Video-rate near-infrared optical tomography using spectrally encoded parallel light delivery

A novel parallel source implementation approach to near-infrared tomography is demonstrated through spectral encoding of the light delivery. This new technique allows many sources to be input into the tissue at the same time, and a high-resolution spectrometer is used to spatially spread out the signals from each spectrally encoded source. The parallel sampling of all sources at all detection locations renders rapid imaging. Acquisition of complete tomographic data sets at a video rate of 35 frames/s is achieved for imaging of a 6.35 mm diameter inclusion with an absorption coefficient of 0.01 mm(-1) and a reduced scattering coefficient of 1.5 mm(-1) that is moving along a circular path inside a 1% Intralipid solution.     

Quantitative spectrally resolved imaging through a spectrograph

A grating spectrograph can be used for spectrally selective two-dimensional imaging if it is operated with a broad entrance slit. The resulting intensity distribution in its exit plane is a one-dimensional convolution of the spatial and spectral distributions of incident light. We present a dedicated deconvolution filter to reconstruct the spatial image from the spectrograph output. The algorithm is illustrated on Raman imaging of an underexpanded dry air jet. Recorded Raman images correspond to density maps convolved with the Raman spectrum of air; the latter essentially acts as a blurring function for the density map. The deconvolution filter combines the individual images recorded in the O2 and N2 Raman bands into a single image of relative air density.     

Performance analysis and improvement of spectrally amplitude encoded/decoded OCDMA system

This paper describes a performance analysis of an incoherent optical code-division multiple-access scheme based on wavelength/time (W/T) codes. The system supports 16 users operating at 2.5Gb/s/user while maintaining bit-error rate (BER) < 10⁻¹¹ for the correctly decoded signal. It has been observed that there are two major problems giving rise to performance degradation of the system in terms of number of users and type of code.In this paper we have studied the optical simulator Encoding/Decoding for different lengths & gain in terms of Quality factor (Q) and Bit Error Rate (BER) performance. The system supports 16 users while maintaining bit-error rate (BER) < 10⁻¹¹ for the correctly decoded signal. Our aim is to design and simulate a Tree Network Topology Optical Code Division Multiple Access System for large number of users using wavelength–time code and to analyze the performance of the system based on BER and Eye Diagram under the influence of number of simultaneous users with different received powers.     

Temporally and spectrally resolved imaging of laser-induced plasmas

We report a hybrid imaging technique capable of performing measurements of the spatial, temporal, and spectral emission characteristics of laser-induced plasmas by use of a single detection system. We apply this technique to study the plasma produced by laser ablation of LiNbO3 and observe phenomena not seen in such detail with standard instruments. These include extreme line broadening up to a few nanometers accompanied by self-absorption near the target surface, and expansion dynamics that differ strongly between the different species. Overall, the wealth of quantitative information provided by this novel technique sheds new light on processes occurring during plasma expansion.     

Piecewise spectrally band-pass for compressive coded aperture spectral imaging

Coded aperture snapshot spectral imaging(CASSI) has been discussed in recent years. It has the remarkable advantages of high optical throughput, snapshot imaging, etc. The entire spatial-spectral data-cube can be reconstructed with just a single two-dimensional(2D) compressive sensing measurement. On the other hand, for less spectrally sparse scenes,the insufficiency of sparse sampling and aliasing in spatial-spectral images reduce the accuracy of reconstructed threedimensional(3D) spectral cube. To solve this problem, this paper extends the improved CASSI. A band-pass filter array is mounted on the coded mask, and then the first image plane is divided into some continuous spectral sub-band areas. The entire 3D spectral cube could be captured by the relative movement between the object and the instrument. The principle analysis and imaging simulation are presented. Compared with peak signal-to-noise ratio(PSNR) and the information entropy of the reconstructed images at different numbers of spectral sub-band areas, the reconstructed 3D spectral cube reveals an observable improvement in the reconstruction fidelity, with an increase in the number of the sub-bands and a simultaneous decrease in the number of spectral channels of each sub-band.     

Three-dimensional polarimetric integral imaging

A three-dimensional (3D) polarimetric image sensing and display technique based on integral imaging is proposed. Three-dimensional polarization distribution of reflected light from a 3D object can be measured as elemental image arrays by a rotating linear polarizer. After the measurement of the polarization of the 3D object, the 3D polarimetric object can be reconstructed optically by displaying the polarization-selected elemental images in spatial light modulators with two quarter-wave plates. Experimental demonstration of 3D polarimetric imaging of a 3D object attached to two orthogonal linear polarizers is presented. To the best of our knowledge, this is the first report on 3D polarimetric sensing imaging and 3D optical reconstruction by integral imaging.     

Self-referencing, spectrally, or spatially encoded spectral interferometry for the complete characterization of attosecond electromagnetic pulses

We propose a method for the complete characterization of attosecond duration electromagnetic pulses produced by high harmonic generation in an atomic gas. Our method is based on self-referencing spectral interferometry of two spectrally sheared extreme ultraviolet pulses, which is achieved by pumping the harmonic source with two sheared optical driving pulses. The resulting interferogram contains sufficient information to completely reconstruct the temporal behavior of the electric field. We demonstrate that such a method is feasible, and outline two possible experimental configurations.     

Three-dimensional synthetic aperture integral imaging

We propose synthetic aperture integral imaging, in which an effectively enlarged aperture (or field of view) is obtained by movement of small integral imaging system. This system substantially increases the field of view and the viewing resolution. The feasibility of our approach is experimentally demonstrated. To the best of our knowledge, this is the first time the synthetic aperture technique has been applied to three-dimensional integral imaging.     

Three-dimensional integral imaging of micro-objects

We propose a method for displaying micro-objects in space that is based on three-dimensional (3D) integral imaging, in which elemental images are calculated from a two-dimensional sampling of the optical field along different depths by use of confocal scanning microscopy. Experimental results are presented to demonstrate that a uniformly magnified 3D biological specimen can be displayed in space, and thus integral imaging can be used for 3D display of confocal microscopy. To the best of our knowledge, this is the first report of 3D integral imaging of (semitransparent) micro-objects.     

Temporally and spectrally resolved sampling imaging with a specially designed streak camera

We present a novel sampling imaging technique capable of performing simultaneous two-dimensional measurements of the temporal and spectral characteristics of light-emission processes by use of a specially designed streak camera. A proof-of-principle experiment was performed with a homemade multifocal multiphoton fluorescence microscope. The system was calibrated with a Fabry-Perot etalon and a standard fluorophore solution (rhodamine 6G in ethanol) and was shown to have temporal and spectral resolution of 6.5 ps and 3 nm, respectively, as well as high accuracy and reproducibility in lifetime and spectrum measurement. Temporally and spectrally resolved images of 4 x 4 foci on the sample can be obtained with a snapshot.     

Three-dimensional pulsed ESR Fourier imaging

Three-dimensional pulsed ESR imaging was performed on a (FA)(2)PF(6) crystal using a three-dimensional Fourier imaging sequence. The best resolution achieved was of 20 microm(3). Comparison with images obtained using the filtered back-projection method shows the superiority of this method under the given conditions.     

Three-dimensional ghost imaging based on periodic diffraction correlation imaging

We experimentally demonstrate a three-dimensional （3D） ghost imaging method based on period diffraction correlation imaging. Compared with conventional ghost imaging, our method can easily retrieve the images of different focal planes. Due to the correlation between the disturbed object beam and the reference beams which do not pass through any scattering, the clear images can be periodically obtained in the uncovered zones even through a scattering medium. The analysis of the 3D imaging resolution reveals that the proper resolution for actual demand can be achieved by designing our devices. The implementation of this experiment is quite simple and low-cost. It facilitates the practical applications of ghost imaging.     

Three-dimensional annihilation imaging of trapped antiprotons

We demonstrate three-dimensional imaging of antiprotons in a Penning trap, by reconstructing annihilation vertices from the trajectories of the charged annihilation products. The unique capability of antiparticle imaging has allowed, for the first time, the observation of the spatial distribution of the particle loss in a Penning trap. The radial loss of antiprotons on the trap wall is localized to small spots, strongly breaking the azimuthal symmetry expected for an ideal trap. Our observations have important implications for detection of antihydrogen annihilations.     

Three-dimensional particle imaging by wavefront sensing

We present two methods for three-dimensional particle metrology from a single two-dimensional view. The techniques are based on wavefront sensing where the three-dimensional location of a particle is encoded into a single image plane. The first technique is based on multiplanar imaging, and the second produces three-dimensional location information via anamorphic distortion of the recorded images. Preliminary results show that an uncertainty of 8 microm in depth can be obtained for low-particle density over a thin plane, and an uncertainty of 30 microm for higher particle density over a 10 mm deep volume.     

Three-dimensional imaging interferometric synthetic aperture ladar

A monostatic strip-map mode interferometric synthetic aperture ladar （SAL） is reported. Using a chirped laser of about 5 mW at 1550 nm wavelength as the illumination source and two cross-track receiving apertures with a baseline of 1.6 mm, the ladar can generate both well-focused two-dimensional SAL images without adopting phase error removing techniques and three-dimensional images by interferometric SAL techniques. Detailed results are illustrated for retro-reflective or diffusive targets at a distance of 2.4 m.     

Three-dimensional imaging of direct-written photonic structures

Third-harmonic generation microscopy has been used to analyze the morphology of photonic structures created using the femtosecond laser direct-write technique. Three-dimensional waveguide arrays and waveguide-Bragg gratings written in fused-silica and doped phosphate glass were investigated. A sensorless adaptive-optical system was used to correct the optical aberrations occurring in the sample and microscope system, which had a lateral resolution of less than 500?nm. This nondestructive testing method creates volume reconstructions of photonic devices and reveals details invisible to other linear microscopy and index profilometry techniques.     

Three-dimensional fourier transform NMR imaging. High-resolution chemical-shift-resolved planar imaging

A conventional high-resolution NMR spectrometer has been adapted for a three-dimensional imaging experiment which involves two spatial coordinates plus chemical shift. One dimension has far greater digital resolution than the other two, and when it is used to encode the chemical shifts it is possible to obtain separate slice images showing the distribution of each chemical species within the imaging plane. The method is illustrated using a tube phantom containing ethanol and water, in this case the ethanol gives sufficiently narrow finewidths that it is possible to obtain a separate image from the individual transitions of each multiplet.