JP2014219199A - Laser beam observation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser beam observation system that can observe a beam profile of the laser beam inexpensively.SOLUTION: When a laser beam enters an absorption plate 11, the absorption plate absorbs the received laser beam and generates heat. A radiation thermometer 12 receives an infrared thermally radiated from the absorption plate, thereby measuring a temperature distribution of the absorption plate.

Description

  The present invention relates to a laser beam observation apparatus that observes the cross-sectional shape of a laser beam.

  A laser beam emitted from a laser light source can be incident on a beam profiler to measure the characteristics of the laser beam (Patent Document 1). As a beam profiler, a pyroelectric camera in which pyroelectric sensors are two-dimensionally arranged is known.

JP 2008-122353 A

  Pyroelectric sensors have the property of high light resistance, but are expensive. An object of the present invention is to provide a laser beam observation apparatus that can observe a beam profile of a laser beam at a lower cost. Another object of the present invention is to provide a laser processing apparatus using this laser beam observation apparatus.

According to one aspect of the invention,
When the laser beam is incident, an absorbing plate that absorbs the incident laser beam and generates heat;
There is provided a laser beam observation apparatus having a radiation thermometer for measuring a temperature distribution of the absorption plate by receiving infrared rays thermally radiated from the absorption plate.

  Infrared rays thermally radiated from the absorbing plate are lower in intensity than the original laser beam. For this reason, a cheap thing with low light-proof intensity | strength can be used as a radiation thermometer.

FIG. 1 is a schematic diagram of a laser beam observation apparatus according to the first embodiment. FIG. 2A is a diagram showing an example of the relative positional relationship between the transmission window of the mask and the beam cross section of the laser beam, and FIG. 2B is an observation by the laser beam observation apparatus in a state where the optical axis adjustment of the laser beam is completed. FIG. 2C is a diagram showing a relative positional relationship between the beam cross section and the transmission window when the optical axis adjustment of the laser beam is insufficient, and FIG. It is a figure which shows an example of the temperature distribution observed with the laser beam observation apparatus in the state of 2C. FIG. 3 is a schematic diagram of a laser beam observation apparatus according to the second embodiment. 4A and 4B are diagrams illustrating an example of a temperature distribution observed on the light receiving surface of the laser beam observation apparatus according to the second embodiment. FIG. 5 is a schematic view of a laser processing apparatus according to the third embodiment.

[Example 1]
FIG. 1 shows a schematic diagram of a laser beam observation apparatus 10 according to the first embodiment. The laser beam observation apparatus 10 according to the first embodiment includes an absorption plate 11, a radiation thermometer 12, and a converging lens 16.
The laser beam emitted from the laser optical system 20 passes through the transmission window 21 </ b> A of the mask 21 and enters the convergent lens 16 of the laser beam observation apparatus 10. The converging lens 16 images the transmission window 21 </ b> A of the mask 21 on the surface of the absorption plate 11. The position where the mask 21 is disposed corresponds to the observed position 23 where the beam cross section of the laser beam is to be observed. That is, the observed position 23 and the absorption plate 11 are in a conjugate relationship via the converging lens 16.

  When the laser beam is incident on the absorption plate 11, the absorption plate 11 absorbs the energy of the laser beam and generates heat. As the absorption plate 11, for example, a copper plate, an aluminum plate, a gold plate, a platinum plate, or the like can be used. The radiation thermometer 12 receives the infrared rays thermally radiated from the surface of the absorption plate 11 heated by the incidence of the laser beam on the side opposite to the surface on which the laser beam is incident, thereby changing the temperature distribution of the absorption plate 11. taking measurement.

  The radiation thermometer 12 includes a lens 13 and an image sensor 14. For example, a microbolometer is used for the image sensor 14. The microbolometer includes a light receiving surface 15 on which two-dimensionally arranged thermal elements whose electric resistance changes as the temperature changes. The lens 13 images the absorption plate 11 on the light receiving surface 15. The optical axis of the lens 13 is perpendicular to the absorption plate 11 and the light receiving surface 15.

  The surface temperature of the absorption plate 11 in the region where the laser beam is incident rises. The heat of the surface on which the laser beam is incident is transmitted in the thickness direction in the absorption plate 11, and the temperature of the opposite surface (hereinafter referred to as the back surface) also rises. Due to this temperature rise, heat radiation is generated from the back surface of the absorption plate 11. The temperature distribution of the absorption plate 11 depends on the light intensity distribution in the beam cross section of the laser beam incident on the absorption plate 11. Since the light intensity distribution in the beam cross section at the observed position 23 is transferred to the absorption plate 11 by the converging lens 16, the light intensity distribution in the beam cross section at the observed position 23 can be measured.

  Since the laser beam observation device 10 is disposed on the back side of the absorption plate 11, the optical axis (center beam) of the laser beam emitted from the laser optical system 20, the converging lens 16 and the lens 13 of the laser beam observation device 10 are displayed. Can be made to coincide with the optical axis. By matching both optical axes, it is possible to observe the light intensity distribution when the laser beam is viewed from the front.

  When the imaging magnification by the converging lens 16 is increased, the light intensity distribution in the transmission window 21A of the mask 21 is enlarged and transferred to the absorption plate 11. Thereby, the spatial resolution in the beam cross section can be increased.

  When a laser beam in the infrared region is directly incident on the image sensor 14 composed of a microbolometer, the microbolometer is damaged. The microbolometer can be prevented from being damaged by converting the energy of the laser beam into heat and observing the thermal radiation. Microbolometers are less expensive than beam profilers using pyroelectric sensors with high light resistance. For this reason, it is possible to reduce the manufacturing cost of the laser beam observation apparatus.

  FIG. 2A shows an example of the relative positional relationship between the transmission window 21A of the mask 21 (FIG. 1) and the beam cross section 25 of the laser beam. The transmission window 21A and the beam cross section 25 are both circular, and the beam cross section 25 is larger than the transmission window 21A. In the state where the optical axis adjustment of the laser beam is completed, the transmission window 21A is included in the beam cross section 25.

FIG. 2B shows an example of a temperature distribution observed by the laser beam observation apparatus 10 (FIG. 1) in the state of FIG. 2A where the optical axis adjustment of the laser beam has been completed. In FIG. 2B, the relatively high temperature region is represented in a darker color than the relatively low temperature region. When the light intensity distribution of the laser beam at the position of the transmission window 21A is top flat, a circular high temperature region 24 is observed.

  FIG. 2C shows the relative positional relationship between the beam cross section 25 and the transmission window 21A when the optical axis adjustment of the laser beam is insufficient. The center of the beam section 25 is shifted from the center of the transmission window 21 </ b> A, and a partial region 21 </ b> B of the transmission window 21 </ b> A does not overlap the beam section 25. The portion of the beam cross section 25 that does not overlap the transmission window 21A is shielded from light. For this reason, the beam cross-sectional shape collapses from a circle as shown by hatching in FIG. 2C.

  FIG. 2D shows an example of a temperature distribution observed by the laser beam observation apparatus 10 (FIG. 1) in the state of FIG. 2C. Since the shape of the beam cross section at the position of the transmission window 21A has collapsed from a circle, the shape of the high temperature region 24 also collapses from the circle. By observing the shape of the high temperature region 24 with the laser beam observation apparatus 10 (FIG. 1), it is possible to verify whether or not the optical axis adjustment of the laser beam has been normally completed.

[Example 2]
FIG. 3 shows a schematic diagram of a laser beam observation apparatus 10 according to the second embodiment. The laser beam observation apparatus 10 according to the second embodiment includes an absorption plate 11 and a radiation thermometer 12. The configurations of the absorption plate 11 and the radiation thermometer 12 are the same as the configurations of the absorption plate 11 and the radiation thermometer 12 of the laser beam observation apparatus 10 according to the first embodiment.

  A collimated laser beam 26 is emitted from the laser optical system 20. A branch optical element 27 is disposed in the main beam path 30 from the laser optical system 20 to the optical device 28. The branching optical element 27 branches the path of the laser beam from the beam main path 30. For the branch optical element 27, for example, a partial reflecting mirror is used. The laser beam observation apparatus 10 is disposed on a branch path 31 branched from the beam main path 30. A laser beam propagating along the branch path 31 enters the absorption plate 11 perpendicularly.

  The optical path length L1 from the branching optical element 27 to the absorption plate 11 is preferably made equal to the optical path length L2 from the branching optical element 27 to the optical device 28. Although the laser beam 26 emitted from the laser optical system 20 is collimated, it is not completely parallel light. When the optical path length L1 is equal to the optical path length L2, the beam cross section at the position of the absorbing plate 11 and the beam cross section at the position of the optical device 28 are congruent. For this reason, the laser beam observation device 10 can more accurately obtain information on the shape and dimensions of the beam cross section at the position of the optical device 28.

  Further, the position in the plane perpendicular to the optical axis at the position where the optical device 28 is disposed and the position in the plane of the absorption plate 11 correspond one-to-one. By associating the coordinates in the light receiving surface 15 of the laser beam observation device 10 with the position of the optical device 28 in advance, it is possible to detect the positional deviation of the beam cross section at the position where the optical device 28 is disposed.

  FIG. 4A shows an example of the temperature distribution observed on the light receiving surface 15. In FIG. 4A, the relatively high temperature region is represented by a darker color than the relatively low temperature region. The optical device 28 and the laser beam observation device 10 are aligned so that the target position of the center of the laser beam incident on the optical device 28 (FIG. 3) corresponds to the center (origin) of the light receiving surface 15. In FIG. 4A, the center of the high temperature region 24 coincides with the origin of the light receiving surface 15. At this time, it is determined that the relative position between the optical device 28 and the optical axis of the laser beam is appropriate.

FIG. 4B shows an example in which the center of the high temperature region 24 is deviated from the origin of the light receiving surface 15. In this case, it is determined that the relative position between the optical device 28 and the optical axis of the laser beam deviates from the target positional relationship. Thus, the laser beam observation apparatus 10 according to the second embodiment can be used to detect the shape and size of the beam cross section and the presence / absence of displacement.

[Example 3]
FIG. 5 shows a schematic diagram of a laser processing apparatus according to the third embodiment. The laser processing apparatus according to the third embodiment is, for example, a laser drill that drills a printed circuit board. The laser beam emitted from the laser light source 50 enters the workpiece 70 along the beam main path 63. The workpiece 70 is held on the stage 61.

  The beam expander 51, the aspherical lens 52, the mask 53, the variable attenuator 54, the collimator lens 55, the branching optical element 56, the folding mirror 57, the branching optical element 58, and the beam scanning are sequentially entered into the beam main path 63 from the upstream side. A container 59 and an fθ lens 60 are arranged.

  For example, a carbon dioxide laser is used for the laser light source 50. The beam expander 51 expands the beam diameter of the laser beam. The aspherical lens 52 makes the light intensity distribution in the beam cross section uniform at the position where the mask 53 is disposed. The mask 53 includes a light shielding region and a transmission window arranged in the light shielding region, and shapes the beam cross section. The variable attenuator 54 attenuates the power of the laser beam.

  The branching optical element 56 branches a part of the laser beam from the beam main path 63. A laser beam observation apparatus 10 </ b> A is arranged on a branch path 64 branched by the branch optical element 56. The laser beam observation apparatus 10A has the same configuration as that of the laser beam observation apparatus 10 (FIG. 1) according to the first embodiment.

  The downstream branch optical element 58 branches a part of the laser beam propagating along the beam main path 63 from the beam main path 63. The laser beam observation apparatus 10B is arranged on the branch path 65 branched by the branch optical element 58. The laser beam observation apparatus 10B has the same configuration as the laser beam observation apparatus 10 (FIG. 3) according to the second embodiment.

  The beam scanner 59 scans the laser beam so that the incident position of the laser beam moves on the surface of the workpiece 70. As the beam scanner 59, for example, a galvano scanner including a pair of galvanometer mirrors is used. The transmission window of the mask 53 is imaged on the surface of the workpiece 70 by the collimating lens 55 and the fθ lens 60.

  The collimating lens 55 and the converging lens 16A of the laser beam observation apparatus 10A form an image of the transmission window of the mask 53 on the surface of the absorption plate 11A of the laser beam observation apparatus 10A. That is, the collimating lens 55 and the converging lens 16A perform the same functions as the converging lens 16 (FIG. 1) of the laser beam observation apparatus 10 according to the first embodiment. The optical system from the laser light source 50 to the aspherical lens 52 corresponds to the laser optical system 20 (FIG. 1) described in the first embodiment. The laser beam observation apparatus 10A can confirm whether the alignment between the mask 53 and the laser beam path is good or bad.

  The branch optical element 58 has a function equivalent to that of the branch optical element 27 (FIG. 3) described in the second embodiment. An optical system from the laser light source 50 to the collimating lens 55 corresponds to the laser optical system 20 (FIG. 3). The beam scanner 59 corresponds to the optical device 28 (FIG. 3). The optical path length from the branch optical element 58 to the beam scanner 59 (corresponding to the optical path length L2 in FIG. 3) and the optical path length from the branch optical element 58 to the absorption plate 11B of the laser beam observation apparatus 10B (optical path length L1 in FIG. 3). Are equivalent). Based on the observation result by the laser beam observation apparatus 10B, it can be determined whether or not the incident position of the laser beam on the beam scanner 59 is appropriate.

  If the incident position of the laser beam on the beam scanner 59 is deviated from the proper position, unexpected vignetting is generated by the galvanometer mirror. When unexpected vignetting occurs, the laser power on the surface of the workpiece 70 decreases. By detecting that the incident position of the laser beam on the beam scanner 59 is deviated from the appropriate position, it is possible to prevent the processing from being continued with inadequate laser power.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

10, 10A, 10B Laser beam observation apparatus 11, 11A, 11B Absorber plate 12 Radiation thermometer 13 Lens 14 Image sensor 15 Light receiving surface 16, 16A Converging lens 20 Laser optical system 21 Mask 21A Transmission window 21B Area not overlapping beam cross section 23 Observed position 24 High temperature region 25 Beam cross section 26 Collimated laser beam 27 Branch optical element 28 Optical device 30 Beam main path 31 Branch path 50 Laser light source 51 Beam expander 52 Aspherical lens 53 Mask 54 Variable attenuator 55 Collimator lens 56 Branch optical element 57 Folding mirror 58 Branch optical element 59 Beam scanner 60 fθ lens 61 Stage 63 Beam main path 64, 65 Branch path 70 Work object

Claims (7)

When the laser beam is incident, an absorbing plate that absorbs the incident laser beam and generates heat;
A laser beam observation apparatus comprising: a radiation thermometer that measures the temperature distribution of the absorption plate by receiving infrared rays thermally radiated from the absorption plate.   The laser beam observation apparatus according to claim 1, wherein the radiation thermometer measures a temperature distribution of the absorption plate heated by incidence of a laser beam.   3. The laser beam observation apparatus according to claim 1, wherein the radiation thermometer receives the infrared rays thermally radiated from a surface of the absorption plate opposite to a surface irradiated with the laser beam.   4. The laser beam observation apparatus according to claim 1, wherein an observation position where a cross section of a laser beam is to be observed and the absorption plate are in a conjugate relationship via the converging lens. 5. . further,
A laser light source;
A stage for holding a workpiece at a position where a laser beam emitted from the laser light source is incident;
A branch optical element for branching the path of the laser beam from the main beam path from the laser light source to the workpiece held on the stage;
The laser beam observation apparatus according to claim 1, wherein the absorption plate is disposed in a branch path branched by the branch optical element. further,
A mask arranged in the beam main path upstream of the branching optical element, including a light shielding region and a transmission window arranged in the light shielding region, and shaping a beam cross section of the laser beam;
The laser beam observation apparatus according to claim 5, further comprising a lens that forms an image of the transmission window of the mask on the absorption plate. And a beam scanner that is disposed on the beam main path downstream of the branching optical element and moves the incident position of the laser beam on the surface of the workpiece held on the stage,
The absorption plate is disposed in a path branched from the beam main path by the branch optical element, and an optical path length from the branch optical element to the beam scanner, and an optical path from the branch optical element to the absorption plate 6. The laser beam observation apparatus according to claim 5, wherein the length is equal.

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