JP2010003755A - Wavelength conversion laser apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength conversion laser apparatus, wherein harmonic pulse laser beam is halved by a beam splitter and one laser beam is re-superimposed on original laser beam through a delay optical path means for doubling frequency, capable of matching the pointing and beam aperture of both beams at a junction of split beams for stable quality in laser beam of delayed merging, even if pointing of the original laser beam fluctuates, thereby realizing stable laser processing. <P>SOLUTION: By setting the length of optical path from a branch point of the laser beam of a beam splitter 2, with a delay optical path means 100, to a junction to 4f, two lenses 41 and 42 of focal length f are arranged on the optical path of the laser beam passing through the delay optical path means 100, and the optical path length between the two lenses is set to 2f. At the delay optical path means 100, the junction and the branching point of the laser beams are image-transfer connected. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wavelength conversion laser device that outputs a laser beam generated by a solid-state laser element after wavelength conversion by a nonlinear crystal.

  The wavelength conversion laser device is one in which a fundamental laser beam is incident on a nonlinear crystal, converted into a harmonic laser beam having a wavelength of 1 / N, and output. Laser light converted to 1/2 wavelength is referred to as 2nd harmonic, 1/3, and 1/4 wavelength, respectively, and 3rd harmonic and 4th harmonic respectively. Since the light corresponds to ultraviolet light, it is called a UV laser. As the fundamental laser, an Nd: YAG laser or Nd: YVO4 laser capable of high-power pulse oscillation using a Q switch is used. The ratio (hereinafter referred to as wavelength conversion efficiency) at which the fundamental laser beam is wavelength-converted to obtain a harmonic laser beam depends on the pulse peak height of the fundamental laser beam irradiated to the nonlinear crystal. That is, a high-peak pulse fundamental laser beam can be wavelength-converted with high efficiency to obtain a high-output harmonic laser beam, but a low-peak pulse fundamental laser beam can be obtained only with a low-output harmonic laser beam. I can't get it.

  Here, a characteristic of the Q-switched pulsed solid-state laser is that the pulse width changes according to the repetition frequency, and that the longer the repetition frequency is, the longer pulse oscillation occurs. Furthermore, pulse energy has a relationship that pulse energy decreases as the repetition frequency increases in inverse proportion to the repetition frequency.As a result, high energy short pulse oscillation occurs at a low repetition frequency, and a high peak pulse with a high spire value is obtained. At the repetition frequency, low peak pulse oscillation with a low energy long pulse occurs. The higher the repetition frequency, the lower the pulse peak exponentially.

  In the wavelength conversion laser, the wavelength conversion efficiency greatly depends on the pulse peak of the fundamental laser beam, and if the pulse peak is low, the wavelength conversion efficiency is lowered. Therefore, a high-power harmonic laser beam cannot be obtained at a high repetition frequency. As the repetition frequency is higher, the output of the harmonic laser beam tends to be exponentially lower. For example, when an Nd: YAG laser of Q-switch oscillation is used as an example of the fundamental laser, when comparing repetition rates of 50 kHz and 100 kHz, the pulse width is about 1.5 to 2 times longer at 100 kHz and per pulse. Therefore, the pulse peak is reduced to about 1/3 to 1/4. As a result, the output of the harmonic laser beam is also reduced to 1/3 to 1/4.

  Note that the rate at which the pulse width of the fundamental laser changes according to the repetition frequency is determined by the characteristics of the laser medium (stimulated emission cross section, etc.), and the Nd: YVO4 laser has a higher stimulated emission cross section coefficient than the Nd: YAG laser. It is possible to oscillate short pulses and high peaks at a high repetition frequency. On the other hand, an Nd: YAG laser in which a large-sized laser crystal has been put into practical use is advantageous for high-power oscillation. Therefore, in general, an Nd: YVO4 laser is used as a fundamental laser for a high repetition frequency, and an Nd: YAG laser is used for a low frequency and high output. In particular, a triple wave UV laser often uses an Nd: YAG laser for a low repetition frequency specification of about 50 kHz or less, and an Nd: YVO4 laser for a high repetition frequency specification of 50 kHz or more.

  By the way, in the drilling of a printed circuit board, which is the main application of the UV laser, in order to improve the processing performance and production capacity of the apparatus, a UV laser oscillator having a repetition frequency as high as possible and a high output is required. Normally, via processing of a printed circuit board with a UV laser is performed by irradiating a pulse beam with an optimal energy condition of several tens to hundreds of shots according to the substrate material to process one hole. Irradiation with a pulsed beam leads to faster processing. In reality, there is a demand for a high-power UV laser with a repetition frequency of about 100 kHz, and a triple-wave UV laser with an average output of 20 W using an Nd: YVO4 laser has been put into practical use. It has been.

  On the other hand, there is a pulse stretch technique for efficiently amplifying the output of a dye laser (for example, see Patent Document 1). As shown in FIG. 1 of Patent Document 1, the pulse beam emitted from the dye laser oscillator is divided into two by a beam splitter, and only one beam is delayed and propagated by a delay optical path composed of two spherical mirrors. This is a technology that synthesizes a single beam with a beam splitter and superimposes two pulse beams that are slightly shifted in time to increase the pulse width in a pseudo manner. By this, the pulse width is optimized. This makes it possible to increase the efficiency of output amplification.

JP-A-1-142524 (FIG. 1)

  This technology is applied to a wavelength conversion laser, the harmonic pulse laser beam is divided into two by a beam splitter, one beam is delayed and propagated through a delay optical path having a sufficiently long propagation time, and again superimposed on the original beam. A technique of doubling the frequency by time-dividing one pulse into two pulses by delay-combining two pulse beams with different timings can be considered.

  To double the pulse frequency in a complete form, it is necessary to give a long delay time corresponding to half the period of the original pulse frequency (for example, a delay time of 10 μs for a pulse frequency of 50 kHz), and spatial propagation When creating a delay time as long as this, the optical path length is on the order of 3000 m, and it is difficult to actually configure it. However, even if such a long delay time is not used, the thermal effect of the workpiece during laser processing is time consuming. If it is converted into a double pulse having a time interval of about several hundred nanoseconds that are independent of each other, it is possible to obtain an effect equivalent to that converted into a double repetition frequency in a pseudo manner. If the delay time is about several hundred nanoseconds, an optical path length of about 100 m is sufficient, and is a feasible length. Further, since the frequency is only converted by time-dividing the pulse, the average output of the original harmonic laser beam is maintained.

  As described above, when a harmonic laser beam having a high repetition frequency is obtained by doubling the repetition frequency of the fundamental laser beam, the average output is reduced to about ¼ due to a decrease in wavelength conversion efficiency. When the pulse of the harmonic laser beam is time-divided and the pulse frequency is doubled, the average output does not change. It can be said that this is a very efficient method for obtaining high-frequency harmonic pulsed laser light. Combining this pulse frequency doubling technology by delayed synthesis with a wavelength conversion laser that uses an Nd: YAG laser, which is advantageous for high output, as a fundamental laser, synthesizes high-power harmonic laser light at a high repetition rate. Can do.

  For example, when a third harmonic wave UV laser is taken as an example of the wavelength conversion laser, a high power UV laser of 50 W or more at 50 kHz can be designed with a UV laser having an Nd: YAG laser as a fundamental wave. In principle, it is possible to produce a high-power UV laser of 40 W or more at a repetition frequency of 100 kHz, and it is conceivable to produce a UV laser device having a higher output than a UV laser oscillator using an Nd: YVO4 laser.

  However, when the pulse frequency is doubled by delay synthesis, a very long delay optical path is required, which causes problems such as deterioration of the quality of the beam that has passed through the delay optical path and severe pointing fluctuations. . As described above, the optical path length of at least about 100 m is required as the delay optical path, and such a long-distance optical path can be realized by a multiple folded optical path using two opposingly arranged mirrors. When the beam passes through the beam, a slight pointing variation of the original laser beam and a change in the beam divergence angle have a great influence on the delayed synthesized beam.

  In the wavelength conversion laser device according to the present invention, in the technique of delay-synthesizes the harmonic pulse laser beam using the delay optical path and converts it into a pulse beam having a double repetition frequency, the path from the start point to the end point of the delay optical path is obtained. An image transfer connection is made.

  Since the present invention is configured so that the start point and the end point of the delay optical path are connected by image transfer, even if the pointing of the original laser beam fluctuates, the pointing of both beams is always performed at the end point of the delay optical path, that is, at the junction of the split beams. Since the beam diameters match, the quality of the delayed synthesized beam is stable, and highly stable laser processing can be realized.

  Embodiments of a wavelength conversion laser device according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration of a wavelength conversion laser device according to a first embodiment of the present invention. A harmonic pulse laser beam 10 (thick solid line in FIG. 1) emitted from a wavelength conversion laser oscillator 1 which is a third harmonic UV laser of an Nd: YAG laser is applied to a polarization beam splitter 2 which is a beam branching means by a bend mirror 3a. The light is guided and branched in two directions by the polarization beam splitter 2. A polarizer may be used as the beam branching means. For the polarization beam splitter 2, the polarization component that becomes S-polarized light becomes a reflected beam, and the P-polarized component becomes a transmitted beam. Here, the polarization component perpendicular to the plane formed by the incident optical axis when the laser beam 10 is incident on the polarization beam splitter 2 and the normal line of the reflection surface of the polarization beam splitter 2 is S-polarized light and parallel polarization components. Is P-polarized light. In the present invention, since one of the beams branched by the polarization beam splitter 2 is delayed, the beam to be delayed is referred to as a delayed beam 12 and the beam not to be delayed is referred to as a forward beam 11. In FIG. 1, since the transmitted beam is delayed, the reflected beam becomes the forward beam 11 (broken line in FIG. 1), and the transmitted beam becomes the delayed beam 12.

  The delayed beam 12 that has passed through the polarization beam splitter 2 passes through the delay optical path 100 and enters the side surface of the polarization beam splitter 2 again, but is transmitted again because it is P-polarized light. Then, it merges with the forward beam 11 reflected by the polarization beam splitter 2 and is superimposed on one beam. Here, the polarization beam splitter 2 functions as a means for combining two beams. The superimposed beam is guided to the processing lens 8 by the bend mirror 3b, and is condensed and irradiated on the processing workpiece 9 arranged on the processing table 4 by the processing lens 8 as it is and used for laser processing.

Here, when the propagation time of the delay beam 12 passing through the delay optical path 100 is t, the delay beam 12 merges with the forward beam 11 with a delay of the delay time t with respect to the forward beam 11. For this reason, as shown in FIG. 2, a double pulse waveform with a time interval t is formed and is delayed and synthesized into a pulse beam with a double repetition frequency in a pseudo manner. Since the speed of light is 3.0 × 10 ^ 8 m / s, for example, a delay time of 333 nsec can be obtained if the optical path length is 100 m. Assuming that the pulse width of the harmonic pulse laser is about 50 nsec, a double pulse waveform in which two pulses having a width of about 50 nsec are arranged at a time interval of 333 nsec is obtained.
In addition, when the delay time t is short and the two pulses are overlapped so as to overlap half as in the conventional patent document 1, this is a pulse width conversion technique for synthesizing a long pulse.

  As shown in FIG. 1, the delay optical path 100 is formed by arranging two multiple folded optical path units 5 composed of two total reflection mirrors 31 and 32 facing each other in series on the laser optical axis. The folded optical path unit 5 realizes a long-distance optical path with a compact configuration by forming an optical path that multiple-reflects several tens of times between the two total reflection mirrors 31 and 32. For example, the two total reflection mirrors 31 and 32 are arranged to face each other with a distance of 1 m, and the angle is strictly adjusted so as to face each other in parallel. The delayed beam 12 is introduced from the side of the total reflection mirror 31 toward the total reflection mirror 32, and is reflected so as to be reflected 25 times between the total reflection mirrors 31 and 32 and emitted from the side of the total reflection mirror 32. The incident angle of 12 is adjusted. Thereby, a delay optical path having a distance of 50 m per unit can be realized. Then, as shown in FIG. 1, two folded optical path units are used, and the delayed beam 11 transmitted through the polarization beam splitter 2 by the bend mirrors 3c, 3d, and 3e is incident on the first folded optical path unit 5a. A long distance of 100 m or more is obtained by guiding the beam coming out from the folding optical path unit 5a to the second folding optical path unit 5b and allowing the beam coming out from the second folding optical path unit 5b to enter the polarization beam splitter 2 again. A delayed optical path 100 can be formed.

  Further, as shown in FIG. 1, a convex lens 41 having a focal length f is provided in the delay optical path 100 at two locations, in front of the first return optical path unit 5a and in front of the second return optical path unit 5b. , 42 are arranged. The two convex lenses 41 and 42 form an image transfer optical path, and an image transfer connection is made between the start point and the end point of the delay optical path 100.

  Here, image transfer will be described. FIG. 3 shows types of image transfer optical paths and their schematic views. 3 are the points where the laser beam 10 in the polarization beam splitter 2 branches into the forward beam 11 and the delay beam 12, respectively, and the points where the forward beam 11 and the delay beam 12 in the polarization beam splitter 2 merge. In fact, as shown in FIG. 1, the points at substantially the same position are shown. FIG. 3A shows an image transfer optical path having a two-lens configuration, in which both lenses 41 and 42 are convex lenses having a focal length f, the distance between them is 2f, and the total optical path length of the delay optical path is 4f. In this case, the optical path system forms an inverted image transfer optical path. The ray matrix of the optical path system at this time is represented by (A, B, C, D) = (− 1, 0, 0, −1). This is called “inverted” because the image is inverted at the start and end points of the optical path. The delay optical path in FIG. 1 is constituted by this inverted image transfer optical path. On the other hand, FIG. 3B is referred to as an upright image transfer optical path, and the two image transfer optical paths in FIG. 3A are arranged in series. The ray matrix of this optical path system is (A, B, C, D) = (1, 0, 0, 1), and the image is not inverted unlike the inverted type.

  When the delay optical path 100 in the configuration of FIG. 1 is represented by a schematic diagram similar to FIG. 3, as shown in FIG. 4A, the branch point → the first lens 41 → the first folded optical path unit 5a → The optical path is configured in the order of the second lens 42 → the second folded optical path unit → the confluence. Here, by setting the focal length of the two lenses 41 and 42 to f and the optical path length of one folded optical path unit 5 to about 2f, the optical distance between the two lenses 41 and 42 is 2f and the branch point. Can be set to 4f, and an inverted image transfer optical path can be formed. As shown in FIG. 4B, the order of branch point → first folding optical path unit 5a → first lens 41 → second folding optical path unit 5b → second lens 42 → confluence point. However, since the image transfer condition shown in FIG. 3A is satisfied, the same effect can be obtained.

  In the configuration of FIG. 1, the P-polarized component laser beam transmitted by the polarizing beam splitter 2 is used as the delayed beam 12, but the S-polarized component laser beam reflected by the polarized beam splitter 2 may be used as the delayed beam 12. The configuration of the wavelength conversion laser device in this case is shown in FIG. As shown in FIG. 5, the P-polarized component transmitted by the polarizing beam splitter 2 is guided as a forward beam 11 by the bend mirrors 3 f and 3 b to the workpiece 9 via the machining lens 8. On the other hand, the S-polarized component reflected by the polarization beam splitter 2 is guided as a delayed beam 12 to the delayed optical path 100 by the bend mirrors 3g and 3h. The delayed beam 12 coming out from the delayed optical path 100 is incident on the polarization beam splitter 2, reflected again, merges with the forward beam 11, and is superimposed on one beam. In the following embodiment, the beam reflected by the polarizing beam splitter 2 will be described as a forward beam 11 and the transmitted beam will be described as a delayed beam 12. However, as shown in FIG. It may be used as a beam.

Next, FIG. 6 shows a configuration of a wavelength conversion laser device using the upright image transfer optical path shown in FIG. Since only the delay optical path is different from FIG. 1, only the delay optical path 101 will be described.
As shown in FIG. 6, the delay optical path 101 is configured by using four folded optical path units and four lenses. The delayed beam 11 transmitted through the polarization beam splitter 2 by the bend mirrors 3c, 3d, 3e, 3i, 3j, 3k, and 3l is guided as follows. First, the delayed beam 11 is incident on the first lens 41, and the beam transmitted through the first lens 41 is incident on the first folded optical path unit 5a. Thereafter, the first folding optical path unit 5a → the second lens 42 → the second folding optical path unit 5b → the third lens 43 → the third folding optical path unit 5c → the fourth lens 44 → the fourth folding optical path unit. The beams are guided in the order of 5d, and the beam emitted from the fourth folded optical path unit 5b is made incident on the polarization beam splitter 2 again.
Here, the focal length of the four lenses 41, 42, 43, 44 is set to f, and the optical path length of one folded optical path unit 5 is set to about 2 f, so that the distance between the first lens 41 and the second lens 42 is increased. Further, the optical distance between the third lens 43 and the fourth lens 44 can be set to 2f, and the optical distance from the branch point to the junction can be set to 8f. The erect image transfer shown in FIG. An optical path is formed.

  When the delay optical path 101 in the configuration of FIG. 6 is represented by a schematic diagram similar to FIG. 3, it is as shown in FIG. In order to form an erect image transfer, the optical distance between the first lens 41 and the second lens 42, the optical distance between the third lens 43 and the fourth lens 44, and from the branch point to the confluence Since the optical distance only needs to be the predetermined distance shown in FIG. 7A, other configurations are also conceivable. For example, as shown in FIG. 7B, the branch point → the first folding optical path unit 5a → the first lens 41 → the second folding optical path unit 5b → the second lens 42 → the third folding optical path unit. 5c → third lens 43 → fourth folding optical path unit 5d → fourth lens 44 → junction point. As shown in FIG. 7C, the branch point → the first lens 41 → the first folding optical path unit 5a → the second lens 42 → the second folding optical path unit 5b → the third folding optical path unit. 5c → third lens 43 → fourth folding optical path unit 5d → fourth lens 44 → junction point. In FIG. 7C, the second folded optical path unit 5b and the third folded optical path unit 5c may be integrated to form a folded optical path unit having an optical path length of 4f. In any case, in order to form an upright image transfer optical path using four lenses, the optical distance shown in FIG.

  The delay optical path 101 shown in FIG. 6 is an example in which an erect image transfer optical path is formed by using four lenses, but it can also be formed by three lenses. FIG. 8A shows a configuration diagram of a delay optical path 102 in which an erect image transfer optical path is configured by three lenses, and FIG. 8B shows a schematic diagram thereof. The arrangement of the lenses is different from that in FIG. 6, and as shown in FIG. 6A, the first lens having a focal length f between the first folded optical path unit 5a and the second folded optical path unit 5b. 41, and a second lens 45 having a focal length f / 2 is disposed between the second folding optical path unit 5b and the third folding optical path unit 5c, and the third folding optical path unit 5c and the fourth folding optical path unit 5c. A third lens 43 having a focal length f is arranged between the optical path units 5e. Accordingly, as shown in FIG. 8B, the optical distance between the first lens 41 and the second lens 45 and the optical distance between the second lens 45 and the third lens 43 are set to 2f. Since the optical distance between the branch point and the merge point is 8f and the ray matrix is (A, B, C, D) = (1, 0, 0, 1), an erect image transfer optical path can be formed.

Next, the effect of the present invention will be described.
A feature of the present invention is that an image transfer connection is made between the start point and the end point of the delay optical path, whereby the difference in beam diameter between the forward beam 11 and the delay beam 12 to be delayed and combined, and pointing fluctuations. The combined pulse beam with excellent beam quality can be formed. This will be described below.

  FIG. 9 compares the effect of the pointing change and the change of the beam diameter upon delay synthesis between the case where the technique of Patent Document 1 is applied (hereinafter referred to as the conventional method) and the present invention. 9A shows the case of the conventional delay optical path 99, FIG. 9B shows the present invention when an inverted image transfer optical system is applied, and FIG. 9C applies the upright image transfer optical system. This is the case of the present invention. Here, the conventional delay optical path 99 has a configuration in which the two lenses 41 and 42 are not provided in the delay optical path 100 of FIG. In each case, the change optical axis when the original laser beam 10 changes in the angle pointing, the forward beam 11 is indicated by a broken line, the delay beam 12 is indicated by a solid line, and the original optical axis is indicated by a one-dot chain line. In addition, two circles on the virtual target 6 installed in the optical path after delayed synthesis represent the beam spot 111 of the forward beam 11 and the beam spot 112 of the delayed beam 12 that are irradiated on the virtual target 6. The size of the circle represents the beam diameter.

  In the case of the conventional method shown in FIG. 9A, when the slight angle pointing change occurs in the original laser beam 10, the delayed beam 12 passes through a very long optical path in the delayed optical path 99. Greatly changes and is largely separated from the optical axis of the forward beam 11. As a result, even if the optical axis is adjusted so as to be superimposed on a single beam, the pointing of the original laser beam 10 changes over time due to a change over time due to temperature fluctuations and mechanical fluctuations due to ambient vibrations. As a result, a phenomenon occurs in which the optical axis of the delayed combined beam is separated into two. On the other hand, in FIGS. 9B and 9C, since the image transfer optical system is applied, even if a pointing change occurs in the original laser beam 10, the optical axis of the delayed beam 12 at the confluence of the polarization beam splitter 2 The optical axis of the forward beam 11 changes so as to always coincide. 9B shows an inverted type image transfer, and therefore the optical axis of the delayed beam 12 has a tilt component in the opposite direction to the optical axis of the forward beam 11, so that the delayed beam 12 The forward beam 11 is slightly separated. However, the optical path length from the merging point to the work is several meters or 1 m or less, and the deviation of the irradiation position between the delayed beam 12 and the forward beam 11 is at a level that hardly causes a problem. In the case of FIG. 9C, the image transfer is an upright type, and the optical axes of the delayed beam 12 and the forward beam 11 always coincide with each other at any position in the optical path after the delay synthesis, and complete beam synthesis is performed.

  As a supplement, FIG. 10 shows the relationship between the delay optical path length and the optical axis variation at the confluence. This is a calculation result when it is assumed that a pointing change of 100 μrad has occurred in the original laser beam 10. As shown in FIG. 10, in the case of the conventional method, the optical axis variation increases in proportion to the delay optical path length. For example, when the delay optical path length is 100 meters, the optical axis variation at the confluence reaches 10 mm. . On the other hand, when the image transfer optical path is applied, the optical axis variation is 0, indicating that the optical axis does not vary.

  FIG. 11 shows the result of comparison of the difference in beam diameter at the junction of the forward beam 11 and the delayed beam 12 by simulation calculation between the conventional method and the method of the present invention. The delay optical path length was 100 meters, the original laser beam diameter was 5 mm, and the laser beam wavelength was 355 nm. Since the beam diameter of the delayed beam expands according to the delay optical path length, the beam diameter increases considerably when a long-distance delay optical path is assembled. In the above calculation, in the case of the conventional method, the delayed beam expands to a beam diameter that is twice or more that of the forward beam. On the other hand, in the case of the present invention to which the image transfer optical path is applied, the beam diameter at the separation point is transferred as it is to the merging point, so the beam diameter does not change even in the long-distance delay optical path, and the forward beam and the delayed beam are the same. Synthesized by beam diameter.

  That is, when the delay synthesis technique is applied as the pulse frequency conversion technique, a long-distance delay optical path is required, but at that time, the influence of pointing fluctuation becomes significant. However, in the delay optical path connected by image transfer, in principle, the optical axis variation at the confluence is zero regardless of the length of the delay optical path, meaning that it is not affected by the pointing variation of the original laser beam. Yes.

  Even if a long-distance optical path is assembled in this way, the configuration of the present embodiment using the image transfer optical path is not affected by pointing fluctuations, and the beam diameter is synthesized with the forward beam and the delayed beam in the same state. Therefore, a high quality and stable pulse beam can be synthesized, and high quality laser processing can be realized.

  Note that the image transfer optical path does not have to be completely image transfer connected between the branching point and the confluence of the delay optical path. An effect is obtained. Specifically, it is effective if the value of the matrix value B when the ABCD ray matrix of the entire delay optical path is numerically calculated in units of meters is a value within 10 or less. Normally, if the optical axis is displaced by several mm or more and deviates from the center of the optical component, or if the base of the beam irradiates the edge of the optical component, the beam becomes unstable and a problem occurs. Considering that the fluctuation amount is 0.1 μrad or less, if the value of B is within 10, the displacement amount is suppressed to 1 mm or less, and it can be said that it falls within the range of no problem.

  In the above embodiment, the Nd: YAG laser triple wave UV laser has been described as the wavelength conversion laser oscillator. However, other harmonic lasers such as a double wave green laser and a fourth wave UV laser are used. However, the effect can be expected, and the present invention is not limited to the triple wave laser.

Embodiment 2. FIG.
FIG. 12 is a diagram showing a second embodiment of the wavelength conversion laser device according to the present invention, FIG. 12 (a) is a configuration diagram of the wavelength conversion laser device, and FIG. 12 (b) is a schematic diagram of a delay optical path. is there. Parts having the same configuration as in FIG. This configuration is based on the same principle as the configuration of FIG. 1 and has the same effect. However, a 90-degree polarization rotating means such as a half-wave plate is installed in the delay optical path, and the delay beam has one folded optical path unit. The difference is that it is passed twice. The operating principle of this configuration is described below.

  First, in FIG. 12A, after the laser beam 10 is incident on the polarization beam splitter 2, the S-polarized component is reflected and becomes the forward beam 11, and the P-polarized component is transmitted and becomes the delayed beam 12 in the delay optical path 103. Incident. The delayed beam 12 passes through a half-wave plate 20 installed in the delayed optical path 103, is converted to an S-polarized delayed beam 12a, and is guided to a lens 41 having a focal length f by a bend mirror 3c. The light passes through the folded optical path unit 5a having a length of about 2f, and is incident on the side surface of the polarization beam splitter 2 by the bend mirrors 3d and 3e. At this time, since the polarization of the delayed beam 12a is S-polarized light, it is reflected by the polarization beam splitter 2 and enters the delayed optical path 103 again. Then, the light passes through the half-wave plate 20 again and is converted to the same P-polarized delayed beam 12 just after being branched. The delayed beam 12 that passes through the delayed optical path 103 in the same manner and is incident on the side surface of the polarization beam splitter 2 is P-polarized light, so that it passes through the polarization beam splitter 2 and is merged and superimposed on the forward beam 11. That is, by inserting the half-wave plate 20 into the delay optical path 103, the delay beam 12 passes through the delay optical path twice. The insertion position of the half-wave plate 20 may be anywhere in the delayed optical path.

The lens 41 in the delay optical path has a design value such that the delayed beam passes through the delay optical path twice so that the image transfer connection is made between the branch point of the delay optical path and the junction. A schematic diagram of the delay optical path 103 is shown in FIG. As shown in FIG. 12B, the focal length of the lens 41 is f, and the optical path length of the folded optical path unit 5a is approximately 2f. Therefore, when the optical path length for one delay optical path is L, L = 2f. Designed to meet. As a result, the total delay optical path length from branching to merging by passing through the delay optical path twice is 2L (= 4f), and the optical path length while passing through the lens 41 twice is 2f. The condition for image transfer connection up to the junction is satisfied. That is, although there is only one actual lens, the configuration is equivalent to the arrangement of two lenses apparently on the delay optical path.
Although the position of the lens 41 is in front of the folding optical path unit 5a in FIG. 13, the image transfer connection condition is satisfied even if it is arranged after the folding optical path unit 5a.

The configuration shown in FIG. 12 is a delayed optical path of an inverted image transfer configuration. Next, a delayed optical path of an upright image transfer configuration will be described.
FIG. 13 is a diagram showing a wavelength conversion laser device having a delay optical path having an upright image transfer configuration when passing through the delay optical path twice as in FIG. 12, and FIG. 13 (a) is a wavelength conversion laser. FIG. 13B is a schematic diagram of a delay optical path. As shown in FIG. 13A, the configuration is substantially the same as in FIG. 1, except that the half-wave plate 20 is arranged in the delay optical path 104. By arranging the half-wave plate in the delay optical path 104, the delay beam 12 passes through the delay optical path twice as in FIG. If the focal length of the two lenses 41 and 42 is f, the optical path length of the two folded optical path units 5a and 5b is about 2f, and the optical path length of the delayed optical path 104 is L, a schematic diagram of the delayed optical path 104 is shown in FIG. )become that way. As shown in FIG. 13B, since L = 4f and the optical path length between the two lenses 41 and 42 is 2f, the total delay optical path length is 2L = 8f, from the branch point to the junction. The condition for image transfer connection in an upright manner is satisfied. That is, although there are two actual lenses, the configuration is equivalent to the arrangement of four lenses on the apparent delay optical path.
In FIG. 14, the two lenses 41 and 42 are arranged before and after the first folding unit 5a. However, even if the lenses 41 and 42 are arranged before and after the second folding optical path unit 5b, the image transfer connection condition is as follows. It is filled.

  With the configuration shown in FIG. 12 or 13, the delayed beam 12 passes through the delayed optical path 104 twice, so that in the case of inverted image transfer, the upright image is compared with FIG. 1 of the first embodiment. In the case of transfer, the number of folding optical path units and the number of lenses for image transfer can be halved as compared with FIG. 6 of the first embodiment, and a long distance delay equivalent to that of FIG. 1 or FIG. An optical path can be realized.

  The half-wave plate 20 in the present embodiment may be other means such as two rotators or two quarter plates as long as the polarization direction is rotated by 90 degrees. It is not limited. In addition, the configuration in which the image transfer optical path is formed by one lens 41 has been described. However, as long as the start point and the end point of the delay optical path are connected by image transfer, a two-lens configuration or a three-lens configuration may be used. The configuration is not limited. In addition, as described in the first embodiment, the image transfer optical path does not have to be completely image transfer connected between the branch point of the delay optical path and the junction point, and the optical path system that provides substantially image transfer. If it is good.

Embodiment 3 FIG.
FIG. 14 is a diagram showing a third embodiment of the wavelength conversion laser device according to the present invention, FIG. 14 (a) is a configuration diagram of the wavelength conversion laser device, and FIG. 14 (b) is a schematic diagram of a delay optical path. is there. Parts having the same configuration as in FIG. This configuration is based on the same principle as the configuration of FIG. 1 and has the same effect. However, two quarter-wave plates and two total reflection mirrors are installed in the delay optical path so that the delay beam passes through the delay optical path. It is different in that it passes back and forth. 1 has the same effect as the configuration of FIG. 6 in that the purpose is to realize a long-distance delay optical path with a more compact configuration, but the optical path configuration different from that of FIG. 6 has the same effect. The effect is realized. This point is described below.

  In FIG. 14A, the P-polarized component of the laser beam 10 passes through the polarization beam splitter 2 and is guided to the delay optical path 105 to become the delay beam 12. The delayed beam 12 passes through the first quarter-wave plate 51 and is converted into circularly polarized light. The delayed beam 12b converted into circularly polarized light is guided to the first folding optical path unit 7a having the optical path length f by the bend mirror 3c, passes through the first folding optical path unit 7a, and then is bent by the bend mirrors 3d and 3e. It passes through the lens 42 of f and the second folded optical path unit 7b having the optical path length f in order. The delayed beam 12 a that has passed through the second folded optical path unit 7 b is reflected by the first total reflection mirror 61. On the contrary, the reflected delayed beam 12b passes through the second folded optical path unit 7b, the lens 42, and the first folded optical path unit 7b in this order, and is delayed by the first quarter wavelength plate 51 with S polarization. 12c and returned to the polarization beam splitter 2. Since the delayed beam 12c is S-polarized light, it is reflected once in the direction opposite to the forward beam 11 by the polarization beam splitter 2, passes through the second quarter-wave plate 52, and is converted to circularly polarized light. The delayed beam 12b converted to circularly polarized light is reflected back in the reverse direction by the second total reflection mirror 62, passes through the second quarter-wave plate 52 again, and is then converted to the original P-polarized light. . The delayed beam 12 returned to the P-polarized light again enters the side surface of the polarization beam splitter 2, and since it is now a P-polarized light, it is transmitted as it is and merges with the forward beam 11 and is superimposed on one beam.

  A schematic diagram of the delay optical path 105 in FIG. 14A is shown in FIG. The delayed beam 12 has a branching point → the first folding unit 7a → the lens 42 → the second folding unit 7b → the first total reflection mirror 61 → the second folding unit 7b → the lens 42 → the first folding unit 7a → It passes in the order of confluence (branch point) → second total reflection mirror 62 → confluence. As shown in FIG. 14B, by setting the optical path length of the folded optical path unit to about f which is half the optical path length of the folded optical path unit 5 of FIG. Thus, the optical path length during two passes through the lens 42 is 2f, and the total delay optical path length of the delay optical path 105 is 4f. Since the focal length of the lens 42 is f, the design condition for the inverted image transfer connection from the branch point to the junction is satisfied. That is, although there is only one actual lens, the configuration is equivalent to the arrangement of two lenses apparently on the delay optical path.

  With the configuration shown in FIG. 14, since the delayed beam 12 reciprocates through the delayed optical path 105, a folded optical path unit whose optical path length is half that of FIG. 1 of the first embodiment can be used and image transfer is performed. Only one half of the number of lenses may be used, and a long-distance delay optical path equivalent to that shown in FIG. 1 can be realized with a compact configuration or size.

The configuration shown in FIG. 14 is a delayed optical path of an inverted image transfer configuration. Next, a delayed optical path of an upright image transfer configuration will be described.
FIG. 15 is a diagram showing a wavelength conversion laser device having a delay optical path having an upright image transfer configuration when reciprocating along the delay optical path as in FIG. 14, and FIG. FIG. 15B is a schematic diagram of the delay optical path. As shown in FIG. 15 (a), the configuration is substantially the same as in FIG. 14, and the optical path lengths of the two folded optical path units in the delay optical path 106 are about 2f as in the first embodiment, and The difference is that a lens 41 having a focal length f is inserted between the first quarter-wave plate 51 and the first folded optical path unit 5a. By arranging the two quarter-wave plates 51 and 52 and the total reflection mirrors 61 and 62 in the delay optical path 106, the delay beam 12 reciprocates in the delay optical path as in FIG. Therefore, the delayed beam 12 is changed from the branch point → the first lens 41 → the first folding unit 5a → the second lens 42 → the second folding unit 5b → the first total reflection mirror 61 → the second folding unit 5b. The light passes through the second lens 42, the first folding unit 5a, the first lens 41, the joining point (branch point), the second total reflection mirror 62, and the joining point.

  Further, as shown in FIG. 15B, the optical path length of the folded optical path unit is set to about 2f, which is the same as the optical path length of the folded optical path unit 5 of FIG. The optical path length between them is 2f, and the total delay optical path length of the delay optical path 106 is 8f. Since the focal length of the two lenses 41 and 42 is f, the design condition for erect image transfer connection from the branch point to the junction is satisfied. That is, although there are two actual lenses, the configuration is equivalent to the arrangement of four lenses on the apparent delay optical path.

  With the configuration shown in FIG. 15, since the delayed beam 12 reciprocates through the delayed optical path 106, the number of folded optical path units and the number of lens for image transfer are halved compared to FIG. 6 of the first embodiment. A long distance delay optical path equivalent to that of FIG. 6 can be realized with a compact configuration or size.

  In the above embodiment, the image transfer connection configuration using one lens or two lenses has been described. However, the configuration using other lenses, the total reflection mirror 61 as a spherical mirror, and the lens. A configuration in which an image transfer optical system is formed in combination is also conceivable and is not limited to the above configuration. As an example, a delay optical path when a spherical mirror is used will be described with reference to FIG.

  FIG. 16 is a diagram showing a wavelength conversion laser device provided with a delay optical path having an upright image transfer configuration when reciprocating along the delay optical path as in FIG. 15, and FIG. 16 (a) is a diagram of the wavelength conversion laser device. FIG. 16B is a schematic diagram of a delay optical path. As shown in FIG. 16A, the configuration is substantially the same as in FIG. 15, and the first total reflection mirror in the delay optical path 106 is replaced with a spherical mirror 63 having a radius of curvature f. A difference is that the lens 41 is not inserted between the quarter-wave plate 51 and the first folded optical path unit 5a. By arranging the two quarter-wave plates 51 and 52, the total reflection mirror 62, and the spherical mirror 63 in the delay optical path 106, the delay beam 12 reciprocates in the delay optical path as in FIG. In this case, the delayed beam 12 has a branch point → first folding unit 5a → lens 42 → second folding unit 5b → spherical mirror 63 → second folding unit 5b → lens 42 → first folding unit 5a → join. Pass in the order of point (branch point) → total reflection mirror 62 → confluence.

  Also, as shown in FIG. 16 (b), the optical path length of the folded optical path unit is set to about 2f, which is the same as the optical path length of the folded optical path unit 5 of FIG. The total optical path length of the delay optical path 106 is 8f. Since the focal length of the lens 42 and the radius of curvature of the spherical mirror are both f, the configuration is the same as in FIG. 8B, and the design condition for erect image transfer connection from the branch point to the junction is satisfied.

  As described in the first embodiment, the image transfer optical path does not have to be completely image transfer connected between the branch point of the delay optical path and the merging point. If it is good.

Embodiment 4 FIG.
FIG. 17 is a diagram showing the configuration of the wavelength conversion laser device according to the fourth embodiment of the present invention. Parts having the same configuration as in FIG. This configuration has the same effect based on the same principle as the configuration of FIG. 1, but is different in that the delayed optical path is covered with a sealed housing.

  In FIG. 17, the entire delay optical path 100 including the two folded optical path units 5 a and 5 b and the two image transfer lenses 41 and 42 is covered with a sealed casing 70. The delayed beam 12 enters the delay unit from the first window 71 provided in the sealed casing 70, exits from the second window 72, passes through the polarization beam splitter 2, and merges with the forward beam 11.

  Here, the delayed optical path composed of the two folded optical path units 5a and 5b has an optical path length of 100 m or more in total length. For example, in the case where the optical path is exposed as shown in FIG. 1, aberration fluctuations due to air fluctuations in the optical path. It will be strongly influenced by. In a normal optical path of about several meters, as shown in the forward beam of FIG. 18A, there is almost no influence of aberration fluctuation, but in the case of a long distance optical path of 100 m scale, FIG. As shown in the delayed beam, pulse variations occur and an influence that cannot be ignored occurs. Such aberration fluctuations in the delay optical path 100 cannot be canceled even by the image transfer optical system, and appear as a phenomenon that the pointing of the beam fluctuates at the merging point, and the pulse stability of the machining beam decreases. End up.

  The cause of aberration fluctuations in the optical path is due to convection of air with a temperature difference, and fluctuates due to airflow from the air conditioning equipment around the apparatus. Therefore, it is effective to cover the delay optical path part with a sealed casing so as not to be affected by the air current from the periphery of the apparatus. In FIG. 18B, the pulse variation of the delayed beam was compared between the case where the sealed casing is not applied and the case where the sealed casing is applied. Here, as shown in FIG. 18A, the pulse height variation ΔP is used as an index as the pulse variation. In FIG. 18B, the leftmost is (1) a normally designed delay optical path and is not sealed, that is, if there are no image transfer lenses 41 and 42 in FIG. 1, the center is (2) the diagram of the first embodiment. When the image transfer connection corresponding to 1 is not sealed, the rightmost is (3) the delay optical path of the image transfer connection and the sealed housing is applied, that is, the configuration of FIG. Compared to the case (1), the pulse variation is halved only by image transfer connection as in the case (2). However, by applying a sealed housing as in the case (3), the pulse variation is reduced to the case (1). ). As a result, effects such as stabilization of the quality of laser processing can be obtained.

  The sealed casing described above is not limited to a container requiring strict leak rate management, such as a gas-filled chamber or a vacuum container, as long as it has a structure that blocks the flow of outside air. A cover structure by bonding sheet metal members is also sufficient. In FIG. 17, the sealed casing 70 is applied to FIG. 1 of the first embodiment, but the same effect can be obtained even when applied to other embodiments.

  The wavelength conversion laser device according to the present invention is suitable for use as a laser pulse synthesizing means in a field where laser processing with a high repetition frequency and a high output is required.

It is a block diagram of the wavelength conversion laser apparatus which shows Embodiment 1 of this invention. It is a figure which shows the pulse beam by the wavelength conversion laser apparatus which is Embodiment 1 of this invention. It is a schematic diagram explaining the structure of an image transfer optical path. It is a schematic diagram of the delay optical path of the inverted image transfer of the wavelength conversion laser device according to the first embodiment of the present invention. It is a block diagram of the other wavelength conversion laser apparatus which shows Embodiment 1 of this invention. It is a block diagram of the other wavelength conversion laser apparatus which shows Embodiment 1 of this invention. It is a schematic diagram of the delay optical path of the upright image transfer of the wavelength conversion laser device according to the first embodiment of the present invention. It is the block diagram and schematic diagram of the delay optical path of the erect image transfer of the other wavelength conversion laser apparatus which is Embodiment 1 of this invention. It is the figure which compared the change of an optical axis and a beam diameter with the wavelength conversion laser apparatus of Embodiment 1 of this invention and what applied the prior art. It is the graph which compared the calculation result of the optical axis variation | change_quantity by what applied the wavelength conversion laser apparatus of Embodiment 1 of this invention, and a prior art. It is the graph which compared the calculation result of the beam diameter variation | change_quantity by what applied the wavelength conversion laser apparatus of Embodiment 1 of this invention, and a prior art. It is the block diagram of the wavelength conversion laser apparatus which shows Embodiment 2 of this invention, and the schematic diagram of the delay optical path of an inverted type image transfer. It is the block diagram of the wavelength conversion laser apparatus which shows Embodiment 2 of this invention, and the schematic diagram of the delay optical path of an erect image transfer. It is the block diagram of the wavelength conversion laser apparatus which shows Embodiment 3 of this invention, and the schematic diagram of the delay optical path of an inverted type image transfer. It is the block diagram of the wavelength conversion laser apparatus which shows Embodiment 3 of this invention, and the schematic diagram of the delay optical path of an erect image transfer. It is the block diagram of the other wavelength conversion laser apparatus which shows Embodiment 3 of this invention, and the schematic diagram of the delay optical path of an erect image transfer. It is a block diagram of the wavelength conversion laser apparatus which shows Embodiment 4 of this invention. It is the figure which compared the experimental result of pulse stability with the wavelength conversion laser apparatus of Embodiment 4 of this invention, the thing of Embodiment 1 of this invention, and the thing to which a prior art is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wavelength conversion laser oscillator 2 Polarizing beam splitter 5, 7 Folding optical path unit 10 Laser beam 11 Forward beam 12 Delayed beam 20 1/2 wavelength plate 41 1st lens 42, 45 2nd lens 43 3rd lens 44 4th Lens 51 first quarter wave plate 52 second quarter wave plate 61 first total reflection mirror 62 second total reflection mirror 63 spherical mirror 70 hermetically sealed casing 71 first window 72 second Window 100, 101, 102, 103, 104 Delayed optical path 111 Beam diameter of forward beam 112 Beam diameter of delayed beam

Claims (10)

A wavelength conversion laser oscillator that outputs a harmonic laser beam;
Laser beam branching means for branching the harmonic laser beam output from the laser oscillator into a plurality of laser beams;
Laser beam synthesis means for superposing and synthesizing the plurality of branched laser beams;
Delay optical path means for making the optical path length of at least one laser beam out of the plurality of branched laser beams longer than the optical path lengths of the other laser beams;
An image transfer unit disposed in the delay optical path unit and configured to transfer an image between a branch point of the laser beam of the branch unit and a converging point of the laser beam of the combining unit;
Provided wavelength conversion laser device. The image transfer means includes
Inverted image transfer
The wavelength conversion laser device according to claim 1. The image transfer means includes
When the optical path length of the laser beam from the branch point to the confluence by the delay optical path means is 4f, two lenses having a focal length f are arranged on the optical path of the laser beam passing through the delay optical path means, The optical path length between the two lenses is 2f.
The wavelength conversion laser device according to claim 2. The image transfer means includes
For upright image transfer,
The wavelength conversion laser device according to claim 1. The image transfer means includes
When the optical path length of the laser beam from the branch point to the converging point by the delay optical path means is 8f, four lenses having a focal length f are arranged on the optical path of the laser beam passing through the delay optical path means, In the four lenses, the optical path length between the lens on the branch point side and the adjacent lens is 2f, and the optical path length between the lens on the confluence point and the adjacent lens is 2f.
The wavelength conversion laser device according to claim 4. The image transfer means includes
When the optical path length of the laser beam from the branch point to the converging point by the delay optical path means is 8f, two lenses having a focal length f on the optical path of the laser beam passing through the delay optical path means and the focal length f / 2 are arranged in the order of a lens having a focal length f, a lens having a focal length f / 2, and a lens having a focal length f, and an optical path length between the lens having the focal length f and the lens having the focal length f / 2. Is 2f,
The wavelength conversion laser device according to claim 4. The delay optical path means includes
The branched laser beam is reflected by a mirror and guided to the combining means to extend the optical path length of the laser beam,
The image transfer means includes
When the optical path length of the laser beam from the branch point to the converging point by the delay optical path means is 8f, the mirror is a spherical mirror having a radius of curvature f, and is on the optical path of the laser beam incident and emitted by the spherical mirror. A lens having a focal length f is disposed, and an optical path length between the lens and the spherical mirror is set to 2f.
The wavelength conversion laser device according to claim 4. A sealed housing provided with a window for entering or exiting a laser beam covering the delay optical path means,
The wavelength conversion laser device according to claim 1. The wavelength conversion laser oscillator outputs a harmonic laser beam using an Nd: YAG laser as a fundamental laser.
The wavelength conversion laser apparatus in any one of Claim 1 to 8. When the ray matrix (A, B, C, D) of the delay optical path means is expressed in meters, the value of B of this ray matrix is within 10;
The wavelength conversion laser device according to claim 1.

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