次世代観測装置用の新しい回折格子の開発状況	 II	1112
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海老塚	 昇 , 森田	 晋也 , 山形	 豊 , 佐々木	 実 , 田辺	 綾乃 , 橋本	 信幸 , 平原靖大 , 青木	 和光 , 高見	 英樹 	 
1理化学研究所，2豊田工業大学，3シチズンホールディングス, 4名古屋大学，5国立天文台	 	

Volume Phase Holographic (VPH) grating	Quasi-Bragg (QB) grating	

70	

VPH grating (360 g/mm,λB= 800nm)	

Surface relief grating 	

(300 g/mm, λB= 750 nm)	#% π ( n − n ) t '%maxmin
ηS = sin 2 $(%& Λ ( nmax + nmin ) sin 2θ B %)VPH grism for MOIRCS of
8.2m Subaru Telescope.	 Diffraction efficiencies of VPH grating#' and surface relief grating for moderate
2 % π ( nmax − nmin ) t cos2θ B %ηP = sin $( dispersion. 	

%& Λ ( nmax + nmin ) sin 2θ B %)Schematic representation of quasi-Bragg (QB) grating (left above & center). Fabricated QB grating,silica glass substrates laminated by adhesive mixed with glass beads (left below). Diffraction
efficiency of QB grating (right, Oka, SPIE 5290, 2004).	

We are planning to perform new fabrication method which mirror plates laminated by pressure
fusion of gold films.	

Calculated polarization diffraction efficiencies vs.
Measured polarized diffraction efficiencies oft of VPH grating. Δn = (nmax - nmin)/2 = 0.017.	

VPH grating. nave= (nmax - nmin)/2 = 1.53,	

(Ebizuka, PASJ, 63, 2011)	

Λ=0.984 μm, t = 20 μm, θB 32.7° @1.02 μm. 	

θB =31.7 deg.	

3rd	

θB =30.9 deg.	

6th	

Δn=0.10	Δn=0.07	Δn=0.04	

10th	

Diffracted beam images of far field of QB gratings. Silica glass substrates laminated by adhesive mixed
with glass beads (left). Silica glass substrates laminated by pressure fusion of gold (center & right).	

Quasi-Bragg immersion grating	Δn=0.02	

Band width becomes narrow toward large diffraction angle
because semi-amplitude of index modulation (Δn) of
dichromated gelatin is up to 0.1.
(Baldry, PASP 116, 2004)	

Diffraction efficiency of a VPH grating
decreases toward higher orders.	

(Oka, SPIE 5290, 2004)	

Volume binary grating	(Ebizuka, SPIE 6273, 2006)	

Schematic representation of quasi-Bragg immersion (QBI) grating. 	

Germanium immersion grating	 GIGMICS	Λ = 5µm, L&S = 9 : 1, nH=1.89, nL= 1.46, θB= 41.3°, w:t = 1:22. (Bianco, SPIE, 8450, 2012)	

Test fabrication of volume binary grating with photoresist (KMPR1000, NIPPON

Ge immersion grating	

KAYAKU Co.Ltd.). Performed by Nanotechnology Platform Program of Toyoda Technological Institute.	

Fabrication of a germanium immersion grating with size of 30 by 30 by 72 spent ~ 400 hours by meansof a nano-precision machine tool and ELID grinding method.	

(Ebizuka, SPIE 4842, 2003)	

Test fabrication of V-grooves on silicon and germanium	

Tilt: 30°, ×1,000	

Tilt: 10°, ×300	

Tilt: 15°, ×2,000	

Scanning electron micrograph of photoresist grating (L&S:10:10µm), groove depth: 46.7/sin30 = 93.4µm (left).	

Diffraction efficiency of photoresist
grating (L&S: 8:12µm, t~50µm). 	

Birefringence Bragg binary (3B) grating	

RCWA calculation of polarized efficiency of
3B grating. n2a = 1.460, nSmax = 1.544,nPmax = 1.598, Λ = 0.424 µm, λ = 0.6 µm, 	θB = 45° t = 5 µm, w:t = 1:23.6. 	

(Ebizuka, SPIE 8450, 2012)	

n2a=1.34*, nS = 1.54, nP =1.74, w:t ~ 1:10?
* Cytop or UFR@AGC	

End mill of single-crystal diamond (left, φ = 0.5mm), fly-cutting for a silicon substrate by using theend mill (center) and V-grooves processed by the end mill (right). 	

V-bit with negative rake angle (left). Setting of a V-bit and silicon wafer to nano-precision machine
tool (center). End points of V-grooves on silicon wafer processed by shave cutting of V-bit (right). 	

Conclusions	

• VPH grating achieves high angular dispersion and high efficiency for the 1st diffraction
order, as well as versatile for moderate angular dispersion.	

Test fabrication of liquid crystal grating (CITIZN Holdings Ltd.)	

• Volume binary grating and birefringence Bragg binary (3B) grating achieve highdiffraction efficiency up to 100% for non-polarized light of the 1st diffraction order andOrientation layer	

of higher diffraction orders (utilized for echelle spectrograph).	

(= Grating vector)	

• Test fabrication of volume binary grating and 3B grating are performed by Toyoda
Technological Institute and by CITIZN Holdings, respectively.	

• Quasi-Bragg (QB) grating and quasi-Bragg immersion (QBI) grating, which mirror
plates laminated by pressure fusion of gold films, are feasible even for echelle
spectroscopy
ofvisible
wavelength.	

Polarizer
angle:~110°	

Polarizer angle: ~ 70°	Polarizer angle: 90°	 
•Siliconandgermanium
immersion
gratings
withstep-likegrooves,which
processedbyPolarized
diffraction
efficiencies
Polarized images of the first diffraction order of 3B grating withthelatest
diamondcutting
tool,
areexpectedtorealize
ideal
performancefornearof3B
gratingwithliquidcrystal.
liquid crystal. 	
infrared and mid-infrared, respectively.	

(L&S: 1:1µm, t=1µm).