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Andrade-Lucio, J. A.; Castillo, M. D. Iturbe; Aguilar, P.A. Márquez; Ramos-Garcı́a, R.

doi:10.1023/a:1006930624765

Cited by 20 publications

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“…The calculation for barium titanate is qualitatively consistent with the reported experimental data [4]. The situation with SBN is more complicated.…”

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confidence: 86%

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Current anisotropy influence on beam self-focusing in photorefractive materials

Korneev¹

2001

Journal of Modern Optics

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We show numerically that the existing photocurrent anisotropy strongly a ects the form of initially circular beam after self-focusing in photorefractive crystals. We estimate the ellipticity of the output beam in strontium barium niobate and barium titanate and compare it with existing experimental data.Single beam self-focusing in photorefractive materials has attracted a lot of attention. Of special interest is the so called soliton regime, in which the di raction is compensated by the nonlinearity, and the beam width is preserved with propagation [1]. A typical arrangement for self-focusing observation is depicted schematically in gure 1. Ferroelectrics are the materials of choice because of their high electro-optical coe cients. In this case the external electric eld is normally applied along the c-axis. The existing theory states that if the input beam is circular and additional illumination is used (the 2D screening soliton), the steady state response of the refractive index is not local and the soliton-type solution cannot have circular symmetry [2,3]. The primary reason for this is that the 2D beam distorts current lines, the y-component of the electric eld appears, and the x-component su ers complicated changes ( gure 1, see also gure 1 of [2]). For the e ective lens induced by Gaussian intensity distribution, the ratio of focal strengths in the direction of the applied eld and perpendicular to it is 3:1 [2]. Thus, it is expected that self-focusing in photorefractives is highly anisotropic.Experiments con rm this conjecture for barium titanate where the output intensity distribution is elliptic with an approximately 3:1 ratio between widths [4]. Experiments with strontium barium niobate (SBN) demonstrate, in some cases, close to circular output [5]. Here we discuss the possibility of resolving this contradiction by taking into account the photoconductivity anisotropy of ferroelectrics. This factor is quite pronounced. For barium titanate, the ratio between conductivities in c-axis and a-axis directions is 1 : 14 ¥ 20 [6][7][8]. For SBN, this ratio is approximately 3:1 [7], i.e. in this crystal the conductivity is greater along the c-axis, whereas in barium titanate it is greater along the a-axis. However, in earlier studies the conductivity was always considered isotropic.It is easy to understand that the SBN-type ratio favours more circular output than the isotropic conductivity case. If the conductivity along the c-axis is much greater than along the a-axis, the current lines are nearly parallel to the c-axis, and Journal of Modern Optics

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“…The calculation for barium titanate is qualitatively consistent with the reported experimental data [4]. The situation with SBN is more complicated.…”

supporting

confidence: 86%

“…Experiments con rm this conjecture for barium titanate where the output intensity distribution is elliptic with an approximately 3:1 ratio between widths [4]. Experiments with strontium barium niobate (SBN) demonstrate, in some cases, close to circular output [5].…”

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confidence: 70%

Current anisotropy influence on beam self-focusing in photorefractive materials

Korneev¹

2001

Journal of Modern Optics

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“…On the other hand, the theoretical model shows that the self focusing behavior is very sensitive to small variations of the input parameters. 7 We remind that at this intensity, SF ratio is always 1.…”

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confidence: 92%

“…Since their first observation [3,4], the PR solitons have been extensively characterized from experimental and theoretical point of view. As such, their properties are well known in typical PR materials (such as SBN, Bi 12 TiO 20 and BaTiO 3 [5][6][7][8]), in which the PR effect is due mainly to only one type of charge carriers and occurs at visible wavelengths. The dynamics of self focusing and soliton formation have been studied and characterized at steady state [9][10][11][12] as well as in transient regime [13,14], together with its dependency on various parameters (temperature, background illumination) for two different iron dopings.…”

Section: Introductionmentioning

confidence: 99%

Experimental control of steady state photorefractive self-focusing in InP:Fe at infrared wavelengths

2011

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This paper reports an experimental study of the self-focusing process in iron doped indium phosphide at an 1.06 micron wavelength, identifying the influence of temperature, beam intensity and background illumination for two different iron dopings. We point out that the iron ionization ratio is at the origin of different qualitative behavior previously reported and we show that it is possible to reproduce the said behaviors in the same crystal by applying a uniform illumination, allowing their eventual control for dynamic wave-guiding.

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“…Until now steady-state bright spatial solitons have been observed in BTO [3], SBN [4], InP:Fe [5], KNbO 3 [6], KLTN [7], and BaTiO 3 [8] crystals. Barium-calcium titanate (BCT) [9,10] is a promising photorefractive material and an alternative to BaTiO 3 , which is much easier to grow and does not have any phase transition within the temperature range from À120 C to 100 C. This crystal also possesses slightly larger electrooptic coefficients r 13 (20 pm/V) and r 33 (130 pm/V) compared to BaTiO 3 .…”

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confidence: 99%

Observation of Two-Dimensional Spatial Solitons in Iron-Doped Barium-Calcium Titanate Crystals

Shandarov

Wesner

et al. 2002

phys. stat. sol. (a)

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Subject classification: 42.65. Dp; 78.20.Jq Since the discovery of photorefractive spatial solitons [1,2], these non-diffracting waves have been the subject of an intense research effort, because they are particularly interesting for building alloptical diodes, transistors, switches, and all-optical computers. Until now steady-state bright spatial solitons have been observed in BTO [3], SBN [4], InP:Fe [5], KNbO 3 [6], KLTN [7], and BaTiO 3 [8] crystals. Barium-calcium titanate (BCT) [9, 10] is a promising photorefractive material and an alternative to BaTiO 3 , which is much easier to grow and does not have any phase transition within the temperature range from À120 C to 100 C. This crystal also possesses slightly larger electrooptic coefficients r 13 (20 pm/V) and r 33 (130 pm/V) compared to BaTiO 3 . However, no studies of photorefractive spatial soliton formation have been reported so far in BCT crystals. In this contribution, we investigate photorefractive spatial soliton formation in iron-doped BCT crystals and observe, for the first time to our knowledge, the formation of steady-state two-dimensional (2D) screening solitons in this material.Samples of the congruently melting composition Ba 0:23 Ca 0:77 TiO 3 are grown in the crystalgrowth laboratory of the Department of Physics at the University of Osnabr€uck [9, 10]. The dimension of our sample that is doped with 290 ppm Fe is 5 Â 5 Â 5 mm 3 . All surfaces are polished to optical quality. On both faces normal to the c-axis of the crystal, electrodes are prepared with silver paste. The light propagates along the a-axis in our experiment. Our experiments are conducted in a standard setup for soliton formation, in which an external electric field E 0 is applied along the ferroelectric c-axis. A frequency-doubled Nd:YAG laser (l ¼ 532 nm) is used as the light source. Because of the low dark conductivity of our sample s d % 6 Â 10 À14 W À1 cm À1 [9], a background illumination is necessary to tune the degree of saturation of the nonlinearity. This ordinarily polarized background light of the same wavelength 532 nm is made spatially incoherent by passing it through a rotating diffuser. The ratio r between the soliton light intensity (extraordinary polarization) and the background irradiance is r % 5. The soliton intensity is always kept below 50 mW/cm 2 to minimize photovoltaic self-defocusing. Figure 1 shows a characteristic result of 2D soliton formation. In this experiment, the beam intensity is I % 30 mW/cm 2 . The beam diameter at the crystal's input face is d in % 14 mm. Without an external electric field E 0 applied, the beam width d increases during propagation due to both, phys. stat. sol. (a) 189, No. 1, R4-R5 (2002) # WILEY-VCH Verlag Berlin GmbH, 13086 Berlin, 2002 0031-8965/02/18901-00R4 $ 17.50þ.50/0 Fig. 1. Formation of 2D solitons in BCT crystals. a) Images of the input beam (left hand), the diffracted output beam (center) and the selftrapped soliton beam (right hand). b) Horizontal (parallel to c-axis, k) and vertical (perpendicular to c-axis...

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Cited by 20 publications

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Current anisotropy influence on beam self-focusing in photorefractive materials

Current anisotropy influence on beam self-focusing in photorefractive materials

Experimental control of steady state photorefractive self-focusing in InP:Fe at infrared wavelengths

Observation of Two-Dimensional Spatial Solitons in Iron-Doped Barium-Calcium Titanate Crystals

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