Download a spectral performance model for the

THE DESIGN AND FABRICATION OF MULTIPLE DICHROIC BEAMSPLITTERS FOR THE MIRI
SPECTROMETER (4.8-29m)
M. Wells1*, G.Hawkins2, G. Olofsson3
1
2
UK ATC Royal Observatory Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ.
The University of Reading, Infrared Multilayer Laboratory, Department of Cybernetics,
Whiteknights, Reading, Berkshire, RG6 6AY.
3
The University of Stockholm, Stockholm Observatory, SCFAB,
Astronomy SE-106 91, Stockholm, Sweden
Abstract
The spectrometer sub-system of the James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) contains
four channels which spectrally multiplex the incoming radiation. This incident radiation, spanning a wavelength range
from 4.8 to 28.8µm is spectrally divided between the channels using sets of three dichroics combined in series along the
optical trains. The four channels, with overlapping wavelengths 4.8-7.8, 7.4-11.9, 11.4-18.3 and 18.3-28.8µm, are inturn each split into three wavelength ranges to provide the required resolving power with the available detector pixels.
This splitting of the wavelengths within each channel is achieved using three separate sets of dichroics and diffraction
gratings, mounted on two wheels.
This paper describes the design of the dichroics together with a spectral performance model developed to simulate the
system spectral throughput for each of the four channels of the MIRI instrument. Details of the spectral design,
manufacture, testing and mounting of the dichroics are presented together with the opto-mechanical layout of the
instrument.
Keywords:- JWST, MIRI, Dichroics, Mid-Infrared, Spectrometer
1.
Introduction and optical description
The Mid-Infrared Instrument (MIRI)9 for the JWST is a thermal-infrared imager and spectrometer currently being
developed by an international consortium comprising the a consortium of European partners, the European Space
Agency, the Jet Propulsion Laboratory, and an international science team.
The spectrometer sub-system of MIRI is designed to cover the two and half octaves of wavelength from 5-28.3μm and to
use Integral Field Units (IFU) to provide spectral images of a rectangular field of view of at least 3 x 3 arcsec. Matching
the number of available detector pixels ( 2 1K x 1K arrays) to required spatial and spectral sampling and the need to
match the image slicing spatial sampling to the diffraction limit of the telescope has lead to a design which has 4
channels each with its own IFU. The IFUs7 are fed by light from a train of dichroics which are the subject of this paper
and in turn feed 4 spectrometers. In order to avoid the reflection to transmission transition region of the dichroics and to
provide sufficient spectral pixels the wavelength range covered by each channel is divided into 3 parts by 3 sets of 3
dichroics. Each of these sub-bands are then dispersed by 3 sets of 4 gratings and imaged onto the detector arrays.
A block diagram of the MIRI spectrometer is shown in Figure 1. Light from the telescope focus is reimaged from an f/20
to an f/40 beam and, in order to minimise the size of the dichroics, the path through them is arranged to have a pupil at
one end and a sky image of equal size at the other. The light paths are also arranged so that, for each channel, the 3 sets
of dichroics and corresponding gratings are mounted on one of 2 wheels. This means that a complete 5-28.3μm
spectrum is obtained as 12 sections in 3 separate observations. The layout of the light paths, the dichroics on their
wheels and the IFUs is shown in Figure 2. The 12 sub-spectra are shown in Figure 2, 4 sub-spectra are observed
simultaneously as indicated by Exposures A, B & C. The spectrometer design allows the spectra from two channels to be
combined at an intermediate focal plane in the cameras so that 4 spectra can be imaged onto 2 focal plane arrays.
*
[email protected]
Collimator
Dichroic 1
IFU 1
Dichroic 2
IFU 2
Dichroic 3
IFU 3
Grating1
Collimator
Grating 2
Collimator
Grating 3
Camera 1
FPA 1
Camera 2
FPA 1
IFU 4
Collimator
Grating
Figure 1 Block diagram of the MIRI integral field spectrometer
The required reflective band for the dichroic 1A is the wavelength range for Channel 1A, while its transmission band
needs to extend from the short end of Channel 2A to the long end of Channel 4A. Similar requirements are placed on
Dichroics 1A to 1C, 2A to 2C and 3A to 3C. All the gratings work in 1 st order so there is also a requirement that the
dichroics, with additional blocking filters where necessary, block wavelengths in the 2nd and higher orders. Because the
dichroics work in series it is possible to use the combined blocking of dichroics 1 and 2 to remove the need for blocking
filters in Channels 3 and 4.
The following considerations were essential to the design of the multilayer structures in order to ensure the manufacture
of the dichroics are realisable. (a) The correct choice of coating materials in order to give the best transmittance and
reflectivity bands with the flattest response and across the wide wavelength regions of interest. (b) Inclusion of the
effects of dispersion of the optical coating materials in the design, particularly as the changes in the refractive index and
extinction coefficient can be significant at long wavelength together with the wide regions of wavelength necessary. (c)
The risk of stress induced failure of thick deposited layers must be minimised by the choice of durable materials and
sequence of layers to minimise disproportionate deposition thicknesses between adjacent layers.
IFU 1
IFU 4
Incoming beam
Dichroic wheel 1
Dichroic 1
Dichroic 2
Dichroic wheel 1
IFU 2
Dichroic 3
IFU 3
Channel 4C
Channel 4B
Channel 4A
Channel 3C
Channel 3B
Channel 3A
Channel 2A
Channel 2B
Channel 2C
Channel 1C
Channel 1B
Channel 1A
Figure 2 Layout of the dichroics and IFUs
Exposure C
Exposure B
30
25
20
15
10
5
0
Exposure A
Wavelength (μm)
Figure 3 The wavelength ranges of each channel and the divisions into 12 sub-spectra. See also Table 1.
2.
Filter Requirements
The spectral design of the dichroic beamsplitters placed the following specification requirements1 for the reflective and
transmissive bands required by the multilayer designs: The cryogenic operating temperature for the dichroics is 7K in an
illuminated converging cone angle of f/37 and tilt angle of 10 degrees. The filters are to be deposited onto 21mm
diameter x 5.0mm thick optical grade CVD cadmium telluride (CdTe) with a coated aperture of 17.7mm diameter.
Short-wavelength interference blocking requires rejection levels of <10-4 for the cumulative path of the optical train for
all wavelengths shorter than the limit placed on the reflective short-wavelength reflection band.
Table 1. Reflective and transmissive bands of MIRI dichroic beamsplitters
Identification
Reflection Band (µm)
Transmission Band (µm)
Dichroic 1-a
4.84 – 5.83
7.40 – 21.22
Dichroic 1-b
5.59 – 6.73
8.55 – 24.73
Dichroic 1-c
6.45 – 7.77
9.87 – 28.83
Dichroic 2-a
7.40 – 8.91
11.39 – 21.22
Dichroic 2-b
8.55 – 10.29
13.16 – 24.73
Dichroic 2-c
9.87 – 11.88
15.20 – 28.83
Dichroic 3-a
11.39 – 13.68
17.45 – 21.22
Dichroic 3-b
13.16 – 15.80
20.34 – 24.73
Dichroic 3-c
15.20 – 18.25
23.72 – 28.83
As a high priority is to achieve the best possible quality of image, the optical metrology and surface quality of the
dichroics is required to be defined with highly specified and accurate tolerancing. The transmitted and reflected
wavefront errors (WFE) and parallelism require the substrates to be <λ/10 Peak-Valley at the shortest wavelength
transmitted (or reflected) bands and are to possess a maximum wedge angle of < 1 arcmin. Careful consideration to the
design of the interference multilayers was therefore necessary in an attempt to minimise thickness differences and avoid
distortions to surface flatness that can result from disproportionate stresses induced between the two substrate surfaces.
The environmental and physical requirements on the filters include the durability to survive testing to the general
provisions of MIL-F-48616 including repeated thermal cycling between 300K and 77K, highest possible coating surface
quality with a minimum of scattering sites caused by coating material surface roughness or spatter / contamination
together with spectral stability for an operational period of 10 years after launch in 2011.
3.
Optical properties of Infrared Materials
The selection of transparent II-IV substrate materials that are available to provide low absorption throughout
the 4-29µm wavelength range is limited, particularly where the use of hygroscopic materials is unacceptable (CsI,
CsBr). CVD Cadmium Telluride (CdTe) is an exotic II-VI material that has proven to provide good optical performance
across a wide range of wavelengths and temperatures in the mid-infrared with acceptable mechanical durability to be
used as a quality substrate material. Compared to the limited selection of alternative materials capable of transmitting
throughout this wavelength range (viz. KRS-5, KRS-6, Diamond), CdTe has a high resistance to moisture sensitivity, is
available at a reasonable price and can operate at elevated deposition temperatures without disassociating. It is however
also one of the softest of the II-VI materials and is most easily scratched or prone to cleaving. The following
temperature-dependent Sellmeier equation in Eq. 1, developed originally by Barnes et al 2 describes the real part of the
refractive index dispersion model that can be applied across a wide range of temperatures. The model has been shown to
provide a good comparative fit when extrapolated to cryogenic temperatures from refractive values determined by
DeBell et al3 from which extrapolation for an operating 7K cryogenic temperature has been applied, as illustrated in
Figure 4.
n
-4
A  B2 /( 2  C )  D2 /( 2  E )
-4
-4
where; A = -2.973x10 T + 3.8466, B = 8.057x10 T + 3.2215, C = -1.10x10 T + 0.1866,
D = -2.160x10-2 T + 12.718, E = -3.160x101 T + 18753
(1)
2.72
2.70
Refractive Index (n)
2.68
2.66
300K
2.64
2.62
7K
2.60
2.58
2.56
2.54
2.52
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
20.0
22.0
24.0
26.0
28.0
30.0
Wavelength (m)
Figure 4 Temperature-dependent refractive index dispersion profile of CdTe at 300, 200, 100, 50 & 7K
As the temperature of the CdTe substrate reduces on cooling, the dominant absorption mechanism caused by strong
multiphonon absorption bands becomes weaker and narrower. This has the effect of increasing the transparency
bandwidth of the material. For CVD CdTe, cooling has particular advantages in the 20-30µm region as at temperatures
<50K the substrate can closely achieve full transparency, as shown in Figure 5 for a calculated 5mm thick substrate for
the temperature range 300K - 50K (16-38m).
80
70
60
Transmission (%)
50K
50
300K
40
30
20
50K
10
0
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
Wavelength (um)
Figure 5 Calculated transmission profile of 5.0mm thick CdTe
(16-38m at 300, 250, 200, 150, 100 and 50K)
The choice of IR layer materials in the mid-infrared that can be deposited on CdTe with high performance optical
properties over the MIRI wavelength range is also limited when high transparency at the longest possible wavelengths
are a primary consideration (>20µm). Lead Telluride (PbTe), Germanium (Ge) and II-IV materials are deposition layer
materials that dominate the design of filters operating in the mid- to long-infrared wavelengths, both at room and
cryogenic temperatures. A high value of refractive index contrast between the high and low index material combination
(nH/nL) is the most desired parameter in the design of the multilayers by minimizing the number of layers together with
their physical thickness to perform an optimal spectral function. The combination of PbTe and II-VI high refractive
index contrast, together with the advantage of the PbTe negative optical expansion coefficient and position of the PbTe
semiconductor absorption edge all help to produce efficient multilayer designs with good transparency5. The refractive
index of PbTe is one of the highest known of usable infrared layer materials with a value of n  5.5 at 300K rising to 
6.0 at 7K. In intrinsic PbTe the refractive index dispersion generally follows a characteristic Sellmeier profile10.
Cadmium Selenide (CdSe) has been selected as the alternating II-IV multilayer material for all of the MIRI dichroics,
providing a high index contrast (n=2.34) and possessing a high molecular weight that exhibits transparency out to
30m in thin film form. CdSe layer material is a hard durable coating compared to PbTe and CdTe, which also
provides good environmental resistance.
For MIRI dichroics 1a and 1b however, as the spectral position of the principal reflectivity bands are required to be
located within the region of the semiconductor absorption edge of PbTe (4.8-5.8), the only choice of alternate H-layer
material for these dichroics was Germanium. Germanium has good high transparency within the 1.6-18µm region in
bulk form, and when deposited as a thin-film shows further extended transparency into to the 20-25µm region. Although
slightly more absorbing than PbTe in this long-wavelength region due to the higher multiphonon extinction coefficient,
it can provide adequate performance for the ultra-wide passband demanded. To achieve maximum wide-band
transparency of the 1a and 1b dichroics, the rear surface is coated with an ultra-wide band antireflection system
developed using a low-index fluoride layer of BaF2 to maximize throughput.
4.
Ultra-wide antireflection coating (4.5-21µm) for CdTe at 7K
An ultra-wide antireflection coating for the rear surface of the shortest wavelength dichroics (1a and 1b) has been
developed to transmit the highest and flattest performance over the 4.8-21µm region. In particular, a coating was
required to operate at the cryogenic temperature of 7K with no loss of spectral or physical performance on cooling. This
is necessary in the design of the MIRI dichroics across the complete reflective and transmissive wavelength ranges to
minimise any effects caused by ghosting artefacts reflected from the rear surface. Barium Fluoride (BaF2) is a low
dispersion material which is transparent in thin-film form to around 20m. It has a low refractive index (n 1.35) and
has shown good physical strength and low stress when deposited as a film6. Prototype depositions have successfully
passed cryogenic measurements at 7K, thermal cycling (RT-77K) and adhesion testing. The BBAR coating developed to
achieve the ultra-wide passband performance, illustrated for a deposited single-sided coating in Figure 6, comprised a
multilayer stack of 14-layers of alternating high and low refractive index layers of Ge and CdSe repectively. The stack is
overlaid with a 3-layer antireflection system comprising layers of CdSe, BaF2 , overcoated with CdSe for mechanical
protection of the thick low-index BaF2 layer. The multilayer was designed with optimised layer thicknesses to provide
the widest and flattest spectral response to provide maximum antireflection across the 4.5 - 21µm region. As with all
fluorides, BaF2 deposited by thermal evaporation forms a soft thin film. To minimise surface roughness and reduce
stress the film is deposited at a higher substrate temperature (≈ 220ºC) than the underlying Ge/CdSe stack, the higher
temperature favouring the nucleation of a denser film.
5.
Spectral Design
The design approach used to meet the high and broad transmission requirements of dichroics 1a and 1b over the spectral
bands of the incident surface was by the refinement of Tchebysheff equi-ripple8 long-wave pass edge filters as starting
designs. These types of filter possess a broad rejection stop-band providing high reflectivity across the prescribed
spectral band together with wide passband transparency. The multilayers are described by alternate low and high index
layers of CdSe/Ge respectively in which variable optimised layer thicknesses increase towards the centre of the
multilayer, where they become equi-thickness, followed by a symmetrical thickness decrease towards the outer surface
layers. This design method and use of materials provides an equivalent index that can approximate to the original
substrate refractive index at its outer surface, matching well to the CdTe and providing a good index match for the
application for a broadband antireflection coating. The ultra-wide broadband antireflection structure to be deposited on
the opposite surface (above) is required to transmit across both the reflectance and transmissive bands of the channel.
This antireflection system is composed of 18 layers, each layer of an optimised unique non-quarterwave fractional
thickness to reduce ripple amplitude. As the bandwidth requirements for the longer wavelength dichroics are required
over a narrower bandwidth, high performance reflection bands and broadband antireflection is achieved by optimised
structures of PbTe/CdSe multilayers. This combination of materials and designs are applied to all of the dichroics in this
wavelength region, the limiting spectral constraints being defined at short-wave by the PbTe semiconductor absorption
edge, into which Ge is substituted, and the long wavelength limit (29µm) by the CdTe multiphonon lattice-absorption.
100
90
M a x S in g le S id e d (7 9 % )
%
T r a n s m it t a n c e
80
70
60
50
40
30
20
10
0
275 0
250 0
225 0
200 0
175 0
150 0
W a v enum ber (1/c m )
125 0
100 0
M E A S URE M E NT A T 7 K
750
500
250
CA L CUL A TIO N
Figure 6. Manufacture of 4.5-21µm BBAR coating deposited on single-sided surface of 4mm thick CdTe substrate
(max transparency 79%) - overlay of calculation and spectral measurement at 7K
100
100
1a (R)
2a (R)
1x-T
1a-R
1a[R] x 1x
90
2x T
1a-T
2a-R
1a[T] x 2a[R] x 2x[T]
90
80
80
1a (T)
1x (T)
70
70
Throughput (%)
Throughput (%)
2x (T)
60
50
40
30
60
50
40
30
Throughput
20
20
10
10
Throughput
0
0
0
5
10
15
20
25
30
0
5
10
20
25
30
Fig. 8. Channel 2a
Dichroics: 1a (T) x 2a(R) x blocking filter 2(T)
Fig 7. Channel 1a
Dichroic: 1a (R) & blocking filter 1 (T)
100
100
1a-T
2a-T
3a-R
1a[T] x 2a[T] x 3a[R]
90
90
1a (T)
80
80
2a (T)
2a
(T)
3a (R)
3a (T)
70
Throughput
Throughput (%)
70
Throughput (%)
15
Wavelength (um)
Wavelength (um)
60
50
40
Throughput
30
60
50
40
30
20
1a-T
2a-T
3a-T
1a[T] x 2a[T] x 3a[T]
20
1a (T)
10
10
0
0
0
5
10
15
Wavelength (um)
20
25
30
0
5
10
15
20
25
30
Wavelength (um)
Fig 9. Channel 3a
Fig 10. Channel 4a
Dichroics : 1a (T) x 2a(T) x 3a(R)
Dichroics : 1a (T) x 2a(T) x 3a(T)
Figures 7-10. Spectral calculation overlay of dichroics in MIRI channels 1-4a for the individual elements
And combined system response
Spectral calculations of the predicted instrument throughput for each set of dichroic channels are illustrated in Figures 718. The total spectral throughput for each channel is calculated by combining the profiles of the dichroics and blocking
filters along the optical train, assuming no multiple beaming is present between the optical surfaces. Hence the
respective system throughput in each channel is defined by computation of the optical train as follows;
Channel 1: Dichroic 1a-c(R) x Blocking Filter 1(T)
Channel 2: Dichroic 1a-c(T) x Dichroic 2a-c(R) x Blocking Filter 2(T)
Channel 3: Dichroic 1a-c(T) x Dichroic 2a-c(T) x Dichroic 3a-c(R)
Channel 4: Dichroic 1a-c(T) x Dichroic 2a-c(T) x Dichroic 3a-c(T)
100
100
1b (R)
2b (R)
1x-T
1b-R
1b[R] x 1x
90
2x T
1b-T
2b-R
1b[T] x 2b[R] x 2x[T]
90
80
80
1b (T)
1x (T)
70
70
Throughput (%)
Throughput (%)
2x (T)
60
50
40
30
60
50
40
30
Throughput
20
20
10
10
Throughput
0
0
0
5
10
15
20
25
30
0
5
10
Wavelength (um)
15
20
25
30
Wavelength (um)
Fig. 11. Channel 1b
Fig. 12. Channel 2b
Dichroics: 1b (T) x 2b(R) x blocking filter 2(T)
Dichroic: 1b (R) & blocking filter 1 (T)
100
100
1b-T
2b-T
3b-R
1b[T] x 2b[T] x 3b[R]
90
90
1b (T)
80
80
2b (T)
2b (T)
70
3b (T)
70
Throughput (%)
Throughput (%)
3b (R)
60
Throughput
50
40
30
60
Throughput
50
40
30
20
20
1b-T
2b-T
3b-T
1b[T] x 2b[T] x 3b[T]
1b (T)
10
10
0
0
0
5
10
15
Wavelength (um)
20
25
30
0
5
10
15
20
25
30
Wavelength (um)
Fig 13. Channel 3b
Fig 14. Channel 4b
Dichroics : 1b (T) x 2b(T) x 3b(R)
Dichroics : 1b(T) x 2b(T) x 3b(T)
Figures 11-14. Spectral calculation overlay of dichroics in MIRI channels 1-4b for the individual elements
and combined system response
100
100
1c (R)
2c (R)
1x-T
1c-R
1c[R] x 1x
90
90
80
80
1c (T)
1x (T)
70
70
Throughput (%)
Throughput (%)
2x (T)
60
50
40
30
60
50
40
30
2x T
1c-T
2c-R
1c[T] x 2c[R] x 2x[T]
Throughput
20
20
10
10
Throughput
0
0
0
5
10
15
20
25
30
0
5
10
Wavelength (um)
15
20
25
30
Wavelength (um)
Fig. 15. Channel 1c
Fig. 16. Channel 2c
Dichroics: 1c (T) x 2c(R) x blocking filter 2(T)
Dichroic: 1c (R) & blocking filter 1 (T)
100
100
90
90
1c (T)
80
80
2c (T)
2c (T)
70
3c (T)
70
Throughput (%)
Throughput (%)
3c (R)
60
Throughput
50
40
30
60
50
Throughput
40
30
1c-T
2c-T
3c-R
1c[T] x 2c[T] x 3c[R]
20
1c (T)
20
10
1c-T
2c-T
3c-T
1c[T] x 2c[T] x 3c[T]
10
0
0
0
5
10
15
Wavelength (um)
20
25
30
0
5
10
15
20
25
30
Wavelength (um)
Fig 17. Channel 3c
Fig 18. Channel 4c
Dichroics : 1c (T) x 2c(T) x 3c(R)
Dichroics : 1c(T) x 2c(T) x 3c(T)
Figures 15-18. Spectral calculation overlay of dichroics in MIRI channels 1-4c for the individual elements
and combined system response
6.
Filter Fabrication
The MIRI dichroic beamsplitters are to be deposited in a Balzers 510 bell-jar vacuum evaporator fitted with a cryopump
and containing a geometry of rotating thermal evaporation sources and stationary substrates. This deposition system is
especially fitted with tooling for deposition of II-VI and group VI mid-infrared materials evaporated from resistance
heated molybdenum sources mounted on a rotating slip ring assembly. This arrangement is unique for the deposition of
filters in this wavelength region as it allows the deposition of uniform thickness layers whilst accurate temperature
control of the stationary filters mounted on a heated block in the upper part of the chamber is maintained. The monitor
and filter substrates are thermally clamped into copper jigwork attached to the block using lead (Pb) annular washers,
backing pieces and disc springs. Optical thickness monitoring is employed throughout the manufacture of the dichroics
using various fixed wavelengths in the region 3.9 to 5.7µm. Fractional layers are deposited using a spreadsheet
implemented algorithm to determine optical thickness from reflectivity fringe levels. A sequence of shutter operations
are used isolate the filter pieces from the centrally mounted monitor to ensure that the computed thickness is deposited
on the dichroics. The depositions take place at 185ºC in a residual vacuum of < 10-6 Torr with O2 being added at a partial
pressure of 5x10-5 Torr to ensure optimum optical properties for PbTe. Details of the thickness monitoring procedures
and deposition technique have been reported elsewhere4.
Conclusions
The spectral design of the dichroic beamsplitters in the MIRI instrument has been described, together with the rationale
behind the choice of substrate and coating materials. A spectral performance model representing the combined
throughput of dichroic beamsplitters in the MIRI instrument has also been presented from which it is shown by using a
systems approach the spectral response that is attainable.
This work is being funded by the MIRI European Consortium , whose support is gratefully acknowledged.
References
James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) : “Requirements specification for the
MIRI spectrometer filters”, document reference MIRI-RS-00004-ATC Issue E, (2004), otherwise unpublished.
2. N.P. Barnes, M.S. Piltch: “Temperature-dependent Sellmeier coefficients and coherence length for cadmium
telluride”, J. Opt. Soc. Am. 67 (5) pp. 628-629 (1977)
3. A.G. DeBell, E.L. Dereniak, J. Harvey, J. Nissley, J.Palmer, A. Selvarajan, W.L. Wolfe: “Cryogenic refractive
indices and temperature coefficients of cadmium telluride from 6µm to 22µmm”, Appl. Opt. 18, pp 3114-3115
(1979)
4. C.S. Evans, R. Hunneman, J.S. Seeley and A. Whatley: “Filters for 2 band of CO2: monitoring and control of
layer deposition” Appl. Opt., Vol 15, pp. 2736-2745 (1976)
5. G.J. Hawkins, R. Hunneman, R. Sherwood, B.M. Barrett: “Infrared filters and coatings for the High Resolution
Dynamics Limb Sounder (6-18µm)”, Appl. Opt. Vol. 39, No. 28, pp 5221-5230 (2000).
6. G.J. Hawkins, R. Hunneman, M.T. Gardner, G.T. Babcock: “An ultra-wide passband (5-30µm) filter for FTIR
studies of Photosystem II”, Infrared Physics & Technology, Vol. 39, pp. 297-306 (1998).
7. David Lee, Colin Dickson, Peter Hastings, Martyn Wells, Melanie Leclerc: “ Image slicers - design for
manufacturability”, Proc SPIE 5494, (2004)
8. J.S. Seeley, H.M. Liddell, and T.C. Chen: “Extraction of Tschebysheff design data for the lowpass dielectric
multi-layer”, Opt. Acta 20, pp 641-661 (1973)
9. Gillian S. Wright, Fabio Bortoletto, Carl F. Bruce, Jr., Ewine F. van Dishoeck, Avinash R. Karnik, PierreOlivier Lagage, Melora E. Larson, Dietrich Lemke, Goran Oloffson, Edward A. Miller, Thomas F. Henning,
Sam Heys, Tom Ray, J. Rodriguez, Eugene Serabyn, Ian Walters: “NGST MIRI instrument” Proc. SPIE 4850,
pp. 493-503 (2003)
10. K. Zhang, J.S. Seeley, R. Hunneman, G.J. Hawkins: “Optical and semiconductor properties of lead telluride
coatings”, Proc SPIE 1125, pp. 45-52 (1989)
1.