Photonics/Optics

Calibrating Photovoltaic Cells

The basic function of a photovoltaic cell is to convert input — sunlight energy expressed in irradiance (W/m2) — into output — useable electrical power — with as little loss as possible. To quantify the ability of the system to accomplish this conversion, one can simply compare the output to the input by forming a ratio of the two. This ratio, expressed in percentages, is known as the power conversion efficiency (PCE) of the device and it is a key parameter of electrical performance. Since the PCE is used to compare the performance of photovoltaic devices, it is critical that accurate estimates be made for the PCE. The estimate is dependent on knowing, with a high degree of accuracy, the actual conditions, including irradiance and cell temperature, under which the parameter is measured.

Posted in: Articles, Features, ptb catchall, Photonics

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New Scanning Probe Microscopy Techniques for Analyzing Organic Photovoltaic Materials

Organic photovoltaic (OPV) materials are an emerging alternative technology for converting sunlight into electricity. OPVs are potentially inexpensive to process, highly scalable in terms of manufacturing, and compatible with mechanically flexible substrates. In an OPV device, semiconducting polymers or small organic molecules are used to accomplish the functions of collecting solar photons, converting the photons to electrical charges, and transporting the charges to an external circuit as a useable current.

Posted in: Application Briefs, Applications, ptb catchall, Photonics

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Qualification and Selection of Flight Diode Lasers for Space Applications

NASA’s Jet Propulsion Laboratory, Pasadena, California The reliability and lifetime of laser diodes is critical to space missions. The Nuclear Spectroscopic Telescope Array (NuSTAR) mission includes a metrology system that is based upon laser diodes. An operational test facility has been developed to qualify and select, by mission standards, laser diodes that will survive the intended space environment and mission lifetime. The facility is situated in an electrostatic discharge (ESD) certified cleanroom and consist of an enclosed temperature-controlled stage that can accommodate up to 20 laser diodes. The facility is designed to characterize a single laser diode, in addition to conducting laser lifetime testing on up to 20 laser diodes simultaneously.

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

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High-Speed Operation of Interband Cascade Lasers

NASA’s Jet Propulsion Laboratory, Pasadena, California Optical sources operating in the atmospheric window of 3–5 μm are of particular interest for the development of free-space optical communication link. It is more advantageous to operate the free-space optical communication link in 3–5-μm atmospheric transmission window than at the telecom wavelength of 1.5 μm due to lower optical scattering, scintillation, and background radiation. However, the realization of optical communications at the longer wavelength has encountered significant difficulties due to lack of adequate optical sources and detectors operating in the desirable wavelength regions.

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

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Hybrid AlGaN-SiC Avalanche Photodiode for Deep-UV Photon Detection

NASA’s Goddard Space Flight Center, Greenbelt, Maryland The proposed device is capable of counting ultraviolet (UV) photons, is compatible for inclusion into space instruments, and has applications as deep-UV detectors for calibration systems, curing systems, and crack detection. The device is based on a Separate Absorption and Charge Multiplication (SACM) structure. It is based on aluminum gallium nitride (AlGaN) absorber on a silicon carbide APD (avalanche photodiode). The AlGaN layer absorbs incident UV photons and injects photogenerated carriers into an underlying SiC APD that is operated in Geiger mode and provides current multiplication via avalanche breakdown.

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

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Mode Selection for a Single-Frequency Fiber Laser

NASA’s Goddard Space Flight Center, Greenbelt, Maryland A superstructured fiber-grating-based mode selection filter for a single-frequency fiber laser eliminates all free-space components, and makes the laser truly all-fiber. A ring cavity provides for stable operations in both frequency and power. There is no alignment or realignment required. After the fibers and components are spliced together and packaged, there is no need for specially trained technicians for operation or maintenance. It can be integrated with other modules, such as telescope systems, without extra optical alignment due to the flexibility of the optical fiber.

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

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Enhancing Tumor Drug Delivery by Laser-Activated Vascular Barrier Disruption

Photodynamic therapy is used to eradicate tumor tissue and provide enhanced drug delivery.An obstacle to successful cancer drug therapy is the existence of drug delivery barriers, which result in insufficient and heterogeneous drug delivery to the tumor tissue. This drug delivery problem not only limits the clinical application of existing chemotherapeutics, but also decreases the effectiveness of many new drugs under development. Photodynamic therapy (PDT), a modality involving the combination of a photo-sensitizer and laser light, is an established cancer therapy. This work demonstrates the effectiveness of vascular-targeting PDT in eradicating tumor tissue, and modifying vascular barrier function for enhanced drug delivery.

Posted in: Bio-Medical, Briefs, TSP, Briefs, TSP, Drug Delivery & Fluid Handling, Patient Monitoring, Lasers & Laser Systems, Photonics

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