The spectrometers of the PGS family are designed for  use in the NIR. InGaAs (indium-gallium-arsenide) is used as a detector material in this wavelength range. The special combination of aspheric collimator and focusing lens allows the use of plane gratings optimized for the NIR, while maintaining good flat field correction of the spectral imaging. Excellent long-term stability is ensured by the permanent connection of all optical components.

Central body

In the PGS family, a special aluminum alloy (coefficient of expansion a ~ 13 x 10-6) is used for the central body. This housing is the carrier of the blazed grating and  of the aspheric collimator and focusing lens. The input fiber and the detector are permanently connected to the central body, therefore providing excellent stability.

Gratings

The gratings for the PGS family are mechanically ruled or holographically recorded plane gratings. The maximum efficiency is adapted to the special wavelength range in the NIR. The grating surface with the clear diameter of the lenses is dimensioned so that the light of a fiber with NA of up to 0.37 can be   hold.

Input fiber

The coupling of light is performed in the standard way  via a glass monofiber. These fibers have a diameter of 600 µm and a NA = 0.22. The end of the fiber features a slit with a height of 500 µm (NIR 1.7) or 250 µm (NIR 2.2). The slit heights at the entrance are adapted to the pixel heights of the InGaAs arrays. A crosssectional conversion similar to the silicon detectors is not necessary.

Detector

For the PGS NIR 1.7 standard InGaAs is used for the wavelength range up to 1700 nm. Detectors with 256  or 512 elements are available. To go up to the wavelength range of 2.2 µm the use of Extended InGaAs is necessary. In the PGS NIR 2.0 and PGS NIR 2.2 detectors with 256 elements are used. For the Extended InGaAs arrays, blocking filter for suppressing the 2nd diffraction order  is applied to the array.