JPH0498216A - Optical device for collimating or converging laser beam - Google Patents

Abstract

PURPOSE:To collimate or converge laser beams outputted from a semiconductor laser element by using a phase adjusting element having prescribed refractive index distribution based upon a material whose refractive index is changed in accordance with the quantity of irradiating light and constituted so as to align the equal phase faces of laser beams. CONSTITUTION:Laser beams projected from a broad area type semiconductor laser element 10 are converted into parallel beams by a collimating lens 12, allowed to pass the phase adjusting element 14 to align the equal phase faces of the beams and then converged by a condenser lens 16. The element 14 is constituted of a transparent base 26 consisting of glass or acrylic resin and a refractive index distribution forming layer 28 formed on one face of the base 26. The layer 28 consists of a material having characteristics capable of changing its refractive index by the irradiation of energy beams. The laser beams passing the element 14 are provided with the equal phase faces spherically aligned by the refractive index distribution of the element 14, the beams can be converged into a small spot up to the limit of diffraction on a beam waist position.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical device for suitably collimating or condensing laser light by aligning equiphase fronts of the laser light.

Conventional technology When configuring an optical system for laser light irradiation, transmission, or optical processing, it is necessary to collimate the laser light output from a laser light source into parallel light with high precision or to focus it with high precision. may be required. For example, a laser beam output from a laser light source is converted into parallel rays by a collimating lens, and the parallel rays are focused into a beam waist by a condensing lens.

Semiconductor laser devices are often used as laser light sources, and in order to generate high-output laser light for solid-state laser excitation, a broad-area semiconductor laser device having a relatively wide oscillation region of, for example, 100 to 200 microns in width is used. In some cases, the beam cross section of the laser beam output from the laser beam is not only rectangular, but also the phase fronts are not aligned, making it difficult to converge the laser beam into a small cross section.

The present invention has been made against the background of the above circumstances,
The purpose is to provide an optical device that can narrow down a laser beam to a small spot regardless of the equiphase front of the laser beam.

Means for Solving the Problems The gist of the present invention to achieve the object is an optical device for collimating or condensing laser light output from a semiconductor laser element, which A phase adjustment element is provided with a predetermined refractive index distribution by a material whose refractive index changes correspondingly, and is inserted into the optical path of the laser light output from the semiconductor laser element to align equiphase planes of the laser light. It consists in including.

Functions and Effects of the Invention In this way, the phase adjustment element inserted into the optical path of the laser beam aligns the equiphase planes of the laser beam, so that the laser beam can be converged into a small cross section. Furthermore, since the phase adjustment element is made of a material whose refractive index changes depending on the amount of light irradiation, a desired refractive index distribution can be provided by changing the position and amount of light irradiation. Laser beams whose phase fronts are not aligned can be simply and easily narrowed down with high precision.

EXAMPLE Hereinafter, an example of the present invention will be described in detail based on one aspect.

FIG. 1 is a diagram showing a laser beam converging section that is a part of the optical device. In the figure, a laser beam output from a broad area semiconductor laser device 10 is converted into parallel light by a collimating lens 12, and then a phase adjustment element 14
By allowing the light to pass through, equiphase fronts are aligned, and then the light is converged by the condenser lens 16.

The broad area type semiconductor laser device IO has a semiconductor chip 2 having a relatively large oscillation region 20 with a width of about 100 to 200 microns, as shown in FIG. 2, for example.
2 is provided in the housing 24. Therefore, although the laser light output from the broad area type semiconductor laser device 10 has a high output, since it is output from a relatively large oscillation region 20, it has a rectangular beam cross section and an equiphase surface. are not complete.

The phase adjustment element 14 is composed of a transparent substrate 26 made of glass or acrylic resin, and a refractive index distribution forming layer 28 provided on one surface of the transparent substrate 26. This phase adjustment element 14 is manufactured as follows.

That is, as shown in FIG. 3(a), for example, polymethyl methacrylate (PMMA: Po) doped with styrene (SL: 5tyrene)
A photosensitive resin made of 1y methylmethacrylate is coated on one surface of the transparent substrate 26 using a spinner or the like to form an SL/PMMAi film 30. As shown in FIG. 4, this St,/PMMA thin film 30 has a property that its refractive index changes depending on the amount of ultraviolet irradiation (exposure amount).

Next, as shown in FIG. 3(b), the St/PMMA thin film 30 is exposed to ultraviolet light by an ultraviolet exposure device 32. , this ultraviolet exposure apparatus 32 includes an X-Y table 34 on which a transparent substrate 26 on which a St/PMMA thin film 30 is formed, and an optical head 40 having an ultraviolet radiation probe 36 and a condensing lens 38. A predetermined location on the St7 PMMA thin film 30 is exposed to a predetermined amount of light by a control device (not shown).

In this embodiment, a broad area type semiconductor laser device 10
In order to obtain a refractive index distribution that allows the equiphase front of the laser beam output from the S t/PMMA to be spherical,
Thin film 30 is exposed. The exposure amount of ultraviolet rays is controlled by a diaphragm mechanism that changes the amount of light and by changing the duty ratio of the ultraviolet pulse. When exposed to ultraviolet light as described above, the exposed portion of the St/PMMAi film 30 becomes P S t (poly 5tylene).
Changes to

Then, as shown in FIG. 3C, when styrene is removed from the St/PMMAi film 30 by vacuum drying, a desired refractive index distribution is formed and the refractive index distribution forming layer is 28 is obtained.

The laser light that has passed through the phase adjustment element 14 configured as described above is converged by the condenser lens 16, and as shown in FIG. Since it has an equiphase surface S,
The beam is narrowed down to the diffraction limit at the beam waist position δ. The electric field component of the electromagnetic wave propagating in the Z direction is (1)
The cross-sectional shape of the Gaussian beam, which is represented by a double arrow, is shown in FIG.

however, λZ one It is.

λ λl Here, j in the above equations (1) and (2) is an imaginary unit, ω
(Z) is the beam diameter at coordinate Z, ω. indicates the beam diameter (minimum spot diameter) at the beam waist. Further, r is the distance from the Z axis, Eo is the electric field intensity at 2=0 and r=o, n is the refractive index of the medium, and λ is the wavelength of light.

Although the beam cross section of the laser beam is elliptical, assuming that it is circular for the sake of simplicity, the Gaussian beam has a diffraction field of 1@field spot size ω. The equiphase surface S is a spherical surface with a curvature R expressed by the above equation (2).

Due to the reversibility of the propagation of light, a traveling wave with equiphase planes S aligned spherically as shown in Figure 5 can obtain a diffraction-limited spot, but if the equiphase planes are not aligned, , it is not possible to focus down to the diffraction limit, and the spot diameter becomes large. Therefore, the laser beam output from the broad-area semiconductor laser device 10 is different from the laser beam output from the narrow-area semiconductor laser device 10, which has a semiconductor chip 50 whose oscillation region is several microns wide, as shown in FIG. Conventionally, light could not be focused down to a small spot diameter.

Although one embodiment of the present invention has been described above in detail based on the drawings, the present invention can also be applied to other aspects.

For example, in the phase adjustment element 14 of the above embodiment, the refractive index distribution forming layer 28 was manufactured from the St/PMMA thin film 30, but it may be made of other materials. In short, any other material may be used as long as the material has the property of changing its refractive index when irradiated with an energy beam, and it may be manufactured using any other manufacturing method.

Moreover, instead of or in addition to the optical system of the embodiment shown in FIG.
A prism or a cylindrical lens may also be used.

Further, in the above-mentioned embodiment, the explanation is given that the laser light output from the broad-area semiconductor laser device 10 is converged, but even with other types of laser light sources, the laser output area is relatively large. If so, by applying the above-mentioned phase adjustment element 14, a certain degree of effect can be enjoyed.

It should be noted that the above-mentioned embodiment is merely one embodiment of the present invention, and various modifications may be made to the present invention without departing from the spirit thereof.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a part of an optical system including an embodiment of the present invention. FIG. 2 is a diagram illustrating the configuration of the broad area type semiconductor laser device of FIG. 1. FIG. 3 is a diagram illustrating a method for manufacturing the phase adjustment element shown in FIG.
FIG. 3(a) shows the coating process, FIG. 3(b) shows the exposure process, and FIG. 3(C) shows the vacuum drying process. Figure 4 shows the St/P used in the phase adjustment element in Figure 1.
FIG. 3 is a diagram showing the relationship between the amount of ultraviolet light exposure and the change in refractive index of the MMAFi film. FIG. 5 is a diagram illustrating the convergence effect at the beam waist of a Gaussian beam. Figure 6 shows
FIG. 2 is a diagram showing the configuration of a narrow area type semiconductor laser device. 10 Nibroad area type semiconductor laser device 14: Phase adjustment device Applicant Brother Industries, Ltd. 02 Supervision υ ＼r

Claims (1)

[Claims] An optical device for collimating or condensing laser light output from a semiconductor laser element, the optical device having a predetermined refractive index distribution made of a material whose refractive index changes in accordance with the amount of light irradiation. 1. An optical device comprising: a phase adjustment element that is inserted into the optical path of a laser beam output from the semiconductor laser element and aligns equiphase fronts of the laser beam.