JP3076836B2 - Laser beam focusing and irradiation equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser beam condensing / irradiating apparatus for converging and irradiating a laser beam spatially smoothly.

[0002]

2. Description of the Related Art In a high-power laser device, it is not only difficult to obtain a complete Gaussian beam output due to the influence of the nonlinear refractive index and the like, but also a Gaussian beam has a low energy extraction efficiency in the laser device and is practical. is not. For this reason, in most current high power laser devices, a rectangular beam output is extracted in most cases, and the output wavefront is considerably distorted due to the influence of the nonlinear refractive index and the like. When this is condensed on an object by a lens or the like, an extremely non-uniform intensity distribution corresponding to the Fourier transform of the spatial frequency is obtained on the condensing surface,
Furthermore, a place called a hot spot where energy is concentrated occurs due to the distortion of the wavefront, which has been an obstacle in use.

To solve this problem, a phase plate such as a random phase plate or a composite Fresnel zone plate is inserted on the optical axis before or after the condenser lens or the condenser mirror to control the phase. A method of controlling the spatial intensity distribution of the laser light after the light is considered.

[0004] However, in the technique of splitting a laser beam having high coherence into a minute beam by such a phase plate and condensing and irradiating the beam, the spatial intensity distribution of the laser beam on an object is a very small one called a speckle pattern. It becomes an aggregate of spots and has a severe spike-like unevenness when viewed microscopically.

In the past, the inventor of the present invention used a combination of a broadband laser device and a wavelength-dispersive medium on a random phase plate (Japanese Patent No. 2611169) and a multiple reflecting mirror for the purpose of removing the non-uniformity due to the speckle pattern. A combination (Patent No. 2580540) has been invented.

[0006]

However, in the former invention (Japanese Patent No. 2611169), the direction of uniformization is only one-dimensional, and non-uniformity remains in a direction perpendicular to the direction. There is the latter (Patent No. 2580540
No. 2) enables a two-dimensional smoothing effect, but there is a problem in that energy loss occurs because the multiple reflecting mirror is inserted on the optical axis.

The present invention eliminates non-uniformity due to speckle patterns without using a wavelength dispersive medium or multiple reflecting mirrors, and provides a smooth spatial intensity distribution of laser light controlled by a phase plate on an object. It is intended to be realized.

In order to solve the above-mentioned problems, the present invention provides a laser device for generating a laser beam, and a laser beam comprising a condenser lens or a condenser mirror for condensing and irradiating the generated laser beam to an object. In the condensing irradiation device, the laser device is a broadband laser beam having a wide wavelength width.
And resonate after increasing the diameter of the laser medium
Oscillation by inserting it into a plane resonator with a short length
Using a wide-band wide-divergence laser device that generates a wide-divergence laser beam with a wide beam divergence angle, the phase plate for controlling the light-collecting characteristics is combined with the laser device and the condensing lens or the condensing lens A laser beam condensing / irradiating device is provided between the optical mirrors or on the optical axis between the condenser lens or the condenser mirror and the object.

The phase plate is a random phase plate.

[0010] The phase plate may be a composite Fresnel zone plate formed by randomly arranging a plurality of small Fresnel zone plate sets having a complementary phase relationship on the same plane.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on embodiments with reference to the drawings. FIG. 1 shows an embodiment of the present invention. Laser oscillator 1 for generating laser light,
The relay optical system 2, the random phase plate 3, and the condenser lens 4 are arranged on the same optical axis, a laser beam is focused on the object 5, and required processing is performed.

The laser oscillator 1 is composed of a laser medium A and a plane mirror B, and generates a laser having a wide wavelength width and a wide beam divergence angle, that is, a wide band wide divergence angle laser.

The laser oscillator 1 uses an excimer laser, a dye laser, a titanium sapphire laser or the like using krypton / fluorine gas as a laser medium. By oscillating without taking special measures, a broadband laser beam having a wide laser beam wavelength width can be obtained.

On the other hand, in the laser oscillator 1, a laser medium having a large diameter is inserted into a plane resonator having a short resonator length, and the laser medium is oscillated. can get. A larger divergence angle can be obtained by using a spontaneous emission light (ASE) oscillator having no resonator or a means of once irradiating a diffuser with laser light and amplifying scattered light therefrom.

In this embodiment, a krypton / fluorine gas laser medium A having an effective portion having a thickness of 2 mm is used for the laser oscillator 1, and the length of the resonator constituted by the plane mirror B is 30 cm.

When the beam divergence angle was measured by operating this laser oscillator, the value was 2 mrad, and it was confirmed that a beam having a wide divergence angle of 20 times the diffraction limit was generated.
In addition, since no wavelength selection element is provided in the resonator, the krypton / fluorine gas laser generates a broadband laser beam having a laser beam wavelength width of 0.3 nm.

The relay optical system 2 spreads the laser light, and in this embodiment, spreads the laser light to a thickness of 17 cm. If a large amount of energy is required for industrial applications such as laser processing, not only expand the beam system with a relay optical system, but also install one or multiple stages of amplifiers here to achieve the required energy. Perform amplification up to.

The random phase plate 3 controls the light collecting characteristics, and is arranged between the laser oscillator 1 and the light collecting lens 4 or the light collecting mirror. Further, the random phase plate 3 may be arranged on the optical axis between the condenser lens or the condenser mirror and the object.

Examples of the random phase plate 3 include a random phase plate used in Japanese Patent No. 2611169 and Japanese Patent No. 2580540 according to the invention of the present inventor, and a random phase plate disclosed in Japanese Patent Application No.
As described in 9-65973, it is possible to use a composite Fresnel zone plate (a plurality of small Fresnel zone plate pairs having complementary topological relationships are randomly arranged on the same plane) and the like. is there.

The random phase plate 3 divides the beam into minute beams and randomly gives a phase difference of 0 or π. The phase plate used in this example has 0 and π of a cell size of 2 mm square.
However, various types of phase plates corresponding to the irradiation purpose such as a composite Fresnel zone plate can be used. This laser beam has a focal length of 1.2m
In 4, the light is focused and irradiated on the object 5.

The operation of the above configuration will be described. A wide divergence laser beam with a wide beam divergence angle generated by a wide divergence laser device can be considered to be equivalent to a continuous accumulation of a large number of laser beams having slightly different angles in space.

By the way, Patent No. 26 of the present inventor's invention is disclosed.
In Japanese Patent No. 11169, the divergence angle of a laser beam is widened by a wavelength dispersive medium such as a prism or a diffraction grating, and in Japanese Patent No. 2580540 according to the inventor's invention, a large number of lasers having slightly different angles are multiply reflected by a mirror. A beam bundle of light was obtained.

In the present invention, by using the above-mentioned wide divergence laser device, a laser beam equivalent to these is obtained, and the laser beam is condensed and irradiated on the object by a phase plate and a condensing lens. , In which a large number of minute light spots formed by a phase plate and a light collecting lens are overlapped with a slight positional shift, thereby achieving a smooth light collecting pattern. It is.

Further, since the laser device generates a broadband laser device having a wide laser light wavelength width, smoothing can be achieved in a very short time without causing mutual interference when overlapping.

That is, regarding the arrangement of the phase plate of this embodiment, if it is a combination with a conventional laser device having a high coherence, it is calculated from the calculation that an intense spike-like speckle having a pitch of 1.8 μm is formed on the object. Non-uniformity called a pattern will occur.

However, by combining the above-mentioned phase plate with a wide band wide divergence laser device which is a feature of the present invention,
In a laser device, the divergence angle is 2 mrad, and beams slightly displaced over an area 20 times the pitch of 1.8 μm continuously overlap on the object.

As a result, intense spike-like speckle patterns are averaged, and a smooth spatial intensity distribution of laser light is realized. In addition, since the laser light wavelength width is 0.3 nm, the time required for smoothing is 1 ps, and the smoothing can be achieved in a very short time.

FIG. 2 shows the result of actually measuring the condensed light intensity distribution of the laser light on the object with respect to the embodiment shown in FIG. The intensity distribution is smoothed and uniformized, proving that the effect is actually increasing.

[0029]

According to the present invention having the above-described structure, the spatial intensity distribution of the laser beam focused and irradiated on the object by the focusing lens can be obtained by using the wide-band wide-divergence laser device and the phase plate. By controlling and smoothing, it is possible to solve the disadvantages of the conventional invention, such as the loss due to the multiple reflecting mirror and the one-dimensional smoothing direction.

Accordingly, the present invention can be used to improve the quality and efficiency of industrially important laser application apparatuses such as laser processing and laser processing. Also, in the case of future energy development such as laser fusion, obtaining a high-efficiency and smooth irradiation shape is indispensable technology, but the present invention is also useful in promoting the development.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an optical arrangement according to an embodiment of the present invention.

FIG. 2 is a diagram in which the embodiment of the present invention of FIG. 1 is actually produced as a prototype, and the measured values of the spatial intensity distribution of the condensed irradiation on the target object are displayed as contour lines.

[Description of sign]

 DESCRIPTION OF SYMBOLS 1 Laser oscillator 2 Relay optical system 3 Random phase plate 4 Condensing lens 5 Object (workpiece)

Claims (3)

(57) [Claims] And 1. A laser generates a laser beam device, the laser beam convergent irradiation apparatus comprising a condenser lens or the condenser mirror for irradiating light collecting to the object a laser light the occurrence, of the laser device As a laser oscillator, it is a broadband laser beam with a wide wavelength width, and the laser medium is widened by inserting a laser medium into a plane resonator with a short resonator length after oscillating by widening its diameter. Using a wide-band wide-divergence laser oscillator that generates a wide-divergence laser light, a phase plate for controlling the light-gathering characteristics is provided between the laser device and the light-collecting lens or the light-collecting mirror, or the light-collecting lens or A laser beam condensing / irradiating device, which is arranged on an optical axis between the converging mirror and the object. 2. The laser beam condensing / irradiating apparatus according to claim 1, wherein said phase plate is a random phase plate. 3. The phase plate is a composite Fresnel zone plate formed by randomly arranging a plurality of small Fresnel zone plate pairs having a complementary phase relationship on the same plane. Item 4. A laser beam condensing and irradiating apparatus according to Item 1.