Optical device, optical machining device, microscope device, and scanning method

Abstract

An optical device (10) of an optical machining device (1) includes: an optical fiber amplifier that amplifies pulsed light; a diffraction grating (12) that disperses, by a diffraction phenomenon, pulsed light (PL) output from the optical fiber amplifier; a collimator lens (13) that collimates the pulsed light (PL) scattered at the diffraction grating (12); and an objective lens (17) that condenses the pulsed light (PL) transmitted through the collimator lens (13). By changing the amplification rate of the optical fiber amplifier, the position at which time focus occurs is changed in the optical axis direction of the objective lens (17).

Description

Optical device, optical processing device, microscope device, and scanning method

[0001] The present invention relates to an optical device, an optical processing device, a microscope device, and a scanning method.

[0002] Some optical processing devices and microscopes include an optical device that outputs pulsed light. A technique called temporal focus is known for improving the resolution of a microscope equipped with an optical device that outputs pulsed light (see, for example, Non-Patent Document 1).

[0003] Durst E. et al., Simultaneous spatial and temporal focusing for axial scanning, Optics Express, 2006, 14, 12243

[0004] The optical device according to the present invention includes an amplifier that amplifies pulsed light, a dispersive element that disperses the pulsed light output from the amplifier, and an objective lens that focuses the pulsed light dispersed by the dispersive element, and is capable of changing the amplification factor of the amplifier.

[0005] The optical processing apparatus according to the present invention has an optical device that scans a workpiece with pulsed light, and the optical device is the optical device described above.

[0006] A microscope apparatus according to the present invention has an optical device that scans a sample with pulsed light, and the optical device is the optical device described above.

[0007] A scanning method according to the present invention includes amplifying pulsed light using an amplifier, dispersing the pulsed light output from the amplifier using a dispersive element, focusing the pulsed light dispersed by the dispersive element using an objective lens, and changing the gain of the amplifier to change the position at which a time focus of the pulsed light focused using the objective lens occurs in the optical axis direction of the objective lens, thereby scanning.

[0008] FIG. 1 is a schematic diagram showing the configuration of an optical processing apparatus equipped with an optical device according to a first embodiment. FIG. 2 is a schematic diagram showing an example of an optical system using time focusing. FIG. 3 is a graph showing the relationship between the pulse time width of pulsed light output from an optical fiber amplifier and the average output of the optical fiber amplifier. FIG. 4 is a graph showing the relationship between the spectral width of pulsed light output from an optical fiber amplifier and the average output of the optical fiber amplifier. FIG. 5 is a graph showing the relationship between the amount of chirp (GDD) of pulsed light output from an optical fiber amplifier and the average output of the optical fiber amplifier. FIG. 6 is a schematic diagram showing the configuration of a light source unit. FIG. 7 is a plan view of a compressor. FIG. 8 is a side view of a compressor. FIG. 9 is a graph showing the compression characteristics of the pulse time width of pulsed light output from an optical fiber amplifier. A flowchart showing the flow of a scanning method using pulsed light. FIG. 10 is a schematic diagram showing the configuration of a light source unit according to a modified example. FIG. 11 is a plan view of a compressor according to a modified example. FIG. 12 is a schematic diagram of an optical device according to a modified example. FIG. 13 is a graph showing the compression characteristics of the pulse time width of pulsed light in an optical device according to a modified example. FIG. 14 is a schematic diagram showing the configuration of a microscope apparatus equipped with an optical device according to a second embodiment.

[0009] Preferred embodiments of the present invention will be described below. First, an optical processing apparatus according to a first embodiment will be described with reference to FIG. 1 . As shown in FIG. 1 , the optical processing apparatus 1 according to the first embodiment includes a stage 5, an optical device 10, and an observation unit 60. The optical processing apparatus 1 can process a workpiece W, which is an object to be processed, into a desired shape by controlling the optical device 10, the stage 5, and other components using a control device (not shown) based on processing data created according to the desired shape. The workpiece W is placed on the upper surface of the stage 5. The material of the workpiece W may be, for example, metal, resin, or glass. The stage 5 may also be configured to displace the workpiece W placed on the upper surface of the stage 5 at least in a direction perpendicular to the optical axis of the optical processing apparatus 1. By driving the stage 5 to adjust the position of the workpiece W, pulsed light from the optical device 10 can be irradiated even at a position beyond the scanning width of the optical device 10, which will be described later.

[0010] The observation unit 60 includes an illumination light source 61, a half mirror 62, an imaging lens 63, and an imaging unit 64. The observation unit 60 further includes the dichroic mirror 15 and the objective lens 17 of the optical device 10. The illumination light source 61 is configured using an LED (Light Emitting Diode) or the like. The illumination light source 61 emits illumination light in the visible light wavelength band. The half mirror 62 reflects a portion of the illumination light emitted from the illumination light source 61 toward the dichroic mirror 15. The half mirror 62 transmits light from the workpiece W reflected by the dichroic mirror 15 toward the imaging lens 63. The transmittance-to-reflectance ratio of the half mirror 62 is set to, for example, 1:1. The imaging lens 63 forms an image of the light from the workpiece W that has passed through the half mirror 62. The imaging unit 64 is configured using an imaging element such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor). The imaging unit 64 captures the image of the workpiece W formed by the imaging lens 63 .

[0011] The image of the workpiece W captured by the imaging unit 64 is displayed on a display device (not shown). The workpiece W can be observed via the image displayed on the display device. Note that the control amount of the optical device 10 and the stage 5 by a control device (not shown) may be corrected based on the image data of the workpiece W captured by the imaging unit 64.

[0012] Next, the optical device 10 will be described. The optical device 10 focuses pulsed light PL onto the workpiece W. The pulsed light PL has a pulse duration on the order of femtoseconds (fs), for example. Such pulsed light PL is also called ultrashort pulsed light, but will be simply referred to as "pulsed light" in the following description. A technique called time focusing is used to improve the resolution in the optical axis direction of the optical processing device 1 and the microscope device 201 (described later). In the following description, this technique called time focusing may be simply referred to as "time focusing." Furthermore, the optical axis direction of the optical processing device 1 (or the microscope device 101) equipped with the optical device 10 may be referred to as the z direction, and the directions perpendicular to the optical axis may be referred to as the x direction and the y direction. For example, the directions indicated by the arrows in Figures 2, 7, 8, and 11 will be referred to as the x direction, y direction, and z direction, respectively.

[0013] Here, let us consider the case where pulsed light is focused on an object surface (for example, the surface to be processed of a workpiece W). The focused radius of the pulsed light is w, the wave number of the pulsed light is k, and the wavelength of the pulsed light is λ. In this case, the range in the z direction where the beam diameter of the pulsed light is approximately constant, i.e., the confocal length, is kw. 2 = 2πw 2 / λ. Reducing the focusing radius w of the pulsed light shortens the confocal length, and the resolution in the optical axis direction (z direction) of the optical processing device increases. For example, if the wavelength λ of the pulsed light is 1 μm and the focusing radius w of the pulsed light is narrowed to about 1 μm, the region in the z direction where the light intensity of the pulsed light is high (i.e., the confocal length) is limited to about 6 μm. If the focusing radius w of the pulsed light is widened to about 50 μm, the confocal length becomes about 16 mm, and the resolution in the optical axis direction (z direction) of the optical processing device decreases.

[0014] A technology called time focusing has been proposed that can increase the resolution in the optical axis direction (z direction) even when the focusing radius w of the pulsed light is increased. An example of an optical system using time focusing is shown in FIG. 2. In FIG. 2, a diffraction grating 510 disperses pulsed light PL emitted from a light source unit (not shown) through diffraction. The pulsed light PL dispersed by the diffraction grating 510 enters a collimator lens 520. The pulsed light PL transmitted through the collimator lens 520 is collimated and enters an objective lens 530. The pulsed light PL transmitted through the objective lens 530 is focused on an object plane OB located at the focal point of the objective lens 530. In the following description, unless otherwise specified, the object plane OB is assumed to be the surface to be processed.

[0015] Furthermore, the diffraction grating 510 and the object plane OB are conjugate to each other. As the pulsed light PL dispersed by the diffraction grating 510 travels toward the collimator lens 520, the pulse time width of the pulsed light PL increases. Then, when the pulsed light PL passes through the collimator lens 520 and the objective lens 530 and reaches the object plane OB, which is conjugate to the diffraction grating 510, the pulse time width of the pulsed light PL decreases, and the original pulse time width upon incidence on the diffraction grating 510 is restored. This phenomenon is called temporal focusing. At positions farther away from the object plane OB in the z direction, the pulse time width of the pulsed light PL increases relatively, thereby reducing the peak power of the pulsed light PL and reducing the processing efficiency of the pulsed light PL. As a result, it is possible to improve the resolution in the optical axis direction (z direction) of the optical processing device.

[0016] In the optical system using time focusing illustrated in FIG. 2, the pulse time width of the pulsed light PL in the vicinity of the object plane OB is approximately expressed by the following equation (1).

[0017]

[0018] Here, τ0 represents the pulse time width of the pulse light PL when the pulse light PL is a Fourier limited pulse (Transform Limited Pulse), that is, when there is no chirp and GDD (Group Delay Dispersion) = 0. Here, it is assumed that the pulse light PL of a Fourier limited pulse is incident on the diffraction grating 510. Also, z R is approximately expressed by the following equation (2).

[0019]

[0020] Here, f denotes the focal length of the objective lens 530. k0 denotes the wave number at the center frequency in the spectrum of the pulsed light PL dispersed by the diffraction grating 510. The x-direction coordinate of a monochromatic wave of frequency ω in the spectrum of the pulsed light PL at the incident position on the objective lens 530 is expressed as x = αω. Note that the frequency ω is offset so that the center frequency in the spectrum of the pulsed light PL is zero (0). α is a coefficient determined by the dispersion (or linear density, angle of incidence) of the diffraction grating 510, the focal length fc of the collimator lens 520, etc. Ω is the maximum frequency in the spectrum of the pulsed light PL. The width in the x-direction of the pulsed light PL at the incident position on the objective lens 530 (i.e., the width in the dispersion direction of the pulsed light PL dispersed by the diffraction grating 510) is approximately 2αΩ. Here, it is assumed that the diameter s of the monochromatic wave in the spectrum of the pulsed light PL (see FIG. 2) satisfies s<<αΩ.

[0021] Furthermore, the position of z=0 corresponds to a position conjugate with the diffraction grating 510. As can be seen from equation (1), when z=0, the pulse time width of the pulsed light PL becomes the minimum, and z>z R When z>z, the pulse time width of the pulsed light PL becomes significantly wider. R , the pulse time width of the pulsed light PL increases and the peak power of the pulsed light PL decreases. Therefore, the resolution in the optical axis direction (z direction) of the optical processing device becomes R For example, when f = 10 mm, αΩ = 3 mm, and λ = 1 μm, z Ris about 3 μm. In other words, even if the focusing radius w of the pulsed light is about 50 μm, the resolution in the z direction of the optical processing device will be on the order of μm due to the effect of time focusing. In this way, even if the focusing radius of the pulsed light is widened, the resolution in the optical axis direction (z direction) of the optical processing device is increased due to the effect of time focusing, making it possible to perform fine processing such as removal processing on the workpiece. Furthermore, if the workpiece is made of transparent resin or glass, the effect of time focusing makes it possible to perform fine processing on the inside of the workpiece. By setting the peak power of the pulsed light at the position z = 0 near the processing threshold at which processing of the workpiece is possible, it is possible to further improve the resolution in the optical axis direction (processing resolution) of the optical processing device.

[0022] The position in the z-direction where the time focus occurs can be changed by chirping the pulsed light PL (changing the frequency with time). The amount of chirp is, at the lowest order, GDD (fs 2 Or P.S. 2 The relationship between the amount of chirp β and the change in position Δz in the z direction at which time focusing occurs is approximately expressed by the following equation (3):

[0023]

[0024] Here, β=GDD / 2. For example, β=10000 fs 2 (GDD=20000fs 2 ), z R In the case of 10 μm or less and Ω≈0.033 rad / fs (corresponding to pulsed light of 70 fs or less), Δz≈110 μm.

[0025] There are several ways to chirp the pulsed light of a Fourier-limited pulse, such as passing it through a glass material such as quartz, or using a prism pair or a diffraction grating pair. When using a prism pair, the GDD of the pulsed light can be changed by changing the spacing between the prisms or the extent to which the prism is inserted into the optical path. When using a diffraction grating pair, the GDD of the pulsed light can be changed by changing the spacing between the diffraction gratings. In the literature "Durst E. et al., Simultaneous spatial and temporal focusing for axial scanning, Optics Express, 2006, 14, 12243," it is reported that the GDD can be reduced to 11,000 fs by adjusting the prism pair. 2 Experiments have shown that by changing the angle of the prism, the position where time focusing occurs can be changed by 140 μm. This method mechanically changes the position of the prism, so it takes time to change the position where time focusing occurs. In this embodiment, a light source unit using an optical fiber amplifier is combined with an optical system that utilizes time focusing to quickly change the position where time focusing occurs.

[0026] An optical fiber amplifier is composed of an optical fiber having a length of about 1 m to several tens of meters. The core diameter of the optical fiber is about several μm to several tens of μm. Since an optical fiber with such a long length and a small core diameter is used, both dispersion and nonlinearity in the optical fiber amplifier are large. When pulsed light is amplified by an optical fiber amplifier, the pulse time width and spectral width of the pulsed light output from the optical fiber amplifier change depending on the amplification factor of the optical fiber amplifier. The chirp (GDD) of the pulsed light is roughly proportional to "pulse time width / spectral width (ps / nm)". Note that ps / nm and ps 2 For example, for pulsed light with a central wavelength of 1.06 μm, ps / nm=−1.68 ps 2The way in which the pulse time width of pulsed light changes with changes in the gain of an optical fiber amplifier and the way in which the spectral width of pulsed light changes with changes in the gain of an optical fiber amplifier are generally different. Therefore, it is expected that the chirp (GDD) of pulsed light will change depending on the gain of the optical fiber amplifier.

[0027] Figure 3 shows the relationship between the pulse duration of pulsed light output from an optical fiber amplifier and the average output power of the optical fiber amplifier. Figure 4 shows the relationship between the spectral width of pulsed light output from an optical fiber amplifier and the average output power of the optical fiber amplifier. In the graphs shown in Figures 3 and 4, pulsed light with a period of 350 fs and a wavelength of 1.56 μm is used as the input to the optical fiber amplifier. The optical fiber amplifier used is an erbium-doped fiber amplifier (EDFA) with a length of approximately 16 m, a mode field diameter (MFD) of approximately 5 μm, and normal dispersion. The average output power of the optical fiber amplifier is proportional to the pulse energy (energy per pulse) of the pulsed light. Figures 3 and 4 show that the rate of increase in the spectral width when the pulse energy is increased is greater than the rate of increase in the average output power of the optical fiber amplifier, i.e., the pulse duration when the pulse energy is increased.

[0028] Fig. 5 shows the relationship between the amount of chirp (GDD) of the pulse light output from the optical fiber amplifier and the average output power of the optical fiber amplifier, which was obtained from Fig. 3 and Fig. 4. Fig. 5 shows that the amount of chirp (GDD) of the pulse light output from the optical fiber amplifier varies from 0.17 to 0.2 ps according to the change in the average output power of the optical fiber amplifier, i.e., the pulse energy. 2 (170000~200000fs 2 ) indicates that the temperature varies within the range

[0029] As shown in Fig. 1, an optical device 10 according to the first embodiment includes a light source unit 20, a first mirror 11, a diffraction grating 12, a collimator lens 13, a second mirror 14, a dichroic mirror 15, and an objective lens 17. The light source unit 20 emits pulsed light PL having a wavelength band of, for example, 1 µm. The first mirror 11 reflects the pulsed light PL emitted from the light source unit 20 toward the diffraction grating 12. The diffraction grating 12 disperses the pulsed light PL reflected by the first mirror 11 by diffraction. The collimator lens 13 collimates the pulsed light PL dispersed by the diffraction grating 12.

[0030] The second mirror 14 reflects the pulsed light PL that has passed through the collimator lens 13 toward the dichroic mirror 15. Note that instead of the second mirror 14, a galvanometer mirror (not shown) that reflects the pulsed light PL that has passed through the collimator lens 13 toward the dichroic mirror 15 may be provided. The galvanometer mirror can change the direction of travel of the pulsed light PL by changing the orientation of the reflecting surface. By changing the direction of travel of the pulsed light PL with the galvanometer mirror, it is possible to perform scanning on a plane (machined surface) of the workpiece W that is perpendicular to the optical axis of the objective lens 17. It is desirable that the galvanometer mirror be provided at the pupil position of the objective lens 17 or at a position conjugate to the pupil.

[0031] The dichroic mirror 15 transmits the pulsed light PL incident on the dichroic mirror 15 toward the objective lens 17. The dichroic mirror 15 also reflects the illumination light from the observation unit 60 (half mirror 62) that has entered the dichroic mirror 15 toward the objective lens 17. The dichroic mirror 15 reflects the light (visible light) from the workpiece W that has entered the dichroic mirror 15 via the objective lens 17 toward the observation unit 60 (half mirror 62).

[0032] The objective lens 17 focuses the pulsed light PL that has passed through the dichroic mirror 15 onto the workpiece W. The diffraction grating 12 and the workpiece W (surface to be processed) are conjugate with each other. The objective lens 17 also irradiates the workpiece W with the illumination light reflected by the dichroic mirror 15. Light from the workpiece W irradiated with the illumination light is incident on the objective lens 17. The light (visible light) from the workpiece W that has entered the objective lens 17 passes through the objective lens 17 and is reflected by the dichroic mirror 15.

[0033] Next, the light source unit 20 will be described with reference to FIGS. 6 to 8 . As shown in FIG. 6 , the light source unit 20 includes an oscillator 22, a first optical isolator 23, a second optical isolator 24, a first optical fiber amplifier 25, a second optical fiber amplifier 26, a collimator lens 29, and a compressor 31. The oscillator 22 is configured using a mode-locked fiber laser. The oscillator 22 generates pulsed light that is a Fourier-limited pulse with a pulse duration of approximately 100 fs to 1 ps. The first optical isolator 23 is provided between the oscillator 22 and the first optical fiber amplifier 25. The second optical isolator 24 is provided between the first optical fiber amplifier 25 and the second optical fiber amplifier 26. The first optical isolator 23 and the second optical isolator 24 transmit only pulsed light traveling in the forward direction and block light traveling in the reverse direction.

[0034] The first optical fiber amplifier 25 is configured using a normal-dispersion erbium-doped optical fiber amplifier (EDFA). The first optical fiber amplifier 25 may also be configured using a normal-dispersion ytterbium-doped optical fiber amplifier (YDFA). The first optical fiber amplifier 25 is provided with a first pump LD (laser diode) 27. The first pump LD 27 inputs pumping light (also referred to as pump light) into the first optical fiber amplifier 25. The first optical fiber amplifier 25 amplifies the pulsed light generated by the oscillator 22 using the pumping light input from the first pump LD 27. The gain (i.e., output) of the first optical fiber amplifier 25 can be changed by changing the pumping current of the first pump LD 27. The first optical fiber amplifier 25 is an optical fiber amplifier that is longer and has a smaller core diameter than the second optical fiber amplifier 26. As a result, the chirp characteristics (GDD) of the pulsed light are determined by the first optical fiber amplifier 25, which has relatively large dispersion and nonlinearity.

[0035] The second optical fiber amplifier 26 is configured using an erbium-doped optical fiber amplifier (EDFA). The second optical fiber amplifier 26 may also be configured using an ytterbium-doped optical fiber amplifier (YDFA). The second optical fiber amplifier 26 is provided with a second pump LD (laser diode) 28. The second pump LD 28 inputs pumping light (also referred to as pump light) into the second optical fiber amplifier 26. The second optical fiber amplifier 26 amplifies the pulsed light output from the first optical fiber amplifier 25 using the pumping light input from the second pump LD 28. The gain (i.e., output) of the second optical fiber amplifier 26 can be changed by changing the pumping current of the second pump LD 28. The second optical fiber amplifier 26 is an optical fiber amplifier that is shorter and has a larger core diameter than the first optical fiber amplifier 25. As a result, the output (pulse energy of the pulsed light) is determined by the second optical fiber amplifier 26, which has relatively low dispersion and nonlinearity.

[0036] By using the first optical fiber amplifier 25, which has relatively large dispersion and nonlinearity, and the second optical fiber amplifier 26, which has relatively small dispersion and nonlinearity, as amplifiers, it is possible to reduce fluctuations in the pulse energy of the pulsed light while changing the amount of chirp (GDD) of the pulsed light output from the amplifiers (first optical fiber amplifier 25 and second optical fiber amplifier 26). Note that a solid-state amplifier may be provided as the second amplifier instead of the second optical fiber amplifier 26. If even greater pulse energy is required, a third amplifier may be provided after the second amplifier. Furthermore, if fluctuations in pulse energy due to changes in the amount of chirp (GDD) of the pulsed light can be tolerated, the second optical fiber amplifier 26 may be omitted. In this case, in the following description, the output of the second optical fiber amplifier 26 may be read as the output of the first optical fiber amplifier 25.

[0037] The collimator lens 29 collimates the pulsed light output from the second optical fiber amplifier 26. The compressor 31 compresses the pulse time width of the pulsed light output from the second optical fiber amplifier 26 and transmitted through the collimator lens 29, and emits pulsed light PL which is a Fourier-limited pulse.

[0038] 7 and 8, the compressor 31 includes an output mirror 32, a diffraction grating pair of a first diffraction grating 33 and a second diffraction grating 34, and a roof mirror 35. The pulsed light transmitted through the collimator lens 29 passes through a position away from the output mirror 32 in the −y direction perpendicular to the optical axis. The pulsed light that passed through the output mirror 32 is spatially dispersed by the first diffraction grating 33 and the second diffraction grating 34. The pulsed light dispersed by the first diffraction grating 33 and the second diffraction grating 34 is reflected by the roof mirror 35 and returns to the second diffraction grating 34 and the first diffraction grating 33 in this order. The pulsed light that returned to the second diffraction grating 34 and the first diffraction grating 33 in this order is offset in the +y direction by the roof mirror 35, and is therefore reflected by the output mirror 32 and emitted to the outside (first mirror 11). Such a compressor 31 has negative dispersion (GDD<0), but the dispersion of the compressor 31 can be changed by changing the distance between the first diffraction grating 33 and the second diffraction grating 34 .

[0039] 9 shows the compression characteristics of the pulse time width of the pulsed light output from the two-stage amplifier (first optical fiber amplifier 25 and second optical fiber amplifier 26) shown in FIG. 6. The horizontal axis of the graph shown in FIG. 9 represents the dispersion (ps) of the compressor 31 having a diffraction grating pair arranged after the first optical fiber amplifier 25 and the second optical fiber amplifier 26. 2 =10 6 fs 2 ), and the vertical axis represents the pulse time width (fs) of the pulsed light. The triangle marks in the graph shown in FIG. 9 represent compression characteristics when the pump current of the first pump LD 27 in the first optical fiber amplifier 25 is 600 mA. The square marks in the graph shown in FIG. 9 represent compression characteristics when the pump current of the first pump LD 27 in the first optical fiber amplifier 25 is 1000 mA. Note that the pump current of the second pump LD 28 in the second optical fiber amplifier 26 is constant whether the pump current of the first pump LD 27 in the first optical fiber amplifier 25 is 600 mA or 1000 mA. When the pump current of the first pump LD 27 in the first optical fiber amplifier 25 is 600 mA, the dispersion amount of the compressor 31 to obtain the minimum pulse time width is −0.163 ps. 2 , that is, the chirp amount (GDD) of the pulsed light is +0.163 ps 2 When the pumping current of the first pump LD 27 in the first optical fiber amplifier 25 is 1000 mA, the dispersion of the compressor 31 to obtain the minimum pulse duration is −0.148 ps. 2 , that is, the chirp amount (GDD) of the pulsed light is +0.148 ps 2 As a result, by changing the excitation current of the first pump LD 27 in the first optical fiber amplifier 25 in the range of 600 mA to 1000 mA, the chirp amount (GDD) of the pulsed light output from the two-stage amplifier (the first optical fiber amplifier 25 and the second optical fiber amplifier 26) was reduced to 0.015 ps. 2 = 15000 fs 2 It can be seen that it is possible to change only

[0040] Furthermore, when the pumping current of the first pump LD 27 in the first optical fiber amplifier 25 was 600 mA, the output of the second optical fiber amplifier 26 was 477 mW. When the pumping current of the first pump LD 27 in the first optical fiber amplifier 25 was 1000 mA, the output of the second optical fiber amplifier 26 was 537 mW. In this experiment, the pumping current of the second pump LD 28 in the second optical fiber amplifier 26 was kept constant, so the output of the second optical fiber amplifier 26 fluctuated slightly. However, by adjusting the pumping current of the second pump LD 28, it is possible to maintain the output of the second optical fiber amplifier 26 within a constant range. Furthermore, when the pumping current of the first pump LD 27 in the first optical fiber amplifier 25 was 600 mA or 1000 mA, the minimum pulse duration of the pulsed light was approximately the same (up to 115 fs). As described above, the two-stage amplifier (first optical fiber amplifier 25 and second optical fiber amplifier 26) shown in FIG. 6 makes it possible to change only the amount of chirp (GDD) of the pulsed light while keeping the pulse energy of the pulsed light and the minimum pulse time width after compression approximately constant.

[0041] In the example of the two-stage amplifier (first optical fiber amplifier 25 and second optical fiber amplifier 26) shown in FIG. 6, ΔGDD is about 15000 fs 2 , Ω ∼ 0.02 rad / fs (corresponding to pulsed light of ∼ 115 fs), so from the above equation (3), Δz ∼ 3 × z R It becomes. z R As described in the above equation (2), is set using a coefficient α determined by the dispersion (or linear density, incident angle) of the diffraction grating 12, the focal length fc of the collimator lens 13, and the focal length f of the objective lens 17. R = 10 μm, the change Δz in the position in the z direction where time focusing occurs is 30 μm. That is, in the above example, by modulating the excitation current of the first pump LD 27 between 600 mA and 1000 mA, it is possible to change the position where time focusing occurs by 30 μm in the optical axis direction (z direction) and perform scanning.

[0042] When the first optical fiber amplifier 25 and the second optical fiber amplifier 26 are erbium-doped optical fiber amplifiers (EDFAs) or ytterbium-doped optical fiber amplifiers (YDFAs), the gain response to modulation of the pump light (pump light) of the first pump LD 27 and the second pump LD 28 (i.e., the gain response to modulation of the pump current) often extends up to about 10 kHz, although this varies depending on the core diameter and pumping state. In other words, it is possible to change the gain of the first optical fiber amplifier 25 and the second optical fiber amplifier 26 at a high speed of about 10 kHz. Based on the above experimental results, this means that it is possible to change the chirp amount (GDD) of the pulsed light at a speed of about 10 kHz. This method allows for simple and fast change of the chirp amount (GDD) of the pulsed light, compared to mechanical methods such as changing the position of a prism. In this way, by modulating the excitation current of the first pump LD 27 and the second pump LD 28 at high speed, it is possible to change the gain (amplification factor) of the first optical fiber amplifier 25 and the second optical fiber amplifier 26 at high speed, so that the amount of chirp (GDD) of the pulsed light can be changed at high speed, and the position where time focus occurs can be changed at high speed, making it possible to perform high-speed scanning in the optical axis direction (z direction).

[0043] Next, a pulsed light scanning method using the optical device 10 of the optical processing apparatus 1 configured as described above will be described. Fig. 10 is a flowchart showing the flow of the pulsed light scanning method. First, pulsed light is generated by the oscillator 22 of the light source unit 20 (step ST1). At this time, the oscillator 22 generates pulsed light that is a Fourier limit pulse.

[0044] Next, the pulsed light is amplified by the first optical fiber amplifier 25 and the second optical fiber amplifier 26 (step ST2). The pulsed light generated by the oscillator 22 passes through the first optical isolator 23 and enters the first optical fiber amplifier 25. The first optical fiber amplifier 25 amplifies the pulsed light generated by the oscillator 22. The pulsed light output from the first optical fiber amplifier 25 passes through the second optical isolator 24 and enters the second optical fiber amplifier 26. The second optical fiber amplifier 26 amplifies the pulsed light output from the first optical fiber amplifier 25. The pulsed light output from the second optical fiber amplifier 26 passes through a collimator lens 29 to become parallel and enters the compressor 31. The compressor 31 compresses the pulse time width of the pulsed light that has passed through the collimator lens 29 and emits pulsed light PL, which is a Fourier-limited pulse.

[0045] Next, the pulsed light PL is dispersed by the diffraction grating 12 (step ST3). The pulsed light PL emitted from the compressor 31 of the light source unit 20 is reflected by the first mirror 11 and enters the diffraction grating 12. The diffraction grating 12 disperses the pulsed light PL reflected by the first mirror 11 by a diffraction phenomenon. The pulsed light PL dispersed by the diffraction grating 12 passes through the collimator lens 13, becomes parallel, and enters the second mirror 14. At this time, the diffraction grating 12 and the collimator lens 13 generate a spatial chirp of the pulsed light PL required for time focusing.

[0046] Next, the pulsed light PL is focused by the objective lens 17 (step ST4). The pulsed light PL reflected by the second mirror 14 passes through the dichroic mirror 15 and enters the objective lens 17. The objective lens 17 focuses the pulsed light PL that has passed through the dichroic mirror 15 onto the workpiece W. At this time, the pulse time width of the pulsed light PL is reduced due to the effect of time focusing, and the original pulse time width when it enters the diffraction grating 12 on the processing surface of the workpiece W is reproduced. For example, even if the focusing radius w of the pulsed light PL is approximately 50 μm, the effect of time focusing can increase the resolution in the optical axis direction (z direction) of the optical processing device 1, making it possible to perform micromachining such as removal processing on the workpiece W. Furthermore, if the material of the workpiece W is transparent resin or glass, the effect of time focusing can make it possible to perform micromachining on the interior of the workpiece W. As described above, due to the occurrence of temporal focusing, the pulse time width of the pulsed light PL focused by the objective lens 17 becomes the pulse time width of the pulsed light PL when it is incident on the diffraction grating 12. This includes not only the case where the pulse time width of the pulsed light PL focused by the objective lens 17 is (completely) the same as the pulse time width of the pulsed light PL when it is incident on the diffraction grating 12, but also the case where it is approximately the same as the pulse time width of the pulsed light PL when it is incident on the diffraction grating 12.

[0047] Then, scanning is performed by changing the position where the time focus occurs in the optical axis direction of the objective lens 17 (step ST5). At this time, the amplification factors of the first optical fiber amplifier 25 and the second optical fiber amplifier 26 are changed by modulating the excitation currents of the first pump LD 27 and the second pump LD 28. This changes the amount of chirp (GDD) of the pulsed light PL, and changes the position where the time focus occurs in the optical axis direction of the objective lens 17, thereby performing scanning in the optical axis direction (z direction). Note that when the pulsed light PL from the optical device 10 is continuously irradiated onto the workpiece W, the above-mentioned step of generating pulsed light (ST1), step of amplifying the pulsed light (ST2), step of dispersing the pulsed light (ST3), step of focusing the pulsed light (ST4), and step of scanning (ST5) are each performed in parallel.

[0048] According to the first embodiment, the optical device 10 of the optical processing apparatus 1 includes a first optical fiber amplifier 25 and a second optical fiber amplifier 26 that amplify pulsed light, a diffraction grating 12 that disperses the pulsed light, and an objective lens 17 that focuses the pulsed light dispersed by the diffraction grating 12, and the gains of the first optical fiber amplifier 25 and the second optical fiber amplifier 26 can be changed independently. Note that the pulse duration of the pulsed light focused by the objective lens 17 becomes the pulse duration of the pulsed light when it is incident on the diffraction grating 12 due to temporal focusing. As described above, the gain of the first optical fiber amplifier 25 can be changed at high speed by modulating the excitation current of the first pump LD 27 at high speed. This makes it possible to change the amount of chirp (GDD) of the pulsed light at high speed, and to change the position (position in the z direction) where temporal focusing occurs at high speed, thereby enabling high-speed scanning in the optical axis direction. Furthermore, the effect of time focusing increases the resolution in the optical axis direction (z direction) of the optical processing device 1, and therefore, by quickly changing the position (position in the z direction) where time focusing occurs, it becomes possible to quickly perform fine processing such as removal processing on the workpiece W. Furthermore, by appropriately controlling the excitation current of the second pump LD 28, it is possible to adjust the amplification factor of the second optical fiber amplifier 26 and change the amount of chirp (GDD) of the pulsed light while keeping the change in the output of the pulsed light within a certain range.

[0049] Furthermore, the pulse energy of the pulsed light may be controlled by installing a light intensity regulator such as an acousto-optical device (AOM) on the input side or output side of the second optical fiber amplifier 26. This makes it possible to reduce fluctuations in the pulse energy of the pulsed light while changing the amount of chirp (GDD) of the pulsed light.

[0050] Furthermore, a compressor 31 may be provided to compress the pulse time width of the pulsed light output from the second optical fiber amplifier 26. This makes it possible to obtain pulsed light that is a Fourier-limited pulse.

[0051] In the first embodiment described above, the oscillator 22 is provided, but this is not limiting. For example, the oscillator 22 may not be provided, and the first optical fiber amplifier 25 may amplify pulsed light from a pulsed light generator provided outside the optical processing apparatus 1. In this case, the step (ST1) of generating pulsed light described above can be omitted.

[0052] In the first embodiment described above, the diffraction grating 12 that disperses the pulsed light by diffraction is provided, but the present invention is not limited to this. A prism or the like may be provided as a dispersive element that disperses the pulsed light instead of the diffraction grating 12. Note that dispersing the pulsed light by a dispersive element means spatially separating the optical paths of the pulsed light according to the wavelengths of the pulsed light.

[0053] In the first embodiment described above, the gains of the first optical fiber amplifier 25 and the second optical fiber amplifier 26 are changed by modulating the pump currents of the first pump LD 27 and the second pump LD 28, but this is not limiting. For example, the gain of the first optical fiber amplifier 25 may be effectively changed by controlling the amount of input pulsed light using an acousto-optic element (AOM) or the like provided on the input side of the first optical fiber amplifier 25, thereby changing the amount of chirp (GDD) of the pulsed light. Alternatively, the gain of the second optical fiber amplifier 26 may be effectively changed by controlling the amount of pulsed light using an acousto-optic element (AOM) or the like provided on the input or output side of the second optical fiber amplifier 26, thereby maintaining the output of the second optical fiber amplifier 26 within a certain range.

[0054] In the first embodiment described above, the light source unit 20 includes a two-stage amplifier (the first optical fiber amplifier 25 and the second optical fiber amplifier 26). However, this is not limiting and the light source unit 20 may include only one amplifier. For example, as shown in FIG. 11 , a light source unit 70 may include an oscillator 22, an optical isolator 73, an optical fiber amplifier 75, a collimator lens 29, and a compressor 31. The optical isolator 73 has a configuration similar to the first optical isolator 23 according to the first embodiment. The optical fiber amplifier 75 has a configuration similar to the first optical fiber amplifier 25 according to the first embodiment. The collimator lens 29 collimates the pulsed light output from the optical fiber amplifier 75. The optical fiber amplifier 75 is provided with a pump LD 77. The pump LD 77 has a configuration similar to the first pump LD 27 according to the first embodiment. The amplification factor (i.e., output) of the optical fiber amplifier 75 can be changed by changing the pump current of the pump LD 77. Alternatively, the oscillator 22 may not be provided, and the optical fiber amplifier 75 may amplify pulsed light from a pulsed light generator provided outside the optical processing device.

[0055] In the first embodiment described above, the compressor 31 is configured using a diffraction grating pair (grating pair). However, this is not limiting and the compressor 31 may be configured using a prism pair. For example, as shown in FIG. 12 , the compressor 131 may include an output mirror 32, a prism pair consisting of a first prism 133 and a second prism 134, and a roof mirror 35. The pulsed light transmitted through the collimator lens 29 passes through a position spaced apart from the output mirror 32 in the −y direction perpendicular to the optical axis. The pulsed light that passes through the output mirror 32 is spatially dispersed by the first prism 133 and the second prism 134. The pulsed light dispersed by the first prism 133 and the second prism 134 is reflected by the roof mirror 35 and returns to the second prism 134 and the first prism 133, in that order. The pulsed light returning in this order through the second prism 134 and the first prism 133 is offset in the +y direction by the roof mirror 35, and is therefore reflected by the output mirror 32 and emitted to the outside (first mirror 11). Although this compressor 131 has negative dispersion (GDD<0), the dispersion of the compressor 131 can be changed by changing the distance between the first prism 133 and the second prism 134.

[0056] In the first embodiment described above, the compressor 31 is provided in the light source unit 20, but this is not limiting, and the compressor does not necessarily have to be provided in the light source unit. For example, as shown in Fig. 13 , an optical device 110 according to a modified example includes a light source unit 120, a diffraction grating pair of a first diffraction grating 111 and a second diffraction grating 112, a mirror 114, and an objective lens 117. The light source unit 120 includes an oscillator 122, an optical isolator 123, an optical fiber amplifier 125, and a collimator lens 129.

[0057] The oscillator 122 is configured using a mode-locked fiber laser. The oscillator 122 generates pulsed light, which is a Fourier-limited pulse with a pulse duration of approximately 100 fs to 1 ps. The optical isolator 123 is provided between the oscillator 122 and the optical fiber amplifier 125. The optical isolator 123 transmits only the pulsed light traveling in the forward direction and blocks light traveling in the reverse direction.

[0058] The optical fiber amplifier 125 is configured using a normal-dispersion erbium-doped optical fiber amplifier (EDFA). Alternatively, the optical fiber amplifier 125 may be configured using a normal-dispersion ytterbium-doped optical fiber amplifier (YDFA). The optical fiber amplifier 125 is provided with a pump LD (laser diode) 127. The pump LD 127 inputs pump light (pump light) into the optical fiber amplifier 125. The optical fiber amplifier 125 amplifies the pulsed light generated by the oscillator 122 using the pump light input from the pump LD 127. The gain (i.e., output) of the optical fiber amplifier 125 can be changed by changing the pump current of the pump LD 127. The collimator lens 129 collimates the pulsed light output from the optical fiber amplifier 125. The optical fiber amplifier may be the two-stage amplifier (first optical fiber amplifier 25 and second optical fiber amplifier 26) according to the first embodiment. Alternatively, the oscillator 122 may not be provided, and the optical fiber amplifier may amplify pulsed light from a pulsed light generator provided outside the optical processing device.

[0059] The light source unit 120 emits pulsed light PL having a positive chirp via the optical fiber amplifier 125. If the GDD of the pulsed light PL emitted from the light source unit 120 is Dp, then Dp > 0. The pulsed light PL emitted from the light source unit 120 is spatially dispersed by the first diffraction grating 111 and the second diffraction grating 112. The dispersion of the diffraction grating pair of the first diffraction grating 111 and the second diffraction grating 112 is Dg. The spacing between the first diffraction grating 111 and the second diffraction grating 112 is adjusted so that Dg = -Dp. A spatial chirp is generated in the pulsed light PL that has passed through the diffraction grating pair of the first diffraction grating 111 and the second diffraction grating 112. Since the frequency components of the pulsed light PL that has passed through this diffraction grating pair are spatially separated, the GDD of the pulsed light PL is 0 (i.e., Dp + Dg = 0), but the pulse time width does not become the pulse width of a Fourier-limited pulse. In a compressor having a conventional diffraction grating pair, the pulse light passes through the diffraction grating pair twice (double pass), so that spatial chirp does not occur and a pulse time width of the Fourier limit pulse is obtained.

[0060] The pulsed light PL that passes through the diffraction grating pair of the first diffraction grating 111 and the second diffraction grating 112 is reflected by the mirror 114 and focused onto the workpiece W by the objective lens 117. Note that a dichroic mirror (not shown) according to the first embodiment described above may be provided between the mirror 114 and the objective lens 117. The pulsed light PL that has passed through the diffraction grating pair (the first diffraction grating 111 and the second diffraction grating 112) and has generated spatial chirp is focused by the objective lens 117, thereby achieving a time focusing effect. That is, the pulse time width of the pulsed light PL is maximum immediately after passing through the objective lens 117, and the pulse time width of the pulsed light PL decreases as it approaches the workpiece W (the focal plane of the objective lens 117), until the pulse time width of the pulsed light PL is minimum at the processed surface of the workpiece W (the focal plane of the objective lens 117).

[0061] In the optical device 110 according to the modified example, the diffraction grating pair of the first diffraction grating 111 and the second diffraction grating 112 not only removes GDD from the pulsed light PL emitted from the light source unit 120 but also imparts the spatial chirp necessary for temporal focusing to the pulsed light PL emitted from the light source unit 120. As a result, similar to the first embodiment described above, the amplification factor of the fiber amplifier 125 can be rapidly changed by rapidly modulating the excitation current of the pump LD 127, thereby rapidly changing the amount of chirp (GDD) of the pulsed light and rapidly changing the position (position in the z direction) where temporal focusing occurs. Furthermore, the effect of temporal focusing increases the resolution of the optical processing device in the optical axis direction (z direction). Therefore, by rapidly changing the position (position in the z direction) where temporal focusing occurs, it becomes possible to perform micromachining, such as removal machining, on the workpiece W with high resolution and high speed.

[0062] 14 shows the compression characteristics of the pulse time width of the pulsed light output from the optical fiber amplifier 125 of the optical device 110 according to the modified example. The horizontal axis of the graph shown in FIG. 14 represents the dispersion amount (fs 2), and the vertical axis represents the pulse time width (fs) of the pulsed light. However, when the compression characteristics of FIG. 14 were experimentally obtained, the compressor was configured as a double-pass compressor. The ◆ mark in the graph shown in FIG. 14 indicates the compression characteristics when the excitation current of the pump LD 127 in the optical fiber amplifier 125 is 1.0 A. The ■ mark in the graph shown in FIG. 14 indicates the compression characteristics when the excitation current of the pump LD 127 in the optical fiber amplifier 125 is 2.8 A. The ▲ mark in the graph shown in FIG. 14 indicates the compression characteristics when the excitation current of the pump LD 127 in the optical fiber amplifier 125 is 5.0 A.

[0063] When the pump current of the pump LD 127 in the optical fiber amplifier 125 was 1.0 A, the output of the optical fiber amplifier 125 was 122 mW. When the pump current of the pump LD 127 in the optical fiber amplifier 125 was 2.8 A, the output of the optical fiber amplifier 125 was 918 mW. When the pump current of the pump LD 127 in the optical fiber amplifier 125 was 5.0 A, the output of the optical fiber amplifier 125 was 1970 mW. As can be seen from FIG. 14 , by changing the output of the optical fiber amplifier 125 in the range of 100 mW to 2000 mW, the amount of chirp (GDD) of the pulsed light output from the optical fiber amplifier 125 was reduced to approximately 48,000 fs 2 13, it is possible to change the amount of chirp (GDD) of pulsed light while keeping the minimum pulse duration of compressed pulsed light approximately constant.

[0064] In the optical device 110 according to the modified example, ΔGDD is 48000 fs 2 , Ω ∼ 0.026 rad / fs (corresponding to pulsed light of ∼ 90 fs), so from the above equation (3), Δz ∼ 16 × z R As in the first embodiment, if z R = 10 μm, the change in position Δz in the z direction at which time focusing occurs is 160 μm.

[0065] Next, a microscope apparatus according to a second embodiment of the present application will be described with reference to Fig. 15 . As shown in Fig. 15 , the microscope apparatus 201 according to the second embodiment includes a stage 205, an optical device 210, and a detection unit 260. The microscope apparatus 201 is also referred to as a two-photon excitation fluorescence microscope or a multi-photon excitation fluorescence microscope. A sample SA is placed on the upper surface of the stage 205. The sample SA may be, for example, a cell.

[0066] The detection unit 260 includes a condenser lens 261 and a detector 262. The detection unit 260 further includes a dichroic mirror 215, galvanometer mirrors 216, 216, and an objective lens 217 of the optical device 210. The condenser lens 261 condenses the fluorescence from the sample SA reflected by the dichroic mirror 215. The detector 262 is configured using a photomultiplier tube (PMT), a photodiode (PD), or the like. The detector 262 detects the fluorescence from the sample SA condensed by the condenser lens 261 and outputs a detection signal. An image processor (not shown) performs image processing based on the detection signal detected by the detector 262, and an image of the sample SA obtained by image processing in the image processor is displayed on a display device (not shown).

[0067] Next, an optical device 210 according to a second embodiment will be described. The optical device 210 focuses pulsed light, which is excitation light, onto a sample SA. The pulse duration of the pulsed light is, for example, on the order of femtoseconds (fs). As shown in FIG. 15 , the optical device 210 includes a light source unit 20, a first mirror 11, a diffraction grating 12, a collimator lens 13, a second mirror 14, a dichroic mirror 215, galvanometer mirrors 216, 216, and an objective lens 217. The light source unit 20, the first mirror 11, the diffraction grating 12, the collimator lens 13, and the second mirror 14 have the same configurations as the light source unit 20, the first mirror 11, the diffraction grating 12, the collimator lens 13, and the second mirror 14 according to the first embodiment. Therefore, the same reference numerals as those in the first embodiment are used, and detailed description thereof will be omitted.

[0068] The dichroic mirror 215 transmits the pulsed light PL incident on the dichroic mirror 215 toward the galvanometer mirrors 216, 216. The dichroic mirror 215 also reflects the fluorescence from the sample SA, which has entered the dichroic mirror 215 via the objective lens 217 and the galvanometer mirrors 216, 216, toward the detection unit 260 (condenser lens 261).

[0069] The galvanometer mirrors 216, 216 reflect the pulsed light PL that has passed through the dichroic mirror 215 toward the objective lens 217. The galvanometer mirrors 216, 216 also reflect the fluorescence from the sample SA that has passed through the objective lens 217 toward the dichroic mirror 215. The galvanometer mirrors 216, 216 can change the traveling direction of the pulsed light PL by changing the orientation of their reflecting surfaces. Changing the traveling direction of the pulsed light PL with the galvanometer mirrors 216, 216 makes it possible to perform scanning on a plane (observation plane) on the sample SA that is perpendicular to the optical axis of the objective lens 217. The galvanometer mirrors 216, 216 are preferably provided at the pupil position of the objective lens 217 or at a position conjugate with the pupil.

[0070] The objective lens 217 focuses the pulsed light PL reflected by the galvanometer mirrors 216, 216 onto the sample SA. The diffraction grating 12, the sample SA (observation surface), and the detection unit 262 are conjugate with one another.

[0071] Next, a scanning method using pulsed light using the optical device 210 of the microscope device 201 configured as described above will be described. The scanning method according to the second embodiment is similar to the scanning method described in the first embodiment, and will therefore be described with reference to FIG. 10, which is the same as in the first embodiment. First, pulsed light is generated in the same manner as in the first embodiment (step ST1). Next, the pulsed light is amplified in the same manner as in the first embodiment (step ST2).

[0072] Next, the pulsed light PL is dispersed by the diffraction grating 12 (step ST3). In the second embodiment, the light source unit 20 emits pulsed light PL in a wavelength band of, for example, 1 μm as excitation light. The pulsed light PL emitted from the light source unit 20 is reflected by the first mirror 11 and enters the diffraction grating 12. The diffraction grating 12 disperses the pulsed light PL reflected by the first mirror 11 by a diffraction phenomenon. The pulsed light PL dispersed by the diffraction grating 12 passes through the collimator lens 13, becomes parallel, and enters the second mirror 14. At this time, the diffraction grating 12 and the collimator lens 13 generate a spatial chirp of the pulsed light PL required for time focusing.

[0073] Next, the pulsed light PL is focused by the objective lens 217 (step ST4). The pulsed light PL reflected by the second mirror 14 passes through the dichroic mirror 215 and is reflected by the galvanometer mirrors 216. The pulsed light PL reflected by the galvanometer mirrors 216 is incident on the objective lens 217. The objective lens 217 focuses the pulsed light PL reflected by the galvanometer mirrors 216 onto the sample SA. Note that, due to temporal focusing, the pulse time width of the pulsed light PL focused by the objective lens 217 becomes the pulse time width of the pulsed light PL when it is incident on the diffraction grating 12. This includes not only cases where the pulse time width of the pulsed light PL focused by the objective lens 217 is (completely) the same as the pulse time width of the pulsed light PL when it is incident on the diffraction grating 12, but also cases where it is approximately the same as the pulse time width of the pulsed light PL when it is incident on the diffraction grating 12.

[0074] Then, scanning is performed by changing the position where the time focus occurs in the optical axis direction of the objective lens 217 (step ST5). At this time, the amplification factors of the first optical fiber amplifier 25 and the second optical fiber amplifier 26 are changed by modulating the excitation currents of the first pump LD 27 and the second pump LD 28. This changes the amount of chirp (GDD) of the pulsed light PL, and changes the position where the time focus occurs in the optical axis direction of the objective lens 217, thereby performing scanning in the optical axis direction (z direction). At this time, scanning is performed in directions perpendicular to the optical axis of the objective lens 217 (X and Y directions) by changing the propagation direction of the pulsed light PL using the galvanometer mirrors 216. Note that, when the pulsed light PL from the optical device 210 is continuously irradiated onto the sample SA, the above-mentioned step of generating pulsed light (ST1), step of amplifying the pulsed light (ST2), step of dispersing the pulsed light (ST3), step of focusing the pulsed light (ST4), and step of scanning (ST5) are performed in parallel.

[0075] Irradiation of the pulsed light PL, which is excitation light, causes two-photon excitation of fluorescent substances contained in the sample SA, resulting in the emission of fluorescence with a shorter wavelength than that of the excitation light (pulsed light PL). At this time, the pulse time width of the pulsed light PL is reduced due to the effect of time focusing, and the original pulse time width when it is incident on the diffraction grating 12 is reproduced at the observation plane of the sample SA (the focal plane of the objective lens 217). The effect of time focusing increases the resolution in the optical axis direction (z direction) of the microscope device 201, so that two-photon excitation occurs only in a minute region near the focal point of the objective lens 217. Therefore, scanning in the optical axis direction (z direction) can be performed by changing the position where time focusing occurs (position in the z direction). By combining this with scanning in a direction perpendicular to the optical axis by the galvanometer mirrors 216, 216, a three-dimensional image of the sample SA can be generated.

[0076] Fluorescence from the sample SA is incident on the objective lens 217. The fluorescence that has passed through the objective lens 217 is reflected by the galvanometer mirrors 216 and 216 and is incident on the dichroic mirror 215. The fluorescence that has passed through the dichroic mirror 215 is reflected by the dichroic mirror 215 and is incident on the condenser lens 261. The fluorescence that has passed through the condenser lens 261 is condensed on the detection unit 262. The diffraction grating 12, the sample SA (observation surface), and the detection unit 262 are conjugate with one another. Therefore, by configuring the pulsed light PL, which is excitation light, to be condensed on the observation surface of the sample SA by the objective lens 217, it is possible to ensure that all of the fluorescence generated by two-photon excitation that passes through the objective lens 217 reaches the detection unit 262.

[0077] According to the second embodiment, the optical device 210 of the microscope apparatus 201 includes a first optical fiber amplifier 25 and a second optical fiber amplifier 26 that amplify pulsed light, a diffraction grating 12 that disperses the pulsed light, and an objective lens 217 that focuses the pulsed light dispersed by the diffraction grating 12, and is capable of changing the gains of the first optical fiber amplifier 25 and the second optical fiber amplifier 26. Note that, due to temporal focusing, the pulse time width of the pulsed light focused by the objective lens 217 becomes the pulse time width of the pulsed light when it is incident on the diffraction grating 12. As in the first embodiment, the gain of the first optical fiber amplifier 25 can be changed at high speed by modulating the excitation current of the first pump LD 27 at high speed, and therefore the amount of chirp (GDD) of the pulsed light can be changed at high speed, and the position (position in the z direction) where temporal focusing occurs can be changed at high speed. Furthermore, due to the effect of time focusing, even if the focusing radius of the pulsed light is set to about 5 to 10 μm, the resolution in the optical axis direction (z direction) of the microscope device 201 is high, so that scanning in the optical axis direction (z direction) can be performed at high speed by quickly changing the position (position in the z direction) where time focusing occurs. Therefore, by combining this with scanning in a direction perpendicular to the optical axis by the galvanometer mirrors 216, 216, it becomes possible to quickly generate a three-dimensional image of the sample SA.

[0078] Furthermore, similarly to the first embodiment, the output of the pulsed light output from the second optical fiber amplifier 26 may be kept within a certain range by adjusting the amplification factor of the second optical fiber amplifier 26 by controlling the pumping current of the second pump LD 28. Alternatively, the pulse energy of the pulsed light may be controlled by installing a light intensity regulator such as an acousto-optic device (AOM) on the input side or output side of the second optical fiber amplifier 26. This makes it possible to reduce fluctuations in the pulse energy of the pulsed light while changing the amount of chirp (GDD) of the pulsed light.

[0079] As in the first embodiment, a compressor 31 may be provided to compress the pulse time width of the pulsed light output from the second optical fiber amplifier 26. This makes it possible to obtain pulsed light of a Fourier-limited pulse.

[0080] In the second embodiment described above, similarly to the first embodiment, the oscillator 22 may not be provided, and the first optical fiber amplifier 25 may amplify pulsed light from a pulsed light generator provided outside the microscope device 201. In this case, the step (ST1) of generating pulsed light described above can be omitted.

[0081] In the second embodiment described above, similarly to the first embodiment, a prism or the like may be provided instead of the diffraction grating 12 as a dispersive element for dispersing the pulsed light.

[0082] In the second embodiment described above, similarly to the first embodiment, the gain of the first optical fiber amplifier 25 may be effectively changed and the amount of chirp (GDD) of the pulsed light may be changed by controlling the amount of input pulsed light using an acousto-optic element (AOM) or the like provided on the input side of the first optical fiber amplifier 25. Furthermore, the gain of the second optical fiber amplifier 26 may be effectively changed and the output of the second optical fiber amplifier 26 may be maintained within a certain range by controlling the amount of pulsed light using an acousto-optic element (AOM) or the like provided on the input or output side of the second optical fiber amplifier 26.

[0083] In the second embodiment described above, the light source unit 20 is not limited to a two-stage amplifier configuration (first optical fiber amplifier 25 and second optical fiber amplifier 26) as in the first embodiment, but may have only one amplifier.

[0084] In the second embodiment described above, the compressor 31 is not limited to a diffraction grating pair (grating pair) as in the first embodiment, but may be configured using a prism pair.

[0085] In the second embodiment described above, the compressor 31 is provided in the light source unit 20, as in the first embodiment, but this is not limiting, and the compressor does not have to be provided in the light source unit. For example, the optical device of the microscope device 201 may be configured in the same manner as the optical device 110 according to the modified example of the first embodiment.

[0086] In the above-described second embodiment, a two-photon excitation fluorescence microscope (multi-photon excitation fluorescence microscope) has been described as an example of the microscope device 201, but the microscope device 201 is not limited to this and may be, for example, a second harmonic generation (SHG) microscope or a third harmonic generation (THG) microscope.

[0087] REFERENCE SIGNS LIST 1 Optical processing apparatus (first embodiment) 10 Optical device 12 Diffraction grating 13 Collimator lens 17 Objective lens 20 Light source unit 22 Oscillator (pulsed light generator) 25 First optical fiber amplifier 26 Second optical fiber amplifier 27 First pump LD 28 Second pump LD 31 Compressor 110 Optical device (modified example) 111 First diffraction grating 112 Second diffraction grating 117 Objective lens 120 Light source unit 122 Oscillator (pulsed light generator) 125 Optical fiber amplifier 127 Pump LD 201 Microscope device (second embodiment) 210 Optical device 217 Objective lens PL Pulsed light

Claims

1. An amplifier that amplifies pulsed light; A dispersion element that disperses the pulsed light output from the amplifier; An objective lens that condenses the pulsed light dispersed by the dispersion element, and An optical device capable of changing the amplification factor of the amplifier.

2. A collimator lens that makes the pulsed light dispersed by the dispersion element parallel, The objective lens condenses the pulsed light that has passed through the collimator lens, and The optical device according to claim 1, wherein the pulse time width of the pulsed light condensed by the objective lens becomes the pulse time width of the pulsed light when incident on the dispersion element due to time focusing.

3. Having a second amplifier that amplifies the pulsed light output from the amplifier, The dispersion element disperses the pulsed light output from the second amplifier, and The optical device according to claim 1, wherein the amplification factor of the second amplifier can be changed.

4. By changing the amplification factor of the amplifier, the position where time focusing occurs is changed in the optical axis direction of the objective lens, and The optical device according to claim 3, wherein by changing the amplification factor of the second amplifier, the output of the pulsed light output from the second amplifier is within a certain range.

5. The optical device according to claim 3, having a compressor that compresses the pulse time width of the pulsed light output from the second amplifier.

6. Having an optical device that scans pulsed light irradiated onto a workpiece, and An optical processing device, wherein the optical device is the optical device according to any one of claims 1 to 5.

7. Having an optical device that scans pulsed light irradiated onto a sample, A microscope apparatus, wherein the optical device is the optical device according to any one of claims 1 to 5.

8. Amplifying pulsed light using an amplifier; Dispensing the pulsed light output from the amplifier using a dispersion element; Condensing the pulsed light dispersed by the dispersion element using an objective lens; A scanning method including changing a position where temporal focusing of the pulsed light condensed using the objective lens occurs in the optical axis direction of the objective lens by changing an amplification factor of the amplifier and scanning.