JPH05220189A - Ablation device by laser beam - Google Patents

Abstract

PURPOSE:To execute an ablation of uniform depth by a simple constitution by providing a reflecting system optical element for scanning a laser beam in the direction having an ununiform intensity distribution, and a diaphragm which can control an opening area, in the device being suitable for straightening a curvature of a diaphragm. CONSTITUTION:The device is provided with an excimer laser light source 10 in which an intensity distribution in the horizontal direction (x axis direction) of a beam is a roughly uniform distribution F (W), and an intensity distribution in the vertical direction (y axis direction) becomes a Gaussian distribution (gauss distribution) F (H), with regard to a cross sectional shape of an emitted laser beam. In such a state, the laser beam emitted therefrom is deflected by 90 deg. by plane mirrors 11, 12, respectively, and thereafter, is made incident on a dichroic mirror 13, sets an optical axis of an objective lens of an observing system and the laser beam to the same axial state, and is allowed to irradiate a diaphragm 15 through an aperture 14 for limiting an ablation area, whose opening diameter is variable. The plane mirror 12 is synchronized with a laser pulse in the (z) axis direction, and moved in parallel in accordance with depth of the ablation, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention identifies an object by a laser beam (typically an excimer laser) having a beam cross-section in one direction that is uniform and a direction orthogonal thereto has a non-uniform intensity distribution such as a Gaussian distribution. The present invention relates to an area ablation device, and more particularly to a laser beam ablation device suitable for correcting the curvature of the cornea.

[0002]

2. Description of the Related Art Recently, attention has been focused on a technique for correcting the refractive error of the eyeball by ablating the surface of the cornea with a laser beam and changing its curvature. In order to change the cornea to a desired curvature by ablation, it is necessary to be able to control the ablated region so as to have a uniform depth. Therefore, conventionally, in order to perform ablation with this uniform depth, a method has been adopted in which the intensity distribution of the laser beam used for ablation is made uniform. JP 63-150069 (USP 4,911,711 "
Sculpturte apparatus for correcting curvature of t
(He cornea "L'Esperance Francis A Jr. application") shows a method of making uniform by using a filter having a special transmittance distribution and a method of making uniform by bending the laser beam. The former method of using a filter with a special transmittance distribution reduces the high-intensity part by passing a filter with a transmittance distribution opposite to that of the laser beam, and makes the laser beam intensity uniform. That is, the laser beam having the intensity distributions shown in (b) and (c) of FIG.
(A) of FIG. 2 having the transmittance distributions of (b) and (c) of FIG.
After passing through the filter (1), the intensity of the laser beam (the center of (c) of FIG. 1) is reduced by the low transmittance of the filter (the center of (c) of FIG. 2). On the other hand, the portion where the laser beam intensity is low (the end portion of (c) of FIG. 1) passes through the portion where the transmittance of the filter is high (the end portion of (c) of FIG. 2), so the intensity is almost reduced. do not do. As a result, the intensity of the low-intensity portion of the laser beam is approximately the same as that of the central portion, and uniformization is achieved. In the latter method of bending the laser beam, the laser beam is divided into a plurality of portions, and the portions are overlapped again so as to be uniform. An example of this homogenizer is shown in FIG. The homogenizer is
The central triangular prism 2a, the two outer small triangular prisms 2b and 2c, and the first and second between the triangular prisms.
Beam splitter surfaces 3a, 3b, mirrors 4a, 4b spaced apart for splitting the laser beam 1, and a pair of outer mirrors 5a, 5b and 6a, 6b. The laser beam 1 having the width of the dimension H is reflected by the mirrors 4a and 4b.
Is divided into three parts. The central 1/3 portion that has passed between the mirrors 4a and 4b proceeds straight as it is,
It is incident on the triangular prism 2b. Then, the upper one-third portion reflected by the mirror 4a and incident on the triangular prism 2a via the mirrors 5a and 5b is superposed on the beam splitter surface 3a. The superposed laser beam travels rightward in the triangular prism 2a, is reflected by the mirror 4b on the beam splitter surface 3b, and is reflected by the mirrors 6a and 6b.
It is overlapped with the lower 1/3 part that has passed through. FIG. 4 shows the intensity distribution of the superposed laser beams. The intensity distribution of the laser beam before division is P, and the mirror 4
The intensity distribution of the upper one-third portion that has transmitted a, 5a, 5b is P ', and the intensity distribution of the lower one-third portion that has transmitted the mirrors 4b, 6a, 6b is P''. The laser beam passed through this homogenizer will have a dimension of H / 3 and will have an intensity distribution as shown by the solid line P _R. Further, Japanese Patent Laid-Open No. 63-289519 (filed by "Irradiator" Canon Inc.) discloses a method using a cylindrical lens array in which small cylindrical lenses are closely arranged. Figure 5
Is an example, the laser beam is a toric lens 7,
The irradiation target surface S is reached through the cylindrical lens array 8. The laser beam is condensed by the toric lens 7 which has a strong light condensing property in the y direction but a weak light converging property in the x direction, and then a large number of small cylindrical lenses are closely arranged in the y direction. The light enters the cylindrical lens array 8. Since the refraction in the y direction by the cylindrical lens array 8 is randomized, the intensity distribution of the laser beam on the irradiation target surface S is uniformly averaged.

[0003]

The laser beam homogenizing apparatus as described above has the following problems. In the first method using a filter having a special transmittance distribution, a uniform intensity distribution can be obtained even when actually passing through a laser beam because the transmittance distribution of the filter is inaccurate despite the difficulty in manufacturing the filter. Often not. Further, if the intensity distribution of the laser beam changes or the optical axis shifts, there is a drawback that the intensity distribution of the laser beam cannot be canceled by the transmittance distribution of the filter. Further, since the high portion is lowered in order to match the low strength portion, there is a drawback that energy loss is large.

Next, in the method of bending the second laser beam, it takes a long time for adjustment because of the complicated structure using a large number of mirrors. Further, when the intensity distribution of the laser beam changes or the optical axis shifts, a uniform intensity distribution cannot be obtained. Further, there is a drawback that a large amount of energy is lost when the beams split by the beam splitter are re-superposed. The method using the third cylindrical lens array has a drawback that the manufacturing of the cylindrical lens array is complicated and time-consuming like the filter of the first method.

In view of the above problems, an object of the present invention is to provide an apparatus capable of performing ablation with a uniform depth with a simple structure without using an optical element and a complicated optical system which are difficult to manufacture. Especially.

[0006]

In order to achieve the above object, the laser beam ablation device of the present invention has the following features. (1) In a laser beam ablation device for ablating a certain area of an object with a laser beam having a beam cross-section with one direction being uniform and a direction orthogonal thereto having a non-uniform intensity distribution such as Gaussian distribution, It is characterized by having a reflective optical element that guides an object and scans a laser beam in a direction having a non-uniform intensity distribution, and a diaphragm whose area of an opening can be controlled.

(2) The laser beam of (1) is characterized by being an excimer laser.

(3) The reflection type optical element of (1) is a mirror for deflecting a laser beam in the direction of an object.
Is controlled to move in the incident direction of the laser beam.

(4) The laser beam ablation device of (1) is characterized in that it corrects the curvature of the cornea.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 6 is a layout diagram of the optical system of the first embodiment.
Reference numeral 10 denotes an excimer laser light source, and the cross-sectional shape of the laser beam emitted from the laser light source is, as shown in FIG. 7, a distribution F (W) in which the intensity distribution in the horizontal direction (x-axis direction) of the beam is substantially uniform. Then, the intensity distribution in the vertical direction (y-axis direction) is a Gaussian distribution (Gaussian distribution) F (H). Reference numerals 11 and 12 are plane mirrors, which make the laser beam 90 °
The laser beam emitted from the laser light source 10 in the horizontal direction is deflected upward by 90 ° by the plane mirror 11, and further deflected in the horizontal direction by the plane mirror 12. The plane mirror 12 can be moved in parallel in the z-axis direction (movement will be described later).

Reference numeral 13 is a dichroic mirror, which makes the optical axis of the objective lens of the observation system coaxial with the laser beam.
The aperture 14 is for limiting the ablation region, and the diameter of the opening can be changed. Aperture 1
It is desirable that 4 is as close as possible to the cornea 15 to avoid the influence of diffraction. For this reason, the aperture 14 is made of a material such as transparent glass that can secure the operator's visual field so as not to interfere with the observation with the surgical microscope. The cornea 15 of the eye is pre-positioned so that it has a predetermined positional relationship with the device (the positioning means is not shown).

The apparatus having the above-mentioned structure is as follows.
The movement control of the plane mirror 12 will be described. As described above, the plane mirror 12 translates in the z-axis direction and translates the beam in the Gaussian distribution direction. Plane mirror 12
Moves in synchronization with the laser pulse, but at a certain position 1
After irradiation of the pulse or several pulses, the plane mirror 12 is moved to the next position, and the mirror 1 after irradiation of one pulse or several pulses again.
Move 2. This operation is performed in the opening 1 of the aperture 14.
Repeat from end to end. This is repeated irradiation of one pulse or several pulses at a predetermined interval in the ablation area,
By overlapping the pulses, it is possible to perform ablation with a uniform depth.

The amount of movement of the plane mirror 12 depends on the depth of ablation, the required degree of uniformity and the intensity of the beam.
It is determined by the correlation of each element such as intensity distribution. The intensity of the laser beam and the depth of ablation per pulse can also be adjusted by adjusting the output of the laser light source within a certain range. For convenience of explanation, it is assumed that the plane mirror 12 is moved for each pulse. FIG. 8 shows changes in the intensity distribution of the laser beam on the aperture 14 in the y-axis direction at this time, and FIG. 9 shows changes in the intensity distribution in the y-axis direction on the cornea 15. FIG. 10 shows FIG.
Shows the process of ablation.

At the first pulse, when the laser beam having the intensity distribution shown in FIG. 8A on the aperture 14 passes through the aperture, the intensity distribution on the cornea 15 becomes as shown in FIG. 9A. By the irradiation of this laser beam, the cornea 15 is ablated at the hatched portion in FIG. At the second pulse, since the plane mirror 12 moves in the z-axis direction, the intensity distribution on the aperture 14 changes as shown in FIG. 8B. Therefore, the intensity distribution on the cornea 15 is as shown in FIG. 9B, and the hatched portion in FIG. 10B is ablated. At the third pulse, the intensity distribution shown in FIG. 8C on the aperture 14 and that on the cornea 15 in FIG. 9C are obtained.
The shaded area in (c) of FIG. 10 is ablated, and the same is true for the fourth and subsequent pulses, and the aperture 14 at the nth pulse
The upper part is the intensity distribution of FIG. 8D, the upper part of the cornea 15 is the intensity distribution of FIG. 9D, and the shaded part of FIG. 10D is ablated. As described above, the mirror 12 is synchronized with the laser pulse.
When the laser beam is moved in parallel and is irradiated while scanning the laser beam in the direction of the non-uniform intensity distribution, the result as shown in FIG. 10 (e) is obtained, and the ablation with a substantially uniform depth can be performed.

11A and 11B are timing charts for explaining the control mechanism for moving the plane mirror 12 in synchronization with the laser pulse. FIG. 11A shows the optical output of the laser, and FIG. 11B shows the plane mirror. The output signal of the detector which detects 12 positions is shown. Here, the amount of movement of the plane mirror 12 required to perform ablation with a uniform depth is determined by a position detector (for example, a rotary encoder mounted on the drive shaft of a motor for driving the mirror). ) Output signal corresponding to m pulses. When the output signal of the position detector of the plane mirror 12 at the time of laser irradiation at the first pulse is the first pulse, the m + 1th output signal at the time of laser irradiation at the second pulse and the laser at the third pulse At the time of irradiation, the 2m + 1th output signal,
The plane mirror 12 is moved so that a laser pulse is emitted every m pulses of the output signal of the position detector of the plane mirror 12. By repeating such laser irradiation, uniform abrasion by laser irradiation is achieved.

The term indicating the direction in the description of this embodiment is used to specify the relationship with the energy distribution direction of the laser and has no further meaning. The operation of this device is controlled by the microcomputer.
In the above embodiments, the description was made with the so-called radial ablation of the cornea in mind, but it is obvious that the invention can be used for other processing without exceeding the technical idea of the present invention.

[0017]

According to the present invention, it is possible to perform ablation with a uniform depth by a laser beam having a non-uniform intensity distribution by a simple mechanism without using a complicated optical system or optical element.

Further, according to the present invention, it is possible to prevent the loss of the light quantity of the laser beam due to the conventional optical components for homogenization.
Can perform efficient ablation.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an example of laser energy distribution.

FIG. 2 is a diagram for explaining one of the conventional techniques.

FIG. 3 is a diagram illustrating a second conventional technique.

FIG. 4 is a diagram illustrating an intensity distribution obtained by a second conventional technique.

FIG. 5 is a diagram illustrating a third conventional technique.

FIG. 6 is a layout diagram of an optical system according to one embodiment of the present invention.

FIG. 7 is a diagram illustrating an example of energy distribution of an excimer laser.

FIG. 8 is a diagram showing the intensity distribution in the y-axis direction of the laser beam on the aperture.

FIG. 9 is a diagram showing the intensity distribution of the laser beam on the cornea in the y-axis direction.

FIG. 10 is a diagram illustrating a process of ablation in FIG.

FIG. 11 is a timing chart illustrating a control mechanism that moves a plane mirror in synchronization with a laser pulse.

[Explanation of symbols]

 10 Excimer Laser Light Source 11, 12 Planar Mirror 13 Dichroic Mirror 14 Aperture 15 Cornea

Claims (4)

[Claims] 1. A laser beam ablation device for ablating a certain area of an object by a laser beam having a beam cross-section with one direction being uniform and a direction orthogonal thereto having a non-uniform intensity distribution such as a Gaussian distribution. A laser beam characterized by having a reflective optical element that guides the beam to an object and scans the laser beam in a direction having a non-uniform intensity distribution, and a diaphragm whose area of the opening can be controlled. Ablation device. 2. The laser beam ablation device according to claim 1, wherein the laser beam is an excimer laser. 3. The ablation by a laser beam, wherein the reflective optical element according to claim 1 is a mirror for deflecting a laser beam in the direction of an object, and the movement of the mirror is controlled in the incident direction of the laser beam. apparatus. 4. The laser beam ablation device according to claim 1, wherein the laser beam ablation device corrects the curvature of the cornea.