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AUSTRALIAN
NATIONAL UNIVERSITY System Design Note 5.22 Created: 13 April 2000 Last modified: 13 April 2000 |
NIFS ORDER BLOCKING FILTERS
Ian Price
Research School of Astronomy
and Astrophysics
Institute of Advanced
Studies
Australian National
University
Revision History
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Revision No. |
Author & Date |
Approval & Date |
Description |
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Revision 1 |
Ian Price 15 September 1999 |
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Original document. |
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Revision 2 |
Peter J. McGregor 13 April 2000 |
Jan van Harmelen 14 April 2000 |
Reformatted for Word 2000. Updated after CoDR. |
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Contents
4.3 Optical
Coating Laboratories
1 Purpose
This document describes the order blocking filters that will be used in the Gemini Near-infrared Integral-Field Spectrograph.
2 Applicable Documents
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Document ID |
Source |
Title |
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IGPO |
NIFS CoDR Statement of Work |
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RSAA |
NIFS Grating Selection |
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3 Introduction
The Gemini Near-infrared Integral-Field Spectrograph (NIFS) will use at least four gratings and each of these will be operated in first order (NIFS Grating Selection, SDN0005.21). A filter wheel will contain 25 mm diameter order blocking filters to prevent out-of-band light reaching the detector. Order blocking filters for Gemini instruments are required to have high transmission (> 80%) over the wavelength range of interest and low transmission (< 10-4) at all other wavelengths over the full sensitivity range of the detector (NIFS CoDR Work Scope, GEM00196A).
Order blocking filters for the baseline grating suite (NIFS Grating Selection, SDN0005.21) are considered below. The wavelength ranges for these gratings in NIFS are listed in Table 1.
Table 1: Wavelength ranges for each of the NIFS gratings.
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Grating |
central wavelength (mm) |
Spectral Coverage (mm) |
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J1 |
1.05 |
0.94-1.15 |
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J2 |
1.25 |
1.15-1.35 |
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H |
1.65 |
1.49-1.80 |
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Ks |
2.15 |
1.95-2.36 |
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Kl |
2.29 |
2.09-2.50 |
Standard near-infrared photometric filters have insufficient throughput to meet the requirements of the NIFS Work Scope. Quotations have been sought from several manufacturers for the design and production of custom filters. These quotations are presented below.
4 Filter Availability
4.1 NDC IR Engineering
NDC IR Engineering have produced filters for NIRI, GNIRS, and NIFS through a Gemini consortium. The GC#4 and GC#3 filters designed for this consortium can be used as order blocking filters for NIFS in the H and K bands (Figure 1) and were purchased through the consortium. The GC#5 filter could also be used for the J2 grating, but no filter was purchased for NIFS at the time of the consortium and the pass band is tight. The filter for the J1 band would require a redesign, at an estimated cost of UK£5-6K. Similarly, a batch run independent of the Gemini consortium would cost UK£5-6k per filter. Costs for the Gemini consortium filters were provided by Henry Orr (hjborr@ireng.com), and are shown in Table 2.
Table 2: IR Engineering Quotation
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J1 |
J2 (GC #5) |
H (GC #4) |
K (GC #3) |
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50% Cut-On (mm) |
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1.14 +/- 0.011 |
1.47 +/- 0.015 |
1.92 +/- 0.019 |
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50% Cut-Off (mm) |
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1.35 +/- 0.013 |
1.80 +/- 0.018 |
2.52 +/- 0.025 |
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Peak Transmission |
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>80% |
>75% |
>75% |
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Blocking |
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10-4 |
10-4 |
10-4 |
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Diameter (mm) |
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<25 |
<25 |
<25 |
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Price for 2 filters |
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US$1508 |
US$1643 |
US$1293 |
Figure 1: Transmission curves for H (left) and K (right) grating order blocking filters purchased from NDC Infrared Engineering. The band passes of the H and K gratings (option A) are shaded.
4.2 Barr Associates
The following quote was provided by Dale Taylor from Barr Associates (73001.2655@compuserve.com) on Tue 17-AUG-1999.
Table 3: Barr Associates Quotation
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J1 |
J2 |
H |
K |
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50% Cut-On (mm) |
0.94 +/- 0.01 |
1.14 +/- 0.011 |
1.49 +/- 0.015 |
2.00 +/- 0.02 |
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50% Cut-Off (mm) |
1.16 +/- 0.011 |
1.35 +/- 0.013 |
1.80 +/- 0.018 |
2.42 +/- 0.024 |
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Peak Transmission |
>75% |
>75% |
>75% |
>75% |
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Blocking |
10-4 |
10-4 |
10-4 |
10-4 |
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Diameter (mm) |
25.4 |
25.4 |
25.4 |
25.4 |
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Price per filter |
US$3900 |
US$3900 |
US$3740 |
US$3360 |
The transmission of these filters is lower than the requirement in the NIFS Work Scope. These passbands exactly match the grating wavelength ranges; broader pass bands would be required for actual filters.
4.3 Optical Coating Laboratories
Optical Coating Laboratories Inc. (OCLI) offer a catalog filter that would be suitable for the J2 band. The characteristics of this filter (W01239-14) are listed in .
Table 4: OCLI Cost
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J2 ( OCLI W01239-14 ) |
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50% Cut-On (mm) |
1.13 |
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50% Cut-Off (mm) |
1.35 |
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Peak Transmission |
80% |
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Blocking |
10-4 |
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Diameter (mm) |
25.4 |
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Price per filter |
US$275 |
Appendix A: List of Figures
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Figure 1 |
fil_handk.gif |
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