Development of a cryogenic FTIR system for measuring very small
attenuation coefficients of infrared materials
Sayumi Kajia, Yuki Sarugakub,c, Yuji Ikedac,d, Kenshi Nakanishic, Naoto Kobayashic,e,Sohei Kondoc, Takayuki Arasakic, and Hideyo Kawakitaa,caDepartment of Physics, Faculty of Science, Kyoto Sangyo University, Motoyama, Kamigamo, Kitaku, Kyoto 603-8555, Japan;b
Kiso Observatory, Institute of Astronomy, University of Tokyo, 10762-30 Mitaka, Kiso-machi,
Kiso-gun, Nagano 397-0101, Japan;cLaboratory of Infrared High-resolution spectroscopy (LiH), Koyama Astronomical Observatory,
Kyoto Sangyo University, Motoyama, Kamigamo, Kita-ku, Kyoto 603-855, Japan;dPhotocoding, 460-102 Iwakura-Nakamachi, Sakyo-ku, Kyoto 606-0025, Japan;eInstitute of Astronomy, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015,Japan
ABSTRACT

We have been working on a longterm project for developing a variety of infrared immersion gratings for near- to midinfrared wavelengths. The transmittance of material is essential to realize high-efficiency immersion gratings for
astronomical applications. For a typical grating, the attenuation coefficient αatt must be <0.01 cm−1 for the absolutediffraction efficiency of >70%. However, as there are few reports of αatt < 0.01 cm−1 for infrared optical materials in theliteratures, we performed high-accuracy measurements of αatt for a variety of infrared materials applicable to immersion
gratings. We have already reported αatt at room temperature for single-crystal Si, single-crystal Ge, CVD-ZnS, CVDZnSe, and high-resistivity single-crystal CdZnTe (Ikeda et al. 2009[7], Kaji et al. 2014[10], and Sarugaku et al. 2016[9]).
Next, we proceeded with the measurements of αatt at cryogenic temperatures of 20–80 K range, which is the typicaloperational temperatures of infrared instruments, and for which the shifts of the band gap and/or the sharpness of thelattice absorption lines from the corresponding room temperature values are expected. Thus, we developed a newcryogenic FTIR system that enables high-accuracy measurements at cryogenic temperatures. The system has amechanism with which two sample cells and a reference cell can be easily and quickly switched without any vacuum
leak or temperature change. Our preliminary measurement of Ge using this cryogenic FTIR system found that both the
cut-on and cut-off wavelengths shift to the shorter (from 2.0 to 1.7 µm) and longer (from 10.6 to 10.9 µm) wavelengths,
respectively, when the temperature is decreased from room temperature to the cryogenic temperature (<28 K). We plan
to complete cryogenic measurements for a variety of infrared materials by the end of 2016.
Keywords: immersion grating, infrared material, attenuation coefficient, absorption coefficient, infrared, high-resolution,
cryostat, transmittance, absorption

1. INTRODUCTION
Immersion grating is a type of diffraction grating with the immersed diffraction surface in an optical material having ahigh refractive index of n > 2[2]. As the wavelength in the material is reduced to 1/n, an immersion grating can provide aspectral resolution n times higher than that of a classical reflective grating with the same clear aperture, or can reduce thediameter of the collimated beam Φ, namely the instrumental volume, by a factor of n compared to a classical reflective
grating with the same spectral resolution. Thus, immersion gratings are useful for building high-resolution spectrographswith R ≥ 50,000 for ground-based 30-m class telescopes and realizing airborne spacecraft spectrographs with R ≥ 20,000
in the infrared wavelength region.
Our group belongs to Laboratory of Infrared High-resolution spectroscopy (LiH) at Koyama Astronomical Observatoryof Kyoto Sangyo University*, Japan, and has been working on a longterm project for the development of a variety of
infrared immersion gratings for near- to mid-infrared wavelengths. In this project, we have comprehensively studied the*LiH: http://merlot.kyoto-su.ac.jp/LIH/index.html

processing techniques for obtaining ultrafine groove shape[1-6], the selection of suitable materials for immersion
gratings[7-10], the development of coating techniques[3-5,8,9,11], and the design and assembly of spectrographs using
immersion gratings[1,12-20]. This paper focuses on material selection.
For a high-efficiency immersion grating, the transmittance of material is essential for application of the grating inastronomy because when the typical optical path length in the immersion grating becomes >100 mm, a significant
degradation of the total efficiency occurs even for a very small attenuation (a total energy loss of ~10% is expected for a
Ge immersion grating with an assumed attenuation coefficient of αatt = 0.01 cm−1 for a spectral resolution R = 100,000 at
λ = 8 µm). However, there have been few reports of infrared materials with αatt <0.01 cm−1. Therefore, we performed
high-accuracy measurements of the attenuation coefficients αatt for a variety of infrared optical materials with n > 2 thatare applicable to immersion gratings. We have previously reported some results on αatt at room temperature. Ikeda et al.
(2009) revealed that both CVD-ZnS and CVD-ZnSe materials showed αatt = 0.01–0.03 cm−1 at 0.9–0.6 µm, and singlecrystal Si shows αatt ≤0.001 cm−1 at 1.3–1.6 µm[7]. Kaji et al. (2014) suggested usable wavelength ranges for several
materials as immersion gratings based on the measurements between 1.3 and 20 µm using a custom-improved highaccuracy FTIR system[10]; near-infrared wavelengths (2–5 µm) were suggested for single-crystal Si and CVD-ZnS,
thermal infrared wavelengths (3–10 µm) were suggested for single-crystal Ge and CVD-ZnSe, and mid-infrared
wavelengths (5–20 µm) were suggested for high-resistivity single-crystal CdZnTe. Sarugaku et al. (2016) proposed thatthe attenuation of high-resistivity single-crystal CdZnTe could originate from Mie scattering by the sub-µm size of Te
particles[9].
Next, we proceeded with the measurements of αatt at cryogenic temperatures of 20–80 K that are the typical operationaltemperatures. For these measurements, the shifts of the band gap and/or the sharpness of the lattice absorption lines fromthe corresponding room temperature values are expected (e.g., Hawkins 1998[21]). Even a small difference can critically
influence the design of an instrument (for the optimum wavelength region) and the science cases, because the measurable
atomic and molecular lines change. Therefore, in this paper, we describe the details of the cryogenic FTIR systemdeveloped by us and the testing results in section 2 and 3, respectively, and report the preliminary result obtained for theattenuation coefficients of single-crystal Ge at cryogenic temperatures in section 4.

2. CRYOGENIC FTIR SYSTEM
2.1 Requirements

Figure 1. High-accuratcy FTIR system for measurements of internal attenuations of infrared materials at room temperature (Kaji et al.
2014[10]). The newly developed cryostat unit is located within a box drawn by the dashed line.

To enable the measurements of the attenuation coefficients for infrared optical materials at cryogenic temperatures, we
attached a new cryostat unit for cooling the samples to the current high-accuracy FTIR system that was originallydeveloped for performing measurements at room temperature, as reported by Kaji et al. (2014)[10]. The newly built unit
was inserted in a space between the aperture and the first off-axis parabola mirror, where the collimated beam is
propagated (see Figure 1). Table 1 shows the requirements that must be satisfied by the new cryostat. For the highaccuracy measurement, we employ “a double sample method” that was used for measurements at room temperature by
Ikeda et al. (2009) [7] and Kaji et al. (2014) [10]. Because this method requires the measurements of two samples (a thicksample and a thin sample) in addition to that of the reference (no sample), three samples cells that can be quickly
switched during a single heat cycle must be provided.
Table 1. Requirements of the new cryostat for sample cooling

Item

Specifications

Beam height

90 mm

Size of the windows>Φ 12 mm (for clear aperture)

Wavelength

1.3–20 µm

Physical size

<340 mm (W) × 245 mm (L) × 340 mm (H)

Total weight<30 kgMinimum temperature of measurement

20 K

Maximum time for cooling<2 daysNumber of sample cells

3

Positional repeatability of samples<0.5 mm

Measurement method

Double sample method (Ikeda et al. (2009) [7]
and Kaji et al. (2014) [10]2.2 Thermal design
The most challenging requirement for this cryostat system is that the samples must be cooled to temperatures below~20 K with a stability of ± 0.1 K despite the presence of two large windows required for the entrance and exit beams.
Assuming that the ambient environment is a black body at 300 K, the thermal radiative inflows from those windows to
the inside are calculated to be relatively large (0.42 W). Thus, a careful and quantitative thermal design is crucial.
To achieve a quantitative thermal design, we used a thermal-flow block diagram of our cryostat (Figure 2). This
diagram simulates thermal flows between the parts in the cryostat. In the diagram, we present an expected mechanicalpart with no temperature gradient as one block. The thermal flows between the parts are shown with connecting arrows.
We consider the thermal conduction (shown with dashed lines) and the thermal radiation (shown with solid lines) as thethermal flows. While the surface area and the emissivity are defined for each block, the thermal conductivity is definedfor each connecting arrow. Assuming that the temperatures of the ambient environment and the cryocooler cold head or
the thermal inflows and outflows are the boundary conditions of system, the equilibrium temperature and the thermal
inflows/outflows between the parts can be calculated. Therefore, using this diagram, we can optimize the surface areas
and emissivities (i.e., the material) of the parts and the conductivities (i.e., the material, length, and cross section) of theconnecting arrows to achieve the target temperature of the sample holder at 20 K.

Figure 2. Thermal-flow block diagram for thermal design. Each box represents a mechanical part expected to have a single
temperature in the cryostat. Lines connecting boxes show thermal flows: solid lines represent radiation, and dashed lines
represent thermal conduction. Assumed emissivity and conductivity values for each part are given in Table 2.

To perform the actual optimization, we adopted 300 K as the ambient temperature, 10 K as the cold head temperature of
the cryocooler, and 9.0 W as the cooling power of cryocooler, with the temperature and power of the cryocooler takenfrom the values in the catalogue by Sumitomo Heavy Industries, Ltd. Table 2 shows the final thermal design. Even withthe very small thermal inflow to the cryocooler of 1.9 W (which is less than 1/4 of the maximum power), we obtained asolution for cooling the sample holders to 16 K. As expected, it was critical to suppress the radiative inflows of theambient thermal radiation. The temperature at the sample holder is achieved by using “three radiation shields (outer andinner radiation shields, and photon shield).” Each radiation shield is supported with three glass epoxy legs with a low
thermal conductivity of 0.5 W m−1 K−1 in order to prevent the temperatures of the radiation shields from effectively
increasing.

Table 2. Assumed and obtained parameters of each block after optimization.

Material

Emissivity

Thermalconductivity[W m−1 K−1]

Effective
surface area[m2]

Cross section[m2]× length [m]Remarks

Outer wall

A6061-T6

0.1

-

0.41

-

-

Outer Radiation
shieldSUS304

0.07

-

0.29

-

-

Inner Radiation
shieldSUS304

0.07

-

0.26

-

-

Photon shield

SUS304

0.07

-

0.09

-

-

Cold work surface

Oxygen-freecopper
C1020

0.05

-

0.01

-

-

Cold plate

Oxygen-freecopper
C1020

0.05

-

6.0×10−3--

Entrance window

KBr

1

-

6.2×10−4--

Exit window

KBr

1

6.2×10−4--

Cryocooler coldhead

OFHCcopper--

3.4×10−3--

Cables

Copper-401@273K-

1.3×10−7 × 0.25

Including 7
cablesSupport poles

Glass epoxy

-

0.5

-

6.4×10−5 × 0.011

Including 9
poles

2.3 Mechanical design
Figure 3 shows the mechanical design of the new cryogenic unit. The dimensions of the cryostat are 327 mm (W) × 240
mm (L) × 270 mm (H), and its weight including the inside sample switcher unit and the cryocooler cold head isapproximately 28 kg. These physical parameters satisfy the requirements described in section 2.1. The thermal radiationfrom the ambient environment is reduced by inner and outer radiation shields as well as by the photon shield. The sample
switcher unit is located in the space that is entirely surrounded by the photon shield. This unit comprises an oil-freelinear motion guide (SR15MSW produced by THK Co., Ltd.), a rotary/linear motion feedthrough (FCH025-H produced
by INFICON Co., Ltd.), a roller plunger (CBPJ9 bought from MISUMI Inc.), and the custom-made sample holders, cold
work surface, and guide-wall (see Figure 4). As the sample holders are located on the linear motion guide together withthe cold work surface, we can easily and quickly switch the samples from the outside of the cryostat by hooking the tipof the motion feed through to the linear motion guide, and pulling or pushing it (see Figure 4 and 5). Because the linear
motion feedthrough can be thermally detached from the cold work surface, there is no direct thermal inflow from theoutside. To realize good positional repeatability for the sample holders (<0.5 mm) in the switching, we use the roller
plunger with a bearing on the side of the cold work surface (in Figure 5). This roller plunger is designed to continue topush the guide wall with the tensile force applied by the spring contained in the plunger. The guide-wall has threegrooves that correspond to the positions of the two samples and the reference, wherein the roller plunger falls in thegrooves with the restoring force and can be accurately fixed at the aiming position with a good positional repeatability.

Figure 3. 3D drawing of the newly developed cryogenic unit attached to the FTIR system.

Figure 4. Inner structure of the cryostat.

Figure 5. The mechanical structures of the sample switching unit.

Figure 6. Mechanism of feedthrough and hook for sample switching. First, the hook (colored in green) at the tip is inserted into theclaw under the cold work surface on the linear motion guide (colored in orange) by rotating the motion feedthrough(colored in silver). Then, the sample holders together with the cold work surface are moved by pushing or pulling of the
motion feedthrough.

2.4 Optical design
We selected KBr as the material for entrance and exit windows because KBr transmits wavelengths of 1.3–20 µm witha transparency of ~80%. Although the most of energy loss is generated by Fresnel reflection on the surface, we use thewindow without anti-reflection coating in order to suppress the condensation of the atmospheric water on the window.
The dimensions of the windows are Φ 45 mm × t 8 mm with a clear aperture of Φ 28 mm.
The maximum flexure by the atmospheric pressure and the maximum bending of the optical bench by the self-weight ofthe cryostat are calculated to be 0.1 µm and 0.31 mm, respectively. Although these produce an optical aberration of the
focused beam on the FTIR detector and the miss-alignment of the optical train, we confirmed by using the ray tracingthat both these effects are negligible.

3. FABRICATION AND TESTING
Figure 7 shows time variations of the pressure and the temperature in the cryostat during a testing run. Temperatures atthe cryocooler cold head, the cold work surface, the photon shield, and the outer and inner radiation shields were
measured using the Si diode temperature sensors (DT-670 produced by Lake Shore Cryotronics, Inc.), and the poweron/off timings of the cryocooler are indicated with triangles. The ambient temperature, controlled by the air-conditioner,
was approximately 20°C. It took approximately one day for the sample holder to reach the equilibrium temperature,satisfying the requirement for the cooling time to be less than two days (see Table 1). The lowest attained temperaturesof various parts in the cryostat are shown in Table 3. The temperature of the cold work surface did not reach the required
temperature of 20 K, probably because the cryocooler cold head could not reach the operating temperature (=10 K)
guaranteed by the developer. In addition, the detected FTIR signals were found to be slightly unstable because of theinfluence of vibrations propagated from the cryocooler to the FTIR unit. After detailed investigations, we plan to fix
these problems to enable more accurate measurements.

Figure 7. Time variations of the pressure and temperature in the cryostat during a testing run from March 4th, 2016.
Table 3. End-point temperature of each component

Target [K]Designed [K]Measured [K]Cryocooler cold head

10

10

25

Cold work surface

20

17

29

Photon shield

20

17

32

Inner radiation shield

200

175

206

Outer radiation shield

260

255

259

4. PRELIMINARY RESULTWe measured the attenuation coefficient of the single-crystal Ge produced by TDY Inc. that has already been measured
at room temperature. The dimensions of the two samples were Φ 20 mm × t 30 mm and Φ 20 mm × t 5 mm. The
attenuation coefficient is derived from equation (2) in the work of Kaji et al. (2014) [10] using the transmittances of thin (t5 mm) and thick (t 30 mm) samples. The wavelength range was from 1.3 to 28 µm (7800–350 cm−1), and the spectral
resolution was 4 cm−1. To improve the signal to noise (S/N) ratio, we obtained 1,280 spectra for one sample. During themeasurements, we turned off the power of the cryocooler in order to minimize the influence of the vibration propagatedfrom the cryocooler to the FTIR instrument (see the previous section). The temperature variation due to the temporal
turning-off of the cryocooler is estimated to be <15 K.
Figure 8 shows the preliminary result for the attenuation coefficients of Ge at the cryogenic temperature (blue circles).
We also plotted our previous results obtained at room temperature as well as the absorption coefficient values given in
the literature. Even though we encountered a problem during the measurements in that the thermometer came off thesample holder, the temperature was estimated to be at most 28 K based on the temperatures measured by thisthermometer during other cooling runs. In Figure 8, the cut-on wavelength, defined as the shortest wavelength for αatt <0.01 cm−1, shifts from 2.0 µm (at room temperature) to 1.7 µm (at cryogenic temperature). This indicates that at
cryogenic temperatures, Ge immersion grating can cover the entire K-band (2.0–2.4 µm), including the longer
wavelength region of the H-band (1.5–1.8 µm). In addition, the cut-off wavelength, defined as the longest wavelength for
αatt < 0.01 cm−1, shifts from 10.6 µm (at room temperature) to 10.9 µm (at cryogenic temperature) with the decrease of
the attenuation coefficients by a factor of ~3 and the sharpness of the lattice absorption lines. The wavelength
dependence of the attenuation coefficient around the cut-off wavelength is in good agreement with the results at 20 K
reported by Fray et al. (1965) [23]. It is found that Ge immersion grating cannot cover the entire N-band (8–13 µm) evenat the cryogenic temperatures.

Figure 8. Attenuation coefficients at cryogenic temperature (blue circles). Red circles show the results at room temperature obtainedby Kaji et al. (2014) [10]. Black lines and green lines show the measurements in the literatures at 300 K (Palik 1997[22]) and
20 K (Fray et al. 1965 [23]). Magenta dashed lines show absorption coefficients theoretically predicted by Hawkins (1998)[21].

5. SUMMARY
We are working on a project to measure the attenuation coefficients of a variety of infrared optical materials at
cryogenic temperatures in order to select materials that are suitable for use in immersion gratings. For this purpose, wedeveloped a new cryogenic unit that can be attached to the current FTIR system used for measurement at room
temperature. Using an originally designed sample switching unit that enables us to switch two samples cells and areference cell easily and quickly without any vacuum leak or temperature change, we achieved high-accuracy
measurements of the attenuation coefficients at cryogenic temperatures using “the double sample method.” In our
preliminary result for Ge that were obtained using this system, both the cut-on wavelength and the cut-off wavelength
are shifted from 2.0 µm (at room temperature) to 1.7 µm (at cryogenic temperature), and from 10.6 µm (at room
temperature) to 10.9 µm (at cryogenic temperature) with the decrease of the attenuation coefficients by a factor of ~3 andthe sharpness of the lattice absorption lines, respectively. The wavelength dependence of the attenuation coefficientaround the cut-off wavelength is in good agreement with the previous results obtained at 20 K by Fray et al. (1965) [23].
We intend to improve the cooling efficiency and fix the problem of vibrations due to the cryocooler in order to moreaccurately measure a variety of infrared materials at approximately 20 K; we intend to complete these measurements by
the end of 2016.

ACKNOWLEDGMENTS
We are grateful to the staff of the Koyama Astronomical Observatory of Kyoto-Sangyo University for supporting us
during this program. This study is financially supported by JSPS KAKENHI (16684001) Grant-in-Aid for Young
Scientists (A), JSPS KAKENHI (20340042) Grant-in-Aid for Scientific Research (B), JSPS KAKENHI (21840052)
Grant- in-Aid for Young Scientists (Start-up), and MEXT Supported Program for the Strategic Research Foundation atPrivate Universities, 2008–2012 (No. S0801061) and 2014–2018 (No. S1411028).

REFERENCES[1] Ikeda, Y., Kobayashi, N., Kondo, S., Yasui, C., Motohara, K., and Minami, A., “WINERED: a warm nearinfrared high-resolution spectrograph,” Proc. SPIE 6269, 62693T (Jul. 2006).
[2] Ikeda, Y., Kobayashi, N., Kuzmenko, P. J., Little, S. L., Yasui, C., Kondo, S., Minami, A., and Motohara, K.,“Diamond-machined ZnSe immersion grating for NIR high-resolution spectroscopy,” Proc. SPIE 7018, 70184R(Jun. 2008).
[3] Ikeda, Y., Kobayashi, N., Terada, H., Shibayama, A., Ozawa, A., Yasui, C., Kondo, S., Pyo, T., and Kawakita,
H., “High-efficiency silicon immersion grating by electron-beam lithography,” Proc. SPIE 7014, 701469 (Jun.
2008).
[4] Ikeda, Y., Kobayashi, N., Kuzmenko, P. J., Little, S. L., Yasui, C., Kondo, S., Mito, H., Nakanishi, K., andSarugaku, Y., “Fabrication and current optical performance of a large diamond-machined ZnSe immersion
grating,” Proc. SPIE 7739, 77394G (Jul. 2010).
[5] Ikeda, Y., Kobayashi, N., Kuzmenko, P. J., Little, S. L., Mirkarimi, P. B., Alameda, J. B., Kaji, S., Sarugaku, Y.,
Yasui, C., Kondo, S., Fukue, K., and Kawakita, H., “ZnSe immersion grating in the short NIR region,” Proc.
SPIE 9151, 915144 (Jul. 2014).
[6] Ikeda, Y., Kobayashi, N., Sarugaku, Y., Sukegawa, T., Sugiyama, S., Kaji, S., Nakanishi, K., Kondo, S., Yasui,C., Kataza, H., Nakagawa, T., and Kawakita, H., “Machined immersion grating with theoretically predicteddiffraction efficiency,” Applied optics, 54, 5193-5202 (Jun. 2015).
[7] Ikeda, Y., Kobayashi, N., Kondo, S., Yasui, C., Kuzmenko, P. J., Tokoro, H., and Terada, H., “Zinc sulfide andzinc selenide immersion gratings for astronomical high-resolution spectroscopy: evaluation of internal
attenuation of bulk materials in the short near-infrared region,” Optical Engineering, 48, 084001 (Aug. 2009).
[8] Sarugaku, Y., Ikeda, Y., Kobayashi, N., Sukegawa, T., Sugiyama, S., Enya, K., Kataza, H., Matsuhara, H.,
Nakagawa, T., Kawakita, H., Kondo, S., Hirahara, Y., and Yasui, C., “Development of CdZnTe immersion
grating for spaceborne application,” Proc. SPIE 8442, 844257 (Jul. 2012).
[9] Sarugaku, Y., Kaji, S., Ikeda, Y., Kobayashi, N., Sukegawa, T., Nakagawa, T., Kataza, H., Kondo, S., Yasui, C.,
Nakanishi, K., and Kawakita, H., “Infrared attenuation spectrum of bulk high-resistivity CdZnTe single crystal

in transparent wavelength region between electronic and lattice absorptions,” Journal of Electronic Materials(2016 in prep.).
[10] Kaji, S., Sarugaku, Y., Ikeda, Y., Kobayashi, N., Nakanishi, K., Kondo, S., Yasui, C., and Kawakita, H., “Theprecise measurement of the attenuation coefficients of various IR optical materials applicable to immersion
grating,” Proc. SPIE 9147, 914738 (Jul. 2014).
[11] Kuzmenko, P. J., Ikeda, Y., Kobayashi, N., Mirkarimi, P. B., and Alameda, J. B., “Reflective coating for nearinfrared immersion gratings,” Proc. SPIE 8450, 84503O (Sep. 2012).
[12] Ikeda, Y., Kobayashi, N., Kondo, S., Otsubo, S., Hamano, S., Sameshima, H., Yoshikawa, T., Fukue, K.,
Nakanishi, K., Kawanishi, T., Nakaoka, T., Kinoshita, M., Kitano, A., Asano, A., Takenaka, K., Watase, A.,
Mito, H., Yasui, C., Minami, A., Izumi, N., Yamamoto, R., Mizumoto, M., Arasaki, T., Arai, A., Matsunaga, N.,
and Kawakita, H., “High sensitivity, wide coverage, and high resolution NIR non-cryogenic spectrograph,
WINERED,” Proc. SPIE (2016 in prep.).
[13] Yasui, C., Ikeda, Y., Kondo, S., Motohara, K., and Kobayashi, N., “WINERED: optical design of warm infraredechelle spectrograph,” Proc. SPIE 6269, 62694P (Jul. 2006).
[14] Yasui, C., Kondo, S., Ikeda, Y., Minami, A., Motohara, K., and Kobayashi, N., “Warm infrared echelle
spectrograph (WINERED): testing of optical components and performance evaluation of the optical system,”
Proc. SPIE 7014, 701433 (Jul. 2008).
[15] Terada, H., Ikeda, Y., Kobayashi, N., Yasui, C., Pyo, Tae-Soo., Usuda, T., Hayashi, M., and Kawakita, H.,“High resolution spectrograph unit (HRU) for the SUBARU/IRCS,” Proc. SPIE 7014, 701434 (Jul. 2008)[16] Kobayashi, N., Ikeda, Y., Kawakita, H., Enya, K., Nakagawa, T., Kataza, H., Matsuhara, H., Hirahara, Y., andTokoro, H., “Mid-infrared high-resolution spectrograph for SPICA,” Proc. SPIE 7010, 701032 (Aug. 2008).
[17] Kataza, H., Sakon, I., Wada, T., Sarugaku, Y., Fujishiro, N., Ikeda, Y., Mitani, S., Ohyama, Y., and Kobayashi,N., “Performance estimation of the mid-infrared camera and spectrometer abroad SPICA,” Journal of
Astronomical Instrumentation 04, 1550001 (Jun. 2015).
[18] Kondo, S., Ikeda, Y., Kobayashi, N., Yasui, C., Mito, H., Fukue, K., Nakanishi, K., kawanishi, T., Nakaoka, T.,
Otsubo, S., Kinoshita, M., Kitano, A., Hamano, S., Mizumoto, M., Yamamoto, R., Izumi, N., Matsunaga, N.,
and Kawakita, H., “A warm near-infrared high-resolution spectrograph with very high throughput(WINERED),” eprint arXiv 1501.03403 (Jan. 2015)[19] Arasaki, T., Kobayashi, N., Ikeda, Y., Kondo, S., Sarugaku, Y., Kaji, S., and Kawakita, H., “VINROUGE: avery compact 2 – 5 µm high-resolution spectrograph with Germanium immersion grating,” Proc. SPIE (2016 in
prep.).
[20] Otsubo, S., Ikeda, Y., Kobayashi, N., Sukegawa, T., Kondo, S., Hamano, S., Sameshima, H., Fukue, K.,
Yoshikawa, T., Nakanishi, K., Watase, A., Takenaka, K., Asano, A., Yasui, C., Matsunaga, N., and Kawakita,
H., “First high-efficiency and high-resolution (R = 80,000) NIR spectroscopy with high-blazed echelle grating:
WINERED HIRES-modes,” Proc. SPIE (2016 in prep.).
[21] Hawkins, G. J., “Spectral characterization of infrared optical materials and filters,” (1998).
[22] Palik, E. D., [Handbook of Optical Constants of Solids], Academic Press, England (1997).
[23] Fray, S. J., Johnson, F. A., Quarrington, J. E., Williams, N., “lattice bands in germanium,” Proceedings of the
Physical Society 85, 153 (Jan. 1965).