Evaluation method for thermal expansion properties of titania-containing silica glass body, and manufacturing method for titania-containing silica glass body

A method for evaluating thermal expansion properties of a glass body, the glass body comprising a TiO2—SiO2 glass or a fluorine doped TiO2—SiO2 glass,

• the method comprising:
• measuring a longitudinal wave sound velocity or transverse wave sound velocity of the glass body at a predetermined temperature Tx;
• obtaining a Raman spectrum of the glass body;
• analyzing the Raman spectrum to determine a ratio value I1/I0 or I2/I0 wherein a peak intensity at 440 cm−1 or 820 cm−1 is denoted by I0, a scattered peak intensity at 495 cm−1 is denoted by I1, and a peak intensity at 605 cm−1 is denoted by I2, and
• to determine a ratio value I3/I0 or I4/I0 when the peak intensity at 440 cm−1 or 820 cm−1 is denoted by I0, a peak intensity at 960 cm−1 is denoted by I3 and a peak intensity at 1.140 cm−1 is denoted by I4;
• calculating the coefficient of thermal expansion and/or the slope of the coefficient for thermal expansion by inserting the measured physical parameters obtained in equations (1) and/or (2);
• CTE at Tx=a1[A]+b1[B]+c1[C]+d1 (1),
• CTE-SLOPE at Tx=a2[A]+b2[B]+c2[C]+d2 (2)
• wherein
• [A] is a term containing a longitudinal wave sound velocity VL or a transverse wave sound velocity VS in the glass body;
• [B] is a term containing I1/I0 or I2/I0;
• [C] is a term containing I3/I0 or I4/I0;
• and a1, b1, c1, d1, a2, b2, c2, and d2 σre coefficients calculated by regression calculation by a least-square method from the relational expressions (1) and (2) employing TiO2—SiO2 glass or a fluorine doped TiO2—SiO2 glass samples of known composition using values of CTE and CTE-slope obtained by direct measurement.