5H8GE<-*4M?96 VI
7F .1, #2 N 1,C= @1,D> + 1, "& I1, 1 2,  J3,2 PK3, : ()4, = 4, 0L /5, !$ '5, O1 51;A, 2 I=%%, 3 3, , 4 3;, 5 B,

Reflection and transmission gratingDiameter 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).
→Transmission grating is able to realize perfect Littrow mounting.
Spectrum

CameraCollimator

Transmissiongrating
CameraSlit

Slit

VPH grating

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

q 2 < 90n = 1.5, q 0 ≤ 30
n = 1.8, q 0 ≤ 36
n = 2.3, q 0 ≤ 45
n = 3.0, q 0 ≤ 54

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

 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.
Collimator

Echelle grism (Volume binary grating) for MOIRCS

Spectrum

Reflection grating

WFOS: Wide Field Optical SpectrographSlit width: 0.3”
5th, R= 4,630@1.02 µm

TMT FOCAL SURFACE& WFOS SLIT MASK(1086  392 mm)

RED FOLD
RED DETECTOR

BLUE DETECTOR
BLUE CAMERAX-DISPERSION PRISMS

RED CAMERAGRATINGS

The first generation instrument for TMT. R= 500~5,000(150~7.500 goal) @0.75” slit

4th, R= 4,420@1.25 µm
3rd, R= 4,270@1.65 µm

COLLIMATOR
DICHROIC (~1m x ~1.7m)

Gratings for WFOS
Incident and diffraction angle: q 0 = 36~53 
Period : Λ= 2~5 µm
Siz : 400 x 550~750 [mm]S-pol.

Diffraction efficiency of volume
binary grating (RCWA). L&S=
4.6:0.5 [µm], θ0=28.4  , n 1=1.33,
n 2=1.6, n 3=1.6, t=16 µm.

Fabrication process of the volume binary grating
Reactive Ion beam

ResistSiliconSilicasubstrate

Reflector facet transmission (RFT) grating

Schematic representationof volume binary grating.

Schematic representationof echelle grism

P-pol.
Upper
substrate

Resist mask
patterning onto
SOQ* substrate

Cycle etching(Bosch process)Silicon mold for
replication test

Oxidation ofsilicon surface

2~3 times

High-index
resin
Silicasubstrate

Schematic representation ofRFT grating,Diffraction efficiency of RFT grating (RCWA). Λ=5µm, θ0=45, n=1.54, γ=38.3.

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

Removal of oxide

Oxidation oftotal silicon* SOQ: Silicon on Quartz

Volume binary grating of silicon.
Fabricated by Nanotechnology platformof Toyota Institute of Technology.

Grism for MIMIZUKU

Entrance facet

Tilted toright 30

Top view

Tilted toleft 30

5.0μm

Fly cutting of Si grism

First trial fabrication
Second trial fabrication
SEM photograph of master grating.

Shaper cutting of mold.

Microscope photographof Si grism.

Si grism: α = 4.2,Λ= 17.09µm.

Efficiency of prototype Si grism(including reflection loss).

Fabrication method for RFT grating and for SR grating of MOIRCS hybrid grism
Glass substrate
Clear resin
Master grating

Shaper cutting of master grating.
Work Ni-P alloy of non-electrolytic plating

Replication

FinishLightSmyth Transmission Grating

Fly cutting of Ge grism

for MOIRCS J and H band grisms instead of VPH grisms

Catalogue value

Diffraction efficiency
at blazed angle

Ge grism α = 3.41,
Λ= 17.07µm.

Transmission of Si and Ge(including reflection loss).

Summary

Current status
Size: φ130 (Max)l range : 800~2,500nm
AOI*: 30~68
*Angle of Incidence

SEM photograph ofGe grism.

Optimal Eff. [%]Order (l-l µm)

Status of development

RFT grating

2th~~ 80
Performed diamond shaper cutting of master gratings.
(0.3~2.4) Planning the third trial fabrication in this April.

Hybrid grism

2rd~

Performed diamond shaper cutting of a master grating and~ 70
replication. Planning fabrication of optimum master grating(0.3~2.4)
for MOIRCS medium dispersion grism in this March.

LightSmythGrating

1st~ 100 Ordered numerical calculations of performance evaluation(0.8~3.0) for MOIRCS J and H band grisms and samples.

Volume binary(VB) grating

1st~~ 80
Performing replication test by using a Si grating and test
(0.2~3.0) fabrications of silica VB gratings by using the new technique.

Si or Ge grism

1st~ 80
Performed direct diamond cutting of Si grisms. Planning(1.2~14) fabrication of a Si and Ge grisms in this November.

MOIRCS H bandgrism (corrected)

Acknowledgements
800nm, 1397 g/mm, measured

1,650nm, 677 g/mm, converted
Integrating sphere(detector)

Transmission
Monochrograting matic light

Measurement for diffraction efficiency at blazed angle.

Measurement for peakefficiency of super blaze.

We appreciate Mr. Kajiura of the Toyota Institute of Technology for their assistance on the trial
fabrications of the VB gratings. The experiments of replication process using the prototype moldwere performed by Dr. Makino in cooperation with Shimadzu Corp. SEM photographs weretaken by Mr. Esaki of NAOJ, Mr. Inoue and Dr. Akiyama of RIKEN. We utilize facility of theAdvanced Technology Center of the National Astronomical Observatory of Japan (NAOJ) forgrating 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 and performance evaluations. This work is supported by thegrant-in-aid of NAOJ for TMT strategic basic R & D.