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KLMNOPQRSTUV
Status on Developments of Novel Gratings

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2 /<=>(6 =6?,4INAF Osservatorio Astronomico di Brera, Italy,

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5CDEFG TMTHIJ

VPH (Volume phase holographic) grating
Used fordetermination of thehighest z galaxy

VPH grism with
ZnSe prism

Diffraction efficiency of a surface relief grating (left) for TE
polarization decreases steeply below 4 !/". Diffraction efficiencyof a VPH grating (right, #n ~ 0.02) for TE (or TM) polarizationachieves up to 100% below 4 !/".
(Oka et al., SPIE 5005, 2003)

VPH grism

Echelle grism

VPH grating(360 g/mm, Blaze: 800nm,!/"=3.47, R~1,600 )Surface relief grating(300 g/mm, Blaze: 750 nm,!/"=4.44, R~1,400 )Surface relief grism

Grisms for FOCAS of the Subaru
Telescope. Size: 110 ! 106 ! 106(max). 4 surface relief grisms: 300 <R < 1,400. 1 Echelle grism: R~2,500.
8 VPH grisms (3 grisms with ZnSeprisms): 1,600 < R < 7,000.
Developed by in collaboration withJapan Wemen’s Univ., NAOJ andRIKEN.
(Ebizuka et al., PASJ, 63, 2011)

Diffraction efficiencies of VPH grating and surface
relief grating for moderate dispersion of FOCAS.

Limitations of VPH grating' # ( n max $ n min ) t *"S = sin 2 (+) %( n max + n min ) sin2& ,$ =31.7 deg.

' # (n $ n ) t cos2% *"P = sin2 ( max min+) &(n max + n min ) sin2% ,3rd#n=0.10#n=0.07

6th10th!

!

#n=0.04#n=0.02$ =30.9 deg.
KMPR-1035

Diffraction efficiency of a VPH grating
decreases toward higher orders.
(Oka et al., SPIE 5290, 2004)

Volume binary gratingBand width of a VPH grating becomes narrow in
diffraction angle ($) above 30° because semi-amplitude ofindex modulation (#n) of dichromated gelatin (DCG) is up
to 0.15 ~ 0.2.
(Baldry et al., PASP, 116, 2004)
f = 0.5

Measured polarized diffraction
efficiencies of VPH grating.

Calculated polarization diffraction
efficiencies vs. t of a VPH grating.

nave= (nmax - nmin)/2 = 1.53, !=0.984 µm,
t = 20 µm, ! =19.8° @1.02 µm.

#n = (nmax - nmin)/2 = 0.017(Ebizuka et. al. PASJ, 63, 2011b)

Birefringence VPH grating

Ge immersion gratingn Smax " n Smin(n " n Pmin ) cos2# P= Pmax
(n Smax + n Smin )sin2# S (n Pmax + n Pmin )sin2# P!

n Smax " n Smin(n Pmax " n Pmin ) cos2$ P=(n Smax + n Smin ) # 2sin$ S cos$ S ( n Pmax + n Pmin ) # 2sin$P cos$ P!
$n Smax " n Smin ( n Pmax " n Pmin ) cos2# P$cos # Scos# P!

• #n = (nmax-nmin)/2 ~ 1.5. (Gerritsen & Jepsen,• Diffraction efficiencies Appl. Opt., 37,1998)
of S and P polarization Filling factor: f=w/$
coincide with each other n =1.46, n =1.0,
HL
by tuning of f and t for" =45 deg.
given # n.
• Aspect ratio(Gupt & Peng, Appl.
t : w = 1:20 ~ 100.
Opt., 32, 1993)

f = 0.2

Volume binary grating for higher diffraction orders!

Fabrication of a germanium immersion grating with size of
30 by 30 by 72 spent ~ 400 hours by means of a nanoprecision machine and ELID grinding method.
(Ebizuka et. al. SPIE 4842, 2003)

Silicon immersion grating
Birefringence VPH grating and calculated polarized
diffraction efficiencies versus grating thickness t.

Birefringence binary Bragg (3B) grating

Test fabrication of a silicon
immersion grating for nearinfrared is going to start byusing an ultra highprecision machine anddiamond tools incollaboration with RIKEN.

Novel immersion grating© DISCO• Machining of dicing sawmakes smooth surface.
• A dicing saw offers easytooling.
• Fabrication of a grating with size of 120 by 120 by 270 is
supposed to be several 100 hours.

nH=1.89, n L=1.46, " =41.3°, f = 0.1, t:w = 1:22
(Bianco & Ebizuka, SPIE, 8450, 2012)(Ebizuka et. al. SPIE 6273, 2006)

Photolithography with photo resist for thick film layer
Test fabrication ofvolume binary gratings(250, 333 and 500
grooves /mm) are
performing incollaboration withNanotechnology Platform
Program of Toyoda
Technological Institute.
Nippon Kayaku, KMPR 1000

ConclusionsPolarized diffraction efficiencies
of Dicson’s VPH grating(Polarizer) calculated byKogelnik method.
nL= 1.46, nH=1.54, ! B =48.5°.

t:w = 1:20~100 !"1:4~20• VPH grating achieves high dispersion and high efficiency,
as well as versatile for moderate dispersion.
• Volume binary grating achieves wide bandwidth and utilizes
for an echelle spectrograph. Test fabrication of photolithography is performing.
• Volume birefringence gratings achieve high efficiency up toPolarized diffraction
100% for non polarized light.
efficiencies of 3B grating• Test fabrication of a silicon immersion grating is undercalculated by RCWA.
nL=1.46, ns= 1.544, np = 1.60,preparation.
!B =45°.
• Novel immersion grating achieves smaller scattering loss
(Ebizuka et. al. SPIE 8450, 2012)
and able to reduce fabrication cost.