次世代観測装置用の新しい回折格子 III�
海老塚 昇1, 岡本 隆之1,竹田 真宏1,細畠 拓也1, 山形 豊1, 佐々木 実2, 魚本 幸3,島津 武仁3, 佐藤 慎也4, 橋本 信幸4, 田中 壱5, 服部 暁5, 尾崎 忍夫5, 青木 和光5
1 理研, 2 豊田工大・工, 3 東北大・工, 4 シチズン時計・開発部, 5 国立天文台

Birefringence volume phase holographic (B-VPH) grating

Limitation of surface relief (SR) grating
Transmission gratings for WFOS
Vertex angle: θ0 = 36~53°
Period: Λ= 2~5 μm
Size: 400 x 550~750 [mm]sinθ0 = n sinθ1n sin(α -θ1) = sinθ2θ2 = α +θ0n sin(α -θ1) = sin(α +θ0)n (sinα cosθ1- sinθ1 cosα) = sinα cosθ0 + sinθ0 cosα(n cosθ1 - cosθ0) sinα = (sinθ0 + n sinθ1) cosα
= 2sinθ0 cosα
tanα = 2sinθ0 / (n cosθ1 - cosθ0)

n = 1.5, θ0 ≤ 30° (θ2 < 90°)n = 1.8, θ0 ≤ 36°
n = 2.3, θ0 ≤ 45°
n = 3.0, θ0 ≤ 54°
Diamond: n = 2.46@400nm⎧⎪ π ( n⎫P max − nP min ) t cos2θ P ⎪ηP = sin ⎨⎬⎪⎩ Λ ( nP max + nP min ) sin 2θ P ⎪⎭⎧⎪ π ( n⎫⎪S max − nS min ) tηS = sin ⎨⎬⎪⎩ Λ ( nS max + nS min ) sin 2θ S ⎪⎭22(nS max − nS min ) = (nP max − nP min ) cos2θ P(nS max + nS min ) sin 2θ S (nP max + nP min ) sin 2θ P
nP max − nP min ) cos2θ P(nS max − nS min )(=(nS max + nS min ) * 2sin θ S cosθ S (n=P max + nP min ) * 2sin θ P cosθ P(nS max − nS min ) = (nP max − nP min ) cos2θ Pcosθ SSR grating with saw tooth grooves is not feasible for the high-dispersion transmission grating.�

cosθ P

Volume Binary Grating
Loss by evanescent resonance?

Birefringence VPH grating
and calculated polarized
diffraction efficiencies versus
grating thick-ness t. Λ= 0.646
μm, nL=1.46, ns= 1.544, np =1.60, θB=45°.

Gain by Brewster’s angle?

S-pol.

Total reflection at boundary
between ridge and groove.
→ Function as a Quasi
Bragg grating.

Polarized diffraction
efficiencies of Dicson’s
VPH grating (Polarizer)
calculated by Kogelnikmethod. Λ= 0.646, nL=1.46, nH=1.54, θB=48.5°.

P-pol.

Diffraction efficiency of volume binary grating calculated by RCWA.
Λ=5µm, L&S=4.75:0.25 [µm], θ0=45°, n1=1.0, n2=1.54, n3=1.5, t=9µm.

Reflector facet transmission (RFT) grating
S-pol.

θB~27°

P-pol.

UV~21°
curable LC (no=1.55,ne=1.72) + normal LC
θ
~33°
θ
B
B
(no=1.50,ne=1.65), t=10 μm, 2,235 grooves/mm(Λ~ 0.45 μm), UV (315nm) : 1.3mW/cm2, 1sec.

Vis curable resin (nd=1.51) + UV curable LC(no=1.55, ne=1.72), t=20 μm, 616 grooves/mm(Λ= 1.62 μm), Vis (532nm) : 2.0mW, 100sec.

Quasi-Bragg immersion grating
Diffraction efficiency of RFT grating calculated by RCWA. Λ=5µm, θ0=45°, n=1.54.

Hybrid grism for MOIRCS (as a prototype of RFT grating)Prism material: ZnSe (n1= 2.4529@1.65 μm)
Plate: S-FPM3 (n2= 1.5240@1.65 μm)
Prism vertex angle : α = 23.8°
Grating period: Λ= 10.79μm (92.68 grooves/mm)
Incident angle: θ0= 5°
Groove blaze angle : β = 64.8°
Groove vertex angle : γ = 61.8°

Slit width: 0.3”
7th, R= 2,900@0.88 μm
6th, R= 2,790@1.02 μm
5th, R= 2,750@1.25 μm
4th, R= 2,800@1.65 μm
3rd, R= 2,770@2.20 μm

Substrate
Clear resin
Master grating
Shaper cutting of master grating.
Work： Ni-P alloy of non-electrolytic plating

Schematic representation of quasi-Bragg immersion (QBI) grating. (Ebizuka, SPIE 6273, 2006)

Size of QBI grating.
Replication

Block of mirror substrates
stacked by fusion of gold.

QB grating withtilted mirror lattice.

Cutting position of wire saw.�

FinishSpatial filter

Fabrication method of SR grating for RFT grating and MOIRCS hybrid grism

ScreenDiffraction pattern (about 1,000th order) ofQB grating. Beam is split up and down.

QB immersion
grating

He-Ne Laser
Collimatorand imaging
lens

Pinhole of spatial filter

RCWA
Diffracted beam

Ultra-high precision machine (Nagase-I,NPIC-M200).

Quasi-Bragg
grating

Measured
Test cuttings for condition setting.

Single-crystal diamond tool.

Surface mirror

Littrow prismAttached by matching oil.

Surface reflectionof prism

Measurement optical system.

The diffracted beam is concentrated (blazed).
However diffraction orders cannot separate becausea point source image is larger than the interval of thediffraction orders (about 2,000th orders).

SummaryMaster ; PV: 0.79λ, RMS: 0.12λ,(upper left)
1st replica ; PV: 0.76λ, RMS: 0.12λ(upper right)
2nd replica; PV: 0.48λ, RMS: 0.07λ(left)

Mold for replication
experiment size: 50×50 [mm].

Optimal Eff. [%]Order (λ-λ [µm])Diffraction efficiency of replicatedtransmission grating.

Echelle grism (Volume binary grating) for MOIRCS
Slit width: 0.3”
5th, R= 4,630@1.02 μm
4th, R= 4,420@1.25 μm
3rd, R= 4,270@1.65 μm
Schematic representation of volume binary grating (left) function as aquasi-Bragg (QB) grating and diffraction efficiency calculated by RCWA
(right). L&S=4.6:0.5 [µm], θ0=28.4°, n1=1.33, n2=1.6, n3=1.6, t = 16 µm

Schematic representation ofechelle grism for MOIRCS

Fabrication process of the volume binary grating
5.1Single crystalsilicon

0.44

10

Bosch process(isotropic etching)

0.8

[µm]

20

Substrate

Si3N4(high refractive index)

Cross section A-A’

Mold of silicon

Clear resin(low refractive index)

AA’
Side view

2th~Hybrid grism

2rd~Volume binarygrating

1st~

VPH grating→B-VPH grating

1st�Quasi-Bragg
immersion grating

5th~

Evaluations of diffraction efficiency by~ 80(0.32~2.4)� numerical calculations of RCWA. �
Performing diamond cutting of a master~ 70
gratingofNi-P
alloyforMOIRCS.
(0.32~2.4)�
Replication method is under developing.�
Performing test fabrications by using~ 80(0.2~1000)� MEMS technique.�
Installed in FOCAS, MOIRCS, Kools and~90 →~100 WSGS2. (photopolymer)(0.32~2.4)� Developing new recording materials forvolume hologram with liquid crystal.�
Performed test fabrications of lamination~ 80
byatoms
fusionbondingandlaminationof(0.2~1000)�
embossed substrates.�

Current and future works• Trial fabrication of a mold for the RFT grating is on going.
• SOQ (silicon on quartz) wafer will use for a substrate of the VB grating.

SubstrateRemoval of Si

Reflector facettransmission grating

Status of development

Silicon mold for volume binary grating.
Fabricated by Nanotechnology platformof Toyota Institute of Technology.

• Performance of a 3D holographic printer (colinear two beam exposure system) for theVPH grating with a large size (~1x1 [m]) will be evaluated.
• The mold for the hybrid grism of the MOICS will fabricate in this business year.