The darks yield a map of the persistence pattern, and can be used to subtract a significant amount of the unwanted persistence signal. The scheduling of these dark exposures is automatic and transparent to the user. In order to reduce the degrading impact of cosmic ray persistence (see Chapter 4 of the NICMOS Instrument Handbook for details) after passage through the South-Atlantic Anomaly (SAA), a pair of ACCUM dark exposures will be obtained immediately after each HST orbit through the SAA. in different filters) to be taken at each dither position (for details, refer to Appendix D of the NICMOS Instrument Handbook for Cycle 14).
Near infra red spectrograph zemax file pdf#
This allows the NCS to circulate cryogenic Neon gas through the cooling coils in the dewar, thus providing the cooling power to bring the instrument into the temperature range required for operation.Ī summary of general recommendations for both Phase I and Phase II proposal preparation is available in Chapter 1 of the NICMOS Instrument Handbook observers are strongly urged to review the material therein.ĪPT Phase II examples for coronagraphy, polarimetry, and grism spectroscopy are available for download in pdf format.Ī new syntax for dither patterns has been developed which now allows multiple exposures (e.g. During SM3B, the NCS was connected to the bayonet fittings of the NICMOS interface plate. The external plumbing at the dewar aft end, which was used for the periodical recooling of the solid nitrogen during ground testing, will now form the interface to the NICMOS Cooling System (NCS). View a schematic of the NICMOS instrument. However, the thermal short developed by NICMOS after installation on HST caused Camera 3 to be no longer parfocal with the other two cameras (Camera 1 and 2 are still close to parfocality) thus, operating Camera 3 simultaneousely with the other two cameras is not scientifically viable as a re-focussing of the instrument is involved. The dewar was built with a design lifetime of approximately 4.5 ± 0.5 years. The VCS is itself enclosed within two layers of thermal-electrically cooled shells (TECs). Cold gas vented from the dewar was used to cool the vapor cooled shield (VCS) which provides a cold environment for both the dewar and the transmissive optical elements (i.e., the filters, polarizers, and grisms). The NICMOS dewar was designed to use solid nitrogen as a cryogen. The instrument has three adjacent but not contiguous cameras, designed to operate independently and simultaneousely. The large bench serves to establish the alignment and dimensional stability between the HST optics (via the latches or fittings), the room temperature fore optics bench, and the cryogenic optics and detectors mounted inside the dewar. Its enclosure contains four major elements: a graphite epoxy bench, the dewar, the fore-optics bench, and the electronics boxes. The images at the bottom compares the spot diagrams with or without a freeform grating.NICMOS is an axial bay instrument which replaced the Faint Object Spectrograph (FOS) in the HST aft shroud during the Second HST Servicing Mission in February 1997. The image below shows and compare the modulation transfer function for the same system with either a spherical grating or a freeform grating. The freeform shape is expected to improve the resolution by more than 2 folds. The grating was made freeform using XY polynomials. The next step is to diamond turn the spherical primary and tertiary mirror and machine the freeform convex grating (secondary mirror). I couldn’t resist giving you a snapshot of the system received today! The system was then exported into Inventor 2018®, and a mechanical design was produced using Thorlabs® components and a Raptor Photonics® camera OWL 640 Mini VIS-SWIR.ĭurham University workshop has machined the parts. The image below shows how the spectrograph was designed on Zemax®. The spectrograph has been designed to be small (much less than 10 cm), and to look with a near diffraction limited performance, at a slit or slice 6mm long. The aim is to probe in detail, the water absorption region around the wavelength 1.4μm to quantify the effect of moisture content in the observed sample. April 2019 : A single channel Offner-Chrisp spectrograph is being machined and will see its first light soon!Ī spectrograph using an Offner-Chrisp design has been designed to cover the SWIR band with a spectral resolution of 3.5nm, a F number of 2.8 (to maximize its sensitivity) and a field of view of 6mm.
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