Showing papers on "Waveplate published in 2009"

Stellar Spectropolarimetry with Retarder Waveplate and Beam Splitter Devices

Abstract: Nighttime polarimetric measurements are often obtained very close to the limits of the instrumental capabilities. It is important to be aware of the possible sources of spurious polarization, and to adopt data reduction techniques that best compensate for the instrumental effects intrinsic to the design of the most common polarimeters adopted for nighttime observations. We define a self-consistent framework starting from the basic definitions of the Stokes parameters, and we present an analytical description of the data reduction techniques commonly used with a polarimeter (consisting of a retarder wave plate and a Wollaston prism) to explore their advantages and limitations. We first consider an ideal polarimeter in which all optical components are perfectly defined by their nominal characteristics. We then introduce deviations from the nominal behavior of the polarimetric optics, and develop an analytical model to describe the polarization of the outgoing radiation. We study and compare the results of two different data reduction methods, one based on the differences of the signals, and one based on their ratios, to evaluate the residual amount of spurious polarization. We show that data reduction techniques may fully compensate for small deviations of the polarimetric optics from their nominal values, although some important (first-order) corrections have to be adopted for linear polarization data. We include a detailed discussion of quality checking by means of null parameters. We present an application to data obtained with the FORS1 instrument of the ESO VLT, in which we have detected a significant amount of cross talk between circular and linear polarization. We show that this cross-talk effect is not due to the polarimetric optics themselves, but is most likely caused by spurious birefringence due to the instrument's collimator lens.

Fabrication of liquid crystal polymer axial waveplates for UV-IR wavelengths.

Abstract: We show the opportunity of fabricating axially symmetric waveplates fine tuned to a desired wavelength. High quality waveplates are obtained using liquid crystal polymer layers on photoaligning substrates extending their functional range from UV to IR wavelengths. We characterize the effect of the waveplate on laser beams showing formation of a doughnut beam with over 240 times attenuation of intensity on the axis. We pay attention that the power density is strongly reduced on the doughnut ring as well and use this opportunity for taking charge coupled devices (CCDs) out of a deep saturation regime. Strong deformation of the beam profile is observed when the vortex axis is shifted towards the periferies of the beam. We demonstrate feasibility of using this phenomenon for shaping the profile of light beams with a set of waveplates.

Strongly birefringent cut-wire pair structure as negative index wave plates at THz frequencies

Abstract: We report a new approach for the design and fabrication of thin wave plates with high transmission in the terahertz (THz) regime. The wave plates are based on strongly birefringent cut-wire pair metamaterials that exhibit refractive indices of opposite signs for two orthogonal polarization components of an incident wave. As specific examples, we fabricated and investigated a quarter- and a half-wave plate that revealed a peak intensity transmittance of 74% and 58% at 1.34 THz and 1.3 THz, respectively. Furthermore, the half wave plate displayed a maximum figure of merit (FOM) of 23 at 1.3 THz where the refractive index was -1.7. This corresponds to one of the highest FOMs reported at THz frequencies so far. The presented results evidence that negative index materials enter an application stage in terms of optical components for the THz technology.

Circularly polarized light in the single-cycle limit: the nature of highly polychromatic radiation of defined polarization

Abstract: We have developed a general analytic description of polarized light pulses and explored the properties of circularly polarized single-cycle pulses. The temporal evolution of the electric-field vector of such spectrally broad pulses, which may be described in terms of a Hilbert transform relationship, differs significantly from the well-known behavior of quasi-monochromatic radiation. Single-cycle circularly polarized pulses have been produced and characterized experimentally in the terahertz spectral region.

Microbolometer-infrared imaging Stokes polarimeter

Abstract: A long-wave infrared division of amplitude imaging Stokes polarimeter is presented. For the first time, to our knowledge, application of microbolometer focal plane array (FPA) technology to polarimetry is demonstrated. The sensor utilizes a wire-grid beamsplitter with imaging systems positioned at each output to analyze two orthogonal linear polarization states simultaneously. Combined with a form birefringent wave plate, the system is capable of snapshot imaging polarimetry in any one Stokes parameter (S1, S2, or S3). Radiometric and polarimetric calibration procedures for the instrument are provided, and the reduction matrices from the calibration are compared to rigorous coupled wave analysis and ray-tracing simulations. Image registration techniques for the sensor are discussed, and data from the instrument are presented, demonstrating the ability to measure intensity variations corresponding to polarized emission in natural environments. As such, emission polarimetry can be exploited at significantly reduced cost, sensor size, and power consumption over instruments based on more expensive mercury-cadmium telluride FPAs.

High-contrast dark resonances with linearly polarized light on the D1 line of alkali atoms with large nuclear spin.

Abstract: High-contrast coherent population trapping signals were observed on the Cs D1 line by use of a bichromatic linear polarized light (lin‖lin field). A maximum absorption contrast of about 10% was obtained. This was nearly twice as high as that measured with the standard configuration of bichromatic circularly polarized light (σ−σ field). The results are compared with density matrix calculations of 4 and 5 level systems.

Diode-pumped dual-frequency microchip Nd : YAG laser with tunable frequency difference

Abstract: The diode-pumped dual-frequency microchip Nd : YAG laser with tunable frequency difference is presented. The gain medium used is a microchip 2 mm in thickness for miniaturized and integrated design. Two quarter-wave plates are placed into the laser cavity and the intra-cavity birefringence produces two orthogonally linearly polarized modes. The rotation of one of the two quarter-wave plates introduces a controlled and variable cavity birefringence which causes a variable frequency difference between the two orthogonally polarized modes. The frequency difference can be tuned through the whole cavity free spectral range. The obtained frequency difference ranges from 14 MHz to 1.5 GHz. The variation of the beat frequency over a period of 10 min is less than 10 kHz. The lock-in between modes is not found. Experimental results are presented, which match well with the theoretical analysis based on Jones matrices.

Metal nano-grid reflective wave plate.

Abstract: We propose an optical wave plate using a metal nano-grid. The wave plate operates in reflection mode. A single-mode truncated mode-matching theory is presented as a general method to design such nano-grid wave plates with the desired phase difference between the reflected TM and TE polarizations. This analytical theory allows angled incidence calculations as well, and numerical results agree-well with comprehensive finite-difference time-domain electromagnetic simulations. Due to the subwavelength path-length, the reflective wave plate is expected to have improved broad-band functionality over existing zero-order transmissive wave plates, for which an example is provided. The proposed wave plate is simple and compact, and it is amenable to existing nanofabrication techniques. The reflective geometry is especially promising for applications including liquid-crystal displays and laser feedback experiments.

Recovering the frequency dependent modulation function of the achromatic half-wave plate for POL-2: the SCUBA-2 polarimeter

Abstract: A spectro-polarimetric method is presented to allow the recovery of the frequency dependent polarization modulation function for an achromatic half-wave plate. We show how the non ideal nature of the modulator can be characterized for removal of both instrument effects and variations related to the source spectral index.

Vector holograms using radially polarized light

Abstract: We have demonstrated the vector holograms using the radially polarized light. The inhomogeneous polarized light well controlled the spatial distribution of the optical anisotropy in the solid state polymeric materials. The theoretical calculation revealed formation mechanism and optical properties of the vector holograms.

Computer generated hologram, exposure apparatus and device fabrication method

Abstract: The present invention provides a computer generated hologram which forms a light intensity distribution on a predetermined plane by giving a phase distribution to a wavefront of incident light, comprising an anisotropic layer whose refractive index with respect to linearly polarized light in a first direction is different from a refractive index of the anisotropic layer with respect to linearly polarized light in a second direction perpendicular to the linearly polarized light in the first direction, and an isotropic layer whose refractive index with respect to the linearly polarized light in the first direction is equal to a refractive index of the isotropic layer with respect to the linearly polarized light in the second direction.

Passive alignment method and its application in micro projection devices

Abstract: An optical micro-projection system comprising the following components: -at least one light source (401); -at least one mirror (200) based on MEMS technology for deviating light from said light source; -at least one beam splitter (403); -at least one wave plate (400); wherein mutual alignment of at least two of said components is provided by mutual direct contact between reference contact faces (500) of said components. The proposed architecture enables avoiding the use of dynamic optical assembly methods and to minimize the light loss within the system.

Liquid crystal optical device configured to reduce polarization dependent loss and polarization mode dispersion

Abstract: An LC-based optical device compensates for differences in optical path lengths of polarization components of input beam. As a result, PDL and PMD of the optical device are reduced. The compensation mechanism may be a glass plate that is disposed in an optical path of a polarization component so that the optical path length of that polarization component can be made substantially equal to the optical path length of the other polarization component that traverses through a half-wave plate. Another compensation mechanism is a birefringent displacer that has two sections sandwiching a half-wave plate, wherein the two sections are of different widths and the planar front surface of the birefringent displacer can be positioned to be non-orthogonal with respect to the incident input light beam.

Self-collimating photonic-crystal wave plates.

Abstract: We present theoretical results of quarter- and half-wave plates based on two-dimensional photonic crystal that has a polarization-independent self-collimating effect. The designed low-order wave plates have achromatic characteristic with high phase accuracy of +/-0.01π in the normalized frequency range 0.273-0.281a/λ, which is about 45 nm in the telecommunication band (around 1550 nm). Profiting from the self-collimating guiding mechanism, the wave plates (even the relative high-order ones) have low beam divergence and transmission loss. In addition, on the basis of the formed birefringence effect, a method for designing high-order wave plates is proposed. The wave plates presented in this Letter have potential applications in future photonic integrated circuits.

Full optical fiber current transformer adopting double closed loop control

Abstract: The invention relates to a full optical fiber current transformer. After passing through a Loyt depolarization device, a light beam emitted by a light source enters an integrated optical device and produces two beams of linearly polarized light through the processing of the integrated optical device; and after passing through a polarization maintaining optical fiber delay line and a lambada/4 wave plate, the two beams of the linearly polarized light are converted into two beams of elliptically polarized light and enter sensitive optical fibers for transmission. Due to the Faraday magnetic optical effect, the two beams of the elliptically polarized light produce a phase difference under the action of a magnetic field produced by a tested current; subsequently the two beams of the light enter the sensitive optical fibers again after being reflected by a reflector; and the two beams of the light interchange the light paths and produce the phase difference again under the action of the magnetic field produced by the tested current. The two beams of the elliptically polarized light carrying current information return to the integrated optical device via the lambada/4 wave plate and the polarization maintaining optical fiber delay line to form interference light which is sent to a photo detector. The photo detector converts a light intensity signal carrying the information of the tested current into a voltage signal which is sent to a double closed loop control device. The double closed loop control device respectively completes the phase zero setting closed loop control and the modulated wave resetting closed loop control of the two beams of the linearly polarized light according to the voltage signal.

Endoscope observation system

Abstract: An endoscope observation system includes a light source section generating different types of light in at least partly different wavelength bands for observation of a polarized light-based observation image and for observation of a non polarized light-based observation image, respectively; an irradiation side polarization separation element subjecting the illumination light from the light source section to polarization separation; a light reception side polarization separation element performing polarization separation, in a particular wavelength band of the light from the observation target, by transmitting polarized light with a predetermined polarization component while reflecting polarized light with a polarization component other than the predetermined polarization component, and in a wavelength bend other than the particular wavelength band, exhibiting same transmission and reflection characteristics for both polarized light and non polarized light; and an image pickup element receiving the transmitted or reflected light.

Backscattering of linearly and circularly polarized light in randomly inhomogeneous media

Abstract: The scattering of linearly or circularly polarized light from a semibounded randomly inhomogeneous medium is considered. A new technique for simulating the electromagnetic radiation transport using the Monte Carlo method is proposed, which makes it possible to avoid cumbersome calculation of Muller matrices. Expressions are obtained for the co- and cross-polarized components of backscattered light for incident light of arbitrary polarization. The coherent and incoherent backscattering components are calculated for arbitrary combinations of incident and scattered light polarizations. It is shown that the main contribution to coherent backscattering is from the co- and cross-polarized components for linearly and circularly polarized light, respectively. The backscattering from an optically active random medium is calculated.

Comment on “Limits on Fluorescence Detected Circular Dichroism of Single Helicene Molecules”

Abstract: In his paper, “Limits on Fluorescence Detected Circular Dichroism...”,1 Cohen makes some rather sweeping and dismissive claims regarding chiroptical spectroscopy of single molecules in general, and our previously published work in particular. As the name of one of us (M.D.B.) appears in the acknowledgments without advanced knowledge or consent, we feel an obligation to comment directly. It is true that Prof. Cohen contacted M.D.B. prior to submission of the manuscript, to which a detailed response was sent shortly after. We were certainly grateful for the opportunity to view the manuscript prior to publication; however, most of our comments and suggestions for revision were largely ignored. Thus, the fact that we were acknowledged in the paper is troubling in that it implies that we (collectively) agree with the main conclusions of this paper. The central issue is distortion of the circular polarized excitation field at the sample plane induced by dichroic filters commonly used in fluorescence microscopy of single molecules. It is well-known that ellipticities in excitation polarization can generate linear dichroism in fluorescence that could appear as large circular dissymmetries in fluorescence excitation. As Cohen demonstrates, interrogation of the polarization state of a circular polarized laser can be significantly distorted (≈50-60% induced ellipticity) upon reflection from a dichroic filter. We have long understood this effect, and any implication or direct claim that we were ignorant or naive with respect to such distortions (and the inherent artifactual results that could be generated in an experiment) is certainly not true. In both our published papers2,3 (refs 1 and 18 in the Cohen paper), the polarization state was well characterized, and control runs were made with dye-doped polymer nanospheres as well as for achiral linear dipole molecules to quantitatively assess any artifactual response. This has already been well documented. In our typical mode of polarization tuning, we looked at the retroreflection of a circularly polarized input beam into the microscope and assessed the degree of ellipticity via the extinction of the retroreflected beam (which changes polarization sense on reflection). As Prof. Cohen called that into question in the current paper, we interrogated directly the fidelity of the circular polarization state of the laser after reflection from the dichroic mirror (Omega Optical XF2027485DRLP), and at the sample plane with both the dichroic mirror and objective in place. We first prepared a circular (right or left) polarized excitation beam by placing a linear (vertical) polarizer followed by an achromatic quarter waveplate oriented at (45°; the purity of the input circular polarization was determined to be 98.8% by passing the light through another quarter waveplate and looking at the intensity ratio in H/V basis of the retroreflected beam. We then looked at the fidelity of the circular polarization as the beam was reflected off the dichroic mirror alone, which gave a circular polarization purity of 98.7%. Finally, we measured the polarization of the beam, as it was reflected from the dichroic mirror and through the objective, to be 98.7%. This number was established by two detection methods; first, by converting the circular polarization back to linear polarization and looking at the intensity ration of H and V components using a second quarter waveplate and analysis of H and V intensities using a rotating linear polarizer, and second, by resolving the H and V components using a Wollaston prism. The results were the same to within experimental error. Thus the induced distortion in the circular polarization of our excitation source through the microscope (all optics included) is of order 0.1%snot 40%, as suggested in the Cohen paper. Thus, our experiments are based on a circular polarization that is not dissimilar from Cohen’s using his defined compensation approach generating CPL at the sample. The second issue regards the breadth and shape of the single-molecule dissymmetry parameter distributions. In Figure 3B, the results shown by Cohen for CPL generated at the sample span a (≈3σ) range of (0.5. In our published results for triaryl amine helicene excited at 457 nm, approximately 90% of the probability density is contained in the range of g-values of ≈(0.7, which is not grossly dissimilar from Cohen’s result obtained from CPL at the sample. Cohen points to shot-noise, blinking, and photobleaching as the main contributors to the width of his observed distributions, which again is at odds with our own observations. It is (obviously) true that fluorescence intermittency and photobleaching limit information content in any single-molecule measurement. As we pointed out in our original paper, we looked closely at control distributions of both multichromophoric polymer nanosphere samples, as well as linear (achiral) dipole systems to construct a kind of “instrument response function” for our experiment. Both those control distributions were symmetric about g ) 0 and had similar widths (fwhm ≈ 0.2). In our results, we sampled molecules with long enough photochemical lifetime to observe (with several exposures for a particular excitation polarization) intensity variations for at least 1.5 R/L excitation polarization cycles. As we pointed out in our private communication with Prof. Cohen (but not mentioned in his paper), we believe that the principal difference between these two sets of data lie in different subpopulations of the molecules sampled. We (necessarily) selected molecules with high photostability so that we could have long enough exposure times (A) to integrate out any short-time intensity fluctuations (blinking, etc.) and (B) to rotate through multiple J. Phys. Chem. A 2009, 113, 9757–9758 9757

Dual-frequency laser interferometer

Abstract: The invention provides a dual-frequency laser interferometer, which comprises a first polarization splitting prism, a second polarization splitting prism, a compensating mirror and a first cube-corner prism which are arranged in the reflected light direction of the first polarization splitting prism, a quarter wave plate and a reflector which are arranged in the transmitted light direction of the first polarization splitting prism, and a second cube-corner prism which is opposite to the second polarization splitting prism and arranged at the other side of the first polarization splitting prism; wherein the thickness of the compensating mirror is 2 times of that of the quarter wave plate. On one hand, the dual-frequency laser interferometer with high stability can increase the extinction ratio of the reflected light and reduce the nonlinear error in the premise of not increasing the processing difficulty of the polarization splitting prism; and on the other hand, the dual-frequency laser interferometer reduces the heat drift error to the maximum; therefore, the dual-frequency laser interferometer has the advantages of low heat drift error, low nonlinear error, simple assembling and adjusting, easy component processing and the like.

Device for large distance light parallel regulation

Abstract: The utility model relates to a long-distance light parallel adjusting device which belongs to the technical field of photoelectric detection. The device comprises a collimation laser device (1), a polarization optical splitter (2), a plane reflector (12) arranged on the reflected light path of the polarization optical splitter (2), a Gama/4 wave plate (3) arranged in the middle of the polarization optical splitter (2) and the polarization optical splitter (2), a two-dimensional adjustable plane reflector (5) arranged on the transmission light path of the polarization optical splitter (2), a second Gama/4 wave plate (4) arranged in the middle of the polarization optical splitter (2) and the two-dimensional adjustable plane reflector (5), a lens (7) arranged at a secondary reversely-reflected light path, and a detector (8) placed on the transmission light path of the lens (7), wherein, the plane reflector (12) is arranged on a guide rail pair (11) of a linear guide rail (10) and can adjust a two-dimensional angle. The device can simply adjust the large-distance parallel light beams and has high adjustment accuracy.

Quarter wave plate, optical pickup device, and reflective liquid crystal display device

Abstract: A quarter wave plate that is a crystal plate made of an inorganic material having birefringence and optical rotatory power and has an optical axis, includes an incident surface positioned on one surface of the crystal plate; and an emitting surface positioned on another surface, which is opposed to the incident surface, of the crystal plate. In the quarter wave plate, linearly-polarized light incident from the incident surface is converted into circularly-polarized light so as to be emitted from the emitting surface, and circularly-polarized light incident from the incident surface is converted into linearly-polarized light so as to be emitted from the emitting surface. Further, in the wave plate, an angle φ formed by a normal line on the incident surface and the optical axis is set in a range of 0°<φ<90°, and an optical axis azimuth angle θ formed by an optical axis projection line, which is formed by projecting the optical axis on the incident surface, and a polarization plane of the linearly-polarized light is set in one of a range of 0°<θ<90° under θ≠45° and a range of 90°<θ<180° under θ≠135°.

Reconstruction of polarized optical images in two- and three-dimensional vector holograms

Abstract: In the present paper, we extensively study the optical diffraction in two- and three-dimensional vector holograms and demonstrate the reconstruction of polarized optical images recorded in azobenzene-containing amorphous polymers (AP) and polymer-dissolved liquid-crystalline composites (PDLCC). The polarization states of the interference light are not modulated in the isotropic AP films, while modulated in the anisotropic PDLCC films. The information of the polarized optical image is recorded as the polarization induced anisotropy in the AP and PDLCC medium and is reconstructed as the polarized optical images. The theoretical consideration well explained the characteristics of the reconstructed polarized optical images from both two- and three-dimensional vector holograms.

Fast multispectral remote sensing polarization imager

Abstract: The invention relates to a fast multispectral remote sensing polarization imager. A system can work under an active mode and a passive mode and can improve the detectability of a target by controlling the polarization state and the wavelength of incident light. The system essentially consists of an emitting part, a receiving part, a controlling part and an image processing part. The emitting part essentially consists of a multi-wavelength pulse light source, a polarization module and a beam shaping, collimating and beam expanding part. The receiving part consists of a scanning and receiving telescope, the polarization module and a multispectral camera. A control system essentially controls the polarization state of the emitting part and the receiving part and obtains images under various polarization modes. The image processing part realizes the pseudo-color coding of an intensity image and a polarization degree image. The polarization state of the incident light can be adjusted by a fast adjustable liquid crystal wave plate; imaging range is enlarged in a way of scanning and receiving; and finally the noise is eliminated by image processing, so as to realize a pseudo-color coding image with exact real-time intensity and polarization degree.

Small optics cell for miniature nuclear magnetic resonance gyroscope

Abstract: A beamsplitter (60) is arranged to split an incident laser beam into a pump beam (61) and a detection beam (83). The pump beam (61) passes through the beam splitter (60) and then reflects from a pair of mirrors (66, 78) to a quarter waveplate (74) into an interaction cell (76). After passing through the interaction cell (76), the pump beam (61) reflects from a mirror to a first photodetector. The detection beam (83) reflects from the beam splitter (60) and propagates on a path perpendicular to the path of the pump beam (61) through the interaction cell (76). After passing through the interaction cell (76), the detection beam (83) is incident upon a polarizer (84). The polarized portion of the detection beam (83) then is incident upon a photodetector (86).

Single frequency inner cavity frequency-doubling laser

Abstract: The invention provides a single-frequency intracavity frequency doubling laser, comprising a laser crystal (2), a laser resonant cavity consisting of cavity mirrors, a pumping source (1), an intracavity frequency doubling crystal (5), a Faraday rotator (3) and a one-half wave plate (4) The laser crystal (2) is an anisotropic uniaxial crystal, and two light-pass surfaces of the crystal are cut along a certain angle so as to form a non-parallel wedge shape Because of the birefringence effect of the wedge-shaped laser crystal, the laser stably oscillates and operates with a polarized laser (8), and a polarized laser (9) perpendicular to the polarized laser (8) is inhibited because of geometric optical loss The laser can also comprise an optical etalon (6) and a Q-switching element (7) The single-frequency intracavity frequency doubling laser designed by the invention has the advantages of the capability of operating stably at single frequency for a long time, high laser polarization degree, high optical-optical conversion efficiency, compact structure, simple regulation, etc, thereby having broad application prospects in the scientific research, national defense construction, bio-medical treatment, information industry and other fields

Optical Information Recording in Films of Photoinduced Birefringent Materials and Application to Retardagraphy

Abstract: Optical information of linearly polarized light recorded on a photoinduced birefringent medium was clearly expressed using an optical anisotropy matrix in the circular polarization basis. The theoretical expression was related to the principle of retardagraphy, that is, an optical recording technique for the retardance pattern of an optical anisotropic object. Furthermore, the polarization holographic characteristics were explained by the principle. As a demonstration of optical information recording, a retardance pattern displayed on a parallel aligned liquid-crystal spatial light modulator was recorded on an azobenzene copolymer film, and the retardance pattern was reconstructed by imaging polarimetry. The transmission axis of a polarizer in the imaging polarimetric system was adjusted using a homogeneous pattern.

Laser-driven clockwise molecular rotation for a transient spinning waveplate.

Abstract: Our simulations show a copropagating pair of laser pulses polarized in two different directions can selectively excite clockwise or counterclockwise molecular rotation in a gas of linear molecules. The resulting birefringence of the gas rotates on a femtosecond timescale and shows a periodic revival structure. The total duration of the pulse pair can be subpicosecond, allowing molecular alignment at the high densities and temperatures necessary to create a transient spinning waveplate.