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A new generation of reconfigurable optical components is conceived by bridging the photothermal properties of gold nanoparticles and the thermosensitivity of liquid crystalline materials. As such, gold nanorods (GNRs) heated using light are used to activate efficient hidden diffraction gratings realized in a blend made of a room temperature polymerizable liquid crystal (PLC) and nematic liquid crystal (NLC). Holographic liquid crystal polymer dispersed liquid crystal (HLCPDLC) gratings containing a small percentage of GNRs are fabricated with periodicity of 2.6 ?m by means of a conventional UV holographic recording setup. The HLCPDLC structures are characterized using morphological, optical, and thermooptical techniques. Because of the initial refractive index match between the polymer-rich and LC-rich regions, the "grating" is hidden and the films appear transparent and nondiffractive. Illumination of these GNR-containing structures with a suitable light source (808 nm) induces a local heating due to the plasmonic absorption of the GNRs. This heating induces a refractive index mismatch between the PLC and the NLC as the latter undergoes a phase transition from nematic to isotropic, finally resulting in a transmission diffractive structure activated over a few seconds exhibiting an efficiency of about 70%. The same HLCPDLC samples have also been tested as thermosensitive waveplates, enabling a new, fast methodology for quantifying the photoinduced plasmonic heating with a thermal sensitivity of ?0.04 °C. Moreover, thermoplasmonic driven waveplates represent a new avenue in the field of light controllable optical phase modulators.

Diffractive waveplates (DWs) are highly efficient optical components realized by means of a polarization holography setup that makes use of UV/blue laser sources. It is more convenient to perform the holographic recording process with green lasers (e.g., continuous wave operating at 532 nm) because they offer compactness, efficiency, and high power. Unfortunately, the photo-alignment materials used for DW fabrication exhibit limited sensitivity at 532 nm. Herein, we report the realization of cycloidal diffractive waveplates (CDWs) by employing a polarization holographic setup using a high-power, diode-pumped solid-state laser operating at 532 nm. The enabling factor is the use of a photo-alignment material with a broad absorption band extending into the visible part of the spectrum. Samples are characterized in terms of morphological and optical properties. They exhibit a well-defined morphology along with very high diffraction efficiency (≈97%). The possibility to realize CDWs with larger apertures is underway, enabling the realization of a new generation of optical components for integration in modern applications.

Near 100% broadband efficiency of polarization holograms provides opportunities for shaping light beams, imaging, and displays. Thin, flexible and switchable between different optical states and functions, novel optical components and systems are smarter than ever.

This feature issue of the journal is the first one to bring together ongoing research from many groups developing diffractive waveplate technology. This technology combines the best of three worlds—the thinness of diffraction gratings, the broad bandwidth and high efficiency of conventional refractive optics, and the low-cost fast manufacturing of polymer optics even in large area. The technology is at the intersection of polarization holography and polarization gratings, Pancharatnam–Berry or geometrical phase optics, waveplates, metasurfaces and planar optics. Optics will never be the same again!

A narrow - linewidth, hot isostatic treated Cr:ZnSe laser was non - mechanically tuned over a total wavelength range of 195 nm by a novel organic liquid crystal etalon. The narrow - linewidth laser was continuously tuned by applying a 1 kHz square wave signal of 1 – 5 Vpp to the intracavity 9 THz nominal free spectral range liquid crystal etalon. The maximum and minimum lasing wavelengths were 2650 nm and 2455 nm, respectively, and a maximum average output power of 475 mW was recorded at 2503 nm. This work demonstrated continuous tuning, while maintaining an intrinsic narrow-linewidth ≤ 900 MHz. The results presented in this work are attributed to the low insertion loss of the liquid crystal etalon at ≤ 5%. It is believed that this is the first demonstration of purely electronic tuning of a mid-IR laser by an organic liquid crystal etalon.

Soft composite materials combined with a holographic photopolymerization process are used for realizing an innovative switchable periodic structure made of slices of almost pure polymer alternated with films of well aligned nematic liquid crystals named POLICRYPS. It exhibits negligible scattering losses, while the effect of the spatial modulation of the refractive index (from polymer to nematic liquid crystal) can be switched on and off by applying a low (few V/μm) electric field. The diffractive properties of the POLICRYPS structure are characterized in terms of cell thickness, impinging probe angle and wavelength revealing a strong correlation between the diffraction efficiency and all the above mentioned parameters. These results are very attractive for many applications such as switchable Bragg gratings for telecom devices, phase modulators, and displays. Other advantages of the technology include absence of an alignment layer, absence of haze, robust structure, and inexpensive manufacturing. In addition, no special alignment layers are required. This is a unique opportunity and a big advantage compared to conventional liquid crystal devices. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 158–162

The fourth generation optics (4G optics) enables the realization of novel optical components (lenses, gratings, vector vortices, etc.) by patterning the optical axis orientation in the plane of an anisotropic film. Such components exhibit near 100% diffraction efficiency for wavelengths meeting half-wave retardation condition. In this framework, we have advanced a step-forward by realizing different diffractive waveplates (DWs) with arbitrary spatial patterns of the optical axis orientation by exploiting the capability of a Digital Spatial Light Polarization Converter (DSLPC). The DSLPC is based on a reflective, high resolution Spatial Light Modulator (SLM) combined with an “ad hoc” optical setup. The most attractive feature of the use of a DSLPC for photoalignment is that the orientation of the alignment layer, and therefore of the fabricated liquid crystal (LC) or liquid crystal polymer (LCP) DWs, can be specified on a pixel-by-pixel basis. By varying the optical magnification or de-magnification between the SLM and the alignment layer, the spatial resolution of the photoaligned layer can be adjusted to be optimal for each application. We show that with a simple “click” it is possible to record different high resolution optical components as well as arbitrary patterns ranging from lenses to invisible and even dual labels.

The thickness of functional layers in liquid crystal photonics devices is negligibly small compared to the substrates. New opportunities provided by multilayer 4G optical systems require minimizing the thickness of each layer. We report about our progress made by developing technology of thin flexible substrates, functional polymer films, solid electro-optical layers, and graphene oxide based electro-conductive coatings.

We report on lenses that operate over the visible wavelength band from 450 nm to beyond 700 nm, and other lenses that operate over a wide region in the near-infrared from 650 nm to beyond 1000 nm. Lenses were recorded in liquid crystal polymer layers only a few micrometers thick, using laser-based photoalignment and UV photopolymerization. Waveplate lenses allowed focusing and defocusing laser beams depending on the sign of the circularity of laser beam polarization. Diffraction efficiency of recorded waveplate lenses was up to 90% and contrast ratio was up to 500:1.

The fourth generation of optics uses modulation of optical axis orientation in anisotropic materials for achieving a wide variety of optical functions. 4G optical components blend the thinness of zero-order waveplates with the high efficiency one gets with Bragg volume holographic gratings and in a broad band of wavelengths typical of conventional glass lenses, prisms, etc. (the first generation of optics). We will discuss the technology for applications in communications and astronomy. Particularly, we will present challenges and opportunities for fabrication of vector vortex waveplates and cross-waveplates for coronagraphy, and waveplate lenses — Pancharatnam-Berry phase lenses — for optical communications and imaging.

Geometrical phase or the fourth generation (4G) optics enables realization of optical components (lenses, prisms, gratings, spiral phase plates, etc.) by patterning the optical axis orientation in the plane of thin anisotropic films. Such components exhibit near 100% diffraction efficiency over a broadband of wavelengths. The films are obtained by coating liquid crystalline (LC) materials over substrates with patterned alignment conditions. Photo-anisotropic materials are used for producing desired alignment conditions at the substrate surface. We present and discuss here an opportunity of producing the widest variety of "free-form" 4G optical components with arbitrary spatial patterns of the optical anisotropy axis orientation with the aid of a digital spatial light polarization converter (DSLPC). The DSLPC is based on a reflective, high resolution spatial light modulator (SLM) combined with an "ad hoc" optical setup. The most attractive feature of the use of a DSLPC for photoalignment of nanometer thin photo-anisotropic coatings is that the orientation of the alignment layer, and therefore of the fabricated LC or LC polymer (LCP) components can be specified on a pixel-by-pixel basis with high spatial resolution. By varying the optical magnification or de-magnification the spatial resolution of the photoaligned layer can be adjusted to an optimum for each application. With a simple "click" it is possible to record different optical components as well as arbitrary patterns ranging from lenses to invisible labels and other transparent labels that reveal different images depending on the side from which they are viewed.

We report on the fabrication and characterization of a switchable plasmonic device based on a conductive graphene oxide (cGO) coated plasmonic nanoparticle (NP) array, layered with nematic liquid crystal (NLC) as an active medium. A monolayer of NPs has been immobilized on a glass substrate through electrostatic interaction, and then grown in place using nanochemistry. This monolayer is then coated with a thin (less then 100nm) cGO film which acts simultaneously as both an electro-conductive and active medium. The combination of the conductive NP array with a separate top cover substrate having both cGO and a standard LC alignment layer is used for aligning a NLC film in a hybrid configuration. The system is analysed in terms of morphological and electro-optical properties. The spectral response of the sample characterized after each element is added (air, cGO, NLC) reveals a red-shift of the localized plasmonic resonance (LPR) frequency of approximately 62nm with respect to the NP array surrounded by air. The application of an external voltage (8Vpp) is suitable to modulate (blue shift) the LPR frequency by approximately 22nm.

Modulating orientation of optical anisotropy axis can transform half-wave retardation films into lenses, prisms, axicons, spiral phase plates, and more. Polarization holography, particularly, digital, expands the variety and capabilities of the new generation optics. Article not available.

Photosensitive liquid crystals (PLCs) are promising materials that can combine a high-refractive-index modulation, typical of LCs, with high photosensitivity, due to the presence of photochromic molecules such as azobenzene and derivates. [1] These can undergo a reversible isomerization from a thermodynamically stable trans to a cis conformation when acted on by UV or visible light; a reverse transition can be obtained upon heating or irradiation with a different (longer wavelength) visible light. Thanks to these materials andprocesses, thepossibility toconfine and stabilize photosensitive materials has been considered in the past [2] and the perspective of producing fast photonic devices of scientific and technological interest looks highly realistic. There is, however, a serious problem represented by instability far from room temperature. [2] One way to reduce this effect has been found in using composite polymeric materials: [3] Holographic diffraction gratings, which exploit LC composite materials (HPDLCs), [4] are low-cost components with a wide range of possible photonic and optoelectronics applications. Therefore, the possibility of fabricating an optically controllable photonic device has been investigated by combining the photosensitivity of azobenzene materials with the optical properties of HPDLCs. [5] Devices of this kind can exhibit, however, an intrinsic drawback when the droplet size of the LC component inside the polymeric matrix is comparable with the wavelength of the diffracted light, thus yielding a strong light scattering. [6] Recently, a good improvement has been obtained by using a new kind of holographic diffraction grating with better optical qualities, which consists of polymer slices alternated to films of regularly aligned nematic LC (NLC). Depending on the particular procedure utilized for its fabrication, this structure is called POLIPHEM [7] orPOLICRYPS [8] andisobtainedby UV-curingofa mixture of monomer and NLC. In a recent attempt [9] to fabricate

We report on the laser and sunlight driven, fast and large oscillation of cantilevers composed of photoresponsive liquid crystal polymer materials. The oscillation frequency, driven with a focused 100 mW laser of multiple wavelengths (457, 488, 514 nm), is as high as 270 Hz and is shown to be strongly correlated to the physical dimensions of the cantilever. The experimental frequency response is accurately described by the calculated natural resonant frequency for a non-damped cantilever. To further understand the conversion efficiency of light energy to mechanical work in the system, the oscillatory behavior of a 2.7 mm × 0.7 mm × 0.04 mm cantilever was examined at pressures ranging from 1 atm to 0.03 atm. A large increase in amplitude from 110° at STP to 250° at low pressure was observed. A first approximation of the system efficiency was calculated at 0.1%. The large increase in amplitude at low pressure indicates strong hydrodynamic loss and thus, the material efficiency is potentially much greater. Using a simple optical setup, oscillatory behavior was also demonstrated using sunlight. This work indicates the potential for remotely triggered photoactuation of photoresponsive polymer cantilevers from long distances with lasers or focused sunlight.

Phototuning of Bragg reflection bandgap from green to blue and from red to green wavelengths was induced with a green (λ = 532 nm) laser beam in a cholesteric liquid crystal based on highly sensitive azobenzene nematic BEAM 1005 (BEAM Co.) and UV transparent non-photoisomerizable optically active dopant ZLI-6248 (R-2011) (Merck Ltd.). Optical switching between reflected and transmitted beams, as well as nonlinear transmission and reflection due to Bragg reflection band shift are studied in detail.

Cholesteric liquid crystals (CLCs) which possess a periodicity in the visible portion of the spectra, exhibit selective reflection of circularly polarized light. The ability to modulate this color through a variety of means has been explored, including work which incorporated azobenzene LCs. Two types of systems have recently been explored utilizing wavelength-specific cis-trans isomerization processes, which enable unprecedented photosensitivity. The first system exhibits large blue or red-shifted changes in reflection wavelength upon visible irradiation. The second system exploits the metastable, long-lived photoinduced isotropic state, whose return to the reflective Grandjean texture can be induced by wavelength-specific radiation. We demonstrate nonlinear transmission from both types of systems, starting with submicrowatt power levels and spanning over four orders of magnitude dynamic range. The power dependence and temporal evolution of this effect (10–100 ms) is documented here for red or green laser wavelengths. The effect for the former case is due to bandgap auto-tuning, when the laser beam is tuning the CLC Bragg reflection band to its own wavelength. For the latter case, autonomous, optical feedback due to bandgap restoration is the cause of the nonlinear transmission properties.

We present new lenses - waveplate lenses created in liquid crystal and liquid crystal polymer materials. Using an electrically-switchable liquid-crystal half-wave retarder we realized switching between focused and defocused beams by the waveplate lens. A combination of two such lenses allowed the collimation of a laser beam as well as the change of focal length of optical system.

We present new lenses – waveplate lenses created in liquid crystal materials. Waveplate lenses allowed focusing and defocusing laser beam depending on the sign of the circularity of laser beam polarization. Using an electrically-switchable liquid-crystal half-wave retarder we realized switching between focused and defocused beams by the waveplate lens. A combination of two such lenses allowed the collimation of a laser beam as well as the change of focal length of optical system. Lenses of varied size and focal length are presented.

Controlling light interactions with matter on the nanometer scale provides for compelling opportunities for modern technology and stretches our understanding and exploitation of applied physics, electronics, and fabrication science. The smallest size to which light can be confined using standard optical elements such as lenses and mirrors is limited by diffraction. Plasmonic nanostructures have the extraordinary capability to control light beyond the diffraction limit through an unique phenomenon called the localized plasmon resonance. This remarkable capability enables unique prospects for the design, fabrication and characterization of highly integrated photonic signal-processing systems, nanoresolution optical imaging techniques and nanoscale electronic circuits. This paper summarizes the basic principles and the main achievements in the practical utilization of plasmonic effects in nanoparticles. Specifically, the paper aims at highlighting the major contributions of nanoparticles to nanoscale temperature monitoring, modern “drug free” medicine and the application of nanomaterials to a new generation of opto-electronics integrated circuits.

A novel chirped polymer/liquid crystal diffraction grating (POLICRYPS) structure with periods ranging from 10 µm to 100 µm is reported. The chirped gratings are realized by using a single beam curing process through a diffractive waveplate mask with varying periodicity. The quality of the nematic liquid crystal (NLC) alignment inside the chirped structures as a function of periodicity was investigated using a polarized optical microscope technique. The extent of phase separation between the polymer and the NLC improves as the average spacing between the polymeric walls gets smaller. In the regions where phase separation is most complete, the duty cycle of the grating is proportional to the initial concentration of the two main components (polymer and NLC). The degree of order of the NLC within the phase separated channels was measured with a Mueller Matrix Spectroscopic Polarimeter. There is strong experimental evidence that the orientation of the NLC molecular director inside the structure is perpendicular to the surface of the polymer phase separated walls. Electro-optic measurements reveal a strong correlation between the on–off response times and the average distance between the polymeric walls. Our findings opens new avenues to realize a new generation of LCs based devices without using surface treatment or functionalization.

Scattering-free liquid crystal polymer-dispersed liquid crystal polymer (LCPDLC) films are fabricated by combining a room temperature polymerizable liquid crystal (LC) monomer with a mesogenic photosensitive LC. The morphological and photosensitive properties of the system are analysed with polarized optical microscopy and high resolution scanning and transmission electron microscopy. A two-phase morphology comprised of oriented fibril-like polymeric structures interwoven with nanoscale domains of phase separated LC exists. The nanoscale of the structures enables an absence of scattering which allows imaging through the LCPDLC sample without optical distortion. The use of a mesogenic monomer enables much smaller phase separated domains as compared to non-mesogenic systems. All-optical experiments show that the transmitted intensity, measured through parallel polarizers, can be modulated by the low power density radiation (31 mW/cm2) of a suitable wavelength (532 nm). The reversible and repeatable transmission change is due to the photoinduced trans-cis photoisomerization process. The birefringence variation (0.01) obtained by optically pumping the LCPDLC films allow their use as an all-optical phase modulator.

Diffractive waveplate technology presents an opportunity for designing arrays of all types of optical components. We present here different architectures of arrays of waveplate lenses and vector vortex waveplates. Due to the continuous nature of diffractive waveplate coatings and the high spatial resolution of the technology, the sizes of array elements can span from micrometers to tens of millimeters. Both fixed and electrically switchable arrays are discussed. Arrays of diffractive waveplates present new challenges and opportunities for digital light polarization holography for applications in polarizer-free displays, smart windows, optical communications, beam shaping, and other photonics technologies.

Holography and lithography allow realization of curved periodic microstructures comprising self-aligned liquid crystal (LC)s. The fabrication concept is based on phase separation of mixture of a photocurable polymer and a LC. Exploitation of an interference pattern allows realization of a periodic nano/microcomposite holographic grating made of slices of almost pure polymer alternating with well-aligned channels of LC. By means of a “Fresnel like” curing pattern, curved polymeric slices can impose radial alignment of nematic LCs. The distinctive features of the periodic structures enable high-quality and self-alignment of ordered fluids without the need for surface chemistry or functionalization.

A different generation of polymer-dispersed liquid crystals (PDLCs) based on a liquid crystalline polymer host is reported wherein the fluid behavior of the reactive mesogenic monomer is an enabler to concentration windows (liquid crystal polymer/liquid crystal) (and subsequent morphologies) not previously explored. These liquid crystal (LC) polymer/LC composites, LCPDLCs, exhibit excellent optical and electro-optical properties with negligible scattering losses in both the ON and OFF states. These systems thus have application in systems where fast phase modulation of optical signal instead of amplitude control is needed. Polarized optical microscopy and high resolution scanning electron microscopy confirm a bicontinuous morphology composed of aligned LC polymer coexisting with a phase separated LC fluid. Operating voltages, switching times, and spectra of LCPDLCs compare favourably to conventional PDLC films. The LCPDLCs exhibit a low switching voltage (4–5 V/μm), symmetric and submillisecond (200 μs) on/off response times, and high transmission in both the as formed and switched state in a phase modulation geometry.

We discuss new possibilities for the measurement of short laser pulses with the aid of liquid crystals: the competingly acting waves (CAW) method and the linear-optical pulse overlap (LOPO) method. CAW is a non-interferometric method providing both the peak energy density of a pulse and its duration in a simple, single shot measurement. LOPO allows measurement of ultra-short pulse duration with no need for nonlinear optical materials and phenomena. We also show the possibility of utilising the electrically controlled birefringence of liquid crystals to replace the opto-mechanical delay lines.

It is experimentally demonstrated that liquid crystals can play the role of ‘streak cameras’ and visualize traces of leakage of optical radiation from microscopic areas of essential fiber-optics components such as tapers, couplers, switches, as well as from uncontrollable inhomogeneity regions and imperfections. By that, extended regions of fibers can be simultaneously monitored and distribution of strain and temperature in long fibers visualized.

Large-scale, high-energy Nd:glass laser systems require beam shapers to control the spatial distribution of the incident intensity. Commercially available liquid crystal (LC) electro-optical spatial light modulators (SLM’s) are frequently employed for this purpose, but their intrinsic requirement for conductive metal or metal-oxide coatings limits their 1054-nm laser-damage thresholds to 230 mJ/cm2 (2.4 ns, 5 Hz), relegating them for use only in low-fluence areas of the laser system. Previously, we demonstrated that passive near-IR LC beam shapers employing coumarin alignment layers patterned by contact photolithography are capable of high resolution and contrast and can withstand incident 1054-nm laser-fluence levels of

Liquid crystals, combining optical non-linearity and self-organizing properties with fluidity, and being responsive to a wide variety of stimuli, have reached a key point in their development for photonic applications, for the realization of devices that could be dynamically reconfigurable, widely tunable and ultra-fast controlled. In this framework, ranging from Holography to Plasmonics , we review our recent efforts on developing a new generation of dynamic, tunable, electro- and all-optical photonic systems.

It is demonstrated that unique properties of orientational interaction of light with liquid crystals allow for high precision all-optical measurement of laser radiation intensity and determination of the focal spot location and its size. With that, non-absorptive character of the basic interaction phenomenon makes unperturbing measurement schemes feasible and ensures their applicability to high power beams. Large detector area and independent operation of its spatially distinct regions can be utilized to carry out parallel measurements for many beams.

Pairs of cycloidal diffractive waveplates can be used to doubly diffract or collinearly propagate laser radiation of the appropriate wavelength. The use of a dynamic phase retarder placed in between the pair can be utilized to switch between the two optical states. We present results from the implementation of an azo-based retarder whose optical properties can be modulated using light itself. We show fast and efficient switching between the two states for both CW and single nanosecond laser pulses of green radiation. Contrasts greater than 100:1 were achieved. The temporal response as a function of light intensity is presented and the optical switching is shown to be polarization independent.

Vector vortex waveplates (VVWs) have a potential of revolutionizing coronagraphy and other space imaging and communication systems. Extensive experimentation identified the role of factors that determined the properties of VVWs. Using photoalignment materials with high photosensitivity and reversible response proved key to minimizing the defect area and reducing the scattered light. Decreasing the exposure energy allowed decreasing the singularity area, and using VVWs for redistribution of light intensity from the axial regions of the beam to its periphery allowed large substrate areas to have similar exposure to the light, and production of large area VVWs. Using VVWs as linear to axial polarization converters allowed printing VVWs with higher topological charge while reducing the photoaligning time from an hour to minutes. Thus we were able to fabricate VVWs with high topological charge tuned to near infrared spectral range while keeping the singularity size to below 5 /am. Achromatic VVWs in IR spectral range were demonstrated with the aid of multilayer coating with twisted orientation.

We report our recent efforts on the fabrication and characterization of light responsive devices realized in soft composite materials. Periodic microstructures obtained by means of a photolithographic technique and a chemical etching process have been used to micro confine a light responsive liquid crystal stabilized through a self-organization processes. The high quality, light responsive, periodic microstructures have been exploited for realizing different all-optical, fast and low power applications. An overview of the realized photonic devices is presented.

We review our comprehensive investigation of light self-localization phenomena in planarly configured azobenzene liquid crystals. Cis-trans isomerization of azobenzene molecules and related changes in the order parameter of the liquid crystals support a high nonlinear response and the formation of optical spatial solitons at microwatt excitations. We describe bright soliton angular steering, deflection, interleaving and merging, as well as dark solitons.

The formation and characterization of a switchable volume reflective element fabricated from a polymer liquid crystal (LC) polymer slice (POLICRYPS) structure by holographic photopolymerization at high temperature (65 °C) using a photosensitive/nematic liquid crystal prepolymer mixture is reported. The submicron Bragg structure formed consists of periodic continuous polymeric walls separated by periodic LC channels. The phase separated NLC self-aligns in a homeotropic alignment between the polymer walls as indicated by polarizing optical microscopy analysis (Maltese cross). The resulting periodic grating structure results in a Bragg reflection notch upon illumination with white light due to the periodic variation in refractive index. Electro-optical experiments realized through in-plane electrodes and temperature experiments confirm that the multilayer structure acts as a Bragg mirror whose reflection efficiency can be controlled by either a small (~3V/µm) electric field or temperature.

We report the characterization of the chaotic behavior in the phenomenon of molecular reorientation induced in nematic liquid crystals by a laser beam in a particular geometry. The conventional approach to the reconstruction of dynamic properties of the measured chaotic signal is used to find the fractal dimension of the attractor and the largest Lyapunov exponent of the system. The intermittency observed in the chaotic regime gives useful informations to develop a satisfactory theoretical framework for the interaction between the light beam and the nonlinear medium.

The development history of polarization gratings (PGs), with origins in holography and Bragg gratings, accentuated and reinforced their perception as gratings. We highlight their nature as waveplates - diffractive waveplates (DWs) - and stress their family connection to vector vortex waveplates. This approach provides a straightforward understanding of the unusual properties of PGs, such as nearly 100% diffraction in thin material layers, the presence of only one diffraction order for a circularly polarized beam, wide diffraction bandwidth and the possibility of achromatic behavior. With technology being ripe for applications such as beam steering, and optical switching, we characterize the resistance of DWs to optical radiation, the effects of temperature and deformations. We also show that the boundary effects in the manufacturing process make it necessary to use substrates larger than the desired aperture of the DW. The multicomponent systems are discussed for developing normally transmissive switchable imaging systems, beam scanning, and achromatic diffraction.

Reversible, fast, all-optical switching of the reflection of a cholesteric liquid crystal (CLC) is demonstrated in a formulation doped with push-pull azobenzene dyes. The reflection of the photosensitive CLC compositions is optically switched by exposure to 488 and 532 nm CW lasers as well as ns pulsed 532 nm irradiation. Laser-directed optical switching of the reflection of the CLC compositions occurs rapidly, within a few hundred milliseconds for the CW laser lines examined here. Also observed is optical switching on the order of tens of nanoseconds when the CLC is exposed to a single nanosecond pulse with 0.2 J/cm(2) energy density. The rapid cis-trans isomerization typical of push-pull azobenzene dye is used for the first time to rapidly restore the reflection of the CLC from a photoinduced isotropic state within seconds after cessation of light exposure.

We report on the electrically controlled optical phase modulator behavior of light sculptured periodic structures made of polymer slices alternated to films of well aligned Liquid Crystals (POLICRYPS). Arbitrarily polarized light normally incident on the structure experiences a birefringence that depends on the anisotropy of the composite liquid crystalline material and on the geometrical cell parameters. The sample behaves as a retardation plate in good agreement with the Jones matrices formalism. Birefringence tuning is obtained by applying a suitable voltage, while a negligible birefringence variation is detected by increasing the incidence power. This makes POLICRYPS structures suitable as switchable phase retarders for high power laser beams. (C) 2008 Optical Society of America.

We demonstrate an optical axis grating (OAG) recorded in a nematic liquid crystal that yields a higher than 80% diffraction efficiency and over 800:1 switching contrast between diffraction orders for a laser beam of a red wavelength in a material layer only 1.5 microm thick. The grating was used for combining two laser beams with high efficiency. These observations prove the feasibility of new generation high-efficiency diffractive optical components, which are most promising for infrared and high-power applications owing to their enhanced transparency and reduced thermal effects in thin material layers.

We study the phenomena of laser beam propagation in azobenzene liquid crystals (azo LCs) in waveguiding configuration. We found that spatial solitons can be formed at microwatt power levels of a He-Ne laser beam. We have observed several well-known processes of nonlinear propagation such as undulation of solitons, their interaction and merging. In addition, we have shown that due to the memory of the nonlinear waveguide in azo NLC, the solitons are steered following mechanical displacement of the LC cell, a phenomenon that can be used for stabilized coupling of radiation into optical fibers. Cis-trans isomerization of azobenzene molecules and related change in the LC order parameter is the underlying mechanism of optical nonlinearity that makes possible formation of solitons. This mechanism is present in the mesophase as well as in the photoinduced isotropic phase of the material. We have shown that the photoinduced isotropic phase may be locally induced to form a waveguide that steers the solitons to large angles without noticeable attenuation of the beam at distances ~ 1 cm. We have presented a simple 3-level theory for describing the complexity of the effects of laser beams on azo LCs.

We show that photovoltaic fields are capable of efficiently reorienting liquid crystals, leading to new concepts of optically addressable light modulators. Using an arrangement consisting of a liquid-crystal layer between LiNbO3:Fe photovoltaic substrates, we observed spatial filtering due to self-phase modulation in a planar-oriented cell and nonlinear transmission between crossed polarizers in a twist-oriented cell. These processes do not require an external electric field. The substrates are arranged such that light propagates along the +c axis in each substrate, allowing a secondary process of power transfer to occur through contradirectional photorefractive two-beam coupling.

We have tested a technique for characterizing optical substrates using high sensitivity of the constant of nonlinear refraction to the structural and compositional homogeneity of the material. The technique consists in two steps: first the substrate is positioned in the focal region of a lens where the signal of the nonlinear phase shift is maximal and, second, the substrate is scanned in directions transverse to the propagation direction of the probe laser beam. The measured variations are proportional to variations in the nonlinear phase shift across the substrate and reflect distribution of parameters that contribute into the nonlinear phase shift, including the absorption coefficient and substrate thickness. This technique can be used for mapping trace amounts of impurities, dopants and inclusions as well as varying external/boundary conditions in glass substrates, liquid crystals, and other materials. As an example, we have visualized subtle changes inflicted on a holographic glass by UV exposure.

We have applied z-scan technique for measuring absorption coefficients of highly transparent optical materials (glass) and have used those for characterizing the power and power density of high power near IR laser beams. Self-phase modulation due to thermal indexing is the process underlying this technique. Glass plates with appreciable absorption coefficients are used for calibration purposes and for verifying the results of measurements. Fundamentally, as low absorption coefficients as 10 -5 cm -1 can be measured by scanning a plate of a transparent optical material in the focal region of a lens. The sensitivity of this technique proved to be high enough to reveal strong variation between the absorption coefficients of optical windows made of the same material BK7 but obtained from different sources. We have suggested and used a novel procedure, scanning nonlinear lens profiling, for characterization of homogeneity of optical glasses and other transparent optical materials. Most importantly, the technique can be used for fast and high precision measurement of power of high power laser beams without evoking large temperature increase and related problems.

Nonlinear optical processes in liquid crystals (LC) can be used for construction of all-optical spatial light modulators (SLM) where the photosensitivity and phase modulating functions are integrated into a single layer of an LC-material. Such spatial light integrated modulators (SLIMs) cost only a fraction of the conventional LC-SLM and can be used with high power laser radiation due to high transparency of LC materials and absence of light absorbing electrodes on the substrates of the LC-cell constituting the SLIM. Recent development of LC materials the photosensitivity of which is comparable to that of semiconductors has led to using SLIM in schemes of optical anti-jamming, sensor protection, and image processing. All-optical processes add remarkable versatility to the operation of SLIM harnessing the wealth inherent to light-matter interaction phenomena.

We report about applications of nonlinear optical processes for laser beam and optics characterization. The basic mechanism of the measurements consists in scanning a thin film of a liquid crystal in the focal region of a laser beam and processing the self-phase modulation signal. This technique allows precise and quick determination of the focal waist position and radius, which, in conjunction with the parameters of the focusing system allows determination of the laser beam divergence. We have demonstrated the capabilities of the technique for measuring submicron waist sizes and characterizing astigmatic optical systems. The technique is applicable to short laser pulses. The measurements were performed using the device implementation of the technique, the Crystal Scan Optical Multimeter.

We present the results of comprehensive characterization of capabilities of Crystal Scan device for measuring laser beams. (1) As small as 0.7 mm waist radius was measured for a laser beam of λ = 409 nm wavelength. The measurement lasts about 1 s with actual scan time being about 300 ms. (2) The focal waist position with accuracy better than 1% using focusing lenses of 6 mm to 50 mm focal length was determined. (3) Laser beam divergence in the range of 10-5rad to 10-2rad was measured and compared both to theoretically anticipated values as well as to the results obtained by conventional techniques. (4) We have identified the specific features of the signal received from astigmatic beams and measured the position and waist radii of both focuses. (5) The technique was successfully applied to measuring of laser beams at 1064 nm, 1341 nm and 10.6 mm wavelengths.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We report on the fabrication and characterization of curved periodic microstructures formed through the controlled phase separation of a liquid crystal and a polymerizing matrix comprising self-aligned liquid crystal. Imaging through a “Fresnel like” structure imparts an intensity profile onto a photosensitive mixture which subsequently forms periodic alternating curved polymeric and liquid crystal slices. The phase separated concentric rings of nematic liquid crystal self-align in a radial alignment in between the polymer walls as indicated by polarizing optical microscopy analysis (Maltese cross). Electro-optical experiments confirm the possibility to control this alignment and the optical properties of the macroscopic structure by means of a quite low external voltage. The system exhibits high-quality and self-alignment of an ordered (liquid crystal) fluid without the need of surface chemistry or functionalization.