An imaging spectrograph presents spatially resolved spectra with all acquired wavelengths simultaneously. When used with a spectrum detector such as a CCD or CMOS camera it becomes an imaging spectrometer. The goal is to enable point to point imaging (see Figure 1)
Traditional spectrometers use diffraction gratings in a Czerny Turner geometry (yes, there are others). Aberrations make it impossible to image a point on the entrance slit as a point on the detector due to significant aberrations. This problem can be obviated with the use of aspheric optics.
More recently holographic gratings with aberration correcting properties made spectral imaging feasible. Using a prism with curved sides provides an elegant alternative solution with state of the art light throughput efficiency. (See figure 2)
Figure 3 shows an example of hundreds of spatially resolved spectra acquired simultaneously with the PARISS imaging spectrograph
Go here to compare the spectral properties of prism vs gratings
PARISS imaging spectrograph specifications
Weight:1,250 g (Excluding a camera) Moving parts: None: Optimizes stability and reproducibility.
Dimensions: 210 x 55 x 85 mm
Aberration Correction: The wavelength dispersive element is a prism with optical “power.” Concave and convex surfaces on the front and rear surfaces correct astigmatism, coma, and spherical aberration.
Spectral range:365 to ~920 nm or 400 to ~920 nm, depending on choice of camera. All spectra acquired simultaneously without order sorting filters
Light throughput efficiency: Internal transmission ~90% from 450 to ~920 nm.
Entrance slit dimensions:Standard 5 mm. by 25 micron, widths of 50 and 100 micron are available in pre-aligned mounting assemblies.
Spatial resolution at the sample: Depends on slit width and camera pixel size ~ 0.6 micron by ~0.6 micron with 40x magnification typical. Nanoparticles may be detected but not resolved
Spectral resolution: ~1 nm measured at the full width at half maximum of the 436 nm Hg line, depends on slit width and camera pixel size.
Optional calibration standards: Available MIDL wavelength calibration lamp and a “SYLPH” NIST certified radiometric light source.
Click herefor a performance comparison between a prism and a diffraction grating.
Figure 1: An imaging spectrograph images a point on the entrance slit as a point on the spectrum detector as a function of wavelength
Figure 2: The PARISS prism with curved sides to enable spatial imaging
Figure 3: A very dense set of spectra acquired simultaneously. Each spatially resolved spectrum correlates with an object projected onto the entrance slit.