Alexander Grabar - Profile on Academia.edu (original) (raw)

Papers by Alexander Grabar

Bulletin of the American Physical Society, Mar 16, 2016

photorefraction.[1,2] The decay of the optically produced Sb 2+ ions was directly measured throug... more photorefraction.[1,2] The decay of the optically produced Sb 2+ ions was directly measured through EPR and was found to have a hyperbolic character:˜1/(t/τ +1) with an activation energy of 0.42 eV. This decay character and a very similar activation energy were also found in photorefraction and optically induced absorption experiments. The observed hyperbolic decay was explained through the set of rate equations that takes into account the EPR result: only Sb 3+ ions are present in Sn 2 P 2 S 6 :Sb in thermal equilibrium. The longwavelength onset of the EPR-measured Sb 2+ "photocreation" spectrum together with the activation energy of the Sb 2+ decay allowed to firmly locate the position of the Sb 2+/3+ electron level in the bandgap of Sn 2 P 2 S 6 : 0.42 eV below the conduction band bottom. [1]

Photocreation and hyperbolic decay of Sb 2+ in Sn 2 P 2 S 6 :Sb

APS, 2016

Dynamic Holographic Interferometry with Doped Sn2P2S6 Photorefractive Crystals

Journal of Physics: Conference Series, 2017

HTTP://ONLINELIBRARY.WILEY.COM/DOI/10.1002/JBIO.201400071/PDF

Photorefractive induced slowdown of nanosecond light pulses in the nanosecond regime

2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2021

Recently, several works have shown that the light group velocity can be reduced using the recordi... more Recently, several works have shown that the light group velocity can be reduced using the recording of dynamic refractive index gratings in photorefractive (PR) crystals [1] , [2] , [3] . The slowdown of light is performed using optical beams wave mixing: it yields the output pulse amplification and increases the light dispersion inside the PR crystal. For example, the TWM method demonstrated that the delay time ∆ τ can be varied as a function of the TWM gain values Γ and the input pulse widths T 0 . However, several works have shown that the results achieved by this method are limited in terms of pulse duration. Indeed, only long pulses with time duration of ms−s can be slowdown in a PR crystal both at the visible and the infrared wavelengths [4] .

Photorefractive effect in Sn2P2S6 ferroelectrics

We developped two new methods to determine separately by the real and imaginary parts of the nonl... more We developped two new methods to determine separately by the real and imaginary parts of the nonlinear susceptibility by femtosecond interferometry. The first one utilizes spacial fringes of a Mach-Zehnder interferometer with a reference interferometer, while the second one utilizes frequency domain interference.

Customization of Sn2P2S6 ferroelectrics by post-growth solid-state diffusion doping

Journal of Materials Chemistry C

For the first time, we demonstrated successful post-synthesis incorporation of metal dopants at e... more For the first time, we demonstrated successful post-synthesis incorporation of metal dopants at elevated temperature into a host structure of Sn2P2S6, known as the grandfather of dichalcogenide ferroelectrics with a formula M2P2X6 (M = metal and X = chalcogen).

Optics Letters

We present a new method to perform acousto-optic imaging based on a spatio-temporal structuration... more We present a new method to perform acousto-optic imaging based on a spatio-temporal structuration of long-duration acoustic plane waves. This approach is particularly relevant when using detectors with long integration time. We show how it is possible to reconstruct an image by measuring its two-dimensional Fourier components. A proof of concept is presented using a photorefractive detection scheme, demonstrating equal performances to direct imaging. The overall acquisition time is compatible with medical monitoring applications.

Fast near infrared photorefraction and phase conjugation in Sn/sub 2/P/sub 2/S/sub 6/

2003 Conference on Lasers and Electro-Optics Europe (CLEO/Europe 2003) (IEEE Cat. No.03TH8666), 2003

Tin hypothiodiphosphate (Sn2P2S6) photorefractive crystals exhibit high beam coupling gain combin... more Tin hypothiodiphosphate (Sn2P2S6) photorefractive crystals exhibit high beam coupling gain combined with relatively fast photorefractive response in the near infrared, which makes them attractive for photorefractive applications in connection with diode or solid state near infrared lasers. An important process in several of these applications is phase conjugation of laser beams. This article investigates the photorefractive properties of Sn2P2S6 in the near infrared wavelength range. Conventional yellow, Te-doped, and modified brown crystals are examined. It was found that the coupling strength in brown is high enough to reach the saturation of reflectivity.

Photorefractive Effects in Sn2P2S6

Photorefractive Materials and Their Applications 2, 2007

ABSTRACT Tin hypothiodiphosphate (Sn2P2S6) is a very promising material for photorefractive appli... more ABSTRACT Tin hypothiodiphosphate (Sn2P2S6) is a very promising material for photorefractive applications in the red and near-infrared wavelength range. The main advantage of Sn2P2S6 as an infrared-sensitive photorefractive material is its high beam-coupling gain combined with relatively fast response, about two orders of magnitude faster than in the conventionally used photorefractive material BaTiO3 doped with rhodium. Compared to oxide ferroelectrics, which are wide-band-gap dielectrics, Sn2P2S6 crystals are characterized by a narrower band gap (2.3 eV) and a higher photorefractive sensitivity, and are transparent in the range of 530– 8000 nm.

Te-doped Sn2P2S6: A new material for fast photorefractive applications at 1.06 μm

2006 Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference, 2006

We demonstrate self-pumped optical phase conjugation in Te-doped Sn2P2S6 up to a wavelength of 1.... more We demonstrate self-pumped optical phase conjugation in Te-doped Sn2P2S6 up to a wavelength of 1.06 mum. A phase conjugate reflectivity of more than 40 percent with a very fast rise time below 100 ms has been measured.

Molecular Crystals and Liquid Crystals, 2004

It was found that doping of tiny ferroelectric particles to a nematic liquid crystal (LC) strongl... more It was found that doping of tiny ferroelectric particles to a nematic liquid crystal (LC) strongly affects dielectric properties of the system. The doping increases dielectric response of the LC due to interaction between LC molecules and particles, which possess large dipole moment and high polarisability. The suspension reveals high dielectric response on either side of the Curie temperature, T Curie , and peculiarity at the vicinity of T Curie . This result points at retention of dipole ordering above Curie temperature that may be a result of a memory effect.

The Critical Behaviour of Ultrasonic Velocity at a Second-Order Phase Transition in Sn2P2S6 Single Crystals

physica status solidi (b), 1999

ABSTRACT

Thermal expansion of Sn 2 P 2 S 6 crystals

Phase Transitions, 2009

ABSTRACT We present the results for thermal expansion coefficients of Sn2P2S6 crystals determined... more ABSTRACT We present the results for thermal expansion coefficients of Sn2P2S6 crystals determined both in the crystallographic system and the system based on eigenvectors of thermal expansion tensor. Peculiarities of temperature evolution of the indicative surface of thermal expansion tensor for Sn2P2S6 are discussed, including the region of their ferroelectric phase transition.

Critical exponents of phase transition in ferroelectric Sn 2 P 2 S 6 : comparison of optical and dilatometric data

Phase Transitions, 2010

... DOI: 10.1080/01411590903553452 Andriy Say a , Oksana Mys a , Dmitro Adamenko a , Alexandr Gra... more ... DOI: 10.1080/01411590903553452 Andriy Say a , Oksana Mys a , Dmitro Adamenko a , Alexandr Grabar b , Yulian Vysochanskii b , Andriy Kityk a c & Rostyslav Vlokh a * pages 123-139. Available online: 16 Feb 2010. ...

Optics Express, 2005

We demonstrate self-pumped optical phase conjugation in Te-doped Sn 2 P 2 S 6 , a semiconducting ... more We demonstrate self-pumped optical phase conjugation in Te-doped Sn 2 P 2 S 6 , a semiconducting ferroelectric crystal, using a 1.06 μm wavelength cw Nd:YAG laser. The photorefractive gain of this crystal has been increased to Γ = (3.9 ± 0.4) cm -1 by Te doping. We observed self-pumped optical phase conjugation in a ring cavity scheme with phase conjugate reflectivities of more than 40 percent and a very fast phase conjugate rise time below 100 ms at a light intensity of 20 W/cm 2 . This is more than two orders of magnitude faster than in any other photorefractive crystal, as e.g. in Rh-doped BaTiO 3 .

Enhanced photorefractive properties of modified Sn2P2S6

Optics Communications, 2001

ABSTRACT

Photorefractive and photochromic effects in Sn2P2S6 at various temperatures

Optics Communications, 2013

ABSTRACT Photochromic effect in nominally pure and doped Sn2P2S6 photorefractive crystals is inve... more ABSTRACT Photochromic effect in nominally pure and doped Sn2P2S6 photorefractive crystals is investigated in the temperature range 120–310 K. This effect determines a mechanism of the amplitude hologram formation at low temperatures, and we show that a competition between the photorefractive (phase) and the amplitude gratings occurs at increasing temperature.

Journal of the Optical Society of America B, 2008

A colloid of ferroelectric nanoparticles in a cholesteric liquid crystal

Journal of Optics A: Pure and Applied Optics, 2009

... Keywords: ferroelectric nano-particle, nematics, cholesterics, dielectric anisotropy, electro... more ... Keywords: ferroelectric nano-particle, nematics, cholesterics, dielectric anisotropy, electro-optic response ... source of the effect is the strong electric field surrounding a ferroelectric particle. ... Among the other es-sential consequences of the ferroelectric nanoparticle insertion is the ...

Bulletin of the American Physical Society, Mar 16, 2016

photorefraction.[1,2] The decay of the optically produced Sb 2+ ions was directly measured throug... more photorefraction.[1,2] The decay of the optically produced Sb 2+ ions was directly measured through EPR and was found to have a hyperbolic character:˜1/(t/τ +1) with an activation energy of 0.42 eV. This decay character and a very similar activation energy were also found in photorefraction and optically induced absorption experiments. The observed hyperbolic decay was explained through the set of rate equations that takes into account the EPR result: only Sb 3+ ions are present in Sn 2 P 2 S 6 :Sb in thermal equilibrium. The longwavelength onset of the EPR-measured Sb 2+ "photocreation" spectrum together with the activation energy of the Sb 2+ decay allowed to firmly locate the position of the Sb 2+/3+ electron level in the bandgap of Sn 2 P 2 S 6 : 0.42 eV below the conduction band bottom. [1]

Photocreation and hyperbolic decay of Sb 2+ in Sn 2 P 2 S 6 :Sb

APS, 2016

Dynamic Holographic Interferometry with Doped Sn2P2S6 Photorefractive Crystals

Journal of Physics: Conference Series, 2017

HTTP://ONLINELIBRARY.WILEY.COM/DOI/10.1002/JBIO.201400071/PDF

Photorefractive induced slowdown of nanosecond light pulses in the nanosecond regime

2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2021

Recently, several works have shown that the light group velocity can be reduced using the recordi... more Recently, several works have shown that the light group velocity can be reduced using the recording of dynamic refractive index gratings in photorefractive (PR) crystals [1] , [2] , [3] . The slowdown of light is performed using optical beams wave mixing: it yields the output pulse amplification and increases the light dispersion inside the PR crystal. For example, the TWM method demonstrated that the delay time ∆ τ can be varied as a function of the TWM gain values Γ and the input pulse widths T 0 . However, several works have shown that the results achieved by this method are limited in terms of pulse duration. Indeed, only long pulses with time duration of ms−s can be slowdown in a PR crystal both at the visible and the infrared wavelengths [4] .

Photorefractive effect in Sn2P2S6 ferroelectrics

We developped two new methods to determine separately by the real and imaginary parts of the nonl... more We developped two new methods to determine separately by the real and imaginary parts of the nonlinear susceptibility by femtosecond interferometry. The first one utilizes spacial fringes of a Mach-Zehnder interferometer with a reference interferometer, while the second one utilizes frequency domain interference.

Customization of Sn2P2S6 ferroelectrics by post-growth solid-state diffusion doping

Journal of Materials Chemistry C

For the first time, we demonstrated successful post-synthesis incorporation of metal dopants at e... more For the first time, we demonstrated successful post-synthesis incorporation of metal dopants at elevated temperature into a host structure of Sn2P2S6, known as the grandfather of dichalcogenide ferroelectrics with a formula M2P2X6 (M = metal and X = chalcogen).

Optics Letters

We present a new method to perform acousto-optic imaging based on a spatio-temporal structuration... more We present a new method to perform acousto-optic imaging based on a spatio-temporal structuration of long-duration acoustic plane waves. This approach is particularly relevant when using detectors with long integration time. We show how it is possible to reconstruct an image by measuring its two-dimensional Fourier components. A proof of concept is presented using a photorefractive detection scheme, demonstrating equal performances to direct imaging. The overall acquisition time is compatible with medical monitoring applications.

Fast near infrared photorefraction and phase conjugation in Sn/sub 2/P/sub 2/S/sub 6/

2003 Conference on Lasers and Electro-Optics Europe (CLEO/Europe 2003) (IEEE Cat. No.03TH8666), 2003

Tin hypothiodiphosphate (Sn2P2S6) photorefractive crystals exhibit high beam coupling gain combin... more Tin hypothiodiphosphate (Sn2P2S6) photorefractive crystals exhibit high beam coupling gain combined with relatively fast photorefractive response in the near infrared, which makes them attractive for photorefractive applications in connection with diode or solid state near infrared lasers. An important process in several of these applications is phase conjugation of laser beams. This article investigates the photorefractive properties of Sn2P2S6 in the near infrared wavelength range. Conventional yellow, Te-doped, and modified brown crystals are examined. It was found that the coupling strength in brown is high enough to reach the saturation of reflectivity.

Photorefractive Effects in Sn2P2S6

Photorefractive Materials and Their Applications 2, 2007

ABSTRACT Tin hypothiodiphosphate (Sn2P2S6) is a very promising material for photorefractive appli... more ABSTRACT Tin hypothiodiphosphate (Sn2P2S6) is a very promising material for photorefractive applications in the red and near-infrared wavelength range. The main advantage of Sn2P2S6 as an infrared-sensitive photorefractive material is its high beam-coupling gain combined with relatively fast response, about two orders of magnitude faster than in the conventionally used photorefractive material BaTiO3 doped with rhodium. Compared to oxide ferroelectrics, which are wide-band-gap dielectrics, Sn2P2S6 crystals are characterized by a narrower band gap (2.3 eV) and a higher photorefractive sensitivity, and are transparent in the range of 530– 8000 nm.

Te-doped Sn2P2S6: A new material for fast photorefractive applications at 1.06 μm

2006 Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference, 2006

We demonstrate self-pumped optical phase conjugation in Te-doped Sn2P2S6 up to a wavelength of 1.... more We demonstrate self-pumped optical phase conjugation in Te-doped Sn2P2S6 up to a wavelength of 1.06 mum. A phase conjugate reflectivity of more than 40 percent with a very fast rise time below 100 ms has been measured.

Molecular Crystals and Liquid Crystals, 2004

It was found that doping of tiny ferroelectric particles to a nematic liquid crystal (LC) strongl... more It was found that doping of tiny ferroelectric particles to a nematic liquid crystal (LC) strongly affects dielectric properties of the system. The doping increases dielectric response of the LC due to interaction between LC molecules and particles, which possess large dipole moment and high polarisability. The suspension reveals high dielectric response on either side of the Curie temperature, T Curie , and peculiarity at the vicinity of T Curie . This result points at retention of dipole ordering above Curie temperature that may be a result of a memory effect.

The Critical Behaviour of Ultrasonic Velocity at a Second-Order Phase Transition in Sn2P2S6 Single Crystals

physica status solidi (b), 1999

ABSTRACT

Thermal expansion of Sn 2 P 2 S 6 crystals

Phase Transitions, 2009

ABSTRACT We present the results for thermal expansion coefficients of Sn2P2S6 crystals determined... more ABSTRACT We present the results for thermal expansion coefficients of Sn2P2S6 crystals determined both in the crystallographic system and the system based on eigenvectors of thermal expansion tensor. Peculiarities of temperature evolution of the indicative surface of thermal expansion tensor for Sn2P2S6 are discussed, including the region of their ferroelectric phase transition.

Critical exponents of phase transition in ferroelectric Sn 2 P 2 S 6 : comparison of optical and dilatometric data

Phase Transitions, 2010

... DOI: 10.1080/01411590903553452 Andriy Say a , Oksana Mys a , Dmitro Adamenko a , Alexandr Gra... more ... DOI: 10.1080/01411590903553452 Andriy Say a , Oksana Mys a , Dmitro Adamenko a , Alexandr Grabar b , Yulian Vysochanskii b , Andriy Kityk a c & Rostyslav Vlokh a * pages 123-139. Available online: 16 Feb 2010. ...

Optics Express, 2005

We demonstrate self-pumped optical phase conjugation in Te-doped Sn 2 P 2 S 6 , a semiconducting ... more We demonstrate self-pumped optical phase conjugation in Te-doped Sn 2 P 2 S 6 , a semiconducting ferroelectric crystal, using a 1.06 μm wavelength cw Nd:YAG laser. The photorefractive gain of this crystal has been increased to Γ = (3.9 ± 0.4) cm -1 by Te doping. We observed self-pumped optical phase conjugation in a ring cavity scheme with phase conjugate reflectivities of more than 40 percent and a very fast phase conjugate rise time below 100 ms at a light intensity of 20 W/cm 2 . This is more than two orders of magnitude faster than in any other photorefractive crystal, as e.g. in Rh-doped BaTiO 3 .

Enhanced photorefractive properties of modified Sn2P2S6

Optics Communications, 2001

ABSTRACT

Photorefractive and photochromic effects in Sn2P2S6 at various temperatures

Optics Communications, 2013

ABSTRACT Photochromic effect in nominally pure and doped Sn2P2S6 photorefractive crystals is inve... more ABSTRACT Photochromic effect in nominally pure and doped Sn2P2S6 photorefractive crystals is investigated in the temperature range 120–310 K. This effect determines a mechanism of the amplitude hologram formation at low temperatures, and we show that a competition between the photorefractive (phase) and the amplitude gratings occurs at increasing temperature.

Journal of the Optical Society of America B, 2008

A colloid of ferroelectric nanoparticles in a cholesteric liquid crystal

Journal of Optics A: Pure and Applied Optics, 2009

... Keywords: ferroelectric nano-particle, nematics, cholesterics, dielectric anisotropy, electro... more ... Keywords: ferroelectric nano-particle, nematics, cholesterics, dielectric anisotropy, electro-optic response ... source of the effect is the strong electric field surrounding a ferroelectric particle. ... Among the other es-sential consequences of the ferroelectric nanoparticle insertion is the ...