9VJ;HF>1.8:G 21, &6 O 1,D? A!1,E@ /1, %* K1, 5 "2,  L3,#I A)3, 6 QM3, < ,-4, ? 5, 4N 35, $' +5, P5 5
1=B, 2K?((, 370 , 47=, 5C0

Reflection and transmission gratingDiameter of a camera lens exceeds maximum size (φ440) of calcium fluoride if a reflection grating is usedas the disperser.

Limitation of surface relief(SR) transmission grating→Transmission grating can reduce size of the camera lens (→total optical system).
CameraCollimator

Transmissiongrating

VPH grating can not achieves high diffraction efficiency fornatural and circular polarizations at high dispersion becausecharacteristics of diffraction efficiencies are different between
S and P polarizations.
→Birefringence VPH grating.

Diamond:n = 2.46@400nm

CameraSlit

VPH (Volume Phase Holographic) grating, in whichrefractive index is modulated sinusoidally achievesdiffraction efficiency up to 100% for S or P polarization.

q2 < 90
n = 1.5, q0 ≤ 30
n = 1.8, q0 ≤ 36
n = 2.3, q0 ≤ 45
n = 3.0, q0 ≤ 54

→Transmission grating is able to realize perfect Littrow mounting.
Spectrum

VPH grating Diffraction efficiencies of VPH
grating decrease in higherorders.
→VPH grating is not feasible foran echelle grating.

SR transmission grating with saw toothgrooves is not feasible for the highdispersion grating.

Slit

Collimator

LightSmyth Transmission Grating

Spectrum

Reflection grating

Volume binary VB) grating for MOIRCS echelle grism

for MOIRCS J and H band grisms instead of VPH grisms

MOIRCS echelle grism
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 Schematic representationof volume binary grating. of echelle grism

Fabrication process of VB grating

AR

Diffraction efficiency of VB grating(RCWA). L&S= 4.6:0.5 [µm], θ0=28.4,
n1=1.33, n2=1.6, n3=1.6, t=16 µm.

Non-AR

Non-AR
AR(Calculated)

Reactive Ion beam

ResistSiliconSilicasubstrate

Upper
substrate
High-index
resin
Silicasubstrate

Measurement of reference

H band grism, 677 g/mm (Test peace)

Measurement for diffraction
efficiency at blazed angle.

VPH grism (corrected)

Resist mask
patterning onto
SOQ* substrate

Cycle etching(Bosch process)Oxidation ofsilicon surface

2~3 times

Adhesion withglass plate byfilling high-index
resin (n~1.72)

Oxidation of
total silicon

J band grism 940 g/mm (T-940C)

Grism for MIMIZUKUBefore (left) and after (right)
Si oxidization of VB grating
fabricated in SOQ substrate.

Removal of oxide* SOQ: Silicon on Quartz
Diffraction beam of VB grating

Fly cutting of Si grismNormalized specifications and performance of VB, SR and RFT gratings
AoI [] Order*
27.8
27.8
45
28.4
4545
45

VPH grism (corrected)

1113+7+7+7+n1/n0

L:S

Duty t [Λ]**

1.54
1.54
1.55
1.6/1.33
1.54
1.54

1:01 0.5
2:01 0.67
4:01 0.8
9:01 0.9
19:01 0.95
-2
2.5
43
1.8
1.8

Aspect Peak eff. BandwidthRemarks
(S:t)
[%]
[λ]***
1:4~90%0.68
MOIRCS, K band
1:7.5~93%
0.77
MOIRCS, K band
1:14~95%
0.33
WFOS, etc.
1:30~75%
MOIRCS, echelle
1:36
~75%
WFOS, VB grating~80%†
WFOS, SR reflection grating~83%
WFOS, RFT grating*Where + indicates additional orders. **Normalized by grating period: Λ. ***Normalized by peakwavelength: λ0 †Efficiency of p polarization is significantly shifted toward longer wavelength.

VB grating

Fly cutting of Ge grism

p-pol.

VB grating

Schematic representation of VB grating (left), diffraction efficiencies of s (TE, middle) and p (TM, right)
polarizations VB grating of θ0=45without anti-reflection coating, n1=1.0, n2=1.54, Λ=5µm, L&S = 4.75:0.25[µm], t = 9µm.

Surface relief (SR) reflection gratings-pol.

p-pol.

Schematic representation of SR grating with Littrow configuration. (left), diffraction efficiencies of s (TE, middle)
and p (TM, right) polarizations* for SR grating of θ0=45 with Al mirror (thickness: 100 nm).

Reflector facet transmission (RFT) gratings-pol.

Si grism: α = 4.2,Λ= 17.09µm.

SEM photograph ofGe grism.

Ge grism α = 3.41,
Λ= 17.07µm.

Efficiency of prototype Si grism(including reflection loss).

Transmission of Si and Ge(including reflection loss).

Summary

VB, SR and RFT gratings for WFOSs-pol.

Microscope photographof Si grism.

p-pol.

Beam propagation in RFT grating for θ0=45 (left), diffraction efficiencies of s (TE, middle) and p (TM, right)
polarizations of the RFT grating without anti-reflection coating. Λ=5µm, θ0=45, n=1.54, γ=38.3.

Optimal Eff. [%]Statusofdevelopment
Order (l-l µm)~ 95
Performed prototype of silica VB gratings by using SOQ
st1 ~(0.2~3.0) substrate.

RFT grating

2th~LightSmythGrating

1stSi or Ge grism

1st~ 80
Compared diffraction efficiency with VB and SR gratings,(0.3~2.4) Planning the third trial fabrication in near future.
~ 100 Buy 3 transmission gratings of catalogue product for(0.8~3.0) MOIRCS J band. Ordered transmission gratings for H band.
~ 80
Performed direct diamond cutting of Si grisms. Planning(1.2~14) fabrication of a Si and Ge grisms.

Acknowledgements
We appreciate Mr. Kajiura of the Toyota Institute of Technology for their assistance on the trial
fabrications of the VB gratings. We utilize facility of the Advanced Technology Center of theNational Astronomical Observatory of Japan (NAOJ) for grating measurements, Nanotechnology
Platform Japan of the Ministry of Education, Culture, Sports, Science and Technology of Japan(MEXT) and RIKEN Center for Emergent Matter Science, for grating fabrications andperformance evaluations. This work is supported by the grant-in-aid of NAOJ for TMT strategic
basic R & D.