We report the observation of space-selective oxidation of Mn 2ϩ to Mn 3ϩ in a transparent and colorless Mn and Fe ions codoped silicate glass at room temperature by using an 800-nm-femtosecond laser. Difference absorption spectrum of the glass after and before the irradiation of the focused infrared femtosecond pulsed laser showed that a portion of Mn 2ϩ ions near the focused part of the laser beam inside the glass were oxidized to Mn 3ϩ ions after the laser irradiation. Mn 3ϩ ions were stable

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... t the temperatures below 300°C. It is suggested that Mn 2ϩ ions act as hole trapping centers while Fe 3ϩ ions as well as active sites in the glass matrix act as electron trapping centers. A promising application was demonstrated for the fabrication of three-dimensional colored image inside a transparent material. Materials with three dimensionally modulated microstructures has potential applications in optical field. 1,2 Up to now, there have been much investigation on the threedimensional microfabrication. 3-5 Braun and Witzius have successfully fabricated three-dimensional structures of semiconductors by template-directed electrochemical deposition. 3 Cumpston et al. have succeeded in the fabrication of microoptical elements with two-photon photopolymerization. 4 Holographic lithography has been used to fabricate threedimensional photonic crystals, which have periodical dielectric structures and can manipulate light in much the same way that a superconductor manipulates electrons. 5 It is well known that laser light can be pulsed and focused to a spot of wavelength order. Ultrashort pulsed laser has been used as a powerful tool to clarify elementary processes, such as excitation-energy relaxation and both electron and proton transfer on nanosecond and picosecond time scales, that occur in a micrometer-sized area. 6,7 Ultrashort pulsed laser can also be used to make microscopic modifications to transparent materials. The reason for using this laser is that its electric field intensity can reach 100 TW/cm 2 , which is sufficient for inducing nonlinear optical effects in materials by use of a focusing lens, when the pulse width is 100 fs and the pulse energy is 1 J. The photoinduced reaction is expected to occur only near the focused part of the laser beam due to nonlinear optical processes. Up to now, there have been a lot of studies on the microscopic modifications in transparent materials by using femtosecond lasers. [8] [9] [10] [11] [12] [13] [14] Various induced structures can be produced by using pulsed laser operating at the nonresonant wavelength with pulse widths of the order of femtosecond; colored lines due to the formation of color center, refractive index spot due to densification and defect formation, microvoid due to remelting and shock wave, microcrack due to destructive breakdown, etc. 14 Composite structures were also observed after the focused femtosecond laser irradiation. 14 Promising applications using these phenomena have also been demonstrated for three-dimensional optical memory, integrated optical circuit, and optical display. [8] [9] [10] [11] [12] [13] [14] In this letter, we report the observation of space selective valence state manipulation of transition metal ions in transparent materials. We observed space selective, persistent photo-oxidation of Mn 2ϩ to Mn 3ϩ in a silicate glass by focusing 120 fs laser pulses from a regeneratively amplified Ti sapphire laser through a microscope objective lens. Absorption and electron spin resonance spectra were measured for the glass before and after the femtosecond laser irradiation. The mechanism of the phenomenon is also discussed. Glass composition of the Mn and Fe ions codoped silicate glass sample used in this study was 0.05Fe 2 O 3 •0.1MnO•70SiO 2 •10CaO•20Na 2 O͑mol %). Regent grade SiO 2 , CaCO 3 , Na 2 CO 3 , Fe 2 O 3 , and MnO were used as starting materials. An ϳ40 g batch was mixed, and placed into a platinum crucible. Melting was carried out in an electronic furnace at 1550°C for 1 h under the ambient atmosphere. Glass sample was obtained by quenching the melt to room temperature. The glass sample thus obtained was transparent and colorless. The glass sample was cut, polished, and subjected to experiments.