Chapter 11 Technical Data - THORLABS Redstone OSA305 Manual

Optical Spectrum Analyzers Chapter 4: Description
The maximum physical movement of the OSA20xC platform is 10 mm from the ZPD, which translates to a
maximum OPD of 40 mm and a spectral resolution of 7.5 GHz or 0.25 cm -1 . The Redstone OSA305 has a
80 mm stroke length capacity, and thus a maximum OPD of 160 mm and a spectral resolution of 1.9 GHz or
0.063 cm -1 . The wavelength resolution is dependent on the wavelength of light being measured. For more details
see Section 4.8 Resolution and Sensitivity. In this context, the spectral resolution is defined according to the
Rayleigh criterion and is the minimum separation required between two spectral features in order to resolve
them as two separate lines. Note that when using the Wavelength Meter or Peak Track tools, the number of
significant figures can far exceed the Rayleigh spectral resolution as those tools use several data points and
curve fitting techniques.
The Thorlabs OSAs utilize a built-in, actively stabilized reference laser to interferometrically record the variation
of the optical path length. This reference laser is inserted into the interferometer and closely follows the same
path traversed by the unknown input light field. To reduce the effects of water absorption on the acquired
spectrum, our OSAs have two 1/4" inner-diameter quick-connection hose fittings on the back panel, through
which the interferometer can be purged with dry air or nitrogen, as detailed in Chapter 6.
Figure 1. Optical Schematic of the Thorlabs OSA20xC Detailing the Dual Retroreflector Design
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