Photonics/Optics

Transforming Gaussian Beams into Uniform, Rectangular Intensity Distributions

The majority of laser types in current use produce output beams with circular or elliptical crosssections, with either Gaussian or near- Gaussian intensity profiles. This Gaussian intensity distribution is acceptable, and often beneficial for many applications in which the laser beam is being focused to a small spot. However, there are also many different uses for which a uniform intensity distribution (often referred to as a “flattop”) would be more optimal. For example, in materials processing tasks, a uniform intensity distribution ensures that the entire laser illuminated area is processed evenly. It is also valuable in situations where the laser light is used essentially for illumination. This is because uniform illumination makes identical features that all appear to have the same brightness, regardless of where they are located in the illuminated field, simplifying the image processing task and increasing contrast and resolution. These same benefits apply over a wide range of other applications that can be broadly classed as “illumination,” from machine vision, through flow cytometry, inspection, and even some medical uses.

Posted in: Articles, Features, Photonics

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Designing Optical Systems With Off-The-Shelf Products

Utilization of COTS (commercial off-the-shelf) products is now almost a bylaw of government and military design projects and is becoming of increasing interest in commercial designs, as well. Optical systems are no exception; the use of stock optics can provide tremendous advantages in terms of reduced cost and development effort. The key is finding the most appropriate way of employing stock optics in a custom design.

Posted in: Articles, Applications, ptb catchall, Photonics

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High-Speed Digital Interferometry

Optical decoding eliminates the need for high-speed detectors and digital signal processing. Digitally enhanced heterodyne interferometry (DI) is a laser metrology technique employing pseudo-random noise (PRN) codes phase-modulated onto an optical carrier. Combined with heterodyne interferometry, the PRN code is used to select individual signals, returning the inherent interferometric sensitivity determined by the optical wavelength. The signal isolation arises from the autocorrelation properties of the PRN code, enabling both rejection of spurious signals (e.g., from scattered light) and multiplexing capability using a single metrology system. The minimum separation of optical components is determined by the wavelength of the PRN code.

Posted in: Photonics, Briefs, TSP, ptb catchall, Tech Briefs, Photonics

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Integrated Optics Achromatic Nuller for Stellar Interferometry

Nuller allows faint off-axis light to be much more easily seen. This innovation will replace a beam combiner, a phase shifter, and a mode conditioner, thus simplifying the system design and alignment, and saving weight and space in future missions. This nuller is a dielectric-waveguidebased, four-port asymmetric coupler. Its nulling performance is based on the mode-sorting property of adiabatic asymmetric couplers that are intrinsically achromatic. This nuller has been designed, and its performance modeled, in the 6.5-micrometer to 9.25-micrometer spectral interval (36% bandwidth). The calculated suppression of starlight for this 15-cm-long device is 10–5 or better through the whole bandwidth. This is enough to satisfy requirements of a flagship exoplanet-characterization mission.

Posted in: Photonics, Briefs, TSP, ptb catchall, Tech Briefs, Photonics

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Near-Infrared Photon-Counting Camera for High-Sensitivity Observations

Extremely faint phenomena and NIR signals emitted from distant celestial objects can be observed and imaged. The dark current of a transferred-electron photocathode with an InGaAs absorber, responsive over the 0.9-to-1.7-μm range, must be reduced to an ultralow level suitable for low signal spectral astrophysical measurements by lowering the temperature of the sensor incorporating the cathode. However, photocathode quantum efficiency (QE) is known to reduce to zero at such low temperatures. Moreover, it has not been demonstrated that the target dark current can be reached at any temperature using existing photocathodes.

Posted in: Photonics, Briefs, TSP, ptb catchall, Tech Briefs, Photonics

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Goniometric Radiometer

The LD8900 Goniometric Radiometer from Ophir Photonics Group (Logan, UT) makes X-Y, holographic, and 3D measurements without moving either the detector or the source. The design allows the farfield profiler to characterize and confirm the divergence of light passing through holographic materials, such as those used for computer display screens, smartphones, and instrument panels. The 3D capability of the LD8900 makes it possible to measure radially symmetric divergences or angularly different types.

Posted in: Products, Products, ptb catchall, Photonics

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Thermal Surveillance Cameras

Vumii (Atlanta, GA) has added four thermal camera lines to its imaging solutions portfolio: CompactSec™, EyeSec™, DualSec™, and RangeSec™. The IP-enabled CompactSec thermal camera is available in three models: 8.5mm lens for 65° field of view; 19mm lens for 28° field of view; and 35mm lens for 15° field of view. The EyeSec, a line of uncooled thermal cameras, has a wide variety of lens and resolution configurations, including a 15-100mm continuous zoom model. The camera provides thermal video through darkness, light fog, or smoke. The EyeSec line features IP or analog communication options with 320 x 240 25μ or 640 x 480 17μ resolution. The DualSec dual-video (thermal and visual) channel pan tilt camera system allows mediumrange observation and detection. The RangeSec imager, a high-sensitivity, cooled midwave (3-5 μm) thermal camera, utilizes a 19mm to 275mm continuous zoom (29° to 2° field-ofview) or a 47.5mm to 687mm continuous zoom lens (12° to 0.8° field-of-view).

Posted in: Products, Products, ptb catchall, Photonics

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