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The NIRSpec instrument on the James Webb Space Telescope (JWST) is a multi-object spectrograph capable of measuring the near infrared spectrum of at least 100 objects simultaneously at various spectral resolutions. It operates under cryogenic conditions (T∼ 35 K). NIRSpec is part of the JWST science instruments suite. Its main purpose is to provide low (R=100), medium (R=1000) and high resolution (R=2700) spectroscopic observations over the wavelength range 0.6 µm -5.0 µm in support of the four JWST science programs. The NIRSpec instrument is being developed by the European Space Agency with EADS Astrium Germany GmbH as the prime contractor The Optical Telescope Element of JWSTThe four JWST science instruments in the Integrated Science Instruments Module (ISIM) pick-off their input beam from the focal surface of the JWST Optical Telescope Element (OTE). The OTE is a "Korsch" type, all-reflective, on-axis, three-mirror anastigmat (TMA), with the addition of a fine steering mirror (FSM) near the exit pupil. As with most on-axis TMA systems, it is used off-axis in field to enable beam clearance after the tertiary mirror. The Field of View (FOV) offset equals -0.13° (or -7.8'). The primary, secondary and tertiary mirrors have conic contours (ellipse, hyperbola, ellipse), while the FSM is a flat. The focal surface is curved, with its radius matched to the FSM to focal surface distance. This feature ensures no defocus when the FSM is operated. The telescope has a primary mirror made out of 18 hexagonal segments with a overall, flat-to-flat diameter of ∼6.6 m. The output f-number is f/20. NIRSpec will assume a maximum Wave-Front Error (WFE) at its optical entrance field plane of 145 nm RMS for all field points, equivalent to a diffraction limited performance at 1.93 µm (Strehl ratio = 0.80). The Optical Design of NIRSpec 2.

The Ozone Monitoring Instrument (OMI) is a nadir viewing wide field imaging spectrometer for ozone monitoring. The instrument is the Dutch/Finnish contribution to the NASA EOS-AURA mission. OMI observes earth's back scattered radiation in two spectral channels: the UV channel (270 nm-350 nm) and the VIS channel (350 nm-500 nm). Each channel employs a CCD detector (576 X 780 px). The extreme wide field of view of 114 degrees, equal to a swath width of 2600 km, is obtained by an all reflective telecentric telescope and enables global ozone coverage in one day.Other key features are the spectral range (270 nm-500 nm) and resolution (spectral sampling distance 0.15-0.32 nm/px), the application of a polarization scrambler and its compact design (400 X 300 X 500 mm). Excellent stray light performance in the UV channel is obtained by an elegant opto-mechanical design of the UV optics where the UV wavelength range is split in two parts with separate optical paths and the separate spectra are imaged on one CCD. Onboard calibration includes a white light source, LEDs, and multi-surface solar-calibration diffuser. The OMI-EOS project follows a Proto-Flight approach, supported by breadboards and engineering qualification models on parts and sub-system level. In order to increase confidence in the design, the instrument development model was built. During intensive testing critical performance parameters were checked, e.g. UV stray light behavior, polarization sensitivity, distortion, spatial and spectral ranges and resolutions.

A chevron-type dielectric bandpass filter set is described which combines laser line rejection by a factor >10 s with a high throughput of Raman scattered light (70%). The rejection bandwidth is 60 cm -~ full width at half-maximum. Stokes and anti-Stokes Raman spectra can be recorded simultaneously from approximately 20 cm -1 from the laser line. The filter set, moreover, takes care of efficient coupling of microscope and spectrometer, replacing an otherwise necessary beamsplitter.