WAVE PLATE AND ITS MANUFACTURING METHOD
A wave plate is disclosed which includes a glass plate having a thickness of at least 0.1 mm and at most 5 mm. The glass plate has a plurality of strip-shaped birefringent regions substantially in parallel with a surface of the glass plate. The axial directions of the strip-shaped birefringent regions are the same with one another, and substantially in parallel with the surface of the glass plate. The wave plate has a retardation value of from 80 to 450 nm as measured with incident light having a wavelength of 540 nm.
1 . A process for producing a wave plate, comprising irradiating a glass plate with a laser beam condensed by a lens or a concave mirror so as to be focused in the glass plate or on a surface thereof, scanning the glass plate or the laser beam in this state to form a birefringent region, and thereby inducing a uniaxial birefringence.
2 . The process for producing a wave plate according to claim 1 , wherein the scanning of the laser beam is linear and parallel with the surface of the glass plate.
3 . The process for producing a wave plate according to claim 1 , wherein the scanning of the laser beam is repeated a plurality of times without changing the depth position of the focal point from the surface of the glass plate.
4 . The process for producing a wave plate according to claim 1 , wherein the scanning of the laser beam is repeated a plurality of times, and the process includes a step of changing the depth position of the focal point from the surface of the glass plate for each scanning.
5 . The process for producing a wave plate according to claim 1 , wherein the glass plate is irradiated with a plurality of beams split from the laser beam by a beam splitting element.
6 . The process for producing a wave plate according to claim 1 , wherein the laser beam has a wavelength of from 190 to 1,100 nm, a pulse width of at least 1 ns and at most 10 ms and a repetition rate of f, and provided that the irradiation fluence to the glass plate is F (J/cm 2 ), the condensed laser beam diameter is d (cm) and the scanning speed is s (cm/s), then, a value F·d·f/s being a product of the irradiation fluence F and the number of laser irradiations in the condensed laser beam diameter d·f/s, is at most 76,000 J/cm 2 .
7 . The process for producing a wave plate according to claim 1 , wherein the laser beam is a continuous wave CO 2 laser beam, and provided that the irradiation power density to the glass plate is PD (W/cm 2 ), the condensed laser beam diameter is d (cm) and the scanning speed is s (cm/s), then, a value PD·d/s being a product of the irradiation power density PD and the condensed laser beam passing time d/s, is from 120 to 200 J/cm 2 .