Patent Publication Number: US-2016220416-A1

Title: Laser eye surgery apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2015-017123 filed on Jan. 30, 2015, the contents of which are incorporated herein by reference in its entirety. 
     BACKGROUND 
     The present disclosure relates to a laser eye surgery apparatus in which an operator mainly treats a transparent tissue (for example, the cornea or the crystalline lens) of a patient&#39;s eye by using photodisruption caused by laser pulses. 
     In the related art, a technology, by which an operator treats a patient&#39;s eye by respectively concentrating laser pulses on multiple target positions in the patient&#39;s eye, and causing photodisruption in a tissue, has been known. A technology, by which the repetition frequency of laser pulses emitted to a patient&#39;s eye is changed during an operation, has also been known. 
     A laser device disclosed in JP-T-2013-520846 includes an oscillator, and a cavity-dumped regenerative amplifier. The oscillator generates multiple seed laser pulses (hereinafter, may also be referred to as a “seed laser pulse train”) at a constant repetition frequency. The cavity-dumped regenerative amplifier picks up and amplifies only every fifth to 20000 th  seed laser pulses from the seed laser pulses train generated by the oscillator. The picked-up seed laser pulses are discharged from the cavity-dumped regenerative amplifier without being amplified. That is, the cavity-dumped regenerative amplifier filters out the seed laser pulse train. The laser device disclosed in JP-T-2013-520846 changes the repetition frequency of emitted laser pulses by changing the percentage of the picked-up and amplified seed laser pulses in the seed laser pulse train generated by the oscillator. 
     The repetition frequency of laser pulses emitted to a patient&#39;s eye is also deemed to be changed by filtering a seed laser pulse train or an amplified laser pulse train using an acoustic-optic modulator (AOM) or the like. 
     SUMMARY 
     When a patient&#39;s eye is treated using ultrashort-pulse laser light, it is desirable that the patient&#39;s eye can be accurately treated within a short amount of time. Accordingly, a laser eye surgery apparatus is required to scan ultrashort-pulse laser light, which is emitted at a higher repetition frequency, at a higher speed. According to a method of changing the repetition frequency by filtering out seed laser pulses train in the related art, the repetition frequency of the laser pulses emitted from the laser device can be changed only to a divisor of the repetition frequency of a seed laser pulse. As a result, according to the method in the related art, the repetition frequency is changed only in a stepwise manner, and cannot be continuously (linearly) changed. According to the method in the related art, the filter-out pulses are not used for treatment, and thus, energy is wasted. 
     A typical object of the present disclosure is to provide a laser eye surgery apparatus in which an operator can accurately treat a patient&#39;s eye within a short amount of time by appropriately changing the repetition frequency of the laser pulses. 
     According to a typical aspect of the present disclosure, there is provided a laser eye surgery apparatus comprising: 
     a laser device which includes a gain-switched seed light source configured to repeatedly generate seed laser pulses with a pulse width of 10 femtoseconds or greater and 1 nanosecond or less and vary repetition frequency of the seed laser pulses according to a set repetition frequency, the laser device being configured to emit laser pulses based on the seed laser pulses generated by the gain-switched seed light source; 
     a condenser configured to condense the laser pulses emitted from the laser device in a transparent tissue of a patient&#39;s eye to cause photodisruption at concentration positions of the laser pulses in the transparent tissue; 
     a scanner configured to scan the concentration position of each of the laser pulses emitted from the laser device; and 
     a controller configured to control the gain-switched seed light source to change the repetition frequency of the seed laser pulses according to a scanning speed at which the concentration position is scanned by the scanner. 
     An operator can accurately treat a patient&#39;s eye within a short amount of time by appropriately changing the repetition frequency of a laser pulse from a laser eye surgery apparatus according to the aspect of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view illustrating the configuration of a laser eye surgery apparatus  1 . 
         FIG. 2  is a schematic view illustrating the configuration of a laser device  10 . 
         FIG. 3  is a flowchart illustrating a repetition frequency changing process executed by the laser eye surgery apparatus  1 . 
     
    
    
     DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Hereinafter, a typical embodiment of the present disclosure will be described. First, the schematic configuration of a laser eye surgery apparatus  1  in the embodiment will be described with reference to  FIG. 1 . The following description will be given on the assumption that a direction of the visual axis of a patient&#39;s eye E is a Z-axis direction, a horizontal direction is an X-axis direction, and a vertical direction is a Y-axis direction. In the drawings, each lens, each mirror, or the like is illustrated by one member. However, each lens, each mirror, or the like may be formed of multiple optical components. 
     &lt;Entire Configuration&gt; 
     The laser eye surgery apparatus  1  in the embodiment is used to treat a tissue (at least one of the cornea, the crystalline lens, and the like) of the patient&#39;s eye. The laser eye surgery apparatus  1  in the embodiment includes a laser device  10 ; a scanner  30 ; an objective lens  53 ; a position detecting unit  55 ; an observation and image capturing unit  60 ; an operation unit  70 ; and a control unit  76 . 
     &lt;Laser Device&gt; 
     The laser device  10  repeatedly emits multiple laser pulses. In the embodiment, the laser pulses emitted by the laser device  10  are used to cut and fragment a transparent tissue by causing the transparent tissue to photodisrupt. More specifically, in the embodiment, the laser pulses are used to induce plasma in the transparent tissue via non-linear interaction. The non-linear interaction is an interaction between light and a substance, and is an action in which a response appears non-proportionally to the intensity of light (that is, the density of photons). The laser eye surgery apparatus  1  in the embodiment causes multiphoton absorption to occur at a concentration position by concentrating (focusing) the laser pulses in the transparent tissue of the patient&#39;s eye E. The probability of the occurrence of the multiphoton absorption is not proportional to the intensity of light, and is non-linear. When an excited state occurs due to the multiphoton absorption, plasma is generated in the transparent tissue, thereby causing photodisruption. The induced plasma may be plasma which accompanies or does not accompany plasma emission. 
     As an example, the pulse width of the laser pulses emitted to the patient&#39;s eye by the laser device  10  may be 10 femtoseconds or greater and 1 nanosecond or less. In the embodiment, the laser pulses with a pulse width of 10 femtoseconds or greater and 10 picoseconds or less are exemplarily used. The laser device  10  will be described in detail later. 
     &lt;Scanner&gt; 
     The scanner  30  scans the concentration position of each laser pulse concentrated by the objective lens  53  (to be described in detail later) by scanning the concentration position of each laser pulse emitted from the laser device  10 . That is, the scanner  30  moves the concentration position of the laser pulses to a target position. The scanner  30  in the embodiment includes a Z scanner  34  and an X-Y scanner  40 . 
     The Z scanner  34  in the embodiment includes a concave lens  36 ; a convex lens  37 ; and a driver  38 . The driver  38  moves the concave lens  36  along an optical axis L 1 . When the concave lens  36  is moved, the diverging state of a beam passing through the concave lens  36  is changed. As a result, the concentration position (laser spot) of the laser pulses is moved in the Z-axis direction. 
     The X-Y scanner  40  in the embodiment includes an X scanner  41 ; a Y scanner  44 ; and lenses  47  and  48 . The X scanner  41  scans laser pulses in the X-axis direction by swinging a galvanometer mirror  42  using a driver  43 . The Y scanner  44  scans laser pulses in the Y-axis direction by swinging a galvanometer mirror  45  using a driver  46 . The lenses  47  and  48  work in conjunction with two galvanometer mirrors  42  and  45 . 
     Mirrors  31  and  32 , and a hole mirror  33  are provided between the laser device  10  and the Z scanner  34 . The mirrors  31  and  32  guide the laser pulses emitted by the laser device  10 . The hole mirror  33  sets the optical axis L 1  of the laser pulses to be coincident with an optical axis L 2  of the position detecting unit  55  (to be described later). Lenses  50  and  51 , and a beam combiner  52  are provided between the X-Y scanner  40  and the objective lens  53 . The laser pulses are relayed through the lenses  50  and  51 . The beam combiner  52  sets the optical axis L 1  of the laser pulses to be coincident with an optical axis L 3  of the observation and image capturing unit  60  (to be described later). 
     The configuration of the scanner  30  can be appropriately changed. For example, the lenses  47  and  48  between the X scanner  41  and the Y scanner  44  may be omitted. The laser eye surgery apparatus  1  may scan the laser pulses in the X-axis direction and the Y-axis direction using an acousto-optic modulator (AOM) or an acousto-optic device (AOD) polarizing the laser pulses, instead of the galvanometer mirrors  42  and  45 . The laser pulses may be scanned in one direction by multiple elements. The laser pulses may be scanned by a resonant scanner, a polygon mirror, or the like. The Z scanner  34  may be positioned on a downstream side of the X-Y scanner  40 , or the Z scanners  34  may be positioned on both of an upstream side and the downstream side of the X-Y scanner  40 . Multiple Z scanners may be mounted on the upstream side or the downstream side of the X-Y scanner  40 . The movement of the objective lens  53  in an optical axis direction allows the laser pulses to be scanned in the Z-axis direction. Other changes can also be added to the scanner  30 . 
     &lt;Objective Lens&gt; 
     The objective lens  53  is provided on an optical path between the scanner  30  and the patient&#39;s eye E. The objective lens  53  concentrates the laser pulses, which has passed through the scanner  30 , on a tissue of the patient&#39;s eye E. In the embodiment, the laser pulses emitted from the objective lens  53  are concentrated on the tissue of the patient&#39;s eye E via a liquid immersion interface  54 . The liquid immersion interface  54  may adopt a structure in which a cup suctioned and fixed to the patient&#39;s eye E is filled with liquid. An interface mounted on the patient&#39;s eye E is not limited to the liquid immersion interface  54 . A contact lens attached to the patient&#39;s eye E may be used instead of the liquid immersion interface  54 . 
     &lt;Position Detecting Unit&gt; 
     The position detecting unit  55  is used to detect the position of the patient&#39;s eye E with respect to the scanner  30 . The laser eye surgery apparatus  1  in the embodiment associates the concentration position of the laser pulses with a tomographic image (to be described in detail later) by detecting the position of the patent&#39;s eye E with respect to the scanner  30 . Control data used to control the scanner  30  and the like can be set by associating the concentration position with the tomographic image. 
     In the embodiment, a portion of the optical system, through which the laser pulses pass, also serves as an optical system of the position detecting unit  55 . The position detecting unit  55  includes the hole mirror  33 ; a concentration lens  56 ; an aperture plate  57 ; and a light receiving element  58 . The hole mirror  33  transmits light incident to the center of the hole mirror  33 , and reflects light, which is reflected by the patient&#39;s eye E, along the optical axis L 2 . The concentration lens  56  concentrates the light, which is reflected by the hole mirror  33 , on an aperture of the aperture plate  57 . The aperture plate  57  is a confocal aperture plate having an aperture at the center thereof. The aperture of the aperture plate  57  is disposed to work in conjunction with the concentration position (laser spot) of the laser pulses in the patient&#39;s eye E. The light receiving element  58  receives light passing through the aperture of the aperture plate  57 . When the position of the patient&#39;s eye E is detected, the laser eye surgery apparatus  1  in the embodiment adjusts the output of laser light emitted from the laser device  10  in order for the laser light not to cause photodisruption at the concentration position. The laser eye surgery apparatus  1  causes the light receiving element  58  to receive light reflected from the patient&#39;s eye E while moving the concentration position three-dimensionally using the scanner  30 . 
     The configuration used to detect the position of the patient&#39;s eye E with respect to the scanner  30  can be appropriately changed. For example, instead of the hole mirror  33 , a polarizing beam splitter may be used to separate irradiating light from reflected light. The position detecting unit  55  may also be omitted. The laser eye surgery apparatus  1  may irradiate a sample substance or the like with the laser pulses, and detect an actual concentration position in the sample substance or the like via a tomographic image (to be described later). 
     &lt;Observation and Image Capturing Unit&gt; 
     An operator observes the patent&#39;s eye E, and captures an image of a tissue, that is, a treatment target using the observation and image capturing unit  60 . As an example, the observation and image capturing unit  60  in the embodiment includes an OCT unit  61  and a front observation unit  65 . The beam combiner  52  sets the optical axis L 3  of the observation and image capturing unit  60  to be coaxial with the optical axis L 1  of the laser pulses. The optical axis L 3  is split into an optical axis L 4  of the OCT unit  61  and an optical axis L 5  of the front observation unit  65  by a beam combiner  63 . 
     The OCT unit  61  acquires a tomographic image of a tissue of the patient&#39;s eye E using optical coherence technology. Specifically, the OCT unit  61  in the embodiment includes a light source; a light splitter; a reference optical system; a scanner; and a detector. The light source emits light required to acquire a tomographic image. The light splitter splits the light emitted from the light source into reference light and measurement light. The reference light is incident to the reference optical system, and the measurement light is incident to the scanner. The reference optical system is configured to change the difference in an optical path length between the measurement light and the reference light. The scanner scans the measurement light on the tissue two-dimensionally. The detector detects a state of coherence between measurement light reflected by the tissue and the reference light passing through the reference optical system. The laser eye surgery apparatus  1  acquires information regarding the depth of the tissue by scanning the measurement light, and detecting a state of coherence between the reflected measurement light and the reference light. The laser eye surgery apparatus  1  acquires a tomographic image of the tissue based on the acquired information regarding the depth. The laser eye surgery apparatus  1  in the embodiment associates the concentration position of the laser pulses with the tomographic image of the patient&#39;s eye E captured prior to an operation. As a result, the laser eye surgery apparatus  1  is capable of preparing control data used to control a laser pulse irradiating operation (for example, the operations of the drivers  38 ,  43 , and  46 ), based on the tomographic image. It is possible to adopt various configurations as the configuration the OCT unit  61 . Any one of an SS-OCT, an SD-OCT, a TD-OCT, and the like may be adopted as the OCT unit  61 . 
     The front observation unit  65  acquires a front image of the patient&#39;s eye E. The front observation unit  65  in the embodiment captures an image of the patient&#39;s eye E irradiated with visible light or infrared light, and displays the captured image on a monitor  72  (to be described later). The operator can observe the front of the patient&#39;s eye E by watching the monitor  72 . 
     The configuration of the observation and image capturing unit  60  can also be appropriately changed. For example, the observation and image capturing unit  60  may adopt at least one of a configuration in which an image of the patient&#39;s eye E is captured using the Scheimpflug principle, a configuration in which an image of the patient&#39;s eye E is captured using ultrasonic waves, and the like. 
     &lt;Operation Unit&gt; 
     The operation unit  70  receives various instructions input from the operator. As an example, the operation unit  70  in the embodiment includes an operation portion  71  with various operation buttons, and a touch panel provided on a surface of the monitor  72 . The operation unit  70  may also adopt other configuration elements such as a joystick, a keyboard, and a mouse. The monitor  72  is capable of displaying various images such as a front image of the patient&#39;s eye E, a tomographic image of a tissue, and various operation menus. 
     &lt;Control Unit&gt; 
     The control unit  76  includes a CPU  77 ; a ROM  78 ; a RAM  79 ; a non-volatile memory (not illustrated); and the like. The CPU  77  is in charge of various types of control (the control of the laser device  10 , the control of the scanner  30 , and the like) of the laser eye surgery apparatus  1 . The ROM  78  stores various programs required to control the operation of the laser eye surgery apparatus  1 , initial values, and the like. The RAM  79  temporarily stores various items of information. The non-volatile memory is a non-transitory storage medium capable of holding stored contents even if the supply of electrical power is shut off. 
     The laser device  10  in the embodiment includes a laser controller  150  (to be described later with reference to  FIG. 2 ) controlling the emission of the laser pulses from the laser device  10 , which will be described in detail later. The control unit  76  sends signals to and receives signals from the laser controller  150 , and controls the emission of the laser pulses to the patient&#39;s eye E in collaboration with the laser controller  150 . That is, in the embodiment, the control unit  76  and the laser controller  150  control the emission of the laser pulses. However, the configuration of the controller controlling the emission of the laser pulses can be appropriately changed. For example, the laser controller  150  may not be provided, and the control unit  76  may be fully in charge of control. Another controller may control the emission of the laser pulses. 
     &lt;Configuration of Laser Device&gt; 
     The schematic configuration of the laser device  10  will be described with reference to  FIG. 2 . As illustrated in  FIG. 2 , the laser device  10  in the embodiment includes a seed light source  110 ; a preliminary amplifier  120 ; a final amplifier  130 ; an attenuator  140 ; and the laser controller  150 . 
     &lt;Seed Light Source&gt; 
     The seed light source  110  repeatedly generates a seed laser pulse (seed light) according to a repetition frequency determined by the controllers (in the embodiment, the control unit  76  and the laser controller  150 ). Particularly, the seed light source  110  in the embodiment is a gain-switched seed light source. 
     Hereinafter, the principle of generation of a seed laser pulse will be described. Examples of a method of generating the laser pulses include a mode synchronization (mode locking) method and a gain switching method (may be referred to as a Q switching method). 
     The mode synchronization method is a method of generating a laser pulse train at a constant repetition frequency by fixing a phase between longitudinal modes of laser light oscillating in multiple modes. The repetition frequency of a seed light source driven by the mode synchronization method is determined by the resonator length of laser light. Accordingly, the seed light source driven by the mode synchronization method used to generate an ultrashort pulse in the related art is not capable of changing the repetition frequency of a generated seed laser pulse. Also, when the seed light source is used according to the mode synchronization method, the filtering out of a non-amplified seed laser pulse, or the filtering out of a portion of multiple amplified laser pulses occurs, thereby resulting in a change in the repetition frequency of the laser pulses emitted to the patient&#39;s eye E. However, since it is necessary to filter out a portion of the multiple laser pulses at the same time intervals in this method, the repetition frequency is changed only in a stepwise manner. The filtered-out laser pulses are wasted. 
     In contrast, the gain switching method is a method of extracting the laser pulses by controlling the gain of a resonator. The gain-switched seed light source  110  is capable of linearly (continuously) changing the repetition frequency of a generated seed laser pulse. Accordingly, the laser device  10  in the embodiment is capable of appropriately changing the repetition frequency of the laser pulses (that is, laser pulse emitted to the patient&#39;s eye E) emitted to the outside of the laser device  10  by changing the repetition frequency of a seed laser pulse generated by the seed light source  110 . 
     Various types of gain-switched light sources can be used as the seed light source  110 . As an example, in the embodiment, a semiconductor laser is used as the seed light source  110 . In this case, the operator can appropriately perform an operation for the patient&#39;s eye E using the laser eye surgery apparatus  1 . A microchip laser can also be used as the seed light source  110 . In this case, the operator appropriately treats the patient&#39;s eye E using the low-cost seed light source  110 . 
     As an example, the seed light source  110  in the embodiment repeatedly generates a seed laser pulse with a pulse width of 10 femtoseconds or greater and 10 picoseconds or less. In this case, the operator can accurately treat a transparent tissue using an ultrashort pulse. However, even if the pulse width is 10 femtoseconds or greater and 1 nanosecond or less, treatment of the transparent tissue by photodisruption can be performed. 
     Multiple seed laser pulses (may also be referred to as a seed laser pulse train) generated by the seed light source  110  may be amplified and emitted to the outside of the laser device  10  without being filtered out. Naturally, a portion of a seed laser pulse train before amplification, or a portion of an amplified laser pulse train can also be filled out. When the amplified laser pulses are filtered out, a device (an acousto-optic device, a Pockels cell, or the like) for filtering out laser pulses may be disposed either inside or outside of the laser device  10 . 
     &lt;Preliminary Amplifier&gt; 
     The preliminary amplifier  120  receives and amplifies a seed laser pulse generated by the seed light source  110 . A seed laser pulse has low energy. Accordingly, also, when a seed laser pulse with a pulse width in the order of femtoseconds is amplified, a probability of damage to the optical system of the preliminary amplifier  120  caused by self-focusing during amplification is low. Accordingly, various types of amplifying mechanisms can be used as the preliminary amplifier  120 . 
     The preliminary amplifier  120  in the embodiment includes a first preliminary amplifier  121 ; a first excitation light source  122 ; a magnifying lens  124 ; a second preliminary amplifier  126 ; and a second excitation light source  127 . Each of the first preliminary amplifier  121  and the second preliminary amplifier  126  is a multi-pass amplifier. Each of the first preliminary amplifier  121  and the second preliminary amplifier  126  contains an amplifying medium. A medium matched to the wavelength of a seed laser pulse may be used as the amplifying medium. The first excitation light source  122  and the second excitation light source  127  excite the amplifying media by irradiating the amplifying media, which are contained in the corresponding amplifiers, with excitation light. The excited amplifying media amplify an incident laser pulse, and emit the amplified laser pulse. The magnifying lens  124  is provided between the first preliminary amplifier  121  and the second preliminary amplifier  126 , and increases the diameter of the laser pulses emitted to the second preliminary amplifier  126  from the first preliminary amplifier  121 . The preliminary amplifier  120  may be a bulk type, or multiple optical fiber amplifiers may be used as the preliminary amplifier  120 . A chirped pulse amplifier (to be described later) can also be used as the preliminary amplifier  120 . Amplification stages may be appropriately set. 
     &lt;Final Amplifier&gt; 
     The final amplifier  130  receives the laser pulses amplified by the preliminary amplifier  120 , and amplifies energy of the laser pulse to an energy level greater than or equal to energy of the laser pulse emitted to the patient&#39;s eye E. Accordingly, since the laser eye surgery apparatus  1  in the embodiment includes the preliminary amplifier  120  and the final amplifier  130 , even if the seed light source  110  generating a seed laser pulse having low energy is used, the operator can appropriately treat the patient&#39;s eye using the laser eye surgery apparatus  1 . 
     As described above, the seed light source  110  in the embodiment generates a seed laser pulse with a pulse width of 10 femtoseconds or greater and 10 picoseconds or less. Since the pulse width is small, when an amplifying mechanism, for example, a master oscillator power amplifier (MOPA), is used as the final amplifier, the intensity of light may be excessively increased due to self-focusing while the seed laser pulse is amplified by the final amplifier. Accordingly, the optical system of the final amplifier may be damaged. As a result, in the embodiment, a chirped pulse amplifier is used as the final amplifier  130 . 
     Specifically, the final amplifier  130  in the embodiment includes an expander  131 ; a final amplifier  132 ; and a compressor  133 . The expander  131  expands the pulse width of the laser pulse received from the preliminary amplifier  120 . The expander  131  in the embodiment expands the pulse width by applying a chirp, which is changed according to the frequency, to the laser pulses having a spectral width. At least one of a diffraction grating, a volume Bragg grating, a chirp mirror, and the like may be used as the expander  131 . The final amplifier  132  amplifies the laser pulse, the pulse width of which is expanded by the expander  131 . Since the laser pulse amplified by the final amplifier  132  has an expanded pulse width, the laser pulse has low peak power compared to the laser pulses, the pulse width of which is not expanded. Accordingly, damage to the optical system is unlikely to occur. It is possible to adopt various configurations as the configuration of the final amplifier  132 . As an example, a regenerative amplifier, which amplifies the laser pulses while the laser pulse passes through multiple mirrors, is used as the final amplifier  132  in the embodiment. 
     &lt;Compressor/Dispersion Compensator&gt; 
     The compressor  133  compresses the pulse width of the laser pulse amplified by the final amplifier  132 . In the embodiment, the compressor  133  compresses the laser pulse by applying a chirp, which is opposite to the chirp applied by the expander  131 , according to the frequency. At least one of a diffraction grating, a volume bragg grating, a chirp mirror, a prism pair, and the like may be used as the compressor  133 . 
     The compressor  133  in the embodiment serves as a dispersion compensator compensating dispersion which is applied to the laser pulse by an element (for example, an amplifier) on an upstream side of the compressor  133  on the optical path. As a result, a change in the pulse width of the laser pulse is compensated. Since the compressor  133  also serves as the dispersion compensator, the amplification and the dispersion compensation of ultrashort-pulse laser light are performed using a simple configuration. 
     Particularly, the laser eye surgery apparatus  1  in the embodiment linearly changes the repetition frequency of a seed laser pulse generated by the seed light source  110 . When the repetition frequency is changed, the amount of dispersion applied to the laser pulse by the amplifiers  121 ,  126 , and  132  may be changed. In this case, the dispersion compensator in the embodiment changes the amount of compensated dispersion according to the repetition frequency of the laser pulse. As a result, even if the repetition frequency is changed, the laser pulses with an appropriate pulse width are emitted to the patient&#39;s eye E. Various methods can be adopted as a method of changing the amount of compensated dispersion. For example, the amount of compensated dispersion is changed by changing at least one of the position and the angle of an optical element included in the dispersion compensator. The laser eye surgery apparatus  1  may include a dispersion compensator separate from the compressor  133  so as to compensate dispersion applied to the laser pulses. In this case, the position of the dispersion compensator can be appropriately set. 
     As described above, the laser device  10  in the embodiment includes the amplifiers (the preliminary amplifier  120  and the final amplifier  130 ). Accordingly, even if a seed laser pulse generated by the seed light source has low energy, the laser eye surgery apparatus  1  is capable of irradiating the patient&#39;s eye with the laser pulses having appropriate energy. 
     &lt;Attenuator&gt; 
     When energy (the amount of amplification) per unit time applied to the amplifiers  121 ,  126 , and  132  is changed, the pulse width and the waveform of each laser pulse may be changed. Accordingly, the controllers in the embodiment change the repetition frequency while constantly maintaining the energy per unit time applied to the amplifiers  121 ,  126 , and  132 . In this case, when the repetition frequency is decreased, energy of each laser pulse is increased, and when the repetition frequency is increased, energy of each laser pulse is decreased. The laser eye surgery apparatus  1  in the embodiment includes the attenuator  140  adjusting energy of the laser pulse amplified by the amplifiers  120  and  130 . The controllers control the attenuator  140  such that the laser pulses having appropriate energy are emitted to the patient&#39;s eye E even if the repetition frequency is changed. When the attenuator  140  is provided, the position of the attenuator  140  can be appropriately set. For example, the attenuator  140  may be provided outside of the laser device  10 . 
     The laser eye surgery apparatus  1  may adjust the amount of amplification by the amplifiers  121 ,  126 , and  132  instead of using the attenuator  140 , or while controlling the attenuator  140 . In this case, the pulse width and the waveform of the laser pulse may be changed. Accordingly, the laser eye surgery apparatus  1  may suppress a change in the pulse width by compensating dispersion according to the amount of amplification using the dispersion compensator. 
     &lt;Laser Controller&gt; 
     The laser controller  150  controls the emission of the laser pulses from the laser device  10 . Specifically, the laser controller  150  in the embodiment is electrically connected to the seed light source  110 , the preliminary amplifier  120 , the final amplifier  130 , and the attenuator  140 , and sends signals to and receives signals from the control unit  76  (refer to  FIG. 1 ) of the laser eye surgery apparatus  1 . The laser controller  150  controls the emission of the laser pulses to the patient&#39;s eye E in collaboration with the control unit  76 . For example, when a signal specifying a repetition frequency is received from the control unit  76 , the laser controller  150  performs control such that the seed light source  110  generates a seed laser pulse at the repetition frequency specified by the signal. In addition, when a signal specifying energy of the laser pulses is received from the control unit  76 , the laser controller  150  controls the seed light source  110 , the preliminary amplifier  120 , the final amplifier  130 , and the attenuator  140  such that the laser pulses having energy specified by the signal are emitted to the outside of the laser device  10 . A microcomputer including a processor, a memory, and the like can be used as the laser controller  150 . 
     In order for ultrashort-pulse laser light to be emitted to the patient&#39;s eye E, it is considered that the pulse width of the laser pulses is compressed to be smaller than the pulse width of a seed laser pulse generated by the seed light source  110 , and the compressed laser pulse is emitted from the laser device  10 . However, when the spectral width of the laser pulse is not larger than the spectral width of the seed laser pulse, in many cases, the compressing of the pulse width becomes difficult. In contrast, the laser device  10  in the embodiment is not required to have a configuration (for example, a configuration in which the spectral width is increased by self-phase modulation) in which the spectral width of the laser pulses is increased. That is, the laser pulses with a spectral width smaller than or equal to the spectral width of a seed laser pulse are emitted to the outside by the laser device  10  in the embodiment. Accordingly, the laser eye surgery apparatus  1  is capable of emitting an appropriate laser pulse to the patient&#39;s eye E using a simple configuration. The expression “spectral width smaller than or equal to the spectral width of a seed laser pulse” also includes a case in which the spectral width of the laser pulses is unintentionally increased to be greater than the spectral width of a seed laser pulse in a process of amplifying the laser pulse. 
     &lt;Repetition Frequency Changing Process&gt; 
     A repetition frequency changing process executed by the laser eye surgery apparatus  1  in the embodiment will be described with reference to  FIG. 3 . The laser eye surgery apparatus  1  in the embodiment executes the repetition frequency changing process such that the repetition frequency of the laser pulses emitted from the laser device  10  is changed according to a scanning speed at which a concentration position is scanned by the scanner  30 . 
     The scanning speed for the concentration position may be affected and changed by performance of the scanner  30 . When a scanning direction is inverted, the scanning speed can be decreased compared to when the concentration position is scanned straightly. When the concentration position is helically scanned, the scanning speed in a central portion of a helix is likely to be decreased compared to the scanning speed on the outside in the helix. When the repetition frequency of the laser pulses is the same before and after the scanning speed is changed, the space between adjacent concentration positions is not constant, and the quality of treatment may be decreased. The laser eye surgery apparatus  1  in the embodiment changes the repetition frequency of the laser pulses according to the scanning speed for the concentration position. As a result, the space between adjacent concentration positions easily becomes uniform, and a decrease in the quality of treatment is suppressed. The laser eye surgery apparatus  1  in the embodiment is also capable of appropriately linearly changing the repetition frequency of the laser pulses with respect to a linear change in the scanning speed. Accordingly, the operator can easily and appropriately treat the patient&#39;s eye E using the laser eye surgery apparatus  1  compared to when the repetition frequency is changed in a stepwise manner. The “linear change” represents a continuous linear change, and is not limited to a straight change. 
     When an instruction indicating start of treatment of the patient&#39;s eye E using the laser pulses is input via the operation portion  71  or the like, the repetition frequency changing process illustrated in  FIG. 3  is executed by the CPU (processor)  77  of the control unit  76 . The CPU  77  executes the repetition frequency changing process illustrated in  FIG. 3  according to the program stored in the ROM  78  or the non-volatile memory. 
     First, the CPU  77  starts the driving of the scanner  30  according to drive data prepared in advance (S 1 ). The CPU  77  acquires a scanning speed for a concentration position (S 2 ). In the embodiment, the scanning speed for the concentration position is a scanning speed for a three-dimensional concentration position in the patient&#39;s eye E. Subsequently, the CPU  77  determines the repetition frequency of the laser pulses, which is emitted from the laser device  10 , proportionally to the scanning speed acquired in step S 2  (S 3 ). As described above, the laser device  10  in the embodiment is capable of linearly changing the repetition frequency. Accordingly, the CPU  77  is capable of more appropriately disposing multiple concentration positions by linearly changing the repetition frequency according to a change in the scanning speed. The CPU  77  may not set the scanning speed to be perfectly proportional to the repetition frequency. 
     Subsequently, the CPU  77  performs controls such that the laser device  10  emits the laser pulses at the repetition frequency determined in step S 2  (S 4 ). In the embodiment, the control unit  76  and the laser controller  150  collaboratively control the emission of the laser pulse from the laser device  10 . Accordingly, in step S 4 , a signal specifying the repetition frequency determined in step S 2  is sent to the laser controller  150  by the CPU  77 . The laser controller  150  makes the laser device  10  emit the laser pulses at the specified repetition frequency by making the seed light source  110  generate a seed laser pulse at the repetition frequency specified by the signal. 
     The CPU  77  determines whether or not a series of treatment steps determined by the drive data is complete (S 5 ). When the series of treatment steps is not complete (NO: S 5 ), the process returns to step S 2 , and steps S 2  to S 5  are repeated. When the series of treatment steps is complete (YES: S 5 ), the driving of the scanner  30  and the laser device  10  is stopped (S 6 ), and the process ends. 
     As described above, the laser eye surgery apparatus  1  in the embodiment includes the laser device  10 , the scanner  30 , and the controllers. The laser device  10  includes the gain-switched type seed light source  110  having a variable repetition frequency. The laser device  10  changes the repetition frequency of the laser pulses emitted to the outside by changing the repetition frequency of the seed light source  110 . The controllers change the repetition frequency of the laser pulses, which is emitted to the patient&#39;s eye E from the laser device  10 , according to a scanning speed at which the concentration position is scanned by the scanner  30 . In this case, the laser eye surgery apparatus  1  is capable of changing the repetition frequency of the laser pulse in a stepwise manner or linearly (continuously). Since the laser eye surgery apparatus  1  is capable of changing the repetition frequency without filtering out a portion of a laser pulse train, energy efficiency is good. Since the repetition frequency of the laser pulse is changed according to the scanning speed for the concentration position, the space between adjacent concentration positions easily becomes uniform. Accordingly, the operator can accurately treat the patient&#39;s eye E within a short amount of time by appropriately changing the repetition frequency of the laser pulses from the laser eye surgery apparatus  1  in the embodiment. The configuration including a device (for example, acousto-optic device) for filtering out a portion of a laser pulse train is not a prerequisite for changing the repetition frequency. 
     The contents in the embodiment are merely exemplified. Accordingly, the contents in the embodiment can be changed. For example, the seed light source  110  in the embodiment generates a seed laser pulse with a pulse width of 10 femtoseconds or greater and 10 picoseconds or less. Accordingly, a chirped pulse amplifier is used as the final amplifier  130  so as to suppress damage to the optical system of the amplifying mechanism. However, when the laser pulses (for example, a laser pulse with a pulse width of 10 picoseconds or greater), which are unlikely to cause the occurrence of damage to the optical system, are used, an amplifying mechanism other than the chirped pulse amplifier may be adopted as the final amplifier. 
     Since the laser eye surgery apparatus  1  in the embodiment includes the preliminary amplifier  120  and the final amplifier  130 , even if the seed light source  110  generating a seed laser pulse having low energy is used, the operator can appropriately treat the patient&#39;s eye using the laser eye surgery apparatus  1 . In contrast, when a seed light source generating a seed laser pulse having high energy is used, the configuration of the amplifier may be changed. For example, the preliminary amplifier may be omitted, and only the final amplifier may be used. The laser device  10  may also be configured not to include the amplifier. 
     The expander  131  and the compressor  133  of the final amplifier  130  in the embodiment are separate components. However, the expander and the compressor may be integrally provided. For example, a volume Bragg grating may be used, and the laser pulses may be compressed by allowing the laser pulse to be incident to the volume Bragg grating from an incident direction opposite to an incident direction during expansion.