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| Measuring light spectrum intensity |
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| scatterandfocus:
I was planning to experiment with some photodiodes with an oscilloscope for measuring light intensity of various sources at wavelengths from uv to infrared. I'm noticing that photodiodes have a peak response given in datasheets by the wavelength specification in nm (nanometers). And it seems that cost goes up drastically when looking at photodiodes with a peak response in the blue to uv spectrum, and cost gets really high at around 400 nm and higher. And phototransistors seem to only go up to around the 500nm wavelength, which would make them not useful for the blue to to uv spectrum. Maybe someone knows of another means for measuring light spectrum intensity, or has other ideas for getting around the cost of expensive photodiodes. |
| StuartA:
Chemical analysts have been using IR, visible and UV spectroscopy since the middle of the last century, so this requirement was being met long before photo-transistors came on the scene. I cannot recall now what devices were used in these systems, but I'm fairly certain that there would have been separate optics for each range. If you Google 'Infrared Spectroscopy' (etc), I suspect that Wiki will come up with an overview of how the different machines evolved. |
| KaneTW:
Photospectrometers use a photon detector (single tube/diode or diode array) with monochromatic light. Monochromacy is achieved either via an adjustable filter (single detector) or a diffraction grating before the diode array. There might be some more ways that I'm not aware of, but that's what I've worked with in the past. |
| kripton2035:
http://chriswesley.org/spectrometer.htm (in german) http://web.archive.org/web/20130815170752/http://bernd-loibl.de/spectra.html https://www.open-electronics.org/spectrometer-on-pc/ https://ams.com/as7265x |
| CatalinaWOW:
Historically the detector was a photomultiplier tube (PMT). Spectral response was determined by the photoemissive properties of the target material and the transmission of the tube envelope. Quartz windows were used to achieve the UV wavelengths. Since response varied with wavelength, just as it does with current semiconductor diodes some method of calibrating the response was needed. Now we tend to use calibration tables to provide a gain adjustment. Then many instruments used a dual optical path to provide a ratio correction. PMTs are still available, are still very good for performance, are far from cheap and require high voltages not readily available in today's hobby labs. The links from previous responders give good options for current use. |
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