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Theory of Operation
Optical System Overview
sampling interval of the diode array is 0.9 nm over the wavelength range
190 nm to 1100 nm. The nominal spectral slitwidth is 1 nm.
Spectrograph Lens
The spectrograph lens is the first of the parts which are collectively known as
the spectrograph. It is mounted on the housing of the spectrograph. The
spectrograph lens refocuses the collimated light beam after it has passed
through the sample.
Slit
The slit is a narrow aperture in a plate located at the focus of the
spectrograph lens. It is exactly the size of one of the photodiodes in the
photodiode array. By limiting the size of the incoming light beam, the slit
makes sure that each band of wavelengths is projected onto only the
appropriate photodiode.
Grating
The combination of dispersion and spectral imaging is accomplished by using
a concave holographic grating. The grating disperses the light onto the diode
array at an angle proportional to the wavelength.
Diode Array
The photodiode array is the heart of the spectrograph. It is a series of 1024
individual photodiodes and control circuits etched onto a semiconductor
chip. With a wavelength range from 190 nm to 1100 nm the sampling interval
is nominal 0.9 nm.
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