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We introduce M/# as a metric for characterizing holographic memory systems. M/# is the constant of proportionality between diffraction efficiency and the number of holograms squared. Although M/# is a function of many variables in a holographic recording system, it can be measured from the recording and erasure of a single hologram. We verify experimentally that the diffraction efficiency of multiple holograms follows the prediction of M/# measured from a single hologram.

The Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) is a robotic arm-mounted instrument on NASA’s Perseverance rover. SHERLOC has two primary boresights. The Spectroscopy boresight generates spatially resolved chemical maps using fluorescence and Raman spectroscopy coupled to microscopic images (10.1 μm/pixel). The second boresight is a Wide Angle Topographic Sensor for Operations and eNgineering (WATSON); a copy of the Mars Science Laboratory (MSL) Mars Hand Lens Imager (MAHLI) that obtains color images from microscopic scales (∼13 μm/pixel) to infinity. SHERLOC Spectroscopy focuses a 40 μs pulsed deep UV neon-copper laser (248.6 nm), to a ∼100 μm spot on a target at a working distance of ∼48 mm. Fluorescence emissions from organics, and Raman scattered photons from organics and minerals, are spectrally resolved with a single diffractive grating spectrograph with a spectral range of 250 to ∼370 nm. Because the fluorescence and Raman regions are naturally separated with deep UV excitation (<250 nm), the Raman region ∼ 800 – 4000 cm−1 (250 to 273 nm) and the fluorescence region (274 to ∼370 nm) are acquired simultaneously without time gating or additional mechanisms. SHERLOC science begins by using an Autofocus Context Imager (ACI) to obtain target focus and acquire 10.1 μm/pixel greyscale images. Chemical maps of organic and mineral signatures are acquired by the orchestration of an internal scanning mirror that moves the focused laser spot across discrete points on the target surface where spectra are captured on the spectrometer detector. ACI images and chemical maps (< 100 μm/mapping pixel) will enable the first Mars in situ view of the spatial distribution and interaction between organics, minerals, and chemicals important to the assessment of potential biogenicity (containing CHNOPS). Single robotic arm placement chemical maps can cover areas up to 7x7 mm in area and, with the < 10 min acquisition time per map, larger mosaics are possible with arm movements. This microscopic view of the organic geochemistry of a target at the Perseverance field site, when combined with the other instruments, such as Mastcam-Z, PIXL, and SuperCam, will enable unprecedented analysis of geological materials for both scientific research and determination of which samples to collect and cache for Mars sample return.

A novel use of liquid-crystal television (LCTV) is described. It is shown that, if the phase nonuniformity of the LCTV is corrected by a liquid gate, then a simple computer-generated hologram can be written and coherently reconstructed.It is well known that spatial light modulators (SLM's) are essential for real-time optical information processing. For that reason, much research has been devoted to them, and many types of SLM have been developed. 1Most of the existing SLM's are either forbiddingly expensive or still in the research and development stages. Recently an extremely inexpensive liquidcrystal television (LCTV) was investigated in relation to its use in optical data processing. 2 -1 0 One advantage of the LCTV is that it can be addressed either electronically or optically. However, because of the thickness variations over the aperture of the screen of the devices, its usefulness for coherent optical processing is limited.We have examined the thickness nonuniformities of the LCTV screen in a Mach-Zehnder interferometer.We have successfully corrected the nonuniformities by submerging the screen in a liquid gate and have demonstrated the feasibility of using this device to write and reconstruct a computer-generated hologram. The results are briefly reported below.The operating principle of the LCTV has been described. When no electric field is applied, the plane of polarization for linearly polarized light is rotated through 90 deg by the twisted liquid-crystal molecules, and no light is transmitted through the second polarizer. However, with an electric field applied, the twist and tilt of the liquid-crystal molecules are altered, resulting in transmission of a controllable and variable fraction of light. The input signal to the LCTV can be from a TV receiver, a computer, or a TV camera.A Mach-Zehnder interferometer was set up to analyze the optical quality of the LCTV screen. A 6.4-cm 2 (1-in.2 ) region of the LCTV screen was illuminated by a collimated He-Ne laser beam. The results are shown in Fig. 1(a). It can be seen that more than five fringes are produced, indicating thickness nonuniformities of the LCTV screen amounting to about 0.046 gm per pixel. It has been found that the phase nonuniformity is due mainly to the poor quality of the polarizer sheets. Because of the nonuniformity, Fraunhofer diffraction patterns show fuzziness in the various orders. 3We investigated two ways of removing the phase distortions. The first was to correct the phase variation by a phase-conjugation method. We used a 10-mW He-Ne laser to produce a holographic filter of the LCTV screen and addressed it with a phase-conjugated beam projected through a holographic plate. Unfortunately, the beam reconstructed through the LCTV was too weak to be observed visually because of the low diffraction efficiency of the hologram and the low power of the laser.