S. Slussarenko - Academia.edu (original) (raw)

Papers by S. Slussarenko

Molecular Crystals and Liquid Crystals, 2008

We report a study devoted to the creation of a distributed feedback device on a basis of waveguid... more We report a study devoted to the creation of a distributed feedback device on a basis of waveguide with periodical composition polymer - liquid crystal. Due to the refractive indices difference between the components the Bragg diffraction grating is formed, which provides coupling of the forward and backward propagating waves. The influence of the gain and conditions of laser oscillation threshold are analyzed for gain-type reflection grating. The conclusion is done on the advantage of second-order Bragg diffraction exploitation. Numerical simulations demonstrated the stability of the waveguide mode.

Journal of the Optical Society of America B, 2009

The coupled-wave approach was used for the analysis of volume gratings in a medium with light gai... more The coupled-wave approach was used for the analysis of volume gratings in a medium with light gain for the sake of oscillation threshold determination in the second-order Bragg diffraction regime. The conditions for self-starting oscillations were analytically determined and found to be optimal for mixed phase-amplitude gratings. The properties of a distributed-feedback laser scheme are derived on the basis of the obtained results.

Optics express, Jan 20, 2010

In this paper we show that an optical setup based on a polarizing Sagnac interferometer combined ... more In this paper we show that an optical setup based on a polarizing Sagnac interferometer combined with a Dove prism can be used as a convenient general-purpose tool for the generation, detection and sorting of spin-orbit states of light. This device can work both in the classical and in the quantum single-photon regime, provides higher sorting efficiency and extinction ratio than usual hologram-fiber combinations, and shows much higher stability and ease of alignment than Mach-Zehnder interferometer setups. To demonstrate the full potential of this setup, we also report some demonstrative experiments of several possible applications of this setup.

ABSTRACT The effect of the light-induced surface reorientation of the LC director in a cell fille... more ABSTRACT The effect of the light-induced surface reorientation of the LC director in a cell filled with an LC-azo dye mixture is obtained. The surface reorientation is caused by LC director reorientation in the bulk, which is initiated by a consequent tans-cis-trans isomerization of azo dye molecules accompanied by a variation of their orientation with respect to the polarization of the exciting light. It is shown that the value and the kinetics of the effect depend on the type of the aligning surface.

Physical Review A, 2009

The recently demonstrated possibility of entangling opposite values of the orbital angular moment... more The recently demonstrated possibility of entangling opposite values of the orbital angular momentum ͑OAM͒ of a photon with its spin enables the realization of nontrivial one-photon spin-orbit four-dimensional states for quantum information purposes. Hitherto, however, an optical device that can able to perform arbitrary unitary transformations on such spin-orbit photon states has not been proposed yet. In this work we show how to realize such a "universal unitary gate" device, based only on the existing optical technology, and describe its operation. Besides the quantum information field, the proposed device may find applications wherever an efficient and convenient manipulation of the combined OAM and spin of light is required.

Physical Review A, 2010

We present an easy, efficient, and fast method to generate arbitrary linear combinations of light... more We present an easy, efficient, and fast method to generate arbitrary linear combinations of light orbital angular-momentum eigenstates = ±2 starting from a linearly polarized TEM 00 laser beam. The method exploits the spin-to-orbital angular-momentum conversion capability of a liquid-crystal-based q plate and a Dove prism inserted into a Sagnac polarizing interferometer. The nominal generation efficiency is 100%, being limited only by reflection and scattering losses in the optical components. When closed paths are followed on the polarization Poincaré sphere of the input beam, the associated Pancharatnam geometric phase is transferred unchanged to the orbital angular momentum state of the output beam.

Optics Express, 2011

Using a photoalignment technique with a sulphonic azo-dye as the surfactant aligning material, we... more Using a photoalignment technique with a sulphonic azo-dye as the surfactant aligning material, we fabricated electrically tunable liquid crystal q-plates with topological charge 0.5, 1.5 and 3 for generating optical vortex beams with definite orbital angular momentum (OAM) 1,3 and 6 per photon (in units ofh), respectively. We carried out several tests on our q-plates, including OAM tomography, finding excellent performances. These devices can have useful applications in general and quantum optics.

Journal of the Optical Society of America A, 2011

We present a novel optical device to encode and decode two bits of information into different Orb... more We present a novel optical device to encode and decode two bits of information into different Orbital Angular Momentum (OAM) states of a paraxial optical beam. Our device generates the four angular momentum states of order ±2 and ±4 by Spin-To-Orbital angular momentum Conversion (STOC) in a triangular optical loop arrangement. The switching among the four OAM states is obtained by changing the polarization state of the circulating beam by two quarter wave plates and the two-bit information is transferred to the beam OAM exploiting a single q-plate. The polarization of the exit beam is left free for additional one bit of information. The transmission bandwidth of the device may be as large as several megahertz if electro-optical switches are used to change the beam polarization. This may be particularly useful in communication system based on light OAM.

Journal of Optics, 2013

We present a tunable liquid crystal device that converts pure orbital angular momentum eigenmodes... more We present a tunable liquid crystal device that converts pure orbital angular momentum eigenmodes of a light beam into equal-weight superpositions of opposite-handed eigenmodes and vice versa. For specific input states, the device may thus simulate the behavior of a π/2 phase retarder in a given two-dimensional orbital angular momentum subspace, analogous to a quarter-wave plate for optical polarization. A variant of the same device generates the same final modes starting from a Gaussian input.

Applied Physics Letters, 2010

Exploiting electro-optic effects in liquid crystals, we achieved real-time control of the retarda... more Exploiting electro-optic effects in liquid crystals, we achieved real-time control of the retardation of liquidcrystal-based q−plates through an externally applied voltage. The newly conceived electro-optic q-plates can be operated as electrically driven converters of photon spin into orbital angular momentum, enabling a variation of the orbital angular momentum probabilities of the output photons over a time scale of milliseconds.

Molecular Crystals and Liquid Crystals, 2008

ABSTRACT We report a study devoted to the creation of a distributed feedback device on a basis of... more ABSTRACT We report a study devoted to the creation of a distributed feedback device on a basis of waveguide with periodical composition polymer - liquid crystal. Due to the refractive indices difference between the components the Bragg diffraction grating is formed, which provides coupling of the forward and backward propagating waves. The influence of the gain and conditions of laser oscillation threshold are analyzed for gain-type reflection grating. The conclusion is done on the advantage of second-order Bragg diffraction exploitation. Numerical simulations demonstrated the stability of the waveguide mode.

Technical Digest. Summaries of Papers Presented at the Conference on Lasers and Electro-Optics. Conference Edition. 1998 Technical Digest Series, Vol.6 (IEEE Cat. No.98CH36178), 1998

ABSTRACT We have observed an extraordinarily large optically induced refractive index change mech... more ABSTRACT We have observed an extraordinarily large optically induced refractive index change mechanism in aligned dye-doped nematic liquid crystal film. The effect is potentially useful for developing a new liquid crystal light valve or spatial light modulator, and for applications in other adaptive optics and coherent wave-mixing devices

Science Advances, 2015

The "quantum walk" has emerged recently as a paradigmatic process for the dynamic simulation of c... more The "quantum walk" has emerged recently as a paradigmatic process for the dynamic simulation of complex quantum systems, entanglement production and quantum computation. Hitherto, photonic implementations of quantum walks have mainly been based on multipath interferometric schemes in real space. We report the experimental realization of a discrete quantum walk taking place in the orbital angular momentum space of light, both for a single photon and for two simultaneous photons. In contrast to previous implementations, the whole process develops in a single light beam, with no need of interferometers; it requires optical resources scaling linearly with the number of steps; and it allows flexible control of input and output superposition states. Exploiting the latter property, we explored the system band structure in momentum space and the associated spin-orbit topological features by simulating the quantum dynamics of Gaussian wavepackets. Our demonstration introduces a novel versatile photonic platform for quantum simulations.

Molecular Crystals and Liquid Crystals, 2006

ABSTRACT Soft materials exhibit very attractive mechanical, optical, and electro-optical properti... more ABSTRACT Soft materials exhibit very attractive mechanical, optical, and electro-optical properties and easy processing techniques. Combined with holographic techniques, they can be patterned quite easily creating many unique structures. We present here few examples, of electrically-switchable passive opto-electronic components based on composite materials obtained from initial mixtures of photocurable monomers and liquid crystalline materials. Holographic exposure results in volume gratings consisting in alternate areas of photo-crosslinked polymer and phase separated LCs, respectively. We discuss the main features of this new generation of gratings and show how most of their performances can be enhanced with respect to other kinds of composite gratings, like H-PDLCs.

Nonlinear Optics '98. Materials, Fundamentals and Applications Topical Meeting (Cat. No.98CH36244), 1998

ABSTRACT We have demonstrated that dye-doped liquid crystals have very interesting optical hologr... more ABSTRACT We have demonstrated that dye-doped liquid crystals have very interesting optical holographic storage capabilities :no image degradation after more than one year, high spatial resolution, high sensitivity, and polarization sensitivity

Conference Digest. 2000 International Quantum Electronics Conference (Cat. No.00TH8504), 2000

We report a detailed study of the transient behavior of the photovoltaic effect detected using bo... more We report a detailed study of the transient behavior of the photovoltaic effect detected using both CW (λ=488 nm line of an Ar ion laser) and pulsed light (second harmonic λ=532 nm of a Q-switched Nd:YAG laser) excitation. The experiments were performed on sandwich-like cells consisting of two parallel plane ITO-coated glass substrates, filled with a mixture of the nematic 5CB LC and a small amount of Methyl Red. The most relevant features experimentally observed are: (a) the change of polarity of the photoinduced electromotive force while reaching the steady-state value under CW irradiation; (b) the generation of a transient photovoltage induced by a single 4 ns laser pulse with moderate energy density. The results obtained can be interpreted in the frame of a model based on the coexistence of a fast and a slow process in the origin of the photovoltaic effect. The former includes the exchange of charges between the stimulated electrode and the solution, and the latter includes the diffusion process of photoinduced charges with different mobility between the positive and the negative carriers. The observed transient photovoltage due to pulsed irradiation allows writing transient holographic gratings with a single 4 ns pulse. The energy density required for the grating formation is below the threshold value for the optical Freedericksz transition in the investigated samples, thus indicating that the light-induced photovoltage enhances the nonlinear response of the cells.

Conference Proceedings LEOS'96 9th Annual Meeting IEEE Lasers and Electro-Optics Society, 1996

ABSTRACT Summary form only given. There have been intense research interests in nonlinear optical... more ABSTRACT Summary form only given. There have been intense research interests in nonlinear optical materials capable of recording permanent holographic planar or volume gratings. Among the goals to be achieved are low writing intensity, high storage density and fast recording/erasure times. We present recent results of an extended study on nematic liquid crystal films doped either with dyes or fullerene C 60. Nematic liquid crystals doped with azo-dyes have been demonstrated to be a very sensitive medium for optical storage application. In these samples, we were able to write permanent optical gratings using energy density as low as 3 J/cm2, with a resolution higher than 100 lines/mm. The memory effect is due to a light induced anchoring on the illuminated surface and is caused by surface adsorption of excited dye molecules. A similar electro-optical holographic storage grating effect is observed in C60-doped nematic liquid crystal films. The effect is attributed to molecular axis reorientation caused by the combination of an applied DC field and an optically induced DC space charge field. The observed nonlinear sensitivity S [defined by S=δn/F, where δn is the induced index modulation, and F is the incident laser energy fluence in units of energy/area] obtained in our preliminary studies already ranks among the largest compared to other materials. We have shown that a value of S~5×10-5 cm2/J can be easily achieved with these films. This is mainly due to the unusually large optical birefringence and dielectric anisotropy of nematic liquid crystals

Frontiers in Optics 2013, 2013

Superdense coding using a classical analogy of quantum entanglement is experimentally investigate... more Superdense coding using a classical analogy of quantum entanglement is experimentally investigated. The spatially inhomogeneous polarization of vector vortex beams, as described by a higher-order Poincare sphere, play the role of maximally entangled Bell states.

Liquid Crystals VI, 2002

ABSTRACT A review of the recent results of our group in the field of light-induced anchoring and ... more ABSTRACT A review of the recent results of our group in the field of light-induced anchoring and reorientation effects in dye-doped liquid crystals (LCs) is presented. In particular, the phenomena of photo-induced anchoring and permanent reorientation over a polymeric boundary surface of a dye-doped LC cell is reported, both in the isotropic phase and in the orientationally ordered nematic phase. The results have been interpreted microscopically in terms of adsorption and desorption of the dichroic azo-dye (methyl-red) molecules onto the illuminated surface during light irradiation. The model proposed is in agreement with recent results on the dynamic and stable grating formation in methyl-red doped LCs .

Molecular Crystals and Liquid Crystals, 2008

We report a study devoted to the creation of a distributed feedback device on a basis of waveguid... more We report a study devoted to the creation of a distributed feedback device on a basis of waveguide with periodical composition polymer - liquid crystal. Due to the refractive indices difference between the components the Bragg diffraction grating is formed, which provides coupling of the forward and backward propagating waves. The influence of the gain and conditions of laser oscillation threshold are analyzed for gain-type reflection grating. The conclusion is done on the advantage of second-order Bragg diffraction exploitation. Numerical simulations demonstrated the stability of the waveguide mode.

Journal of the Optical Society of America B, 2009

The coupled-wave approach was used for the analysis of volume gratings in a medium with light gai... more The coupled-wave approach was used for the analysis of volume gratings in a medium with light gain for the sake of oscillation threshold determination in the second-order Bragg diffraction regime. The conditions for self-starting oscillations were analytically determined and found to be optimal for mixed phase-amplitude gratings. The properties of a distributed-feedback laser scheme are derived on the basis of the obtained results.

Optics express, Jan 20, 2010

In this paper we show that an optical setup based on a polarizing Sagnac interferometer combined ... more In this paper we show that an optical setup based on a polarizing Sagnac interferometer combined with a Dove prism can be used as a convenient general-purpose tool for the generation, detection and sorting of spin-orbit states of light. This device can work both in the classical and in the quantum single-photon regime, provides higher sorting efficiency and extinction ratio than usual hologram-fiber combinations, and shows much higher stability and ease of alignment than Mach-Zehnder interferometer setups. To demonstrate the full potential of this setup, we also report some demonstrative experiments of several possible applications of this setup.

ABSTRACT The effect of the light-induced surface reorientation of the LC director in a cell fille... more ABSTRACT The effect of the light-induced surface reorientation of the LC director in a cell filled with an LC-azo dye mixture is obtained. The surface reorientation is caused by LC director reorientation in the bulk, which is initiated by a consequent tans-cis-trans isomerization of azo dye molecules accompanied by a variation of their orientation with respect to the polarization of the exciting light. It is shown that the value and the kinetics of the effect depend on the type of the aligning surface.

Physical Review A, 2009

The recently demonstrated possibility of entangling opposite values of the orbital angular moment... more The recently demonstrated possibility of entangling opposite values of the orbital angular momentum ͑OAM͒ of a photon with its spin enables the realization of nontrivial one-photon spin-orbit four-dimensional states for quantum information purposes. Hitherto, however, an optical device that can able to perform arbitrary unitary transformations on such spin-orbit photon states has not been proposed yet. In this work we show how to realize such a "universal unitary gate" device, based only on the existing optical technology, and describe its operation. Besides the quantum information field, the proposed device may find applications wherever an efficient and convenient manipulation of the combined OAM and spin of light is required.

Physical Review A, 2010

We present an easy, efficient, and fast method to generate arbitrary linear combinations of light... more We present an easy, efficient, and fast method to generate arbitrary linear combinations of light orbital angular-momentum eigenstates = ±2 starting from a linearly polarized TEM 00 laser beam. The method exploits the spin-to-orbital angular-momentum conversion capability of a liquid-crystal-based q plate and a Dove prism inserted into a Sagnac polarizing interferometer. The nominal generation efficiency is 100%, being limited only by reflection and scattering losses in the optical components. When closed paths are followed on the polarization Poincaré sphere of the input beam, the associated Pancharatnam geometric phase is transferred unchanged to the orbital angular momentum state of the output beam.

Optics Express, 2011

Using a photoalignment technique with a sulphonic azo-dye as the surfactant aligning material, we... more Using a photoalignment technique with a sulphonic azo-dye as the surfactant aligning material, we fabricated electrically tunable liquid crystal q-plates with topological charge 0.5, 1.5 and 3 for generating optical vortex beams with definite orbital angular momentum (OAM) 1,3 and 6 per photon (in units ofh), respectively. We carried out several tests on our q-plates, including OAM tomography, finding excellent performances. These devices can have useful applications in general and quantum optics.

Journal of the Optical Society of America A, 2011

We present a novel optical device to encode and decode two bits of information into different Orb... more We present a novel optical device to encode and decode two bits of information into different Orbital Angular Momentum (OAM) states of a paraxial optical beam. Our device generates the four angular momentum states of order ±2 and ±4 by Spin-To-Orbital angular momentum Conversion (STOC) in a triangular optical loop arrangement. The switching among the four OAM states is obtained by changing the polarization state of the circulating beam by two quarter wave plates and the two-bit information is transferred to the beam OAM exploiting a single q-plate. The polarization of the exit beam is left free for additional one bit of information. The transmission bandwidth of the device may be as large as several megahertz if electro-optical switches are used to change the beam polarization. This may be particularly useful in communication system based on light OAM.

Journal of Optics, 2013

We present a tunable liquid crystal device that converts pure orbital angular momentum eigenmodes... more We present a tunable liquid crystal device that converts pure orbital angular momentum eigenmodes of a light beam into equal-weight superpositions of opposite-handed eigenmodes and vice versa. For specific input states, the device may thus simulate the behavior of a π/2 phase retarder in a given two-dimensional orbital angular momentum subspace, analogous to a quarter-wave plate for optical polarization. A variant of the same device generates the same final modes starting from a Gaussian input.

Applied Physics Letters, 2010

Exploiting electro-optic effects in liquid crystals, we achieved real-time control of the retarda... more Exploiting electro-optic effects in liquid crystals, we achieved real-time control of the retardation of liquidcrystal-based q−plates through an externally applied voltage. The newly conceived electro-optic q-plates can be operated as electrically driven converters of photon spin into orbital angular momentum, enabling a variation of the orbital angular momentum probabilities of the output photons over a time scale of milliseconds.

Molecular Crystals and Liquid Crystals, 2008

ABSTRACT We report a study devoted to the creation of a distributed feedback device on a basis of... more ABSTRACT We report a study devoted to the creation of a distributed feedback device on a basis of waveguide with periodical composition polymer - liquid crystal. Due to the refractive indices difference between the components the Bragg diffraction grating is formed, which provides coupling of the forward and backward propagating waves. The influence of the gain and conditions of laser oscillation threshold are analyzed for gain-type reflection grating. The conclusion is done on the advantage of second-order Bragg diffraction exploitation. Numerical simulations demonstrated the stability of the waveguide mode.

Technical Digest. Summaries of Papers Presented at the Conference on Lasers and Electro-Optics. Conference Edition. 1998 Technical Digest Series, Vol.6 (IEEE Cat. No.98CH36178), 1998

ABSTRACT We have observed an extraordinarily large optically induced refractive index change mech... more ABSTRACT We have observed an extraordinarily large optically induced refractive index change mechanism in aligned dye-doped nematic liquid crystal film. The effect is potentially useful for developing a new liquid crystal light valve or spatial light modulator, and for applications in other adaptive optics and coherent wave-mixing devices

Science Advances, 2015

The "quantum walk" has emerged recently as a paradigmatic process for the dynamic simulation of c... more The "quantum walk" has emerged recently as a paradigmatic process for the dynamic simulation of complex quantum systems, entanglement production and quantum computation. Hitherto, photonic implementations of quantum walks have mainly been based on multipath interferometric schemes in real space. We report the experimental realization of a discrete quantum walk taking place in the orbital angular momentum space of light, both for a single photon and for two simultaneous photons. In contrast to previous implementations, the whole process develops in a single light beam, with no need of interferometers; it requires optical resources scaling linearly with the number of steps; and it allows flexible control of input and output superposition states. Exploiting the latter property, we explored the system band structure in momentum space and the associated spin-orbit topological features by simulating the quantum dynamics of Gaussian wavepackets. Our demonstration introduces a novel versatile photonic platform for quantum simulations.

Molecular Crystals and Liquid Crystals, 2006

ABSTRACT Soft materials exhibit very attractive mechanical, optical, and electro-optical properti... more ABSTRACT Soft materials exhibit very attractive mechanical, optical, and electro-optical properties and easy processing techniques. Combined with holographic techniques, they can be patterned quite easily creating many unique structures. We present here few examples, of electrically-switchable passive opto-electronic components based on composite materials obtained from initial mixtures of photocurable monomers and liquid crystalline materials. Holographic exposure results in volume gratings consisting in alternate areas of photo-crosslinked polymer and phase separated LCs, respectively. We discuss the main features of this new generation of gratings and show how most of their performances can be enhanced with respect to other kinds of composite gratings, like H-PDLCs.

Nonlinear Optics '98. Materials, Fundamentals and Applications Topical Meeting (Cat. No.98CH36244), 1998

ABSTRACT We have demonstrated that dye-doped liquid crystals have very interesting optical hologr... more ABSTRACT We have demonstrated that dye-doped liquid crystals have very interesting optical holographic storage capabilities :no image degradation after more than one year, high spatial resolution, high sensitivity, and polarization sensitivity

Conference Digest. 2000 International Quantum Electronics Conference (Cat. No.00TH8504), 2000

We report a detailed study of the transient behavior of the photovoltaic effect detected using bo... more We report a detailed study of the transient behavior of the photovoltaic effect detected using both CW (λ=488 nm line of an Ar ion laser) and pulsed light (second harmonic λ=532 nm of a Q-switched Nd:YAG laser) excitation. The experiments were performed on sandwich-like cells consisting of two parallel plane ITO-coated glass substrates, filled with a mixture of the nematic 5CB LC and a small amount of Methyl Red. The most relevant features experimentally observed are: (a) the change of polarity of the photoinduced electromotive force while reaching the steady-state value under CW irradiation; (b) the generation of a transient photovoltage induced by a single 4 ns laser pulse with moderate energy density. The results obtained can be interpreted in the frame of a model based on the coexistence of a fast and a slow process in the origin of the photovoltaic effect. The former includes the exchange of charges between the stimulated electrode and the solution, and the latter includes the diffusion process of photoinduced charges with different mobility between the positive and the negative carriers. The observed transient photovoltage due to pulsed irradiation allows writing transient holographic gratings with a single 4 ns pulse. The energy density required for the grating formation is below the threshold value for the optical Freedericksz transition in the investigated samples, thus indicating that the light-induced photovoltage enhances the nonlinear response of the cells.

Conference Proceedings LEOS'96 9th Annual Meeting IEEE Lasers and Electro-Optics Society, 1996

ABSTRACT Summary form only given. There have been intense research interests in nonlinear optical... more ABSTRACT Summary form only given. There have been intense research interests in nonlinear optical materials capable of recording permanent holographic planar or volume gratings. Among the goals to be achieved are low writing intensity, high storage density and fast recording/erasure times. We present recent results of an extended study on nematic liquid crystal films doped either with dyes or fullerene C 60. Nematic liquid crystals doped with azo-dyes have been demonstrated to be a very sensitive medium for optical storage application. In these samples, we were able to write permanent optical gratings using energy density as low as 3 J/cm2, with a resolution higher than 100 lines/mm. The memory effect is due to a light induced anchoring on the illuminated surface and is caused by surface adsorption of excited dye molecules. A similar electro-optical holographic storage grating effect is observed in C60-doped nematic liquid crystal films. The effect is attributed to molecular axis reorientation caused by the combination of an applied DC field and an optically induced DC space charge field. The observed nonlinear sensitivity S [defined by S=δn/F, where δn is the induced index modulation, and F is the incident laser energy fluence in units of energy/area] obtained in our preliminary studies already ranks among the largest compared to other materials. We have shown that a value of S~5×10-5 cm2/J can be easily achieved with these films. This is mainly due to the unusually large optical birefringence and dielectric anisotropy of nematic liquid crystals

Frontiers in Optics 2013, 2013

Superdense coding using a classical analogy of quantum entanglement is experimentally investigate... more Superdense coding using a classical analogy of quantum entanglement is experimentally investigated. The spatially inhomogeneous polarization of vector vortex beams, as described by a higher-order Poincare sphere, play the role of maximally entangled Bell states.

Liquid Crystals VI, 2002

ABSTRACT A review of the recent results of our group in the field of light-induced anchoring and ... more ABSTRACT A review of the recent results of our group in the field of light-induced anchoring and reorientation effects in dye-doped liquid crystals (LCs) is presented. In particular, the phenomena of photo-induced anchoring and permanent reorientation over a polymeric boundary surface of a dye-doped LC cell is reported, both in the isotropic phase and in the orientationally ordered nematic phase. The results have been interpreted microscopically in terms of adsorption and desorption of the dichroic azo-dye (methyl-red) molecules onto the illuminated surface during light irradiation. The model proposed is in agreement with recent results on the dynamic and stable grating formation in methyl-red doped LCs .