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Light
Published in David M. Scott, Industrial Process Sensors, 2018
A neutral density filter is one that reduces the intensity of light equally at all wavelengths over a large portion of the spectrum. The filters are specified in terms of their optical density, which is the negative common logarithm of the transmission coefficient. Therefore, the intensity If of the transmitted light as a fraction of the incident light I0 is given by () If=I010−(OD)
Near-Infrared Imaging with Fluorescent Contrast Agents
Published in Mary-Ann Mycek, Brian W. Pogue, Handbook of Biomedical Fluorescence, 2003
Eva M. Sevick-Muraca, Anuradha Godavarty, Jessica P. Houston, Alan B. Thompson, Ranadhir Roy
A neutral density filter at the photodetector is used to control the amount of excitation light (the emission light is generally an insignificant portion of the detected light) when FDPM measurements of excitation light are made. A combination of holographic filters [12], and interference filters ensures passage of the small component of the emission light with minimized excitation light leakage when emission measurements are to be made. As discussed later, the rejection of excitation light is crucial to the success of fluorescence–enhanced optical imaging with multiply scattered light.
Filters
Published in Solomon Musikant, Optical Materials, 2020
The neutral density filter attenuates light without changing its spectral quality. One way of specifying a neutral filter is by optical density (OD), where OD is defined by the following relation: OD=log101/T
Road Marking Contrast Threshold Revisited
Published in LEUKOS, 2022
Rik Marco Spieringhs, Kevin Smet, Ingrid Heynderickx, Peter Hanselaer
Calibration and characterization of the display were of utmost importance, as we wanted to display small luminance values and luminance differences. To this end, spectral radiance measurements were performed with an air cooled Ocean Optics QE65 Pro spectrometer equipped with a Bentham TEL301 fiber coupled telescope with variable aperture. The integration time of the spectrometer could range from 8 ms up to 15 minutes. Its signal-to-noise ratio was 1000:1 at full signal. The telescope was positioned at a distance of 1.5 m from the display at eye height. Before measuring the stimuli, a dark current measurement was carried out. To convert the spectrometer responses to spectral radiance, two Bentham SRS8 Halogen spectral radiance standards were used. For measuring the low luminance values of our experiment, an aperture size of 3.5 mm was required, but this resulted in saturation when targeting the radiance standard. A second radiance standard, equipped with a neutral density filter with optical density 0.9, was calibrated with respect to the primary radiance standard using a smaller aperture (i.e., 1.17 mm).
Post-processing noise reduction via all-photon recording in dynamic light scattering
Published in Science and Technology of Advanced Materials: Methods, 2021
Takashi Hiroi, Sadaki Samitsu, Kunie Ishioka
All the DLS measurements were performed at room temperature (23°C). A schematic of the developed DLS apparatus is shown in Figure 1. The vertically polarized output of a He-Ne laser (05LHP991, Pacific Lasertec) at wavelength λ0 = 632.8 nm was focused on a quartz cell filled with the sample dispersion. The scattered light was collected at a scattering angle of approximately 90° and focused onto a photon counting module (C11202-050, Hamamatsu Photonics). Details of the calibration of our DLS system are presented in Sect. 2 of the Supporting Information. The intensity of the incident laser was adjusted by a neutral density filter to obtain a count rate of 10–20 kcps. Although the count rate can be increased up to Mcps level, we reduced it to see the effect of pollutants, which increases the count rate drastically, more clearly. The electronic signal pulses from the photon counting module were stretched by a homebuilt pulse stretcher circuit, which eliminates the ringing noise and afterpulsing, and transferred to a time-to-digital converter (TDC) constructed with digital modules (NI-9402 & cDAQ-9174, National Instruments). The TDC recorded the arrival time of each detected photon. The temporal resolution of the module was 12.5 ns, i.e. slower than the state-of-the-art autocorrelators by approximately four orders of magnitude [38] but still sufficiently fast to measure the relaxation of the time correlation function of the scattered light intensity, which was typically >10 μs. Each measurement involved the detection of 106 scattered photons. All the arrival time information was stored in a text file and analyzed after the measurement.
Study on practical application for in-process blowholes detection technology
Published in Welding International, 2022
Kazuki Kasano, Yosuke Ogino, Tomokazu Sano, Satoru Asai
Table 2 shows the observation conditions based on the findings in previous reports [20,21]. The camera is an InGaAs camera (Bobcat 320/Xenics) with photosensitivity in the infrared region. A BPF that selectively transmits light with a wavelength of 1320 nm and a neutral density filter (ND filter) was attached to the lens, and the camera exposure time was 100 μs. The frame rate for the shooting was set at 100 FPS. The images were transferred from the camera to a PC via Ethernet and recorded.