Abstract

An ultralow refractive index is very advantageous when one designs antireflective coatings. We successfully obtained high-quality MgF2 thin films with ultralow refractive indices from autoclaved sols prepared from magnesium acetate and hydrofluoric acid. The MgF2 films consist of nanosized particles, and they have high laser-exposure durability at 193nm. The reflectance of the antireflective coating with five layers, of which the top layer is formed by our method, is lower than 0.6% in the incident angle range of 0°–60° at 193nm.

© 2006 Optical Society of America

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References

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  1. B. E. Yoldas, 'Investigations of porous oxides as an antireflective coating for glass surfaces,' Appl. Opt. 19, 1425-1429 (1980).
    [CrossRef] [PubMed]
  2. I. M. Thomas, 'High laser damage threshold porous silica antireflective coating,' Appl. Opt. 25, 1481-1483 (1986).
    [CrossRef] [PubMed]
  3. I. M. Thomas, 'Porous fluoride antireflective coatings,' Appl. Opt. 27, 3356-3358 (1988).
    [CrossRef] [PubMed]
  4. T. Murata, H. Ishizawa, I. Motoyama, and A. Tanaka, 'Investigations of MgF2 optical thin films prepared from autoclaved sol,' J. Sol-Gel Sci. Technol. 32, 161-165 (2004).
    [CrossRef]

2004 (1)

T. Murata, H. Ishizawa, I. Motoyama, and A. Tanaka, 'Investigations of MgF2 optical thin films prepared from autoclaved sol,' J. Sol-Gel Sci. Technol. 32, 161-165 (2004).
[CrossRef]

1988 (1)

1986 (1)

1980 (1)

Ishizawa, H.

T. Murata, H. Ishizawa, I. Motoyama, and A. Tanaka, 'Investigations of MgF2 optical thin films prepared from autoclaved sol,' J. Sol-Gel Sci. Technol. 32, 161-165 (2004).
[CrossRef]

Motoyama, I.

T. Murata, H. Ishizawa, I. Motoyama, and A. Tanaka, 'Investigations of MgF2 optical thin films prepared from autoclaved sol,' J. Sol-Gel Sci. Technol. 32, 161-165 (2004).
[CrossRef]

Murata, T.

T. Murata, H. Ishizawa, I. Motoyama, and A. Tanaka, 'Investigations of MgF2 optical thin films prepared from autoclaved sol,' J. Sol-Gel Sci. Technol. 32, 161-165 (2004).
[CrossRef]

Tanaka, A.

T. Murata, H. Ishizawa, I. Motoyama, and A. Tanaka, 'Investigations of MgF2 optical thin films prepared from autoclaved sol,' J. Sol-Gel Sci. Technol. 32, 161-165 (2004).
[CrossRef]

Thomas, I. M.

Yoldas, B. E.

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Figures (8)

Fig. 1
Fig. 1

Simulated relation between the refractive index of the top layer of an antireflective (AR) coating and the reflectance: Ave., average; s, s-polarized light; p, p-polarized light. Simulation conditions: substrate, SiO 2 glass; wavelength, 193 nm ; incident angle, 58°; stack, five layers (only the refractive index of the top layer was changed).

Fig. 2
Fig. 2

Relation between the refractive index and the packing density of MgF 2 porous film.

Fig. 3
Fig. 3

TEM images of the primary particles of MgF 2 in the disperse medium of sols: (a) not autoclaved, (b) autoclaved at 140 °C, (c) autoclaved at 180 °C.

Fig. 4
Fig. 4

X-ray diffraction patterns of powders obtained from sols: (a) not autoclaved, (b) autoclaved at 120 °C, (c) autoclaved at 180 °C.

Fig. 5
Fig. 5

SEM images of MgF 2 thin films: (a) not autoclaved, (b) autoclaved at 120 °C, (c) autoclaved at 180 °C.

Fig. 6
Fig. 6

Effect of the autoclave treatment on the refractive indices at 193 nm of MgF 2 thin films on SiO 2 glass substrates. Regardless of film thickness, the refractive indices of the thin films made from sols autoclaved at 140 °C were lower than those of the thin films made from nonautoclaved sols.

Fig. 7
Fig. 7

Transmittance of CaF 2 substrate with antireflective coatings made from the autoclaved sol on both sides: substrate, CaF 2 disk ( ϕ 30 mm ,   thickness = 3 mm ) ; refractive index of MgF 2 thin film, 1.22 at 190 nm ; film thickness, 34 nm ; stack, single layer.

Fig. 8
Fig. 8

Reflectance of wedged SiO 2 substrate with hybrid antireflective coating on one side: substrate, wedge-shaped SiO 2 glass ( ϕ 30 mm ) ; refractive index of MgF 2 thin film, 1.18 at 193 nm ; stack, five layers (the four layers on the substrate side were formed by physical vapor deposition, and the top layer was formed by the solgel process).

Tables (1)

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Table 1 Laser-Exposure Durability of SiO 2 Substrate with Antireflective Coatings Made from the Autoclaved Sol on One Side a

Equations (2)

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( n f 2 1 ) / ( n f 2 + 2 ) = p ( n b 2 1 ) / ( n b 2 + 2 ) .
Mg ( CH 3 COO ) 2 + 2 HF MgF 2 + 2 CH 3 COOH .

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