 302K. The density was measured to be 9.361g/cm3 by the buoyancy method. The thermal conductivity of Nd:Bi12SiO20 was calculated to be 1.328Wm−1K−1 at room temperature (302K). The refractive index of Nd:Bi12SiO20 was measured at room temperature at eight different wavelengths. The absorption and emission spectra were also measured at room temperature. Continuous-wave (CW) laser output of a Nd:Bi12SiO20 crystal pumped by a laser diode (LD) at 1071.5nm was achieved with an output power of 65mW. To our knowledge, this is the first time LD pumped laser output in this crystal has been obtained. These results show that Nd:Bi12SiO20 can serve as a laser crystal.

Growing high-quality Bi12SiO20 crystals of large diameter (85 mm)

Conditions that ensure reproducible growth of 〈110〉-oriented perfect Bi12SiO20 (BSO) crystals by the low-thermal-gradient Czochralski technique, whereby the entire crystallization front is occupied by the (110) crystal face, have been determined with the aid of numerical simulations. Using the established regime, BSO crystals have been obtained with a diameter of 85 mm, a length of 200 mm, and a mass of 10 kg. The density of dislocations in the crystals does not exceed 10 cm−2, and the refractive index inhomogeneity is below 10−3.

Solubility and optical activity of Bi12SiO20 crystals

In this paper the solubility and optical activity of Bi12SiO20 (BSO) single crystals grown in aqueous NaOH under hydrothermal conditions were reported. BSO was found to have a positive solubility coefficient from 350 to 400°C in 0.5–3M NaOH, as well as a positive dependence on mineralizer concentration. The reason why additional SiO2 should be introduced in the mineralizer to grow high quality BSO was analyzed. High quality and colorless BSO crystals were grown using 4M NaOH as a mineralizer and additional 3wt% SiO2 introduced in the mineralizer. Results showed that the optical activity of hydrothermal colorless BSO was superior to that of BSO grown by the Czochralski (Cz) method.

Real-time holography in ruthenium-doped bismuth sillenite crystals at 1064 nm

Real-time holographic recording and an improvement of the response time in ruthenium (Ru)-doped Bi(12)SiO(20) (BSO) crystal at 1064 nm is obtained. Using green light pre-exposure, a significant operation speed of 60 ms is achieved. In addition, the ability for image reconstruction is demonstrated in Ru-doped BSO, supporting further applications as reversible media for real-time image processing at the near-IR spectral range.

A photosensitive Cr3+ center in photorefractive Bi12SiO20 crystals co-doped with chromium and phosphorus

A trigonal Cr3+ (3d3) defect in sillenite type Bi12SiO20 crystals co-doped with chromium and phosphorus has been identified by means of multi-frequency X-band (9.4 GHz), Q-band (35 GHz) and W-band (94 GHz) electron paramagnetic resonance (EPR). A consistent analysis of the observed spectra and their angular dependence was reached using an S = 3/2 spin Hamiltonian with axial symmetry around a 〈111〉 crystallographic direction, an isotropic g-value g = 1.983, and a zero field splitting parameter B20 = 0.1950 cm−1. The spectra are attributed to a chromium ion in the unusual Cr3+ valence replacing a substitutional Si4+ in tetrahedral oxygen coordination. Evidence is found that the symmetry lowering from tetrahedral to trigonal is not spontaneous but induced by an associated defect, for which a P5+ ion in a nearest-neighbor Si4+ site is the most plausible candidate. Optical excitation results in a reversible charge transfer process directly correlated with a photochromic effect: near-UV light leads to a strong reduction of the Cr3+ EPR signals, and induces a broad band at 675 nm in the absorption spectrum, and both effects are reversed under red light excitation.

Growth of Bi12GeO20 and Bi12SiO20 crystals by the low-thermal gradient Czochralski technique

Bi12SiO20 crystals have been grown for the first time by the low-thermal gradient Czochralski technique in the 〈111〉 and 〈110〉 directions. The conditions for reproducible crystal growth with a high-quality polyhedral faceted front are found. The systematic features of shaping Bi12SiO20 and Bi12GeO20 crystals, grown by the low-thermal gradient Czochralski technique, are compared. The defect formation in these crystals is studied and their optical homogeneity is analyzed by interferometry.

Photorefractive properties enhancement of doped bismuth sillenite crystals

The influence of transition metal ions Ru, Co and Co combination with Al on the light-induced and holographic properties of Bi12SiO20 (BSO) crystals is studied. A significant enhancement of the response time is detected at 633 nm when the crystals are simultaneously exposed with green light, i.e. by optical excitation energy close to the location of the main photorefractive center in sillenite structure. Furthermore, prolonged read-out process is detected in Ru-doped BSO, probably due to the Ru ability to exist in three valence states simultaneously, among which some may appear only after appropriate illumination. A possibility to control the electron-hole competition in BSO: Co + Al crystal, due to the charge compensation, is demonstrated. A theoretical model is proposed to explain the complicated holographic behavior.

Effect of SiO2 on Bi12SiO20 crystals grown by hydrothermal technology

In this paper, the effect of SiO2 on the growth of BSO crystals under hydrothermal conditions was studied. With the increase of SiO2's concentration doped in the mineralizer, the color of the grown BSO crystals became more pale and the crystallization became better. Moreover the morphology of BSO crystals changed from that with {111} and {112} facets mainly presented to that with {110} and {100} facets mainly presented. XRD and FTIR spectra for these crystals were analysed and the behaviors were explained by BiSi3+ defect. Stable growth technology was obtained under the condition of 3wt% SiO2 doped in the mineralizer. The X-ray rocking curve and the transmittance spectra of BSO grown under this condition (3wt% SiO2 doped) were investigated. The cutoff wavelength 388nm is shorter than that of Czochralski BSO, and the crystal almost has no absorption shoulder (400–500nm) existing in Czochralski BSO. The FWHM value of 17arcsec for the X-ray rocking curve indicates the good quality of the grown crystal.

Factors determining optical absorption of variously doped single crystals of Bi12SiO20

Bi12SiO20 are widely used in optical devices, spatial-time light modulators and as holographic media depending on their properties in a wide spectral range. This work deals with the optical absorption coefficient of pure and doped Bi12SiO20 (BSO) crystals measured in the energy region 1.5 – 3.2 eV and generalise our already published and new experimental data on crystals doped with Al, P, Cr, Mn, Fe, Co, Ni, Cu, Se, Ru. It is shown that such doping affects differently the optical absorption in both the near-fundamental-edge shoulder (3.2 – 2.2 eV) and on impurity levels in the band gap (2.2 – 1.5 eV). The main factors determining the absorption are concentration and segregation coefficient, electro-negativity of the doping ion and its difference from that of oxygen (DEN), the oxidation states, possible coordination and corresponding ionic radius. The role of some of these factors to the spectral dependence of the optical absorption of BSO is discussed from the view point of a suitable doping of BSO to obtain and modify the optical transparency.

Photoinduced absorption study of carrier dynamics in Ru-doped Bi12SiO20 crystals after nanosecond laser pulse excitation

The charge carrier dynamics in the sillenite type crystal Bi12SiO20 (BSO) doped with ruthenium is studied by monitoring the optical density changes after nanosecond laser pulse excitation using a frequency-doubled Nd:yttrium aluminum garnet laser. Ruthenium doping leads to a relatively high density of trap levels that significantly increase the relaxation time of excited charge carriers in comparison with a nondoped BSO. Relaxation dynamics with two different decay time constants is observed in BSO:Ru in the studied submicron to 100 s time range and their dependences on pump intensity and on temperature are investigated. From the observed temperature dependence of the slower and faster of the two decay components, thermal activation energies of Ea,s=0.80±0.03 eV and Ea,f=0.68±0.03 eV were determined, respectively. The results indicate that in BSO:Ru at least two different traps centers are involved in the long-lived photoinduced carrier dynamics.

10.1007/s11487-008-3016-9

Fiber-optic sensors (FOSs) of the magnetic field and electric current are developed and studied. The sensors are based on the Faraday effect in Bi12GeO20 and Bi12SiO20 crystals. The possibility of an increased sensitivity of such FOSs that is due to the application of multipass sensitive elements is considered. The limits for an increase in the optical-path length in a crystal with multiple passing of light are determined. Temperature drifts of the conversion coefficients are presented for various structures of sensitive elements.

New Interfacial Shear-Horizontal Waves in Piezoelectric Cubic Crystals

This theoretical study reports results on acoustic wave propagation along the interface of two half-spaces representing cubic crystals of both piezoelectric classes ?43m and 23 with strong piezoelectric effect. In similar configurations, the interfacial Maerfeld-Tournois waves can propagate along the interface of two transversely-isotropic materials of class 6 mm, in which the shear-horizontal surface acoustic waves (SH-SAWs) called the Bleustein-Gulyaev (BG) waves can also exist. Cubic piezoelectrics cannot support existence of the surface BG-waves, according to the recent report by Gulyaev and Hickernell. Hence, new interfacial SH-waves are studied in this paper concerning unique direction [101] of wave propagation in cubic crystals using different electrical boundary conditions (EBCs) of both metallized and non-metallized interfaces. The new interfacial SH-waves can always propagate along the interface of two identical piezoelectric crystals with opposite polarization. In this case, the calculated velocities for both EBCs coincide with the velocity of the ultrasonic surface Zakharenko wave (USZW) propagating in direction [101] on the metallized surface of a cubic piezoelectrics. It was also found that the new interfacial SH-waves can exist when wave propagation is along the interface of two dissimilar half-spaces, for instance, the piezoelectric cubic crystals Bi12SiO20 and Bi12GeO20. Several calculations are also carried out as examples. PACS: 51.40.+p, 62.65.+k, 68.35.Gy, 68.35.Iv, 68.60.Bs, 74.25.Ld.

Determination of nanometer vibration amplitudes by using a homodyne photorefractive crystal interferometer

We report a low cost and high accuracy interferometric technique for detecting nanometer vibrations by using a photorefractive crystal interferometer based on two-wave mixing within a Bi12SiO20 (BSO) crystal. The results of small displacement detection on the sample (1–2 nm) and comparison between the sensitivity of Michelson and photorefractive adaptive interferometers are presented. Furthermore, the effect of an external electric field applied to the photorefractive crystal on the Signal to Noise Ratio (SNR) and on the vibrometer sensitivity is investigated.