JPWO2007132508A1 - Lighting device - Google Patents

Abstract

In the first optical system (4), coherent light from the light source unit (2) is guided along the circulation path (T0), and the mirror surface (432) of the tilt mirror (43) is on the circulation path (T0). In FIG. 2, the self-erected image is arranged at an optical position formed by being superimposed while being shifted, and the slit (431) formed in the tilt mirror (43) divides coherent light into a plurality of light beams and a plurality of lights. Beam superposition is performed. The optical path difference from the incident position of the coherent light to the first optical system (4) to the arbitrary two of the plurality of light beams reaching the slit (431) is made longer than the coherence length of the coherent light. As a result, in the illumination device (1) using coherent light, it is possible to obtain illumination light with a uniform intensity distribution while preventing speckles from being generated.

Description

  The present invention relates to an illumination device that illuminates an object.

  Conventionally, line-shaped illumination light has been used in imaging devices, drawing devices, and the like, and in recent years, various methods for making the intensity distribution of such illumination light uniform have been proposed. For example, in Japanese Patent No. 3607604 (Reference 1), light from a laser light source is incident on an incident surface of a columnar prism while being diverged in a predetermined direction by a cylindrical lens, and light is emitted in the direction of diverging in the prism. The intensity distribution is made uniform by taking out from the exit surface opposite to the entrance surface while being reflected by the reflecting surfaces provided on both side surfaces, and imaging the exit surface of the prism on the object using another optical system. A technique for irradiating an object with line-shaped illumination light is disclosed. Further, in US Pat. No. 6,611,382 (Document 2), light from a plurality of light emitting elements arranged is emitted by a cylindrical lens array in which a smaller number of lenses than the number of light emitting elements are arranged. Divided with respect to the arrangement direction of the elements and diverged, and the light from the cylindrical lens array is guided to a linear area on the object while being superposed by another cylindrical lens, so that the linear distribution has a uniform intensity distribution. A technique for irradiating light onto an object has been proposed.

  However, when the illumination light is irradiated onto the object by the methods of the above-mentioned literature 1 and literature 2, if the coherency of the laser light from the light source is high, speckle due to the interference of the laser light occurs. As a result, the uniformity of the light intensity distribution is reduced. In particular, when using a laser beam with a narrow spectral bandwidth, a solid-state laser, or a gas laser, the coherency of the laser beam is higher than when using another light source such as a semiconductor laser. It becomes remarkable.

  The present invention is directed to an illumination device that illuminates an object, and an object of the present invention is to obtain illumination light with a uniform intensity distribution while preventing speckle generation in an illumination device using coherent light. It is said.

  The illumination device includes a light source unit that emits coherent light, and an optical system that divides the coherent light into a plurality of light beams and superimposes the plurality of light beams at a predetermined overlapping position to obtain illumination light. The optical path difference from the position where the coherent light enters the optical system to the position where any two of the plurality of light beams overlap is longer than the coherence length of the coherent light. ADVANTAGE OF THE INVENTION According to this invention, in the illuminating device using coherent light, it can acquire the illumination light by which intensity distribution was equalize | homogenized, preventing generation | occurrence | production of a speckle.

  In one preferred embodiment of the present invention, the optical system introduces a circulation part that guides coherent light along a circulation path that slightly shifts each time it circulates, and introduces coherent light from the light source part into the circulation part. A superposition position is set on a superposition surface located at an optical position where a self-erected image is superposed on the circulation path, and the coherent light is divided and superposed at the superposition position. Illumination light is taken out. Thereby, size reduction of an optical system can be achieved.

  More preferably, the overlapping surface is a mirror surface, and an opening for extracting a plurality of superimposed light beams is formed at the overlapping position on the mirror surface. Thereby, it is possible to take out the light superimposed with a simple configuration.

  In another preferred embodiment of the present invention, the circulation section includes a half-wave plate on the first circulation path in the circulation path, and the coherent light emitted from the light source section is linearly polarized light, and the introduction section However, since it is an optical element that transmits one of p-polarized light and s-polarized light and reflects the other, and also serves as a part of the circulation portion, a miniaturized optical system can be easily assembled.

  In still another preferred embodiment of the present invention, the introduction unit is a mirror disposed at a position that does not block the coherent light circulating in the circulation unit, so that the coherent light in the light source unit can be efficiently used. .

  In one aspect of the present invention, the illumination device further includes another optical system that projects the illumination light extracted from the superimposition position onto a line-shaped region on the projection surface, and circulates coherent light on the superimposition surface. The shift direction in which the irradiation position shifts corresponds to the direction in which the line-shaped region on the projection surface extends. In another aspect of the present invention, the light source unit includes a solid-state laser or a gas laser that generates coherent light.

  The above object and other objects, features, aspects and advantages will become apparent from the following detailed description of the present invention with reference to the accompanying drawings.

It is a figure which shows the structure of an illuminating device. It is a figure which shows a tilt mirror. It is a figure which shows a 2nd optical system. It is a figure for demonstrating the function of each component of a 1st optical system. It is a figure for demonstrating the function of each component of a 1st optical system. It is a figure for demonstrating the function of each component of a 1st optical system. It is a figure for demonstrating intensity distribution of the light taken out from a slit. It is a figure which shows the other example of a 1st optical system.

  FIG. 1 is a diagram showing a configuration of an illumination device 1 according to an embodiment of the present invention. The illumination device 1 is provided, for example, in a pattern drawing device, and irradiates a linear illumination light on a spatial light modulation device such as a GLV (Grating Light Valve) (registered trademark). In the pattern drawing apparatus, the light spatially modulated by the spatial light modulation device is guided onto a drawing target (for example, a semiconductor substrate or a printed wiring board), and pattern drawing is performed on the drawing target.

  1 includes a light source unit 2 having a solid laser or a gas laser as a light source 21, a first optical system 4 for uniformizing the intensity distribution of light from the light source unit 2, and the first optical system 4. A second optical system 5 that guides light to an object 9 to be illuminated (a spatial light modulation device when the illumination device 1 is provided in the pattern drawing device) is provided. The light emitted from the light source 21 is coherent light with high coherence, and the coherence length of the light is, for example, 10 millimeters to several meters. In the light source unit 2, linearly polarized light is extracted from the coherent light by the polarizing plate 22, and is emitted to the first optical system 4 along the Z axis in FIG. The intensity distribution in the direction perpendicular to the Z axis of the coherent light from the light source unit 2 approximates a Gaussian distribution.

  The first optical system 4 is a polarization beam splitter (“Polarization Beam Splitter”) that transmits a p-polarized component (ie, p-polarized light) of incident light and reflects an s-polarized component (ie, s-polarized light). The linearly polarized light from the lens 23 is p-polarized light, passes through the PBS 41, and is guided to the tilt mirror 43 through the lens 42. The tilt mirror 43 has a slit 431 that is long in the X direction in FIG. 1, and a part of p-polarized light is extracted from the slit 431 as described later. The remainder of the p-polarized light is reflected by the tilt mirror 43, guided to the mirror 44 through the lens 42, and reflected toward the PBS 41. The p-polarized light reflected by the mirror 44 is converted into s-polarized light by passing through the half-wave plate 45 and guided to the PBS 41 via the wedge prism 46. Then, the s-polarized light is reflected by the PBS 41, and enters the PBS 41 again through the lens 42, the tilt mirror 43, the lens 42, and the mirror 44 in this order. As described above, the first optical system 4 is a so-called loop optical system that circulates the coherent light from the light source unit 2 via the outside of the optical axis J1 of the lens 42. In FIG. 1, the symbol denoted by reference numeral K1 indicates s-polarized light (the same applies in FIG. 5 described later), and details of the first optical system 4 will be described later.

  FIG. 2 is a view showing the tilt mirror 43. As shown in FIG. 2, the slit 431 of the tilt mirror 43 is elongated in the X direction in FIG. 2 (hereinafter, this direction is also referred to as “longitudinal direction”), and the first optical system 4 in FIG. A part of the circulating coherent light is extracted through the slit 431 and introduced into the second optical system 5, and the remaining coherent light (that is, the region on the mirror surface 432 other than the slit 431 in the tilt mirror 43). Is reflected toward the lens 42.

  FIG. 3 is a diagram showing the second optical system 5 viewed from the (+ Y) side in FIG. 1 toward the (−Y) direction. As shown in FIGS. 1 and 3, the second optical system 5 has cylindrical lenses 51, 52, 53 in order from the tilt mirror 43 side toward the object 9 along the optical axis J <b> 2 of the second optical system 5. The light from the slit 431 is guided onto the object 9 through the cylindrical lenses 51, 52, 53. In the second optical system 5, the light exit surface of the slit 431 and the surface of the object 9 on the second optical system 5 side are perpendicular to both the optical axis J <b> 2 and the longitudinal direction of the slit 431 by the cylindrical lenses 51 and 52. (Ie, a direction parallel to the YZ plane in FIG. 1 and perpendicular to the optical axis J2). Focusing only on this direction, the exit surface of the slit 431 is maintained while the intensity distribution of light from the slit 431 is maintained as it is. The area on the object 9 that is sufficiently longer than the width (the width in the vertical direction in FIG. 2) (hereinafter, the area on the object 9 irradiated with light from the light source unit 2 is referred to as an “illumination area”). Is irradiated with light. The width of the illumination area on the object 9 (that is, the width in the X direction) is larger than the length in the X direction of the exit surface of the slit 431 when the light from the slit 431 is collected by the cylindrical lens 53. Narrow enough. Thus, the illumination area on the object 9 is a line-shaped area extending in a direction perpendicular to the longitudinal direction of the slit 431.

  Next, the function of each component of the first optical system 4 that makes the intensity distribution of light from the light source unit 2 uniform will be described. FIG. 4 is a diagram showing an optical system 40a having only the PBS 41, the lens 42, the mirror 43a, and the mirror 44. As shown in FIG. FIG. 4 is a diagram for explaining the basic configuration of the first optical system 4 of FIG. 1. In the optical system 40 a, the tilt mirror 43 and the normal line of the lens 42 are compared with the first optical system 4. This is replaced with a mirror 43a arranged so as to be parallel to the optical axis J1, and the wedge prism 46 and the half-wave plate 45 are omitted. In FIG. 4, the principal ray of light in the optical system 40 a is indicated by a one-dot chain line denoted by reference sign PR, and the outline of the light beam is indicated by a thin solid line.

  In the optical system 40a of FIG. 4, the light beam section from the light source unit 2 is condensed in the vicinity of the front focal plane of the lens 42 so as to be condensed (that is, the light has a beam waist). The light (p-polarized light) incident on the lens 42 via the PBS 41 so that the principal ray PR is parallel to the optical axis J1 of the lens 42 becomes parallel light and is a mirror 43a disposed on the rear focal plane of the lens 42. Incident to. The reflected light from the mirror 43 a is guided to the mirror 44 through the lens 42 and reflected toward the PBS 41. The reflected light is returned to the reflecting surface of the PBS 41 while its beam waist is formed between the mirror 44 and the PBS 41 at a position equivalent to the front focal plane of the lens 42. Therefore, if the reflected light incident on the PBS 41 from the mirror 44 is s-polarized light, the optical system 40a can circulate the light along the same circulation path (in this case, the principal ray PR in FIG. 4). It becomes possible. That is, the PBS 41, the lens 42, the mirror 43a, and the mirror 44 form a circulation portion 49a that circulates light. The optical path length from the PBS 41 to the PBS 41 via the lens 42, the mirror 43a, the lens 42, and the mirror 44 is approximately 4f, where f is the focal length of the lens 42. The focal length f of the lens 42 is selected so that the optical path length is longer than the coherence length of the coherent light emitted from the light source unit 2.

  Actually, the reflected light incident on the PBS 41 is p-polarized light transmitted through the PBS 41 out of the coherent light from the light source unit 2, so that the reflected light passes through the PBS 41 in the optical system 40 a and circulates the light. I can't. Therefore, in the optical system 40a of FIG. 4, a half-wave plate is provided near the position where the beam waist of the reflected light from the mirror 44 is formed (that is, the position equivalent to the front focal plane of the lens 42) as shown in FIG. By providing 45, the polarization direction of the reflected light is rotated by 90 degrees to convert it into s-polarized light, and the reflected light can be reflected by the PBS 41.

  Further, in the optical system 40b of FIG. 5, the tilt mirror 43 (however, the slit 431 is omitted in the tilt mirror 43 of FIG. 5) so that the normal line thereof is inclined with respect to the optical axis J1 of the lens 42. As a result, the p-polarized light transmitted through the PBS 41 sequentially passes through the lens 42, the tilt mirror 43, the lens 42, and the mirror 44 to the PBS 41, as indicated by the line labeled T1 in FIG. The first path to return (precisely returned as s-polarized light by the half-wave plate 45) and the s-polarized light from the half-wave plate 45 sequentially pass through the lens 42, the tilt mirror 43, the lens 42 and the mirror 44. Then, the route of the second lap returning to the PBS 41 is slightly different. In the circulation section 49a of FIG. 5, the half-wave plate 45 is provided only on the path of the p-polarized light (first path), so that the s-polarized light can be circulated in the second and subsequent rounds. Become. As described above, in the optical system 40b of FIG. 5, the PBS 41 serves as a part of the circulation part 49a while introducing the p-polarized light of the coherent light from the light source part 2 into the circulation part 49a as the introduction part.

  Further, assuming that s-polarized light is introduced into the circulation part 49a of FIG. 4, a position equivalent to the front focal plane of the lens 42 between the PBS 41 and the mirror 44 as shown in FIG. A wedge prism 46 is arranged on the optical path, and the optical path of the light incident on the PBS 41 is slightly bent along the YZ plane in FIG. 6, so that the light from the wedge prism 46 to the PBS 41 on the plane parallel to the YZ plane can be obtained. The angle formed by the path (a part of the circulation path indicated by the line labeled T2 in FIG. 6) and the reflection surface of the PBS 41 can be slightly changed for each circulation. As a result, in the optical system 40c of FIG. 6, the position on the mirror surface of the mirror 43a through which the light circulation path T2 passes is shifted by a certain distance in the (−Y) direction in FIG. Become.

  The first optical system 4 shown in FIG. 1 changes the mirror 43a to the tilt mirror 43 shown in FIG. 5 in the circulating portion 49a of the optical system 40a shown in FIG. This is realized by providing a half-wave plate 45 and arranging a wedge prism 46 at a position equivalent to the front focal plane of the lens 42. Accordingly, in the first optical system 4 of FIG. 1, the PBS 41, the lens 42, the tilt mirror 43, the mirror 44, the half-wave plate 45, and the wedge prism 46 constitute a circulation unit 49, and the mirror of the tilt mirror 43 is circulated every time it circulates. A circulation path T0 in which the position on the surface 432 is slightly shifted in a direction perpendicular to the longitudinal direction of the slit 431 (hereinafter referred to as “shift direction”) is provided in the circulation portion 49. Then, coherent light introduced from the light source unit 2 along the circulation path T0 (more precisely, p-polarized light transmitted through the PBS 41 and s-polarized light converted from the p-polarized light. Are collectively referred to as “.”. Note that the circulation of the circulation path T0 in the above description is equivalent to the circulation of the circulating light. Further, the optical path length of one turn from the tilt mirror 43 to the tilt mirror 43 via the lens 42, mirror 44, wedge prism 46, PBS 41 and lens 42 in the circulation path T0 is approximately 4f, where f is the focal length of the lens 42. A plurality of positions related to a plurality of passes of the mirror surface 432 of the tilt mirror 43 on the circulation path T0 are conjugate to each other, and the mirror surface 432 of the tilt mirror 43 has a self-magnified self-magnification image in the shift direction. The overlapping surface is formed by overlapping while shifting.

  Here, as described above, slits 431 are formed in tilt mirror 43 shown in FIG. 2, and a part of the circulating light guided along circulation path T0 and irradiated onto tilt mirror 43 (actually) (The end on the shift direction side) is taken out as a divided light beam divided by the slit 431. The irradiation position of the circulating light on the mirror surface 432 of the tilt mirror 43 is the width of the slit 431 in the shift direction by the circulation of the circulating light (the vertical width in FIG. 2 and the width of the opening range described later). In order to shift by a corresponding distance, for example, when the light source is a continuous wave laser, actually, a plurality of split light beams (hereinafter simply referred to as “a plurality of light beams”) are simultaneously extracted by the slit 431, and Overlapped at the same time. That is, the slit 431 is a position where the circulating light is divided into a plurality of light beams, and also a position where the plurality of light beams are superimposed (hereinafter referred to as “superimposition position”).

  At this time, in the circulation path T0, the passage position (where n is an integer equal to or greater than 1) from the start point of the circulation path T0 (that is, the position where the coherent light is incident on the first optical system 4) to the tilt mirror 43 (where n is an integer of 1 or more). That is, the difference between the distance to the reflection position) and the distance from the starting point of the circulation path T0 to the (n + 1) th passage position with respect to the tilt mirror 43 is approximately four times the focal length f of the lens 42, It becomes longer than the coherence length of coherent light. Thus, the optical path difference from the incident position of the coherent light to the first optical system 4 to the slit 431 where any two of the plurality of light beams overlap is based on the coherence length of the coherent light. As a result, the illumination apparatus 1 is prevented from generating speckles due to interference of a plurality of light beams at the overlapping position.

  Next, the intensity distribution of a plurality of light beams that are overlapped by the slit will be described. FIG. 7 is a diagram for explaining the intensity distribution of the light extracted from the slit 431 of the tilt mirror 43. The vertical axis in FIG. 7 indicates the position in the shift direction on the tilt mirror 43 (at one position in the longitudinal direction of the slit 431), and the horizontal axis in FIG. 7 indicates the light intensity. Moreover, in FIG. 7, the opening range of the shift direction of the slit 431 is shown by the arrow attached | subjected code | symbol A1.

  The intensity distribution in the shift direction of the circulating light (hereinafter referred to as “original intensity distribution”) in the first passage (that is, reflection) of the circulating light on the tilt mirror 43 is indicated by a solid line denoted by reference numeral 81 in FIG. As shown in the figure, the shape approximates a Gaussian distribution and corresponds to the portion of the original intensity distribution that overlaps the opening range A1 of the slit 431 (the portion indicated by the parallel diagonal lines in FIG. 7) in the first pass. A light beam is extracted. Further, the intensity distribution in the shift direction of the circulating light in the second passage of the circulating light on the tilt mirror 43 is the first time from the original intensity distribution as shown by a two-dot chain line denoted by reference numeral 82 in FIG. The light beam corresponding to the portion that overlaps the aperture range A1 in the intensity distribution in the second pass except for the portion taken out at the time of passage and shifted in the shift direction by the same amount as the aperture range A1. Is taken out.

  Similarly, in each passage of the circulating light after the second time on the tilt mirror 43, a part of the circulating light is similarly extracted by the slit 431, and all of the circulating light is extracted by the seventh passage (of course, the circulating light is extracted). The circulation number from which all of the above are taken out may be other than 7.) In FIG. 7, the intensity distribution in the shift direction of the circulating light in the third to seventh passes is indicated by two-dot chain lines denoted by reference numerals 83 to 87, respectively.

  At this time, the center position in the shift direction in the original intensity distribution is the center of the opening range A1 of the slit 431 when the circulating light passes for the fourth time as shown by a two-dot chain line denoted by reference numeral 84 in FIG. It overlaps with the position P1, and the intensity of the light beam extracted in the fourth pass is approximately constant in the shift direction. The intensity distribution of the light beam extracted by the first pass and the intensity distribution of the light beam extracted by the seventh pass are symmetric with respect to the line indicating the center position P1 of the aperture range A1. It can be considered that the intensity of the light extracted at each of the first and seventh passes changes substantially linearly with respect to the shift direction. The relationship of the intensity distribution of the light beam is the same between the second pass and the sixth pass, and between the third pass and the fifth pass. Therefore, at each position in the longitudinal direction of the slit 431, the intensity of the light that is simultaneously extracted and superimposed by the first through seventh passes of the circulating light with respect to the tilt mirror 43 is indicated by a broken line denoted by reference numeral 80 in FIG. As shown, it is substantially constant within the opening range A1 of the slit 431 (that is, the light intensity distribution has a top-hat shape). Note that the magnitude of the intensity distribution indicated by the broken line 80 is smaller than the actual size for the sake of illustration.

  Actually, the intensity distribution in the longitudinal direction of the slit 431 of the circulating light irradiated on the tilt mirror 43 has a shape approximating a Gaussian distribution. Therefore, in the light extracted by superimposing a plurality of light beams at the overlapping position, the intensity distribution in the shift direction is made uniform, while the intensity distribution in the longitudinal direction is maintained in a shape approximating a Gaussian distribution. . Then, as described above, the illumination light extracted at the overlapping position is a direction corresponding to the shift direction on the second optical system 5 side surface of the object 9 that is the projection surface by the second optical system 5. Is projected onto a line-shaped illumination area extending in a straight line. Thereby, illumination light having a constant intensity is obtained over the entire illumination area in the shift direction.

  As described above, in the illuminating device 1 of FIG. 1, the coherent light emitted from the light source unit 2 is divided into a plurality of light beams by the first optical system 4 and superimposed at the overlapping position, The optical path difference from the incident position of the coherent light to the first optical system 4 to the overlapping position of any two of the plurality of light beams (that is, in each of the two combinations) is the coherence length of the coherent light. Will be longer than. Thereby, in the illuminating device 1 using coherent light, it is possible to acquire illumination light having a uniform intensity distribution while preventing generation of speckle.

  In the first optical system 4, the coherent light from the light source unit 2 is guided along the circulation path T0, and the mirror surface 432 of the tilt mirror 43 causes the self-erected image along the shift direction on the circulation path T0. The optical position is formed by superimposing while shifting, and the slit 431 formed in the tilt mirror 43 divides the coherent light into a plurality of light beams and superimposes the plurality of light beams. Illumination light is extracted. Accordingly, it is possible to reduce the size of the first optical system 4 that superimposes the coherent light while dividing it into a plurality of light beams.

  In the illumination device 1, it is possible to use a pulse laser in addition to the continuous wave laser. In the case of a pulse laser that generates extremely minute pulsed light, strictly speaking, a plurality of light beams are sequentially extracted by the circulation of the pulsed light in the slit 431 of the tilt mirror 43 and are not extracted at the same time. ) Is constant with respect to the shift direction. Accordingly, even in this case, it can be considered that the coherent light is divided and superimposed with the slit 431 as the overlapping position, and illumination light having a constant intensity in the shift direction can be obtained substantially. That is, it is not necessary to simultaneously superimpose a plurality of light beams at the superimposition position if they are performed within a certain time.

  In the first optical system 4 of FIG. 1, the PBS 41 serves as a part of the circulation unit 49 while introducing the p-polarized light of the coherent light from the light source unit 2 into the circulation unit 49 as an introduction unit. The introduction part of the system may be provided as a component independent of the circulation part. FIG. 8 is a diagram illustrating another example of the first optical system. In the first optical system 4a shown in FIG. 8, the PBS 41 in the first optical system 4 in FIG. 1 is replaced with a mirror 41a, and the mirror 41a, the lens 42, the tilt mirror 43, the mirror 44, and the wedge prism 46 are used as the circulation unit 49. The Further, a mirror 47 that introduces coherent light from the light source unit 2 into the circulation unit 49 is provided as an introduction unit between the mirror 44 and the mirror 41a. The mirror 47 is arranged at a position that does not block the coherent light circulating in the circulation unit 49, so that the first optical system 4a tilts the coherent light reflected by the mirror 47 toward the mirror 41a every time it circulates. The position of the mirror 43 on the mirror surface 432 can circulate along the circulation path T0 in which the position slightly shifts in the shift direction.

  As described above, in the first optical system 4a of FIG. 8, the p-polarized light transmitted through the PBS 41 out of the coherent light in the light source unit 2 is provided by providing the mirror 47 as the introduction unit as a component independent of the circulation unit 49. Compared to the first optical system 4 of FIG. 1 that uses only the light, it is possible to efficiently use the coherent light in the light source unit 2. However, in the first optical system 4a of FIG. 8, since it is necessary to arrange the minute mirror 47 and the minute wedge prism 46 close to each other with high accuracy, the viewpoint of easily assembling the miniaturized first optical system. Then, it is preferable that the half-wave plate 45 and the PBS 41 are combined as in the first optical system 4 of FIG.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made.

  In the illuminating device 1 of FIG. 1, a PBS 41 that transmits p-polarized light and reflects s-polarized light is provided, and a half-wave plate 45 is disposed at a predetermined position to guide coherent light along the circulation path T0. Although one optical system 4 is configured, the circulation of coherent light may be realized by using an optical element that transmits s-polarized light and reflects p-polarized light. That is, in the first optical system 4 having the half-wave plate 45, it is necessary to use an optical element that transmits one of p-polarized light and s-polarized light and reflects the other. Further, depending on the design of the first optical system 4, a total reflection mirror that transmits light having a specific incident angle (for example, 45 degrees) and substantially totally reflects light having an incident angle greater than 45 degrees in the circulation unit 49 is provided in the PBS 41. Instead of the coherent light from the light source unit 2 is incident on the total reflection mirror at the specific incident angle and introduced into the circulation unit, and returns to the total reflection mirror along the circulation path. The coherent light circulation may be realized by changing the incident angle to the light beam by the wedge prism 46.

  In the above embodiment, the slit 431 which is an opening is formed at the overlapping position on the mirror surface 432 of the tilt mirror 43, so that the coherent light is divided into a plurality of light beams and the plurality of light beams are superimposed. However, it is possible to take out a plurality of superimposed light beams as illumination light with a simple configuration, but the lower edge of the tilt mirror 43 is positioned at the upper edge of the slit 431 of the tilt mirror 43 in FIG. By disposing the tilt mirror 43 so as to be adjacent to the overlapping position, the end of the circulating light in the shift direction may be cut out as a light beam while omitting the slit 431. However, in order to suppress unnecessary light from being guided to the second optical system 5, the tilt mirror 43 is preferably provided with an opening. Further, when the first optical system is allowed to be somewhat complicated, for example, in the first optical system 4, a split mirror that is long in the X direction is provided at the position of the slit 431 instead of the tilt mirror 43. By further providing another mirror that reflects the light passing outside the split mirror toward the lens 42, the split mirror is performing splitting of coherent light into a plurality of light beams and superposition of the plurality of light beams. The superimposed illumination light may be reflected and extracted in a predetermined direction. As described above, in the first optical system to be miniaturized, the superposition position where the illumination light is extracted while the coherent light is divided and superposed is formed by superimposing the self-erected image on the circulation path while shifting. It is important to set it on the superimposing surface located at the optical position. Of course, depending on the design of the first optical system, a plurality of light beams may be clearly divided individually from the coherent light, and the plurality of light beams may be overlapped at a predetermined overlapping position. Also in this case, the optical path difference from the position where the coherent light enters the first optical system to the position where any two of the plurality of light beams overlap is made longer than the coherence length of the coherent light.

  The light source of the light source unit 2 in the illuminating device 1 may be another light source (for example, a semiconductor laser) that emits coherent light having a lower coherence than a solid-state laser or a gas laser. However, the above-described method for making the light intensity distribution uniform is particularly suitable when a solid-state laser or a gas laser that emits coherent light with extremely high coherence is used as a light source.

  The illuminating device 1 may be used for purposes other than pattern drawing.

  Although the invention has been illustrated and described in detail, the foregoing description is illustrative and not restrictive. Therefore, it will be understood that many variations and embodiments are possible without departing from the scope of the invention.

Claims (7)

A lighting device,
A light source that emits coherent light;
An optical system that divides the coherent light into a plurality of light beams and superimposes the plurality of light beams at a predetermined overlapping position to obtain illumination light;
With
The optical path difference from the incident position of the coherent light to the optical system to any two of the plurality of light beams reaching the superposition position is longer than the coherence length of the coherent light. A lighting device according to claim 1,
The optical system is
A circulation unit for guiding the coherent light along a circulation path that slightly shifts with each circulation;
An introduction unit for introducing the coherent light from the light source unit into the circulation unit;
With
The superposition position is set on a superposition surface located at an optical position formed by superposition of an erect image of the self on the circulation path;
The illumination light is extracted by dividing and superimposing the coherent light at the superposition position. A lighting device according to claim 2,
The circulation unit comprises a half-wave plate on a first circulation path in the circulation path;
The coherent light emitted from the light source unit is linearly polarized light;
The introduction part is an optical element that transmits one of p-polarized light and s-polarized light and reflects the other, and also serves as a part of the circulation part. A lighting device according to claim 2,
The introduction part is a mirror disposed at a position where the coherent light circulating in the circulation part is not blocked. A lighting device according to claim 2,
The superimposing surface is a mirror surface, and openings for extracting the plurality of superimposed light beams are formed at the superimposing position on the mirror surface. A lighting device according to claim 2,
And further comprising another optical system for projecting the illumination light extracted from the superimposed position onto a line-shaped region on a projection surface,
The shift direction in which the irradiation position is shifted by the circulation of the coherent light on the superimposing surface corresponds to the direction in which the linear region extends on the projection surface. A lighting device according to claim 1,
The light source unit includes a solid-state laser or a gas laser that generates the coherent light.

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