An optically multiplexed image camera often requires a photodetector for image sensing in conjunction with an optical multiplexer, such as a digital micromirror device or an amplitude spatial light modulator. For this type of camera, the advantages of using one photodetector, unfortunately, can be outrun by the fairly large acquisition time, consumed in the image multiplexing process. Therefore, we propose a solution to efficiently improve the image acquisition time span and to relax the computational burden in the reconstruction process. Our camera design incorporates a reflection optical multiplexer, for image encoding, in conjunction with multiple photodetectors. The working principle relies on sequential image encoding using multiple low-resolution sets of binary masks, applied synchronously. The reconstructed data sets form the segments of the final image, which are stitched together with dark boundary pixels.
In this paper we report spectral measurements of some relatively common substances but from the hazardous category (possibly to be used like explosives or their manipulation is dangerous) in view to create a database with spectra of such substances. THz transmission spectra of some pure materials and mixed ones are also introduced. The measurements were performed using a Time-Domain system that work in the range of 0.2-4.5 THz. We develop our algorithm to obtain maximum information from the measurement and to minimize the errors.
We developed a measuring technology using a TDS-THz system to construct hyperspectral images of some objects, including hazardous materials. “T-rays” (the THz spectral domain of the light) have a growing importance in security and imagistic domain. Due to their property of penetrating through dielectric objects, and using non-ionizing radiations, the THz systems have become a standard for “hot-places” (airports, train stations etc.). The hyperspectral images are 3D images having 2D spatial dimension and one spectral dimension. In this way, we obtain simultaneously information about the form of the object and its molecular composition. For discriminating between substances, we must first build a database of spectra for hazardous and dangerous substances. We experiment our system on some items (among them a firecracker, a cigarette and a metal collar) and we tried to discriminate between them using the database of spectra.
The paper present our first steps to realize a hyperspectral imaging system. Preliminary experiments in the domain have as purpose to test the capability of a monochromator with a 2D linear CCD camera, to create hyperspectral images. Using a Sciencetech 9055 model monochromator with a Hamamatsu CCD, we have analyzed an array of three LEDs of various colors, obtaining 1D hyperspectral images.
Although nowadays spectrometers reached a high level of performance, output signals are often weak and traditional slit spectrometers still confronts the problem of poor optical throughput, minimizing their efficiency in low light setup conditions. In order to overcome these issues, Hadamard Spectroscopy (HS) was implemented in a conventional Ebert Fastie type of spectrometer setup, by substituting the exit slit with a digital micro-mirror device (DMD) who acts like a coded aperture. The theory behind HS and the functionality of the DMD are presented. The improvements brought using HS are enlightened by means of a spectrometric experiment and higher SNR spectrum is acquired. Comparative experiments were conducted in order to emphasize the SNR differences between HS and scanning slit method. Results provide a SNR gain of 3.35 favoring HS. One can conclude the HS method effectiveness to be a great asset for low light spectrometric experiments.
A grating interferometer that uses the high diffraction orders in conjunction with a Twyman-Green commercial interferometer is used for the measurement of in plane movement of gratings. The high diffraction orders ensures the amplification of the measurement precision with a factor equal to the diffraction order of the measurement in principle, because no imaging of features marking the beginning and the end of the measured length feature is necessary, and therefore the resolution limits associated with microscope imaging are eliminated.