Production method of optical synthetic quartz glass, optical synthetic quartz glass, and annealing furnace

A method of producing an optical synthetic quartz glass, said method comprising a step of raising the temperature of a colunmar optical synthetic quartz glass preform in a furnace to a temperature in a range of from 800° C. to 1200° C., and after preserving the temperature of the preform in said range for a definite time, lowering the temperature, the temperature being lowered with a temperature difference of from 1 to 20° C. between a first temperature T1 at an internal furnace position located outward from a center of at least one of an upper and a lower surface, said surfaces being light transmitting surfaces of the optical synthetic quartz glass preform, by a first distance and a second temperature T2 at an internal furnace position located outward from an outer peripheral side surface of the optical synthetic quartz glass preform by a second distance, at temperature-lowering rates of from 2 to 50° C./hour;

• wherein in the temperature-lowering step, the first temperature T1 is lower than the second temperature T2, and wherein the temperatures T1 and T2 are measured and controlled so as to maintain said temperature difference.

A method of producing an optical synthetic quartz glass, said method comprising a step of raising the temperature of a columnar optical synthetic quartz glass preform to a temperature in a range of from 800° C. to 1200° C., and after preserving the temperature of the preform in said range for a definite time, lowering the temperature, the temperature being lowered with a temperature difference of from 1 to 20° C. between a first temperature T1 at an internal furnace position located outward from a center of at least one of an upper and a lower surface, said surfaces being light transmitting surfaces of the optical synthetic quartz glass preform, by a first distance and a second temperature T2 at an internal furnace position located outward from an outer peripheral side surface of the optical synthetic quartz glass preform by a second distance, at temperature-lowering rates of from 2 to 50° C./hour;

• wherein in the temperature-lowering step, the first temperature T1 is higher than the second temperature T2 and wherein the temperatures T1 and T2, are measured and controlled so as to maintain said temperature difference.

A method of producing an optical synthetic quartz glass, said method comprising a step of raising the temperature of a columnar optical synthetic quartz glass preform to a temperature in a range of from 800° C. to 1200° C., and after preserving the temperature of the preform in said range for a definite time, lowering the temperature, the temperature being lowered with a temperature difference of from 1 to 20° C. between a first temperature T1 at a position located outward from a center of at least one of an upper and a lower surface, said surfaces being light transmitting surfaces of the optical synthetic quartz glass preform, by a first distance and a second temperature T2 at a position located outward from an outer peripheral side surface of the optical synthetic quartz glass preform by a second distance, at temperature-lowering rates of from 2 to 50° C./hour;

• wherein in the step of temperature lowering, separate temperature-controlling mechanisms are used for a surface parallel to the light transmitting surface and a surface perpendicular to the light-transmitting surface.

A method of producing an optical synthetic quartz glass, said method comprising a step of raising the temperature of a columnar optical synthetic quartz glass preform to a temperature in a range of from 800° C. to 1200° C., and after preserving the temperature of preform in said range for a definite time, lowering the temperature, wherein the temperature is lowered with a temperature difference of from 1 to 20° C. between a first temperature T1 of a light transmitting surface of the optical synthetic quartz glass preform and a second temperature T2 of an outer peripheral side surface of the optical synthetic quartz glass preform with said temperatures lowering at rates of from 2 to 50° C./hour, wherein, in the temperature-lowering step, the first temperature T1 is lower than the second temperature T2;

• wherein in the step of temperature lowering, separate temperature-controlling mechanisms are used for a surface parallel to the light transmitting surface and a surface perpendicular to the light-transmitting surface.

A method of producing an optical synthetic quartz glass, said method comprising a step of raising the temperature of a columnar optical synthetic quartz glass preform to a temperature in a range of from 800° C. to 1200° C., and after preserving the temperature of preform in said range for a definite time, lowering the temperature, wherein the temperature is lowered with a temperature difference of from 1 to 20° C. between a first temperature T1 of a light transmitting surface of the optical synthetic quartz glass preform and a second temperature T2 of an outer peripheral side surface of the optical synthetic quartz glass preform with said temperatures lowering at rates of from 2 to 50° C./hour, wherein, in the temperature-lowering step, the first temperature T1 is higher than the second temperature T2, the light transmitting surface being substantially entirely at the first temperature T1 and the outer peripheral side surface being substantially entirely at the second temperature T2.

A method of producing an optical synthetic quartz glass, said method comprising a step of raising the temperature of a columnar optical synthetic quartz glass preform to a temperature in a range of from 800° C. to 1200° C., and after preserving the temperature of preform in said range for a definite time, lowering the temperature, wherein the temperature is lowered with a temperature difference of from 1 to 20° C. between a first temperature T1 of a light transmitting surface of the optical synthetic quartz glass preform and a second temperature T2 of an outer peripheral side surface of the optical synthetic quartz glass preform with said temperatures lowering at rates of from 2 to 50° C./hour, wherein, in the temperature-lowerinig step, the first temperature T1 is higher than the second temperature T2,

• wherein in the step of temperature lowering, separate temperature-controlling mechanisms are used for a surface parallel to the light transmitting surface and a surface perpendicular to the light-transmitting surface.