JP2009088137A - Negative dispersion mirror and mode-locked solid-state laser apparatus including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative dispersion mirror which can generate large negative group-velocity dispersion and can be used as an output mirror of a solid-state laser apparatus. <P>SOLUTION: In a mirror 5 including a dielectric multilayer coating structure 7 formed on a substrate 6, the multilayer coating structure includes three or more mirror-function layer portions ML<SB>1</SB>, ML<SB>2</SB>, ..., each formed by a plurality of layers deposited one on another, and cavity layers C1, C2, ..., that are arranged between the two mirror-function layer portions, and causes light having a predetermined wavelength to resonate between the two mirror-function layer portions. Further, a dispersion value with respect to the light L having the predetermined wavelength is in the range of -600 fs<SP>2</SP>to -3000 fs<SP>2</SP>and a reflectance is in the range of 97 to 99.5%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a negative dispersion mirror and a solid-state laser device including the negative dispersion mirror, and more particularly to a soliton type mode-locked solid-state laser device that is small and capable of short pulse operation.

  Conventionally, solid-state laser devices using a solid-state laser medium (laser crystal, ceramics, glass) to which a semiconductor laser (LD) is used as an excitation light source and rare earth ions or transition metal ions are added have been actively developed. Among them, short pulse laser devices that generate so-called short pulse light in the picosecond to femtosecond range have been sought, proposed, verified, and practically used in a wide variety of application fields such as medicine, biotechnology, machinery industry, and measurement. It has become.

  This type of laser device generates a short pulse by an operation called mode synchronization. In simple terms, mode synchronization means that the phases of many longitudinal modes are all synchronized in the frequency domain during laser oscillation (relative phase difference = 0). This is a phenomenon that results in a very short pulse in the time domain.

  In particular, in soliton mode locking, which is one form of CW (continuous oscillation) mode locking, the negative group velocity dispersion in the laser resonator and self-phase modulation mainly in the laser medium are combined, resulting in a femtosecond region. Pulse generation is possible.

  The solid-state laser device that realizes the soliton mode locking basically includes a solid-state laser medium, a saturable absorption mirror, and a negative group velocity dispersion element in a resonator. In the following, the negative group velocity dispersion may be simply referred to as negative dispersion.

  Conventionally, as the negative group velocity dispersion element, one or a plurality of combinations such as a prism pair, a diffraction grating pair, and a negative dispersion mirror are used.

  Negative dispersion mirrors include chirp-type mirrors that compensate for negative dispersion using the difference in penetration depth between long-wavelength light and short-wavelength light, and light between a total reflection mirror and a partial reflection mirror. And a GTI (Gires-Tournois interferometer) type mirror that compensates for negative dispersion by using the above interference.

  A typical example of a chirped mirror is a mirror in which a high refractive index layer having a relatively high refractive index and a low refractive index layer having a relatively low refractive index are alternately stacked. The optical film thickness and the optical film thickness of the low refractive index layer are laminated so as to change linearly in the lamination direction (for example, see Non-Patent Document 1).

  On the other hand, the GTI type mirror is characterized by having a resonance structure inside a dielectric multilayer film (see, for example, Non-Patent Document 2), and has a double GTI structure having two cavity layers inside the multilayer film. Mirrors (see Patent Document 1) or mirrors configured so that the optical film thickness of each layer constituting the multilayer film changes in accordance with some rules so as to have a resonant structure but no cavity layer (Patent Document 2) ) Etc. are also proposed.

  Further, in Patent Document 3, two or more dielectric multilayer film stacks in which two or more different refractive index layers are alternately stacked are stacked, and the center wavelength of each stack is made different so that not only the second order. A dielectric multilayer film characterized by performing third-order or higher dispersion compensation has been proposed. Patent Document 4 discloses that the reflectance in the visible light band is 95% or more, and the refractive index of the outermost film is A multilayer mirror that has a refractive index lower than the refractive index of the film immediately below the outermost film and is configured to cause negative group velocity dispersion has been proposed.

Furthermore, in order to reduce the size of the mode-locked solid-state laser device, Patent Document 5 proposes to provide a chirped mirror coating on the laser medium, the saturable absorber, or the output mirror.
Special Table 2002-528906 JP-T-2002-523797 Japanese Patent Laid-Open No. 2-23302 JP 2000-138407 A JP-A-11-168252 R. Szipoecs et al., Optics Letters, Vol. 19, 201 (1994) IEEE Transaction on Quantum Electronics, vol. 22, no.1 (1986) pp. 182-185

  In order to reduce the size of a soliton mode-locked solid-state laser device, the present inventors need a negative dispersion mirror that can compensate for a larger amount of negative dispersion than the conventional one and has a reflectivity as an output mirror. I found out.

However, the negative dispersion amount of the conventional negative dispersion mirror is about several tens to several hundreds fs ² , and it is necessary to provide a plurality of mirrors in the resonator as necessary.

  Patent Document 5 proposes an output mirror having a negative dispersion function. However, Patent Document 5 specifically describes light transmittance, negative dispersion amount, and the like when used as an output mirror. There is no specific description of the film constituting the mirror. Patent Document 4 also describes that frequency chirp compensation can be achieved by providing a dielectric multilayer film on the output mirror, but the negative dispersion amount of the multilayer film cited as a specific example is very small. With only one element, sufficient negative dispersion cannot be obtained, and since the reflectivity is 99.9% or more and almost 100%, almost no output light can be obtained and the function as an output mirror is not sufficient.

  In view of the above circumstances, an object of the present invention is to provide a negative dispersion mirror that can cause large negative group velocity dispersion and can be used as an output mirror of a solid-state laser device. It is another object of the present invention to provide a mode-locked solid-state laser device that can realize CW mode synchronization in the femtosecond region with a small size, low cost, and high stability.

The negative dispersion mirror of the present invention is a mirror having a dielectric multilayer structure on a substrate,
The multilayer structure has three or more mirror function layer portions each formed by laminating a plurality of layers, and is disposed between each mirror function layer portion. Consists of a cavity layer that causes resonance of light of a wavelength,
The cavity layer is arranged with the mirror functional layer portion interposed at a predetermined interval throughout the multilayer film structure,
A dispersion amount is −600 fs ² to −3000 fs ² and a reflectance is 97% to 99.5% with respect to light of the predetermined wavelength.

  That is, the negative dispersion mirror of the present invention is characterized by comprising at least three mirror functional layer portions and two cavity layers.

  “Overall” means, for example, a form in which two or three or more cavity layers are arranged close to each other in a part of the multilayer film structure, at least the entire layers constituting the multilayer film structure This means that all the cavity layers are arranged in a continuous half layer region of the number, and that it is provided on average between the substrate side and the outermost layer. .

  When there are three or more cavity layers, the predetermined interval is preferably substantially equal between the plurality of cavity layers. This substantially equal interval means within an average value ± 35% of the interval between the cavity layers.

Here, the dispersion amount of −600 fs ² to −3000 fs ² means a predetermined value within the range of −600 fs ² or more and −3000 fs ² or less, and the reflectance is 97% to 99.5% means a predetermined value within the range of 97% or more and 99.5% or less.

  It is preferable that the substrate has a concave surface and the multilayer structure is provided on the concave surface.

Said predetermined wavelength and has a bandwidth of more than 10nm, that is, the predetermined value range dispersion amount of -600fs ² ~-3000fs ² against 10nm or more bandwidth and reflectivity of 97% A predetermined value in the range of ~ 99.5% is desirable.

  The center wavelength of the predetermined wavelength can be set to a desired value, but is preferably in the range of 1000 nm to 1100 nm, or in the range of 700 nm to 900 nm.

  When the center wavelength of the predetermined wavelength is λ, the optical thickness of the cavity layer is preferably λ / 2 or more. Furthermore, the optical film thickness is preferably up to about 10λ. In particular, the thickness is preferably about 2λ-4λ.

  When the center wavelength of the predetermined wavelength is λ, the optical film thickness of each layer constituting the mirror functional layer is preferably λ / 8 or more and less than λ / 2.

  The mirror functional layer is preferably formed by alternately stacking five or more layers having a relatively high refractive index and layers having a relatively low refractive index.

  The cavity layer is preferably made of the same material as the layer having a high refractive index or the layer having a low refractive index.

  The layer having a high refractive index is, for example, one selected from an oxide of Ti, Zr, Hf, Nb, Al, Zn, Y, Sc, La, Ce, Pr or Ta, and a sulfide of Zn, or , Or a mixture or compound containing one or more of these. Here, the mixture or compound containing one or more may include ones other than the oxides and sulfides listed above, but one or more of the oxides and sulfides listed here may be included. It shall be included as a main component (more than 50% by weight of the total).

  The layer having a low refractive index may be one selected from oxides of Si and fluorides of Ca, Li, Mg, Na, Th, Al, Hf, La, Y, or Zr, or one of these. It may consist of a mixture or compound containing one or more. Here, the mixture or compound containing one or more may include other than the oxides and fluorides listed above, but one or more of the oxides and fluorides listed here may be included. It shall be included as a main component (more than 50% by weight of the total).

  A mode-locked solid-state laser device of the present invention includes a resonator, a solid-state laser medium disposed in the resonator, and a mode-locked element disposed in the resonator, and constitutes one end of the resonator. The output mirror is the negative dispersion mirror of the present invention described above. Here, the phrase “arranged in the resonator” includes the case where the element itself constitutes the end of the resonator. As the mode-locking element, a semiconductor saturable absorption mirror (SESAM), a car-mode locking element, a saturable absorption mirror using a carbon nanotube, or the like can be used. Good.

  The optical pulse dispersion compensator according to the present invention is characterized in that at least two negative dispersion mirrors according to the present invention are arranged so that their multilayer structures are opposed to each other. Here, “the multilayer film structure of each other is opposite” means that the light incident on the surface having the multilayer film structure of one negative dispersion mirror is reflected by the surface and the multilayer film structure of the other negative dispersion mirror It is arranged so as to be incident on a surface provided with.

  The nonlinear optical image device of the present invention is configured to emit fluorescence generated from the sample by irradiating the sample containing the fluorescently labeled substance to be measured with the excitation light irradiation position relative to the sample. A non-linear optical image device that acquires a two-dimensional or three-dimensional image by detecting while scanning in three dimensions or three dimensions, comprising the mode-locked solid-state laser device of the present invention as a light source that outputs the excitation light. It is a feature.

  The laser processing apparatus of the present invention is a laser processing apparatus for irradiating a workpiece with a laser beam to process the workpiece, and the mode-locked solid-state laser of the present invention is used as a light source for outputting the laser beam. A device is provided.

The negative dispersion mirror of the present invention has a dispersion amount of −600 fs ² to −3000 fs ² and a reflectance of 97% to 99.5% with respect to light of a predetermined wavelength. It can be suitably used as an output mirror constituting one end of the resonator of the laser device. The negative-dispersion mirror can be designed amount of dispersion in accordance with the configuration of the mode-locked solid-state laser device to an arbitrary value in the range of -600fs ² ~-3000fs ^2, the amount of dispersion in comparison to conventional negative dispersion mirror Since it is very large, it can sufficiently compensate for negative dispersion alone. Further, the reflectivity can be designed to an arbitrary value in the range of 97% to 99.5%, and it can function as an output mirror because it transmits 3% to 0.5% of light. By using the negative dispersion mirror of the present invention as an output mirror, it is not necessary to provide one or more negative dispersion elements in the resonator, so that the mode-locked solid-state laser device can be made compact.

  Further, the negative dispersion mirror of the present invention has a very large absolute value of the amount of dispersion, and therefore can be effectively used as a simple negative dispersion element.

  If the cavity layer is made of the same material as the layer having a high refractive index or the layer having a low refractive index, an increase in materials and the number of steps during manufacturing can be suppressed, and an increase in cost can be prevented.

  Since the mode-locked solid-state laser device of the present invention includes the negative dispersion mirror of the present invention as an output mirror that constitutes one end of the resonator, the entire device can be significantly reduced and downsized. It can be configured at a low cost, and stabilization of the laser output can be achieved.

  By using the negative dispersion mirror of the present invention, the optical pulse dispersion compensator of the present invention can shorten the optical path length and suppress loss compared to the dispersion compensator using the diffraction grating pair generally used conventionally. Dispersion compensation can be performed with low power loss. Furthermore, the size can be significantly reduced as compared with the diffraction grating pair.

  Since the nonlinear optical imaging apparatus of the present invention includes the mode-locked solid-state laser apparatus of the present invention as a light source, the overall configuration can be reduced in size and stable excitation light can be obtained. Accurate imaging images can be acquired.

  Since the laser processing apparatus of the present invention includes the mode-locked solid-state laser apparatus of the present invention as a light source, the overall configuration can be reduced in size, and a stable pulse laser beam can be obtained. Laser processing can be performed.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

<Negative dispersion mirror>
FIG. 1 is a schematic diagram showing a configuration of a negative dispersion mirror 1 according to a first embodiment of the present invention.

The negative dispersion mirror 1 of the present embodiment is a mirror having a dielectric multilayer film structure 4 on a glass substrate 3, and the multilayer film structure 4 has three or more mirror functional layer portions each formed by laminating a plurality of layers. ML ₁ , ML ₂ ,... ML _{m + 1} and the cavity layers C ₁ , C that are sandwiched between the mirror functional layer portions and cause resonance of the light L having a predetermined wavelength between the mirror functional layer portions. ₂ ... C _m . In the mirror of the present invention, a plurality of cavity layers are arranged with a mirror functional layer portion interposed at a predetermined interval throughout the multilayer film structure.

Each layer of the multilayer structure 4 is laminated from the substrate 3 side in the order of the first layer, the second layer, the (k-1) layer, the kth layer, the (k + 1) layer, the n layer. are, first from the first layer (k-1) is mirror function layer portion to layer ML _1, the k-th layer realizes the cavity layer C _1, · · and the substrate mirror function layer portion from the side ML _m cavity layer C _m Are alternately stacked, and the mirror function layer ML _{m + 1} is disposed on the most air side. In the minimum structure, m = 2, three mirror function layer portions ML, and two cavity layers. In addition, there is no upper limit in particular in m, and the number of m should just increase / decrease as needed.

  The cavity layers are not arranged close to each other in a part of the multilayer film structure 4, but are provided so as to be evenly arranged over the entire multilayer film structure. In the case where there are three or more cavity layers, the gaps between the cavity layers are arranged so as to be substantially equal within an average value of ± 35% of the gaps between the cavity layers.

The negative dispersion mirror 1 has a dispersion amount in the range of −600 fs ² to −3000 fs ² and a reflectance in the range of 97% to 99.5% with respect to the light L having a predetermined wavelength. Here, the light L of a predetermined wavelength has a bandwidth of more than 10nm, that is, the mirror 1 is a predetermined value range dispersion amount of -600fs ² ~-3000fs ² to light bandwidth than 10nm The reflectance shows a predetermined value in the range of 97% to 99.5%, and can be arbitrarily set within these ranges.

Each of the mirror functional layer portions ML ₁ and ML ₂ is alternately composed of a high refractive index layer having a relatively high refractive index n ₁ and a low refractive index layer having a relatively low refractive index n ₂ (<n ₁ ). It is preferable that each of the functional layer portions ML ₁ and ML ₂ has a total of at least five layers of at least a high refractive index layer and a low refractive index layer. For example, the odd layers (first layer, third layer,...) May be formed of a high refractive index layer, and even layers (second layer, fourth layer,...) May be formed of a low refractive index layer.

  Specifically, the high refractive index layer is one selected from an oxide of Ti, Zr, Hf, Nb, Al, Zn, Y, Sc, La, Ce, Pr or Ta, and a sulfide of Zn, or Can be composed of mixtures or compounds containing one or more of these.

  The low refractive index layer includes an oxide of Si, and one selected from Ca, Li, Mg, Na, Th, Al, Hf, La, Y, or Zr fluoride, or one or more thereof. It can consist of a mixture or a compound.

  However, the low-refractive index layer and the high-refractive index layer may be made of a dielectric having a relatively low or relatively high refractive index, and any known material may be used.

  On the other hand, the refractive index of the cavity layer is not particularly limited, but if the material used for the high refractive index layer or the low refractive index layer constituting the mirror functional layer portion is used, it is not necessary to prepare other materials. Therefore, the increase in cost and the number of processes can be suppressed, which is preferable.

  The center wavelength λ of the predetermined wavelength may be set at an arbitrary wavelength in the range of 1000 nm to 1100 nm or 700 nm to 900 nm, and the optical film thickness of each layer is set according to the arbitrary wavelength λ.

The cavity layer generally has a larger optical film thickness than the other layers. Here, the optical film thickness of the cavity layer C is at least twice (λ / 4), that is, λ / 2 or more, preferably (λ / 4). 4 times to 8 times. The optical film thickness of each layer constituting the mirror function layers ML ₁ and ML ₂ is set to be 1/2 or more and less than 2 times λ / 4, that is, λ / 8 or more and less than λ / 2. The optical film thickness is represented by the product n · d of the refractive index n of the layer and the film thickness d (nm) of the layer.

  Next, a specific layer configuration example will be given. FIGS. 2A to 13A show optical film thicknesses of the respective layers with respect to a predetermined center wavelength λ in the design examples 1 to 12, respectively, and FIGS. 2B to 13B show the design examples 1 to 1 shown in FIGS. 2A to 13A, respectively. It is a graph which shows the reflectance and negative dispersion amount which are achieved by 12 layer structure. Design examples 1 to 10 are designed with a center wavelength λ = 1045 nm, and design examples 11 and 12 are designed with a center wavelength λ = 800 nm, both obtained by simulation.

2A to 13A, the horizontal axis indicates the layer number, and the vertical axis indicates the optical film thickness (4nd / λ) normalized by λ / 4. The most substrate side layer is the first layer, and the most air side layer is the 50th layer. 2B to 13B, the horizontal axis represents the wavelength (nm) of the predetermined light, and the vertical axis represents the reflectance (%) and the negative dispersion amount (fs ² ).

2A, the first to tenth layers are mirror functional layers ML ₁ , the eleventh layer is a cavity layer C ₁ , the twelfth to twentieth layers are mirror functional layers ML ₂ , The 21st layer is the cavity layer C ₂ , the 22nd to 30th layers are the mirror function layer ML ₃ , the 31st layer is the cavity layer C ₃ , the 32nd to 42nd layers are the mirror function layer ML ₄ , and the 43rd layer is The cavity layer C ₄ and the 44th to 50th layers respectively constitute the mirror function layer ML ₅ . The number of layers constituting the mirror function layer is 10 layers, 9 layers, 9 layers, 11 layers, and 7 layers, respectively. The intervals between the cavities are 9 layers, 9 layers, and 11 layers, with an average of 9.6 layers, and the cavity layers are arranged at almost equal intervals.

2B has a characteristic that the mirror having the film configuration shown in FIG. 2A satisfies the reflectance = 98.5% and the negative dispersion amount−1200 fs ² in the range of at least ± 5 nm with 1045 nm as the center wavelength. It is shown that.

In the multilayer film structure of design example 2 shown in FIG. 3A, the number of layers constituting the mirror functional layer ML and the cavity layer C is the same as that of design example 1, and the optical film thickness of each cavity layer is that of design example 1. Is almost the same. On the other hand, the optical film thickness of each layer constituting the mirror functional layers ML ₁ and ML ₂ on the substrate side among the mirror functional layers is different from that of the design example 1. FIG. 3B shows that the mirror having the film configuration shown in FIG. 3A has characteristics satisfying reflectance = 98.5% and negative dispersion = −2500 fs ² in the range of at least ± 5 nm with 1045 nm as the central wavelength. It is shown that.

While in the Design Example 1 and Design Example 2 layers structure is similar, in the range of 1040Nm～1050nm, negative dispersion amount is obtained very different characteristics -1200Fs ² and -2500Fs ^2.

In the multilayer structure of design example 3 shown in FIG. 4A, the number of layers constituting the mirror functional layer ML and the cavity layer C is the same as that of design example 1, and the optical film thickness of each cavity layer is that of design example 1. Is almost the same. On the other hand, among the mirror functional layers, the optical film thicknesses of the layers constituting the mirror functional layers ML ₁ and ML ₂ on the substrate side in particular are different from those of the design examples 1 and 2. FIG. 4B shows that the mirror having the film configuration shown in FIG. 4A has characteristics satisfying reflectance = 97.5% and negative dispersion = −2500 fs ² in the range of at least ± 5 nm with 1045 nm as the center wavelength. It is shown that.

  Although design example 2 and design example 3 have different layer structures, substantially the same characteristics can be obtained in the range of 1040 nm to 1050 nm.

In the multilayer film structure of design example 4 shown in FIG. 5A, the number of layers constituting the mirror functional layer ML and the cavity layer C is the same as that of design example 1, and the optical film thickness of each cavity layer is that of design example 1. Is almost the same. On the other hand, the optical film thickness of the layers constituting the mirror functional layers ML ₁ and ML ₂ on the substrate side among the mirror functional layers is different from that of the design example 1. FIG. 5B shows that the mirror having the film configuration shown in FIG. 5A has characteristics satisfying reflectance = 99.5% and negative dispersion = −1200 fs ² in the range of at least ± 5 nm with 1045 nm as the center wavelength. It is shown that.

In the design example 1 to the design example 4, the numbers (arrangements) of the layers constituting the cavity layers C ₁ , C _2, ..., C ₅ are the same, the optical film thicknesses are substantially equal, and the mirror functional layers ML ₁ , ML ₂ ... The number of layers constituting ML ₅ is also the same. However, the properties obtained are very different.

The multilayer film structures of Design Examples 5 to 8 shown in FIGS. 6A to 9A include a layer having a very large optical film thickness as the first layer on the most substrate side, and the mirror function layer ML ₁ is formed from the second layer to the second layer. except that it is composed of 10 layers, other mirror function layer ML ₂ ..., ML ₅ each cavity layer C _1, C ₂ ..., number and number of layers of layers constituting the C ₅ are as design example 1 The optical film thicknesses of the respective cavity layers are almost the same as those of the design example 1.

FIG. 6B shows that the mirror having the film configuration shown in FIG. 6A has a characteristic that the reflectance is 98.5% and the negative dispersion amount is −1200 fs ² in the range of at least ± 5 nm with 1045 nm as the central wavelength. It is shown that.

FIG. 7B shows that the mirror having the film configuration shown in FIG. 7A has characteristics satisfying reflectance = 97% and negative dispersion = −1200 fs ² in the range of at least ± 5 nm with 1045 nm as the central wavelength. It is shown that.

FIG. 8B shows that the mirror having the film configuration shown in FIG. 8A has characteristics satisfying reflectance = 99.5% and negative dispersion = −1200 fs ² in the range of at least ± 5 nm with 1045 nm as the central wavelength. It is shown that.

FIG. 9B shows that the mirror having the film structure shown in FIG. 9A has characteristics satisfying reflectance = 98.5% and negative dispersion = −2500 fs ² in the range of at least ± 5 nm with 1045 nm as the central wavelength. It is shown that.

Even if the first layer arranged on the most substrate side is provided with a layer having a large optical film thickness as in Design Examples 5 to 8, the layer having a large optical film thickness is formed on the first layer as in Design Examples 1 to 4. As in the case of not including the mirror, a mirror having a dispersion amount of −600 fs ² to −3000 fs ² and a reflectance of 97% to 99.5% can be configured.

The multilayer film structure of the design example 9 shown in FIG. 10A is the same as the design examples 5 to 8 in that a layer having a large optical film thickness is disposed on the first layer on the most substrate side. In the multilayer film structure of design example 9, the second to tenth layers are mirror functional layers ML ₁ , the eleventh layer is a cavity layer C ₁ , the twelfth to twentieth layers are mirror functional layers ML ₂ , and the twenty-first layer is Cavity layer C ₂ , 22nd to 30th layers are mirror functional layers ML ₃ , 31st layer is cavity layer C3, 32nd to 44th layers are mirror functional layers ML ₄ , 45th layer is cavity layer C ₄ , is 46 layers from the 50 layers constituting the mirror function layer ML ₅ respectively. The number of layers constituting the mirror function layer is 9 layers, 9 layers, 9 layers, 13 layers, and 5 layers, respectively. The intervals between the cavities are 9 layers, 9 layers, and 13 layers with an average of 10.3 layers, and the cavity layers are arranged at almost equal intervals in the range of the average value ± 30%.

FIG. 10B shows that the mirror having the film configuration shown in FIG. 10A has characteristics satisfying reflectance = 98.5% and negative dispersion = −2500 fs ² in the range of at least ± 5 nm with 1045 nm as the central wavelength. It is shown that.

The multilayer film structure of the design example 10 shown in FIG. 11A is the same as the design examples 5 to 8 in that a layer having a large optical film thickness is disposed on the first layer on the most substrate side. In the multilayer structure of design example 10, the second to tenth layers are mirror functional layers ML ₁ , the eleventh layer is a cavity layer C ₁ , the twelfth to twenty-second layers are mirror functional layers ML ₂ , and the twenty-third layer is The cavity layer C ₂ , the 24th to 30th layers are the mirror function layer ML ₃ , the 31st layer is the cavity layer C ₃ , the 32nd to 44th layers are the mirror function layer ML ₄ , and the 45th layer is the cavity layer C _4. , layers 50th 46th layers constitute a mirror function layer ML ₅ respectively. The number of layers constituting the mirror function layer is 9 layers, 11 layers, 7 layers, 13 layers, and 5 layers, respectively. The intervals between the cavities are 11, 7, and 13 layers, and the average is 10.3 layers. The cavity layers are arranged at almost equal intervals in the range of the average value ± 35%.

FIG. 11B shows that the mirror having the film configuration shown in FIG. 11A has characteristics satisfying reflectance = 98.5% and negative dispersion = −2500 fs ² in the range of at least ± 5 nm with 1045 nm as the central wavelength. It is shown that.

In design examples 8, 9 and 10, the arrangement of the cavity layers is partially different, and the number of layers constituting the mirror functional layer and the layer numbers are slightly different, but as shown in FIGS. 9B, 10B and 11B, In both cases, the reflectance = 98.5% and the negative dispersion = −2500 fs ² are satisfied with respect to the wavelength of 1040 nm to 1050 nm, and the wavelength dependency of the reflectance and the negative dispersion has the same behavior.

The multilayer film structure of the design example 11 shown in FIG. 12A has the same number of layers constituting the mirror functional layer ML and the cavity layer C as in the design examples 1 to 4, but the optical film thickness of each layer is the same as in the design examples 1 to 4. It is different from four. In design example 11, the optical film thicknesses of all the cavity layers are substantially equal. FIG. 12B shows that the mirror having the film configuration shown in FIG. 12A has a characteristic that the reflectance is 98.5% and the negative dispersion amount is −1000 fs ² in the range of at least ± 5 nm with 800 nm as the central wavelength. It is shown that.

The multilayer film structure of the design example 12 shown in FIG. 13A is the same as the design examples 5 to 8 in the number of layers constituting the mirror functional layer ML and the cavity layer C, but the optical film thickness of each layer is that of the design examples 5 to 8. It is different from the thing. In design example 12, the optical film thicknesses of all the cavity layers are the same. FIG. 13B shows that the mirror having the film configuration shown in FIG. 13A has characteristics satisfying reflectance = 98.5% and negative dispersion = −1000 fs ² in the range of at least ± 5 nm with 800 nm as the central wavelength. It is shown that.

  In design example 11 and design example 12, the optical film thickness of the first layer closest to the substrate is greatly different, but the other layer structures are substantially the same, and reflectivity and negative dispersion at least in the wavelength range of 795 nm to 805 nm. The wavelength dependence of the quantity is also consistent.

  In any of the design examples, the cavity layer has an optical film thickness standardized by λ / 4 between 4 and 7, and the optical film thickness of each layer constituting the mirror function layer is 0.5 or more and less than 2 based on 1. It was in range. However, the optical film thickness of the cavity layer is not limited to 4 to 7, and may be 2 or more. In each of the above design examples, the number of layers constituting the multilayer film structure is 50, the mirror function layer portion is five, and the cavity layer is four. However, the number is not limited thereto. . In the above design example, the center wavelength λ is 1045 nm or 800 nm, but the center wavelength can be arbitrarily set. When used in a mode-locked solid-state laser device, one having a center wavelength in the 1 μm band (1000 nm to 1100 nm) or 0.8 μm band (700 nm to 900 nm) is preferably used.

Center wavelength λ, desired dispersion amount in the range of -600 fs ² to -3000 fs ² , desired reflectivity in the range of 97% to 99.5% are set, and other initial conditions are the number of layers, refractive index (film material) , Film structure such as where to provide the cavity layer and how many mirror layers, etc., approximate film thickness (for each layer constituting the mirror functional layer, around the central wavelength λ / 4, center for the cavity layer A computer simulation (simulation using thin film calculation software “Essential Macleod”) is performed after setting an optical thickness of an integral multiple of wavelength λ / 4 × n. Thereafter, these initial conditions are corrected manually or automatically by a computer to obtain a layer structure as in the above-described design example.

When the negative dispersion mirror of the present invention is applied as an output mirror of a mode-locked solid-state laser device, the negative dispersion mirror 5 of the second embodiment shown in FIG. 14 has a predetermined surface on the concave surface of the glass substrate 6 having a concave surface. What provided the multilayer film structure 7 with respect to the light L of a wavelength is suitable. The configuration of the multilayer film structure 7 is the same as that of the first embodiment described above, and three or more mirror function layer portions ML ₁ , ML ₂ ... ML ₅ (here 5 Cavity layers C ₁ and C ₂ that are arranged between the mirror functional layer portions and cause resonance of light L having a predetermined wavelength between the sandwiched mirror functional layer portions. ... C ₄ are composed of (here comprising four cavity layer), with respect to light L of a predetermined wavelength, in the range dispersion amount of -600fs ² ~-3000fs ^2, and the reflectance 97 % To 99.5% range. Specifically, the film configuration as in the design examples 1 to 12 described above may be used.

The light L having a predetermined wavelength is light that is output from the solid-state laser medium and resonates in the resonator, and is determined by the configuration of the mode-locked solid-state laser device to which the negative dispersion mirror 5 is applied. For example, if Yb: KYW (K (WO ₄ ) ₂ ) is used as the solid laser medium, λ = 1045 nm, and if Yb: KGW (Gd (WO ₄ ) ₂ ) is used as the solid laser medium, λ = 1040 nm, λ = 1050 nm for Yb: YAG, λ = 1076 nm for Yb: Y ₂ O ₃ , λ = 750 nm for Alexandrite (BeAl ₂ O ₄ : Cr ³⁺ ), λ for Cr ³⁺ : LiSrAlF ₆ = 850 nm, λ = 850 nm for Cr ³⁺ : LiCaAlF ₆ , and λ = 800 nm for Ti: Al ₂ O ₃ .

  An antireflection film 8 is provided on the surface of the glass substrate 6 opposite to the surface on which the multilayer film structure is provided to prevent light transmitted through the multilayer film structure 7 from being reflected on the surface opposite to the concave surface of the substrate 6. It has been. The reflectance with respect to the light L incident on the mirror from the laminated surface side of the multilayer film structure 7 is 97% to 99.5%, and components of 3% to 0.5% are transmitted to the antireflection film 8 side.

  By using the negative dispersion mirror shown in FIG. 14 as the output mirror of the mode-locked solid-state laser device, the solid-state laser device can be made compact, and stable pulsed laser oscillation in the femtosecond band can be obtained.

<Mode-locked solid-state laser device>
Next, a mode-locked solid-state laser device provided with the negative dispersion mirror shown in FIG. 14 will be described.

  FIG. 15 is a schematic side view showing a soliton mode-locked solid-state laser device according to an embodiment of the present invention. As shown, this mode-locked solid-state laser device includes a semiconductor laser 11 that emits excitation light 10, an excitation optical system 12 that inputs the excitation light 10 into the resonator, and a concave output mirror that forms one end of the resonator. The functioning negative dispersion mirror 5 described with reference to FIG. 14, the SESAM (semiconductor saturable absorption mirror) 16 constituting the other end of the resonator, the solid-state laser medium 15 disposed inside the resonator, the resonator And an output mirror and a concave mirror 19 that guides the light to the SESAM. The concave mirror 19 has a function as a dichroic mirror that transmits the incident excitation light 10 and reflects the oscillation light 18.

  In the present embodiment, Yb: KYW crystal is used as the solid-state laser medium 15 as an example. As the semiconductor laser 11, a laser that emits the excitation light 10 for exciting the solid-state laser medium 15 is used.

  In the above configuration, the pumping light 10 that is output from the semiconductor laser 11, input from the back surface of the concave mirror 19 by the pumping optical system 12, passes through the concave mirror 19, and enters the resonator is solid-state laser medium 15. The solid-state laser medium 15 is excited, and light having a predetermined wavelength (here, center wavelength 1045 nm) generated thereby oscillates by the action of the resonator. The laser oscillation light 18 is partially transmitted through the negative dispersion mirror 5 and extracted outside as output light 18a.

  Here, the negative group velocity dispersion due to the action of the negative dispersion element 17 provided in the output mirror 5 in the laser resonator and the self-phase modulation mainly in the solid-state laser medium 15 are combined to produce a femtosecond region. Pulsed light 18a is obtained. More specifically, SESAM 16 initiates mode synchronization to maintain and stabilize the pulse, and sharpening of the mode synchronization pulse occurs through soliton pulse formation by balancing group velocity dispersion and self-phase modulation, which is of the femtosecond class. Stable soliton pulse generation is possible.

In the mode-locked solid-state laser device shown in FIG. 15, the negative dispersion mirror 5 having a dispersion amount of −800 fs ² and a reflectance of 98.3% is preferable.

  In a mode-locked solid-state laser device, in order to stably generate soliton mode pulse oscillation, the amount of dispersion required for the negative dispersion mirror depends on the solid-state laser medium, the arrangement of optical elements arranged in the resonator, the resonance It can be determined by the resonator structure such as the length of the device.

  FIG. 16 is a schematic diagram illustrating a schematic configuration of the mode-locked solid-state laser device according to the second embodiment. This mode-locked solid-state laser device includes a semiconductor laser 11 that emits pumping light 10, a pumping optical system 12 that inputs the pumping light 10 into the resonator, and the pumping optical system 12 from the outside of the resonator to the resonator optical axis. The dichroic mirror 14 disposed in the resonator that reflects the obliquely incident excitation light 10 toward the solid-state laser medium 15 and transmits the oscillation light 18 that resonates in the resonator, and one of the resonators The negative dispersion mirror 5 constituting the end of the resonator, the SESAM 16 constituting the other end of the resonator, and the solid-state laser medium 15 disposed inside the resonator constituted by the SESAM 16 and the negative dispersion mirror 5 are configured. ing. In the resonator, there is no mirror that reflects oscillation light other than SESAM 16 and output mirror 5 constituting the termination, and the resonator has a linear resonator structure. The solid-state laser medium 15 and the SESAM 16 are arranged close to each other.

  In the above configuration, the pumping light 10 output from the semiconductor laser 11 and incident obliquely to the resonator optical axis by the pumping optical system 12 is reflected by the dichroic mirror 14 and input to the solid-state laser medium 15 to be The laser medium 15 is excited, and light having a predetermined wavelength generated thereby oscillates by the action of the resonator. The laser oscillation light 18 partially passes through the output mirror 5 and is extracted to the outside as output light 18a. In the apparatus of this configuration, the beam waist of the laser oscillation light 18 that resonates in the resonator is formed only on the SESAM 16.

A more specific configuration example of the mode-locked solid-state laser device shown in FIG. 16 will be described. A Yb: Y ₂ O ₃ medium in which Yb ions are added to a ceramic medium Y ₂ O ₃ (yttria) as a base material is used as the solid-state laser medium 15. The oscillation light is 1075 nm in the fluorescence spectrum of the Yb: Y ₂ O ₃ medium.

Here, the Yb: Y ₂ O ₃ medium 15 has a thickness of 0.65 mm to which 10 at% of Yb ions are added, and excitation light 10 having a wavelength of 980 nm is provided on both sides of the Yb: Y ₂ O ₃ medium 15. A coating that satisfactorily transmits any of the oscillation light 18 in the wavelength 1075 nm band is applied.

As SESAM16, use is made of BATOP having a modulation depth of 0.4% and a saturation fluence of 120 μJ / cm ² .

The radius of curvature of the concave surface of the negative dispersion mirror 5 is 30 mm, and the negative dispersion mirror 5 and the SESAM 16 have a resonator length defined between the mirror surface of the negative dispersion mirror 5 and the mirror surface of the SESAM 16 of 30 mm (in air). The Yb: Y ₂ O ₃ medium 15 is arranged at a position where the distance d to the SESAM 16 is 6 mm.

As the semiconductor laser 11, a broad area type having an emission width of 100 μm with a wavelength of 980 nm and an output of 2 W is used. The excitation optical system 12 is a condensing lens, and uses an excitation light beam diameter of about 100 μm in the Yb: Y ₂ O ₃ medium 15. The condensing lens 12 is disposed close to the dichroic mirror 14 so as not to cut the resonator optical path, and the condensing lens 12 causes the excitation light 10 to be near the center of the Yb: Y ₂ O ₃ medium 15 in the thickness direction. It is condensed so that the beam waist comes.

The dichroic mirror 14 is a 1 mm square 0.3 mm thick quartz plate coated with a coating that reflects the excitation light 10 with a wavelength of 980 nm well and transmits the oscillation light 18 with a wavelength of 1075 nm at Brewster angle incidence. And arranged close to the Yb: Y ₂ O ₃ medium 15.

In this mode-locked solid-state laser device, light having a wavelength of 1075 nm that is excited by the pumping light 10 and emitted from the Yb: Y ₂ O ₃ medium 15 resonates between the negative dispersion mirror 5 and the SESAM 16 and is mode-locked by the SESAM 16. Then, it is output from the negative dispersion mirror 5 as output light (pulse laser) 18a.

  The negative dispersion mirror 5 functioning as a concave output mirror compensates for positive group velocity dispersion generated in the resonator, and the group velocity dispersion in the entire resonator is completely compensated (group velocity dispersion = 0) or resonance. This produces negative group velocity dispersion in which the group velocity dispersion in the chamber is negative (group velocity dispersion <0). By providing such a negative dispersion mirror 5, soliton mode synchronization can be induced, and pulsed light having a pulse width of picoseconds or less can be obtained.

For example, by providing a negative dispersion mirror 5 having a group velocity dispersion of −3000 fs ² in the resonator of the mode-locked solid-state laser device of FIG. 16, the entire group velocity dispersion in the resonator is −2700 fs ² and a pulse of 800 fs is obtained. A pulsed laser beam having a width can be obtained.

In general, Yb-doped solid-state laser medium has a large F _{sat, L} , so the mode-locking threshold is large, and when the resonator length L is as short as 30 mm, the intra-cavity pulse energy becomes small. If it is long, mode synchronization is not applied. However, by performing group velocity dispersion compensation in the resonator as described above and forming a state called soliton mode locking, the mode locking threshold can be reduced, and even with a resonator length as short as 30 mm, the mode I was able to synchronize.

  Thus, by using the negative dispersion mirror of the present invention as an output mirror, a very small mode-locked solid-state laser device capable of femtosecond pulse oscillation can be configured. Since the number of optical elements constituting the resonator can be suppressed, the resonator is stable and large negative dispersion compensation can be performed, so that soliton pulse oscillation can also be stably performed.

As the solid laser medium, Yd: Y ₂ O ₃ or Nd: YVO ₄ and Nd or Yb ions are added to various base materials. For example, Nd: GdVO ₄ , Nd: YAG, Nd: glass, Yb Solid laser medium combined with various base materials such as YAG, Yb: KY (WO ₄ ) ₂ , Yb: KGd (WO ₄ ) ₂ , Yb: Gd ₂ SiO ₅ , Yb: Y ₂ SiO ₅ Can be used. Further, the ions to be added are not limited to Nd and Yb ions, but can be applied to all rare earth ions and further to transition metal ions such as Cr and Ti.

  The negative dispersion mirror of the present invention can be used as an optical pulse dispersion compensator, and the mode-locked solid-state laser device provided with the negative dispersion mirror of the present invention includes a nonlinear optical imaging device and a laser processing device. It can be suitably used as a light source.

<Nonlinear optical imaging device>
FIG. 17 shows a schematic configuration of a nonlinear optical imaging apparatus (multiphoton microscope) using the mode-locked solid-state laser apparatus of the present invention.

  This nonlinear optical imaging apparatus excites fluorescence from a sample placed on a movable stage and excited by irradiating the sample containing the fluorescently labeled substance to be measured with the movable stage. The light condensing position is detected while being moved two-dimensionally or three-dimensionally to obtain a two-dimensional image or a three-dimensional image.

  In this embodiment, the nonlinear optical imaging apparatus has a sample 35 mounted thereon, a movable stage 36 that moves the sample 35 in the xy plane and in the depth direction, and a pulse laser beam as excitation light, for example, A mode-locked solid-state laser device 31 having the configuration shown in FIG. 16, a lens pair 32 that expands the pulse laser beam, and a dichroic mirror 33 that reflects the pulse laser beam toward the sample 35 and transmits the fluorescence from the sample 35. The pulse laser beam is condensed on the sample 35, the objective lens 34 for collecting the fluorescence from the sample 35, the photomal 38 for detecting the fluorescence from the sample 35, and the fluorescence on the photomal 38. And a lens 37.

  The pulse laser beam from the mode-locked solid-state laser device 31 is magnified by the lens pair 32, reflected by the dichroic mirror 33, and applied to the objective lens. The pulsed laser beam that has passed through the objective lens 34 is collected on a sample 35 disposed on the movable stage 36, and the sample 35 is excited by multiphoton absorption. The fluorescence from the sample 35 is collected by the objective lens 34, passes through the dichroic mirror 33, and then collected by the lens 37 onto the photomultiplier 38. It is possible to perform three-dimensional imaging by moving the movable stage 36 in the x-y in-plane direction and the z-depth direction to excite a minute region three-dimensionally and acquire fluorescence.

  A conventional mode-locked solid-state laser device used as a light source of a conventional nonlinear imaging apparatus is expensive and has low output stability because the entire apparatus is large and the internal structure is complicated. For this reason, there are problems that the imaging apparatus is increased in cost and the acquired image is deteriorated. However, since the mode-locked solid-state laser device of the present invention is small, low-cost, and has high output stability, the use of this mode-locked solid-state laser device as a light source of a nonlinear imaging device reduces the cost and acquisition of the imaging device. High definition of the image can be achieved.

<Design Change Example of Embodiment of Nonlinear Optical Imaging Apparatus>
FIG. 18 is a diagram showing a modification of the nonlinear optical imaging apparatus of FIG. The non-linear optical imaging apparatus of this design modification is the same as the non-linear optical imaging apparatus of FIG. 17 except that the optical pulse dispersion compensating apparatus 40 comprising the negative dispersion mirror pair of the present invention is provided on the optical path of the pulse laser beam. The pulse laser beam from the mode-locked solid-state laser device 31 is reflected and transmitted through a plurality of optical components before being focused on the sample 35. At that time, the pulse width of the pulse laser beam is greatly expanded due to group velocity dispersion (normally normal dispersion) of the optical members. For this reason, the peak power of the pulse beam laser focused on the sample 35 is lowered, and the fluorescence intensity is lowered as the excitation light is lowered. As a result, the acquired image may be deteriorated. Therefore, as shown in FIG. 18, an optical pulse dispersion compensator 40 comprising the negative dispersion mirror pair of the present invention is arranged on the optical path of the pulse beam laser, and the group velocity dispersion of the optical members constituting the nonlinear optical imaging apparatus is previously determined. By correcting, the pulse laser beam can be focused with the original pulse width of the sample, so that high-definition imaging is possible.

<Optical pulse dispersion compensator>
FIG. 19 is a diagram showing a schematic configuration of an optical pulse dispersion compensating apparatus 40 provided with the negative dispersion mirror of the present invention, which is provided in the nonlinear optical imaging apparatus.

  The optical pulse dispersion compensator 40 of this embodiment has a structure in which, for example, two negative dispersion mirrors 41 each having a multilayer film structure of Design Example 1 formed on a quartz substrate are arranged in parallel. The pulse beam laser 42 is configured to perform multiple reflections between them. The pulse beam laser 42 can compensate for positive group velocity dispersion generated in the nonlinear optical imaging apparatus by multiple reflection between the mirrors 41.

Specifically, in the nonlinear optical imaging apparatus of FIG. 17, the group velocity dispersion that the pulse laser beam undergoes until it is focused on the sample 35 is 8000 fs ² , so that it is reflected eight times by the mirror 41 having a dispersion of −1000 fs ^2. Dispersion compensation was performed. As a result, it was possible to focus the pulse laser beam on the sample 35 with a pulse width equivalent to the pulse width immediately after being output from the mode-locked solid-state laser device 31, and high-definition imaging could be performed.

<Laser processing equipment>
FIG. 20 is a diagram showing a schematic configuration of a laser processing apparatus including the mode-locked solid-state laser apparatus of the present invention as a light source.

  The laser processing apparatus of this embodiment includes a movable stage 60 on which a sample 59 such as a metal thin film to be processed is placed, and moves the sample 59 in the xy plane and in the depth direction, and a pulse laser as excitation light. For example, a mode-locked solid-state laser device 51 configured as shown in FIG. 16, a pulse picker 52 that converts a pulse repetition frequency of a pulse laser beam from the mode-locked solid-state laser device 51, dispersion compensation, and pulse width A chirp pulse amplifier 56 comprising a pulse stretcher 53, a regenerative amplifier 54 and a pulse compressor 55, a mirror 57 for reflecting the pulse laser beam incident through the amplifier 56 and guiding it to the sample, and a pulse on the sample And a lens 58 for condensing the laser beam.

  The pulse laser beam from the mode-locked solid-state laser device 51 is subjected to a pulse repetition frequency of 1 kHz by a pulse picker 52, then a pulse stretcher 53, a regenerative amplifier 54 composed of Yb: KYW, and a chirped pulse amplifier 56 composed of a pulse compressor 55. Is incident on. The pulse stretcher 53 and the pulse compressor 55 are constituted by a diffraction grating pair, and the group velocity dispersion of the pulse is controlled by this diffraction grating pair to expand and contract the pulse width.

  Instead of the diffraction grating pair, a negative dispersion mirror pair having a multilayer film structure on the substrate according to the present invention may be used. If the negative dispersion mirror pair of the present invention is used, the pulse width can be expanded and contracted with a power loss lower than that of the diffraction grating pair, and it can be made smaller than the diffraction grating pair. Thus, the negative dispersion mirror of the present invention is a mere negative dispersion element, and compensates dispersion in an apparatus equipped with an optical system in which the spread of the pulse width of the pulse laser beam due to the increase in positive negative dispersion becomes a problem. Can also be used.

  The pulse width of the pulse laser beam output from the mode-locked solid-state laser device 51, for example, is greatly expanded to 100 ps by a pulse stretcher 53 to 100 ps, and then amplified to a pulse energy of 5 mJ by a regenerative amplifier 54 composed of Yb: KYW. 55 was pulse compressed to 300fs. As a result, a pulsed laser beam with a peak power of 16 GW was obtained. By condensing the pulse laser beam from the chirped pulse amplifier 56 onto the sample 59, which is a metal thin film on the movable stage 60, a highly accurate fine drilling process was achieved.

  The conventional mode-locked solid-state laser device used as the light source of the conventional laser processing device is expensive because the entire device is large and the internal structure is complicated compared to the mode-locked solid-state laser device of the present invention, The output stability was also low. For this reason, there are problems that the laser processing apparatus is increased in cost and the processing accuracy is deteriorated. However, since the mode-locked solid-state laser device of the present invention is small, low-cost, and has high output stability, the use of this mode-locked solid-state laser device in a laser processing device can reduce the cost and accuracy of the laser processing device. Can be processed.

Schematic diagram showing the configuration of a negative dispersion mirror according to an embodiment of the present invention. Example 1 of film configuration of negative dispersion mirror of the present invention The graph which shows the reflectance and dispersion amount in the negative dispersion mirror of the design example 1 Example 2 of film configuration of negative dispersion mirror of the present invention Graph showing reflectance and amount of dispersion in negative dispersion mirror of design example 2 Example 3 of film configuration of negative dispersion mirror of the present invention The graph which shows the reflectance and dispersion amount in the negative dispersion mirror of the design example 3 Example 4 of film configuration of negative dispersion mirror of the present invention Graph showing reflectivity and dispersion amount in negative dispersion mirror of design example 4 Example 5 of film configuration of negative dispersion mirror of the present invention Graph showing reflectance and dispersion amount in negative dispersion mirror of design example 5 Example 6 of film configuration of negative dispersion mirror of the present invention Graph showing reflectance and amount of dispersion in negative dispersion mirror of design example 6 Example 7 of design of film configuration of negative dispersion mirror of the present invention Graph showing reflectivity and dispersion amount in negative dispersion mirror of design example 7 Example 8 of design of film structure of negative dispersion mirror of the present invention The graph which shows the reflectance and dispersion amount in the negative dispersion mirror of the design example 8 Example 9 of film configuration of negative dispersion mirror of the present invention The graph which shows the reflectance and dispersion amount in the negative dispersion mirror of the design example 9 Example 10 of film configuration of negative dispersion mirror of the present invention 10 The graph which shows the reflectance and dispersion amount in the negative dispersion mirror of the design example 10 Example 11 of film configuration of negative dispersion mirror of the present invention The graph which shows the reflectance and dispersion amount in the negative dispersion mirror of the design example 11 Example 12 of film configuration of negative dispersion mirror of the present invention The graph which shows the reflectance and dispersion amount in the negative dispersion mirror of the design example 12 Schematic diagram showing the configuration of a negative dispersion mirror used as an output mirror The schematic diagram which shows schematic structure of the mode-locked solid-state laser apparatus of 1st embodiment of this invention The schematic diagram which shows schematic structure of the mode-locked solid-state laser apparatus of 2nd embodiment of this invention 1 is a schematic configuration diagram showing an embodiment of a nonlinear optical imaging apparatus of the present invention. The figure which shows the example of a design change of embodiment shown in FIG. 1 is a schematic configuration diagram showing an embodiment of an optical pulse dispersion compensation apparatus of the present invention. Schematic configuration diagram showing an embodiment of a laser processing apparatus of the present invention

Explanation of symbols

1, 5 Negative dispersion mirror 3 Glass substrate 4, 7 Multilayer film structure 6 Concave glass substrate C Cavity layer ML ₁ ML ₂ Mirror functional layer 8 Antireflection film
10 Excitation light
11 Semiconductor laser
12 Excitation optics
13, 14 Dichroic mirror
15 Solid-state laser medium
16 SESAM (semiconductor saturable absorber mirror)
18 Solid-state laser oscillation light
18a output light
19 Concave mirror

Claims (15)

A mirror having a dielectric multilayer structure on a substrate,
The multilayer structure has three or more mirror function layer portions each formed by laminating a plurality of layers, and is disposed between each mirror function layer portion. Consists of a cavity layer that causes resonance of light of a wavelength,
The cavity layer is arranged with the mirror functional layer portion interposed at a predetermined interval throughout the multilayer film structure,
A negative dispersion mirror having a dispersion amount of −600 fs ² to −3000 fs ² and a reflectance of 97% to 99.5% with respect to light of the predetermined wavelength.   The negative dispersion mirror according to claim 1, wherein the substrate has a concave surface, and the multilayer film structure is provided on the concave surface.   3. The negative dispersion mirror according to claim 1, wherein the dispersion amount and the reflectance are such that the predetermined wavelength has a bandwidth of 10 nm or more.   The negative dispersion mirror according to any one of claims 1 to 3, wherein a center wavelength of the predetermined wavelength is in a range of 1000 nm to 1100 nm.   4. The negative dispersion mirror according to claim 1, wherein a center wavelength of the predetermined wavelength is in a range of 700 nm to 900 nm. 5. When the center wavelength of the predetermined wavelength is λ,
6. The negative dispersion mirror according to claim 1, wherein the optical thickness of the cavity layer is λ / 2 or more. When the center wavelength of the predetermined wavelength is λ,
7. The negative dispersion mirror according to claim 1, wherein an optical film thickness of each layer constituting the mirror functional layer is not less than λ / 8 and less than λ / 2.   8. The mirror functional layer is formed by alternately laminating five or more layers having a relatively high refractive index and layers having a relatively low refractive index. The negative dispersion mirror according to any one of claims.   9. The negative dispersion mirror according to claim 8, wherein the cavity layer is made of the same material as the layer having the high refractive index or the layer having the low refractive index. The layer having a high refractive index,
One selected from oxides of Ti, Zr, Hf, Nb, Al, Zn, Y, Sc, La, Ce, Pr or Ta, and sulfides of Zn,
The negative dispersion mirror according to claim 8 or 9, wherein the negative dispersion mirror is made of a mixture or a compound containing one or more of them. The layer having a low refractive index,
One selected from oxides of Si and fluorides of Ca, Li, Mg, Na, Th, Al, Hf, La, Y or Zr,
The negative dispersion mirror according to any one of claims 8 to 10, wherein the negative dispersion mirror is made of a mixture or a compound containing one or more of these. A resonator,
A solid-state laser medium disposed in the resonator;
A saturable absorber disposed in the resonator,
The mode-locked solid-state laser device according to claim 1, wherein the output mirror constituting one end of the resonator is the negative dispersion mirror according to claim 1.   12. An optical pulse dispersion compensator comprising: at least two negative dispersion mirrors according to claim 1; and a multilayer film structure facing each other. Fluorescence generated from the sample by irradiating the sample containing the fluorescently-labeled substance to be measured while scanning the irradiation position of the excitation light relative to the sample in two or three dimensions. A non-linear optical image device for obtaining a two-dimensional or three-dimensional image,
13. A non-linear optical image device comprising the mode-locked solid-state laser device according to claim 12 as a light source for outputting the excitation light. A laser processing apparatus for processing a workpiece by irradiating the workpiece with laser light,
A laser processing apparatus comprising the mode-locked solid-state laser apparatus according to claim 12 as a light source for outputting the laser light.

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