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Method for producing a hologram by picosecond laser

外国特許コード F110003898
整理番号 E06009EP
掲載日 2011年7月6日
出願国 欧州特許庁(EPO)
出願番号 03705133
公報番号 1475678
公報番号 1475678
出願日 平成15年2月13日(2003.2.13)
公報発行日 平成16年11月10日(2004.11.10)
公報発行日 令和2年10月14日(2020.10.14)
国際出願番号 JP2003001514
国際公開番号 WO2000069416
国際出願日 平成15年2月13日(2003.2.13)
国際公開日 平成15年8月21日(2003.8.21)
優先権データ
  • 特願2002-036010 (2002.2.13) JP
発明の名称 (英語) Method for producing a hologram by picosecond laser
発明の概要(英語) Disclosed is a method of producing a hologram through a two-beam laser interfering exposure process, which comprises emitting a coherent laser light with a pulse width ( tau ) ranging from greater than 900 femtoseconds to 100 picoseconds and a laser power of 10 mu J/pulse or more using a solid-state laser as a light source, dividing the pulses light from the laser into two beams, controlling the two beams temporally and spatially in such a manner that the two beam are converged on a surface of or inside a workpiece for recording a hologram while matching the respective converged spots of the two beams with one another temporally and spatially to create the interference therebetween so as to record a surface-relief hologram on the surface of the workpiece or an embedded hologram inside the workpiece in an irreversible manner. The present invention can solve a problem with a conventional process of recording a hologram in a non-photosensitive material in an irreversible manner using interfering femtosecond laser pulses, specifically, distortion in the waveforms of pulsed laser beams and resulting instability in recording of an embedded hologram due to a non-linear optical interaction between the femtosecond laser pulses and air/the material. <IMAGE>
従来技術、競合技術の概要(英語) BACKGROUND ART
A method of preparing holographic optical elements or diffraction grating elements by utilizing the interference between laser beams is one of well-known techniques commonly used for years. The diffraction gratings produced by the interfering laser exposure are applied to various devices, such as spectrometer, distributed feedback semiconductor lasers or fiber grating devices. The laser for use in the production process of such diffraction gratings includes a He-Cd laser, an argon ion laser, an excimer laser, a continuous wave laser or a nanosecond pulsed laser. These lasers can emit a beam with a relatively low energy density, and thereby a material to be processed is required to have photosensitivity. The inventors previously developed a method of producing holographic optical elements by utilizing the interference between femtosecond leaser beams.
In this method, the femtosecond laser beams having a high energy density makes it possible to record a diffractive grating in almost all materials without the need for photosensitivity in a material to be processed. However, the femtosecond pulsed beam having an excessively high energy at a pulse peak causes increase in the non-linear optical interaction of the beam with air and a hologram-recording material, resulting in difficulties in stably recording a hologram.
Particularly, in the process of forming an embedded hologram in the inside of a material, it is essential to propagate laser pulses with a high energy through the material, and the waveform of the laser pulses is liable to be irregularly deformed. Thus, in order to suppress such a distortion, it is required to select a specific material, or set the laser energy just below the threshold value for the encoding for recording and allowing the influence of the non-linear optical interaction to be ignored. However, the acceptable energy range of the laser pulse is narrow, and it is extremely difficult to record a hologram having a desired performance.
特許請求の範囲(英語) [claim1]
1. A method of producing a hologram in a non-photosensitive material through a two-beam laser interfering exposure process, said method comprising:
emitting a coherent femtosecond pulsed laser light with a laser energy of 10 µJ/pulse or more using a solid-state laser as a light source;
stretching the pulse width of the femtosecond pulsed laser light for hologram recording;
dividing the stretched pulsed light from said laser into two beams (B1, B2); and
converging the two beams (B1, B2) on a surface of a non-photosensitive workpiece (S1) or within the non-photosensitive workpiece (S1) for recording a hologram in such a manner that the respective converged spots of the two beams (B1, B2) are matched with one another to create the interference therebetween so as to record a surface-relief hologram on the surface of the non-photosensitive workpiece (S1) or an embedded hologram within the non-photosensitive workpiece (S1) in an irreversible manner;
wherein the stretching step comprises:
chirping the wavelength of the femtosecond pulsed laser light and adjusting a pulse-width compression optical circuit to stretch a pulse width of the femtosecond pulsed laser light into a range from greater than 1 picosecond to 10 picoseconds while maintaining the energy per pulse.

[claim2]
2. The method as defined in claim 1, wherein said converged spots of said two beams (B1, B2) are temporally and spatially matched with one another by adjusting an optical delay circuit (M4, M5) and a beam-converging optical system while monitoring the intensity of either one of the third harmonic generation wave of the femtosecond laser light induced by the non-linearity of air, and the second harmonic generation wave of the femtosecond laser light induced by a non-linear optical crystal.

[claim3]
3. The method as defined in either one of claims 1 or 2, wherein said embedded hologram is recorded by having the converged spots of the two beams (B1, B2) match with one another in a depth of 10 µm or more from the surface of the non-photosensitive workpiece (S1) in an irreversible manner.

[claim4]
4. The method as defined in either one of claims 1 or 2, wherein said two-beam laser interfering exposure process is performed plural times to record a plurality of identical or different holograms at one or more positions in a multiple manner within the non-photosensitive workpiece (S1) formed in one piece.

[claim5]
5. The method as defined in either one of claims 1 or 2, including, after recording the hologram on the surface of the non-photosensitive workpiece (S1) or within the non-photosensitive workpiece (S1), changing the depth of said matched spot from the surface of the non-photosensitive workpiece (S1) to record an additional hologram in a multilayer manner.

[claim6]
6. The method as defined in either one of claims 1 to 5, wherein said non-photosensitive workpiece (S1) is made of a material selected from the group consisting of silica glass, BK 5 glass, multi-component glass, MgO, LiNbO3, Al2O3, ZnS, ZnSe, ZnO, YSZ (yttria stabilized zirconia), AIN, GaN, AlAs and GaAs, and mixtures thereof, and formed in bulk or thin-film.

[claim7]
7. The method as defined in either one of claims 1 to 5, wherein said non-photosensitive workpiece (S1) is made of a metal material selected from the group consisting of gold, silver, platinum, copper, nickel, chromium, aluminum, cadmium, tantalum, hardmetal and metal-silicon.
  • 出願人(英語)
  • JAPAN SCIENCE AND TECHNOLOGY AGENCY
  • 発明者(英語)
  • HOSONO HIDEO
  • HIRANO MASAHIRO
  • KAWAMURA KENICHI
  • MIURA TAISUKE
  • KAMIOKA HAYATO
国際特許分類(IPC)
指定国 Contracting States: DE FR GB
参考情報 (研究プロジェクト等) ERATO HOSONO Transparent ElectroActive Materials AREA
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