The Clio prism is a direct-vision design prism, which means it has three wedges that make up the overall prism. The undeviated wavelength is 2 microns. Because it is a prism (not a grating) the dispersion is nonlinear.
Spectral Resolution
The spectral resolution as a function of wavelength for a 0.2" image is
| Wavelength | R (for 0.2" image) |
|---|---|
| 1.65 | 8 |
| 2.2 | 34 |
| 3.5 | 126 |
| 4.0 | 157 |
ZEMAX model of the wavelength vs. position for the Clio direct vision prism:
Wavelength Solution
The nonlinear dispersion of the direct vision prism is well fit by a quadratic equation with wavelength as the independent variable. Fitting the ZEMAX model image positions, expressed in pixels, and solving the quadratic give s the wavelength solution of:
where y is in pixel rows on the detector, and slit is the row position of the slit in imaging mode (260 for the medium slit).
Comparison of this model with filters in front of the prism (data in n101022), suggests it is approximately correct for the L band, but may be inaccurate for H and K band.