Point Defects in Ge-doped SiO_2 Glass-Their Structures and Roles in Nonlinear Optical Effects

(1)在掺Ge的SiO_2玻璃中，通过Kramers-Kronig关系引起光折变的吸收变化的产生机制尚不清楚。在本文中，我们研究了KrF准分子激光在5 eV附近的吸收变化与激光功率的关系。在5 eV附近的诱导吸收由4.50、5.08和5.80 eV三个不同的组分组成，每个吸收组分的增长行为强烈地依赖于能量密度。根据能量密度的不同，三种吸收成分达到不同的饱和程度。此外，高功率KrF准分子激光诱导的吸收被激光漂白，激光的能量密度约为诱导激光的二十分之一。结合数学分析的结果，发现每个吸收的诱导和漂白分别涉及一个双光子过程和一个单光子过程。它还被发现t…实验测量了KrF准分子激光辐照后，Ge掺杂二氧化硅玻璃的微秒量级光吸收随时间的变化。在3 eV以上的吸收与3.1 eV的发光具有相同的时间常数，由此证实了吸收的变化是由于电子从最低激发态三重态向上能态的激发所致。(3)用KrF(5.0 eV)准分子激光和同步辐射激发的光致发光(PL)表征了氧离子注入形成的SiO_2埋层中的缺陷。在4.3 eV和2.7 eV处观察到两个光致发光带，4.3 eV处有5.0和7.4 eV两个光致发光激发带，其衰减时间分别为5.0 eV激发4.0 ns和7.4 eV激发2.4 ns。测得2.7 eV光致发光带的衰变时间为9.7ms。这些结果与在缺氧型块体二氧化硅玻璃中观察到的4.3 eV和2.7 eV发光带非常相似，并归因于氧空位。通过光致发光强度随薄膜厚度的变化，认为埋藏的SiO_2膜在整个氧化物中含有大量的氧空位缺陷。较少

(1) The generation mechanism of the absorption changes, which cause a photorefractive change through the Kramers-Kronig relation in Ge-doped SiO_2 glass, has not been clarified yet. In the present paper, we examined the laser-power dependence of the absorption changes around 5 eV,induced by a KrF excimer laser. The induced absorption around 5 eV is composed of three different components, centering at 4.50,5.08, and 5.80 eV.The increasing behavior of each absorption component depends strongly on the energy density. The three absorption components reach different saturation levels, depending on the energy density. Furthermore the absorption induced by a high-power KrF excimer laser is bleached by a laser, the energy density of which is about one-twentieth of the inducing laser. Combining the results of mathematical analysis, it was found that a two-photon process and a one-photon process are, respectively, involved with the induction and the bleach of each absorption. It was also found t … More hat the precursor defects, which causes the absorption change, is of an oxygen-deficient type.(2) Optical absorption change in the microsecond order in oxygen-deficient Ge-doped silica glass was measured as a function of time just after photon irradiation from a KrF excimer laser. The absorption above 3 eV was found to decay with the same time constant as that of the luminescence at 3.1 eV.From this, it is confirmed that the observed absorption change is due to the excitation of electrons from the lowest excited triplet state to an upper state.(3) Defects in buried SiO_2 films in Si formed by implantation of oxygen ions were characterized by photoluminescence (PL) excited by KrF (5.0 eV) excimer laser and synchrotron radiation. Two PL bands were observed at 4.3 and 2.7 eV.The 4.3 eV band has two PL excitation bands at 5.0 and 7.4 eV,and its decay time is 4.0 ns for the 5.0 eV excitation and 2.4 ns for the 7.4 eV excitation. The decay time of the 2.7 eV PL band is found to be 9.7 ms. These results are very similar to those for the 4.3 eV and the 2.7 eV PL bands, which are observed in bulk silica glass of an oxygen-deficient type and attributed to the oxygen vacancy. Through the change in the PL intensity with the film thickness, the buried SiO_2 film is considered to contain the oxygen vacancy defects in a high amount throughout the oxide. Less