Femtosecond Pulsed Laser Deposition of Indium on Si(100)

Abstract

We have been studying the refractive index changes and vacancies that are induced in transparent materials like glass by the irradiation of femtosecond laser pulses. This technique has been applied to fabricate three-dimensional photonic structures such as optical data storages, waveguides, gratings, and couplers inside a wide variety of transparent materials. We report micro-fabrication experiments of optical elements in glasses with femtosecond laser pulses, including fabrication of couplers, Bragg gratings, and zone plates and holograms on the surface of glass. A trial fabrication experiment on organic materials is also reported.Keywords: femtosecond, laser pulse, fabrication, three-dimensional, optical elements INTRODUCTIONMicromachining by femtosecond laser pulses in transparent materials has recently received much attention. When femtosecond laser pulses are focused inside the bulk of a transparent material, the intensity in the focal volume can become high enough to cause nonlinear absorption, which leads to localized modification in the focal volume, while leaving the surface unaffected. Recent demonstrations of three-dimensional micromachining of glass using femtosecond laser pulses include waveguides [1-9], couplers [10][11][12][13][14], gratings [15][16][17][18][19][20][21][22][23], and three-dimensional binary data storage [24][25][26][27], lenses [28,29], and channels [30][31][32][33]. We present, in this paper, fabrication experiments of three-dimensional photonic devices. Contents of this paper are based on those presented in the International Symposium on Advances and Trends in Fiber Optics and Applications (ATFO 2004), October 11-15, 2004 , Chongqing University, Chongqing, China, and The 6th International Symposium on Laser Precision Microfabrication -SCI-ENCE AND APPLICATIONS -(LPM2005), April 4-8, Williamsburg, Virginia, USA. A 2-mm-long directional coupler to split the optical beam intensities into 1:1 at a wavelength of 632.8 nm is demonstrated [14]. We present in this paper the fabrication experiment of volume gratings induced in silica glass by filamentation of ultrashort laser pulses [17]. We stacked the layers with a period of several microns and fabricated volume gratings. To measure the diffraction efficiency we entered a He-Ne laser beam at the wavelength of 632.8 nm to the grating with the Bragg angle. The maximum diffraction efficiency was 74.8% with the grating that had the period of 3 µm, and the thickness of 150 µm. Fresnel zone plates by embedding voids in silica glass are demonstrated [28]. Holographic data storage on fused silica, soda-lime, and lead glasses with a single 130 fs laser pulse at a wavelength of 800 nm is presented [22]. After the sample is exposed to the interference fringe pattern of the object beam and the reference beam, a relief hologram is recorded through surface ablation. The recorded information can be reconstructed without destruction of the hologram when the power of the reference beam is reduced below the ablation threshold. Finally, we show