JPS6224772B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to lead molybdate single crystal ultrasonic light modulation media. In recent years, applied devices using lasers, such as laser printers, have been put into practical use. Ultrasonic optical modulators are often used as laser beam modulators in high-resolution laser recording devices such as laser printers, and lead molybdate single crystals are increasingly used as optical modulation media. The crystal structure of lead molybdate single crystal is tetragonal, as shown in FIG. Here, the distance between the two planes {100} perpendicular to the crystal axis [100] and the distance between the two planes {010} perpendicular to the crystal axis [010] are 5.435 Å and [100 ] direction and [010] direction are crystallographically equivalent. Also, the {001} plane spacing perpendicular to [001] is 12.110 Å. When using a lead molybdate single crystal as an ultrasonic light modulation medium, as shown in FIG. Supported by sound absorber 4,
The [001] direction is the propagation direction of the ultrasonic wave, and the [100] or crystallographically equivalent [010] direction is the laser beam 5.
Modulated light 6 is obtained as the incident direction. Therefore, the quality required for lead molybdate single crystals is that when the {100} or {010} plane perpendicular to [100] or [010] is mirror-polished and observed visually or with a laser, the laser There must be no defects that cause scattering. Lead molybdate single crystal has a melting point of about 1060°C and is relatively easy to obtain in large crystals, but it is difficult to produce the homogeneous crystals required for optical modulation media. The causes of light scattering that appear during the growth of lead molybdate single crystals include air vesicles, subgrain boundaries, striae, and striations that appear along solid-liquid interfaces. When observed in a plane perpendicular to the pulling axis, the air vesicle is the third
As shown in Figure a, it often appears in the center of the crystal. Subgrain boundaries often appear around crystals, as shown in FIG. 3b. Furthermore, striae appear in a plate shape approximately parallel to the {010} plane, as shown in FIG. 3c. When the striations appearing along the solid-liquid interface are viewed in a plane parallel to the pulling axis, they appear, for example, as shown in FIG. 3d. Among these causes of scattering, the occurrence of air spores and subgrain boundaries can be suppressed relatively easily by changing the growth conditions. Furthermore, striations along the solid-liquid interface are said to occur due to periodic temperature changes caused by shaft rotation or melt convection, and it is generally difficult to suppress their occurrence. Therefore, in the conventional lead molybdate single crystal light modulation medium, when a single crystal with [100] as the pulling axis is grown, air pores and subgrain boundaries in the {100} plane can be easily eliminated. but,
{010} Since it is difficult to eliminate striations at the in-plane solid-liquid interface, {100} does not cause scattering.
It was cut out so that the laser would be incident on it, that is, the direction of laser incidence would be parallel to the pulling axis. This is the case when the diameter of the single crystal is about 30φ or less, and in this case there are relatively few striae appearing in {100}, so it is advantageous in terms of yield as an optical modulation medium. However, when the diameter of the lead molybdate single crystal exceeds approximately 30φ, striae occur more frequently. Therefore, in the conventional optical modulation medium having the {100} plane as the incident surface, the presence of striae on the laser incident surface results in a decrease in yield. Furthermore, with the increase in diameter, it has become possible to suppress the solid-liquid interface striations, which had been considered difficult to suppress, to such an extent that they are no longer a cause of scattering. An object of the present invention is to provide a high-yield optical modulation medium using a lead molybdate single crystal having a diameter of about 30φ or more. The present invention is a lead molybdate single crystal light modulation medium characterized by having a lead molybdate single crystal having a [100] pull axis and having a {010} plane as a laser transmission plane. This will be explained in detail in Examples below. Referring to FIG. 4, a method of cutting out the light modulating medium 41 of the present invention from a lead molybdate single crystal with a diameter of 40φ grown using a [100] seed crystal so that the pulling axis 42 is in the [100] direction. This is what is shown. Slice the single crystal into rounds according to the specified dimensions. The plane of the sliced single crystal, that is, {100}, and the planes perpendicular thereto {010} and {001} are planed by X-ray diffraction to produce dice-shaped blocks. Then, the single crystal block is processed so that {010} becomes the laser transmitting surface in accordance with the dimensions of the optical modulation medium. In the light modulation medium prepared in this way, even if there are plate-like striae parallel to {010} within the cross-section plane of the single crystal, that is, within {100}, the laser beam is directed perpendicularly to the plate-like striae. Since the light is incident, there is little scattering due to striae. Further, Table 1 shows the measurement results of the light transmittance of the optical modulation medium of the example in the optically polished state when the laser incidence axis 43 is [100] and [010].

[Table] It can be said that the optical modulation medium has better characteristics when the [010] axis is selected as the laser incidence axis. Furthermore, when the [010] axis is the laser incidence axis, the light transmittance of the completed light modulation medium with anti-reflection coating applied to {010} is over 90% at a wavelength of 488 nm, making it sufficient for use as a light modulator. be. As described above, the present invention selects the plane {010} parallel to the pulling axis [100] as the laser incidence plane, where solid-liquid interface striations, which were conventionally considered difficult to remove, should be observed. , a lead molybdate single crystal optical modulation medium is obtained which has a high production yield and eliminates the influence of scattering due to plate-like striae appearing parallel to the laser incidence plane.

[Brief explanation of the drawing]

FIG. 1 shows the crystal structure of lead molybdate single crystal. FIG. 2 shows a principle diagram of an ultrasonic optical modulator. 1 is a lead molybdate single crystal light modulation medium, 2 is a diaphragm, 3 is a high frequency oscillator, 4 is a sound absorber, 5 is a laser incident light, and 6 is a laser modulated light. FIG. 3 shows various defects that appear in a lead molybdate single crystal. FIG. 4 shows a method of cutting out a light modulation medium from a lead molybdate single crystal, which is carried out in the present invention. 41 is a lead molybdate optical modulation medium, 42 is a pulling direction, and 43 is a laser incident direction.

Claims (1)

[Claims] 1. An ultrasonic light modulation medium made of a lead molybdate single crystal with the [100] as the pulling axis, and the {010} plane as the laser light transmitting plane.