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39-503: BGO can refer to: Bismuth germanate , a scintillating chemical compound BGO Records (Beat Goes On), a British record label Battlestar Galactica Online , an MMO by Bigpoint Bergen Airport, Flesland (IATA: BGO) in Bergen, Norway Burke-Gaffney Observatory, at Saint Mary's University in Halifax, Nova Scotia, Canada Topics referred to by

78-437: A history of similar duration, again starting with the ancient Greeks. In contrast, the acousto-optic effect has had a relatively short history, beginning with Brillouin predicting the diffraction of light by an acoustic wave, being propagated in a medium of interaction, in 1922. This was then confirmed with experimentation in 1932 by Debye and Sears , and also by Lucas and Biquard. The particular case of diffraction on

117-406: A single diffracted beam. The time taken for the acoustic wave to travel across the diameter of the light beam gives a limitation on the switching speed, and hence limits the modulation bandwidth. The finite velocity of the acoustic wave means the light cannot be fully switched on or off until the acoustic wave has traveled across the light beam. So to increase the bandwidth the light must be focused to

156-423: A small acousto-optic interaction length, ℓ, which is typically less than 1 cm. This type of diffraction occurs at an arbitrary angle of incidence, θ 0 {\displaystyle \theta _{0}} . In contrast, Bragg diffraction occurs at higher acoustic frequencies, usually exceeding 100 MHz. The observed diffraction pattern generally consists of two diffraction maxima; these are

195-460: A small diameter at the location of the acousto-optic interaction. This minimum focused size of the beam represents the limit for the bandwidth. The principle behind the operation of acousto-optic tunable filters is based on the wavelength of the diffracted light being dependent on the acoustic frequency. By tuning the frequency of the acoustic wave, the desired wavelength of the optical wave can be diffracted acousto-optically. There are two types of

234-411: Is a branch of physics that studies the interactions between sound waves and light waves, especially the diffraction of laser light by ultrasound (or sound in general) through an ultrasonic grating . In general, acousto-optic effects are based on the change of the refractive index of a medium due to the presence of sound waves in that medium. Sound waves produce a refractive index grating in

273-486: Is a change of a material's permittivity , ε {\displaystyle \varepsilon } , due to a mechanical strain a {\displaystyle a} . Photoelasticity is the variation of the optical indicatrix coefficients B i {\displaystyle B_{i}} caused by the strain a j {\displaystyle a_{j}} given by, where p i j {\displaystyle p_{ij}}

312-488: Is different from Wikidata All article disambiguation pages All disambiguation pages Bismuth germanate Bi 4 Ge 3 O 12 has a cubic crystal structure ( a = 1.0513 nm, z = 4, Pearson symbol cI76 , space group I 4 3d No. 220) and a density of 7.12 g/cm . When irradiated by X-rays or gamma rays it emits photons of wavelengths between 375 and 650 nm, with peak at 480 nm it produces about 8500 photons per megaelectronvolt of

351-400: Is diffracted due to this generated refraction index, forming a prominent diffraction pattern . This diffraction pattern corresponds with a conventional diffraction grating at angles θ n {\displaystyle \theta _{n}} from the original direction, and is given by, where λ {\displaystyle \lambda } is the wavelength of

390-559: Is given as, where λ {\displaystyle \lambda } is the optical wavelength of the beam and ν {\displaystyle \nu } is the velocity of the acoustic wave. AOD technology has made practical the Bose–Einstein condensation for which the 2001 Nobel Prize in Physics was awarded to Eric A. Cornell, Wolfgang Ketterle and Carl E. Wieman. Another application of acoustic-optical deflection

429-445: Is in acousto-optical devices for the deflection, modulation , signal processing and frequency shifting of light beams. This is due to the increasing availability and performance of lasers , which have made the acousto-optic effect easier to observe and measure. Technical progress in both crystal growth and high frequency piezoelectric transducers has brought valuable benefits to acousto-optic components' improvements. Along with

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468-431: Is much smaller than of BGO and BSO. Unlike somewhat similar performing perovskites , sillenites aren't ferroelectric . The materials can find use in phased-array optics . When sputtering, the target has to be kept below 450 °C as otherwise the bismuth vapor pressure would get the composition out of stoichiometry , but above 400 °C to form the piezoelectric γ phase. Acousto-optical Acousto-optics

507-458: Is nearly equivalent in both orthogonally linearly polarized output beams (differing by the Stokes and Anti-Stokes scattering parameter). Because of dispersion, these beams move slightly with scanning rf frequency. An acousto-optic deflector spatially controls the optical beam. In the operation of an acousto-optic deflector the power driving the acoustic transducer is kept on, at a constant level, while

546-428: Is optical trapping of small molecules. AODs are essentially the same as acousto-optic modulators (AOMs). In an AOM, only the amplitude of the sound wave is modulated (to modulate the intensity of the diffracted laser beam), whereas in an AOD, both the amplitude and frequency are adjusted, making the engineering requirements tighter for an AOD than an AOM. All materials display the acousto-optic effect. Fused silica

585-399: Is the photoelastic tensor with components, i {\displaystyle i} , j {\displaystyle j} = 1,2,...,6. Specifically in the acousto-optic effect, the strains a j {\displaystyle a_{j}} are a result of the acoustic wave which has been excited within a transparent medium. This then gives rise to the variation of

624-415: Is the refractive index for the diffracted optical waves. In general, there is no point at which Bragg diffraction takes over from Raman–Nath diffraction. It is simply a fact that as the acoustic frequency increases, the number of observed maxima is gradually reduced due to the angular selectivity of the acousto-optic interaction. Traditionally, the type of diffraction, Bragg or Raman–Nath, is determined by

663-393: Is the wavelength of the incident light wave (in a vacuum), f {\displaystyle f} is the acoustic frequency, v {\displaystyle v} is the velocity of the acoustic wave, n i {\displaystyle n_{i}} is the refractive index for the incident optical wave, and n d {\displaystyle n_{d}}

702-823: The Czochralski process and usually supplied in the form of cuboids or cylinders. Large crystals can be obtained. Crystal production is typically done around 1100 °C, i.e. around 50 °C above its melting point. Bi 12 GeO 20 has a cubic crystal structure ( a = 1.01454 nm, z = 2, Pearson symbol cI66 , space group I23 No. 197) and a density of 9.22 g/cm . This bismuth germanate has high electro-optic coefficients (3.3 pm/V for Bi 12 GeO 20 ), making it useful in nonlinear optics for building Pockels cells , and can also be used for photorefractive devices for ultraviolet range. The Bi 12 GeO 20 crystals are piezoelectric , show strong electro-optical and acousto-optical effects, and find limited use in

741-402: The acoustic frequency is varied to deflect the beam to different angular positions. The acousto-optic deflector makes use of the acoustic frequency dependent diffraction angle, where a change in the angle Δ θ d {\displaystyle \Delta \theta _{d}} as a function of the change in frequency Δ f {\displaystyle \Delta f}

780-399: The acoustic wave, and Δ n {\displaystyle \Delta n} is the amplitude of variation in the refractive index generated by the acoustic wave, and is given as, The generated refractive index, (2), gives a diffraction grating moving with the velocity given by the speed of the sound wave in the medium. Light which then passes through the transparent material,

819-522: The acousto-optic device is modulating the output along the Bragg diffraction angle, switching it on and off. The device is operated as a modulator by keeping the acoustic wavelength (frequency) fixed and varying the drive power to vary the amount of light in the deflected beam. There are several limitations associated with the design and performance of acousto-optic modulators. The acousto-optic medium must be designed carefully to provide maximum light intensity in

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858-427: The acousto-optic filters, the collinear and non-collinear filters. The type of filter depends on geometry of acousto-optic interaction. The polarization of the incident light can be either ordinary or extraordinary. For the definition, we assume ordinary polarization. Here the following list of symbols is used, α {\displaystyle \alpha } : the angle between the acoustic wave vector and

897-423: The acousto-optic requirements for Bragg diffraction limit the frequency range of acousto-optic interaction. As a consequence, the speed of operation of acousto-optic devices is also limited. By varying the parameters of the acoustic wave, including the amplitude , phase , frequency and polarization , properties of the optical wave may be modulated. The acousto-optic interaction also makes it possible to modulate

936-560: The angle α, such that, v 110 {\displaystyle v_{110}} and v 001 {\displaystyle v_{001}} are the sound velocities along the axes [110] and [001], consecutively. The value of α 1 {\displaystyle \alpha _{1}} is determined by the angles φ {\displaystyle \varphi } and α {\displaystyle \alpha } , The angle β {\displaystyle \beta } between

975-494: The central frequency f i {\displaystyle f_{i}} of the filter are defined by the following set of equations, Refractive indices of the ordinary ( n 0 {\displaystyle n_{0}} ) and extraordinary ( n e {\displaystyle n_{e}} ) polarized beams are determined by taking into account their dispersive dependence. The sound velocity, v {\displaystyle v} , depends on

1014-461: The conditions Q ≫ 1 {\displaystyle Q\gg 1} and Q ≪ 1 {\displaystyle Q\ll 1} respectively, where Q is given by, which is known as the Klein–Cook parameter. Since, in general, only the first order diffraction maximum is used in acousto-optic devices, Bragg diffraction is preferable due to the lower optical losses. However,

1053-487: The crystal; α ℓ {\displaystyle \alpha _{\ell }} : the angle between the input face of the cell and acoustic wave vector; β {\displaystyle \beta } : the angle between deflected and non-deflected light at the central frequency; ℓ {\displaystyle \ell } : the transducer length. The incidence angle φ {\displaystyle \varphi } and

1092-427: The crystallographic axis z of the crystal; γ {\displaystyle \gamma } : the wedge angle between the input and output faces of the filter cell (the wedge angle is necessary for eliminating the angular shift of the diffracted beam caused by frequency changing); φ {\displaystyle \varphi } : the angle between the incident light wave vector and [110] axis of

1131-443: The current applications, acousto-optics presents interesting possible application. It can be used in nondestructive testing , structural health monitoring and biomedical applications, where optically generated and optical measurements of ultrasound gives a non-contact method of imaging. Optics has had a very long and full history, from ancient Greece , through the renaissance and modern times. As with optics, acoustics has

1170-475: The diffracted and non-diffracted beams defines the view field of the filter; it can be calculated from the formula, Input light need not be polarized for a non-collinear design. Unpolarized input light is scattered into orthogonally polarized beams separated by the scattering angle for the particular design and wavelength. If the optical design provides an appropriate beam block for the unscattered light, then two beams (images) are formed in an optical passband that

1209-1134: The field of crystal oscillators and surface acoustic wave devices. Single crystal rods and fibers can be grown by floating zone process from a rod of mixture of bismuth oxide and germanium oxide . The crystals are transparent and brown colored. The crystals of BGO and similar compounds BSO (Bi 12 SiO 20 , bismuth silicon oxide , sillenite ) and BTO (Bi 12 TiO 20 ), are photorefractive and photoconductive . BGO and BSO crystals are efficient photoconductors with low dark conductivity . They can be used in electro-optical applications, like optical PROM , PRIZ spatial light modulators , realtime hologram recording, correlators, and systems for adaptive correction of ultrashort laser pulses, and in fiber optic sensors for electric and magnetic fields. Waveguide structures allow uniform illumination over wide spectral range. Thin film sillenite structures, which can be deposited e.g. by sputtering , have wide range of potential applications. BSO crystals are used in optically addressed spatial light modulators and in liquid crystal light valves . The optical activity of BTO

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1248-411: The first order, under a certain angle of incidence , (also predicted by Brillouin), has been observed by Rytow in 1935. Raman and Nath (1937) have designed a general ideal model of interaction taking into account several orders. This model was developed by Phariseau (1956) for diffraction including only one diffraction order. The acousto-optic effect is a specific case of photoelasticity , where there

1287-663: The high energy radiation absorbed. It has good radiation hardness (parameters remaining stable up to 5.10 Gy ), high scintillation efficiency, good energy resolution between 5 and 20 MeV, is mechanically strong, and is not hygroscopic . Its melting point is 1050 °C. It is the most common oxide-based scintillator. Bismuth germanium oxide is used in detectors in particle physics , aerospace physics, nuclear medicine , geology exploration, and other industries. Bismuth germanate arrays are used for gamma pulse spectroscopy. BGO crystals are also used in positron emission tomography detectors. Commercially available crystals are grown by

1326-404: The material, and it is this grating that is "seen" by the light wave. These variations in the refractive index, due to the pressure fluctuations, may be detected optically by refraction, diffraction, and interference effects; reflection may also be used. The acousto-optic effect is extensively used in the measurement and study of ultrasonic waves. However, the growing principal area of interest

1365-409: The optical beam by both temporal and spatial modulation. A simple method of modulating the optical beam travelling through the acousto-optic device is done by switching the acoustic field on and off. When off the light beam is undiverted, the intensity of light directed at the Bragg diffraction angle is zero. When switched on and Bragg diffraction occurs, the intensity at the Bragg angle increases. So

1404-482: The optical wave, Λ {\displaystyle \Lambda } is the wavelength of the acoustic wave and m {\displaystyle m} is the integer order maximum. Light diffracted by an acoustic wave of a single frequency produces two distinct diffraction types. These are Raman–Nath diffraction and Bragg diffraction . Raman–Nath diffraction is observed with relatively low acoustic frequencies, typically less than 10 MHz, and with

1443-399: The refractive index. For a plane acoustic wave propagating along the z axis, the change in the refractive index can be expressed as where n 0 {\displaystyle n_{0}} is the undisturbed refractive index, Ω {\displaystyle \Omega } is the angular frequency , K {\displaystyle K} is the wavenumber of

1482-403: The same term [REDACTED] This disambiguation page lists articles associated with the title BGO . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=BGO&oldid=1058431312 " Category : Disambiguation pages Hidden categories: Short description

1521-454: The zeroth and the first orders. However, even these two maxima only appear at definite incidence angles close to the Bragg angle, θ B {\displaystyle \theta _{B}} . The first order maximum or the Bragg maximum is formed due to a selective reflection of the light from the wave fronts of ultrasonic wave. The Bragg angle is given by the expression, where λ {\displaystyle \lambda }

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