In this paper, we present a CMOS digital intra-oral sensor for x-ray radiography. The sensor system consists of a custom
CMOS imager, custom scintillator/fiber optics plate, camera timing and digital control electronics, and direct USB
communication. The CMOS imager contains 1700 x 1346 pixels. The pixel size is 19.5um x 19.5um. The imager was
fabricated with a 0.18um CMOS imaging process. The sensor and CMOS imager design features chamfered corners for
patient comfort. All camera functions were integrated within the sensor housing and a standard USB cable was used to
directly connect the intra-oral sensor to the host computer. The sensor demonstrated wide dynamic range from 5uGy to
1300uGy and high image quality with a SNR of greater than 160 at 400uGy dose. The sensor has a spatial resolution
more than 20 lp/mm.
KEYWORDS: Near field optics, Radio optics, Radiometry, Calibration, Semiconductor lasers, Optical calibration, Photodiodes, Feedback loops, Beam splitters, Fluctuations and noise
Power stabilized DL's represent today convenient sources for radiometric applications, as transfer laboratory standards. Stability measurements were carried out and reported by other authors for different time intervals, but only for low optical power levels (max. 16 mW). For calibrating usual optical radiometers, such low emitted power DL's are useless. This paper reports stability measurements carried out on several collimated DL's with (lambda) around 980 nm and emitted power up to 265 mW in near-field/150 mW in far-field. Stabilities of the order 1e-4 for short-time intervals (tens of seconds) and 1e-3 for medium-time intervals (1 hour) were found for a non-thermostated structure, having the control photodiode (PD) in the same enclosure with the DL (at the rear of the structure). The corresponding stabilities for an external control PD resulted of the order 1e-5 for both short and medium time intervals. The schematic of the optical power stabilizer is presented.
In this paper we report an indirect method based on photomultiplier response calibration to measure the radiant power of the internal second harmonic generation (ISHG) from InGaAs/GaAs/AlGaAs strained single quantum well buried heterostructure laser diodes. We observed enhanced ISHG radiant power, of the order of magnitude of 10-8 W. This phenomenon represents a signature of the beginning of the process of catastrophic optical degradation of the LD mirror facet layers, where the nonlinear optical interaction occurs.
In this paper we report an indirect method based on photomultiplier response calibration to measure the radiant power of the internal second harmonic generation (ISHG) from InGaAs/GaAs/AlGaAs strained single quantum well buried heterostructure laser diodes. We observed enhanced ISHG radiant power, of the order of magnitude of 10-8 W. This phenomenon represents a signature of the beginning of the process of catastrophic optical degradation of the LD mirror facet layers, where the nonlinear optical interaction occurs.
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