WO2020231155A1

WO2020231155A1 - Device and method for generating laser pulse

Info

Publication number: WO2020231155A1
Application number: PCT/KR2020/006242
Authority: WO
Inventors: 이희철
Original assignee: 주식회사 루트로닉
Priority date: 2019-05-14
Filing date: 2020-05-13
Publication date: 2020-11-19
Also published as: KR20200131666A; KR102203862B1

Abstract

Provided according to one embodiment of the present invention is a laser pulse generator comprising: a laser generation unit which includes a laser medium, an excitation light source supplying excitation light to the laser medium, a first mirror and a second mirror that form a resonance path in which the light excited in the laser medium is amplified, and a saturation absorbent, a polarizer, and a Pockels cell that are disposed on the resonance path; and a control unit which controls the saturation absorbent or the Pockels cell such that the laser generation unit operates in a single-pulse mode or a multi-pulse mode.

Description

Laser pulse generator and method

Embodiments of the present invention relate to an apparatus and method for generating laser pulses.

Laser beams are used in various fields ranging from industrial, medical and military applications. In particular, medical lasers are widely used in surgery, internal medicine, ophthalmology, dermatology, dentistry, and the like, since they can localize predetermined energy and provide non-invasive treatment.

The laser beam may be provided through a laser device in the form of a single pulse or multiple pulses, and on the other hand, when an operation of generating multiple pulses, the output stability tends to be lower than that of a single pulse, and thus it is necessary to improve this.

It provides a laser pulse generating apparatus and method capable of generating a multi-pulse laser of the shape of the output stability.

According to one type, a laser medium, an excitation light source supplying light to the laser medium, a first mirror and a second mirror forming a resonance path through which the light excited by the laser medium is amplified, and on the resonance path A laser generator including the disposed saturated absorber, polarizer, and Pockels cell; And a controller for controlling the saturation absorber or the Pockels cell so that the laser generator operates in a single pulse mode or a multiple pulse mode.

The control unit is in the multi-pulse mode, the Pockels cell from an initial time point (t ₁ ) at which the current discharge of the excitation light source starts to a threshold time point (t ₁ +Δt _c ) after a predetermined threshold time (Δt _c ) has elapsed. The Pockels cell may be controlled so that the Pockels cell operates in a mode that maintains the phase of the incident light and after the threshold point (t ₁ +Δt _c ), the Pockels cell operates in a mode that delays the phase of the incident light.

The polarizer is a linear polarizer that transmits only a predetermined linearly polarized component of incident light, and the Pockels cell may operate as a quarter wave plate according to a control signal.

The threshold time (Δt _c ) measures the timing jitter of multiple pulses generated from the laser generator while the Pockels cell operates in a mode that maintains the phase of the incident light, and the measured timing jitter is calculated as the current of the excitation light source. It may be a preset value as an elapsed time from the current discharge point at a point in time that matches the discharge curve and indicates timing jitter less than a predetermined value.

The threshold time Δt _c may include a critical time Δt _c _k determined according to the number of desired pulses k (k is a natural number greater than or equal to 1).

The laser pulse generator includes an input unit for inputting the number of pulses to be generated in the laser generation unit; And a memory for storing information of the threshold time Δt _c _k determined according to the number of pulses k.

The laser generator may further include a first position driving unit for driving a position of the saturation absorber so that the saturation absorber deviates from the resonance path.

The laser generator comprises a phase retarder disposed on the resonance path; And a second position driver for driving the position of the phase retarder so that the phase retarder deviates from the resonance path.

The polarizer may be a linear polarizer that transmits only a predetermined linearly polarized component of incident light, and the phase retarder may be a 1/4 wavelength plate.

In the single pulse mode, the controller controls the first position driver and the second position driver so that the saturation absorber deviates from the resonance path and the phase retarder is located on the resonance path, and in the multi-pulse mode, the saturation The first position driver and the second position driver may be controlled so that the absorber is on the resonance path and the phase retarder deviates from the resonance path.

In addition, according to one type, a laser medium, an excitation light source supplying excitation light to the laser medium, a first mirror and a second mirror forming a resonance path through which the light excited by the laser medium is amplified, and the resonance A method of generating a laser pulse using a laser generator including a saturation absorber, a polarizer, and a Pockels cell disposed on a path, the method comprising: selecting whether the laser generator operates in a single pulse mode or a multiple pulse mode; And controlling the saturated absorber or the Pockels cell according to the selection.

The method may further include, for the multi-pulse mode operation, setting a timing at which the Pockels cell operates in a mode that maintains the phase of incident light and then switches to a mode that delays the phase of incident light.

In the above method, when the multi-pulse mode is selected, the Pockels cell phases the incident light from the initial time point (t ₁ ) at which the current discharge of the excitation light source starts to a predetermined threshold time point (t ₁ +Δt _c ) determined by the timing. And controlling the Pockels cell so that the Pockels cell operates in a mode in which the phase of incident light is delayed after the threshold point of time (t ₁ +Δt _c ).

The setting may include operating the Pockels cell in a mode for maintaining the phase of incident light and measuring timing jitter of multiple pulses generated by the laser generator; Measuring a current discharge curve of the excitation light source; And matching the measured timing jitter with the current discharge curve, and setting an elapsed time from the current discharge time point to a threshold time (Δt _c ) at a time point indicating the timing jitter less than or equal to a predetermined value.

The setting may include setting a reference value for timing jitter determined according to the desired number of pulses (k) (k is a natural number greater than or equal to 1); It may further include a step of setting a threshold time (Δt _c _k) corresponding to the number of pulses (k) by referring to the timing jitter reference value.

The method may further include receiving a number of pulses (k) to be generated in the laser generator when the multi-pulse mode is selected, and may further include a threshold time (Δt _c ) corresponding to the number of pulses (k). The Pockels cell may be controlled by reflecting _k) to the critical time point.

The above-described laser pulse generator can generate and output a multi-pulse laser having stable output performance.

The above-described laser pulse generator may selectively position the saturation absorber and the phase retarder in/outside the resonance path to selectively implement a single pulse mode and a multi-pulse mode with stable output.

1 is a block diagram showing a schematic configuration of a laser pulse generator according to an embodiment.

2 shows a schematic structure and optical arrangement of a laser generator employed in the laser pulse generator of FIG. 1.

3 is a conceptual diagram schematically illustrating timing control of an excitation light source and a Pockels cell by the laser generator of FIG. 1.

4 is a graph showing exemplary timing jitter and current discharge curves of pulses generated when driving a laser generator.

5 is a flowchart schematically illustrating a method of generating a laser pulse according to an embodiment.

6 is a flowchart illustrating detailed steps of FIG. 5 by way of example.

7A and 7B show the driving of the laser generator of FIG. 2, respectively, showing the optical paths in which the Pockels cell is turned off and on.

8 is a block diagram showing a schematic configuration of an apparatus for generating a laser pulse according to another embodiment.

9 shows a schematic structure and optical arrangement of a laser generator employed in the laser pulse generator of FIG. 8.

10 is a flowchart schematically illustrating a method of generating a laser pulse performed by the laser pulse generating apparatus of FIG. 8.

11A and 11B show the single pulse mode operation of the laser generator of FIG. 9 and show the optical paths in which the Pockels cell is turned on and off, respectively.

12A and 12B show the multi-pulse mode operation of the laser generator of FIG. 9, respectively, showing the optical paths in which the Pockels cell is turned off and on.

Since the present invention can apply various transformations and have various embodiments, specific embodiments are illustrated in the drawings and will be described in detail in the detailed description. Effects and features of the present invention, and a method of achieving them will be apparent with reference to the embodiments described later in detail together with the drawings. However, the present invention is not limited to the embodiments disclosed below and may be implemented in various forms.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, and when describing with reference to the drawings, the same or corresponding constituent elements are assigned the same reference numerals, and redundant descriptions thereof will be omitted. .

In the following embodiments, terms such as first and second are not used in a limiting meaning, but are used for the purpose of distinguishing one component from another component.

In the following examples, the singular expression includes the plural expression unless the context clearly indicates otherwise.

In the following embodiments, terms such as include or have means that the features or elements described in the specification are present, and do not preclude the possibility of adding one or more other features or elements in advance.

In the following embodiments, when a part such as a region or a component is on or on another part, it includes not only the case that is directly above the other part, but also the case where another region, component, etc. is interposed in the middle. do.

In the drawings, components may be exaggerated or reduced in size for convenience of description. For example, the size and thickness of each component shown in the drawings are arbitrarily shown for convenience of description, and the present invention is not necessarily limited to what is shown.

When a certain embodiment can be implemented differently, a specific process order may be performed differently from the described order. For example, two processes described in succession may be performed substantially simultaneously, or may be performed in an order opposite to the described order.

In the following embodiments, when a region, a component, etc. are connected, it includes not only the case where the region and the constituent elements are directly connected, but also the case where the region and the constituent elements are interposed and indirectly connected. .

1 is a block diagram showing a schematic configuration of a laser pulse generator according to an embodiment, and FIG. 2 is a schematic structure and optical arrangement of a laser generator used in the laser pulse generator of FIG. 1. 3 is a conceptual diagram schematically illustrating timing control of an excitation light source and a Pockels cell by the laser generator of FIG. 1.

The laser pulse generating device 1001 includes a laser generating unit 100 and a control unit 300 for controlling the laser generating unit 100. The laser pulse generating device 1000 may further include a memory 500 in which information used for controlling the laser generating unit 100 is stored, and information used for controlling the laser generating unit 100 It may further include an input unit 400 to be input.

As illustrated in FIG. 2, the laser generator 100 forms a resonance path of the laser medium 135, an excitation light source 132 that supplies excitation light to the laser medium, and the light amplified by the laser medium 135. And a first mirror 110 and a second mirror 180, a saturation absorber 120, a polarizer 150, and a Pockels cell 170 disposed on the resonance path.

Each element constituting the laser generator 100 will be described in detail as follows.

The excitation light source 132 and the laser medium 135 may constitute the pump chamber 130. The excitation light source 132 may be a flash lamp, and emits light by receiving power from a power supply (not shown) and providing light to the laser medium 135. The excitation light source 132 is not limited to a flash lamp and may include a laser diode. The laser medium 135 absorbs energy of light supplied from the excitation light source 132 and emits amplified light. The laser medium 135 may be a neodymium-doped yttrium aluminum garnet (Nd:Yag), but is not limited thereto, and Er:Yag may be used as the laser medium 135.

The first mirror 110 and the second mirror 180 are disposed to face each other with the laser medium 135 interposed therebetween to form a resonance path of the light amplified by the laser medium 135. One of the first mirror 110 and the second mirror 180 may be a reflective mirror and the other may be an output mirror. In the drawings, the first mirror 110 is illustrated as an output mirror and the second mirror 180 is illustrated as a reflection mirror, but the present invention is not limited thereto. The first mirror 110, which is an output mirror, is configured to reflect part of the light and transmit a part of it, and the second mirror 180, which is a reflective mirror, may be configured to reflect most of the light. The reflectance of the first mirror 110 and the second mirror 180 is not particularly limited, and the reflectance may be appropriately set in a range in which the reflectance of the output mirror is higher than that of the reflective mirror.

The Pockels Cell 170 may control a phase of incident light by using an electro-optical material that exhibits a phenomenon in which optical properties change according to an applied electrical signal. The Pockels cell 170 is electrically controlled and may operate in a mode that maintains the phase of incident light or may operate in a mode that delays the phase of incident light. For example, when an electric signal is not applied, the Pockels cell 170 passes light without affecting the phase of the incident light, and when a predetermined electric signal is applied, the Pockels cell 170 may delay the phase of the incident light and pass the light. . However, the present invention is not limited thereto, and the Pockels cell 170 may operate in a mode that maintains the phase of the incident light according to a predetermined electrical signal, and may operate in a mode that delays the phase of the incident light according to another predetermined electrical signal. I can. In a mode in which the phase of incident light is delayed, the Pockels cell 170 may operate as a quarter wave plate. However, the present invention is not limited thereto, and the Pockels cell 170 may operate as a half wave plate according to the application of an electric signal. The Pockels cell 170 is also referred to as an active Q-switch because it is employed in a laser device and can actively control the Q value.

The polarizer 150 converts unpolarized light emitted from the laser medium 135 into light of a predetermined polarization. The polarizer 150 may be a linear polarizer that transmits a predetermined linearly polarized light component of incident light and absorbs a linearly polarized light component in a different direction.

The saturated absorber 120 may serve to absorb light having an intensity less than a certain level and pass light having an intensity greater than or equal to a certain level. The saturated absorber 120 is also referred to as a passive Q-switcher. The saturated absorber 120 may include a Cr4+:YAG (four-valence Chromium Doped Yttrium Aluminum Garnet). Among the light excited by the laser medium 135 by the light supplied from the excitation light source 132, light having an intensity of less than a certain standard is absorbed by the saturation absorber 120, and light having an intensity of a certain intensity or more is absorbed by the saturation absorber 120 ) And amplified while reciprocating the resonance path between the first mirror 110 and the second mirror 180. In this way, light having a certain intensity or more generates laser oscillation and is output at regular time intervals through the first mirror 110 as an output mirror, and multiple pulses may be generated.

The laser pulse generator 1000 generates and outputs a multi-pulse laser as described above, and at this time, the controller 300 controls the timing of on/off of the Pockels cell 170 for stable output. In consideration of the timing jitter of the pulse generated by the laser generator 100, the controller 300 turns off the Pockels cell 170, that is, maintains the phase of the incident light until a predetermined time indicating a timing jitter less than an appropriate value. The laser generator 100 is controlled so that the pulse is not output by operating in a mode so that a pulse is output, and thereafter, the Pockels cell 170 is turned on, that is, operated in a mode that delays the phase of the incident light. The predetermined time may be determined in consideration of the current discharge curve of the excitation light source 132. For example, the Pockels cell 170 is turned off from the time point t ₁ where the current discharge of the excitation light source 132 starts to the critical time point (t ₁ +Δt _c ) after a predetermined threshold time (Δt _c ) has elapsed, That is, the excitation light source 132 operates in a mode that maintains the phase of the incident light, and turns on the Pockels cell 170 after the threshold point (t ₁ +Δt _c ), that is, delays the phase of the incident light. And controls the Pockels cell 170.

For this control, as illustrated in FIG. 3, the timing controller 310 may transmit a timing signal to the excitation light source 132 and the Pockels cell 170. The timing control unit 310 may be included in the control unit 300 illustrated in FIG. 1. The timing controller 310 may include a local oscillator that generates a gigahertz (GHZ) band or a higher frequency to generate an appropriate timing signal. The timing control unit 310 is configured to lock-in the excitation light source 132 and the Pockels cell 170 in order to operate the Pockels cell 170 after a predetermined time after the current discharge of the excitation light source 132 starts. Control to be possible. The timing control unit 310 may generate a first timing signal TS1 at which the excitation light source 132 starts current discharge, and the first timing signal so that the Pockels cell 170 is in an off state at the time point. (TS1) may be transmitted to the Pockels cell 170. The timing controller 310 may generate and send the second timing signal TS2 to the Pockels cell 170 so that the Pockels cell 170 is turned on when the threshold time Δt _c elapses. That is, the time difference between the first timing signal TS1 and the second timing signal TS2 is a preset threshold time Δt _c .

This threshold time (Δt _c ) measures the timing jitter of each of the multiple pulses generated by the laser generator 100 while the Pockels cell 170 operates in a mode that maintains the phase of the incident light, and the timing jitter is predetermined. It can be set in advance so that only pulses below the value are generated. For example, the measured timing jitter may be matched with the current discharge curve of the excitation light source 132 to set the elapsed time from the current discharge time point at which the timing jitter is less than a predetermined value to the threshold time (Δt _c ). . In addition, such a threshold time (Δt _c ) may be determined in plural according to the number of pulses to be generated by the laser generator 100. For example, the number of pulses (N) that can be generated by the laser generator 100 is set, and a plurality of threshold times (Δt _c _k) corresponding to an arbitrary number of pulses less than N (1 ≤ k ≤ N ) Can be set in advance.

As such, information on a plurality of preset threshold times may be stored in advance in the memory 500, and the number of pulses to be generated by the laser generator 100 may be input through the input unit 400. The control unit 300 drives the laser generator 100 by using information on a threshold time (Δt _c _k) (1 ≤ k ≤ N) corresponding to the number of input pulses.

The number of pulses output on the current discharge curve and the timing jitter of each pulse are displayed. In the drawing, it is illustrated that four pulses are output, and it can be seen that the timing jitter gradually increases as the number of pulses increases. This is a phenomenon that occurs when the energy stored in the laser medium 135 is depleted as the laser pulse is generated and the amount of pump energy gradually decreases in the process of being stored again. The flash lamp used as the excitation light source 132 that supplies pump energy There is a cause of the change in the amount of current of the saturation absorber 120 and the nonlinearity of the absorption and emission characteristics of the saturated absorber 120. This increased timing jitter eventually causes a decrease in the stability of the output energy. Therefore, when a pulse with a large timing jitter is not generated, a high output energy stability can be obtained while implementing multiple pulses.

For example, the fourth to prevent pulses from being generated, setting the generated up to the completion time of the third pulse from the discharge start timing of the flash lamp to the threshold time (Δt _c), and, after the threshold time (Δt _c) has passed a pulse is generated Controls the Pockels cell 170 so that it is not.

In the drawing, the threshold time Δt _c is determined based on the completion of the third pulse generation, but the method of setting the threshold time Δt _c is not limited thereto. The shape of the current discharge curve may vary according to the detailed configuration of the laser generator 100 and driving requirements, and the threshold time may be appropriately set in consideration of the timing jitter reference value and the desired number of pulses in each situation.

5 is a flowchart schematically illustrating a method of generating a laser pulse according to an exemplary embodiment, and FIG. 6 is a flowchart illustrating detailed steps of FIG. 5 by way of example. 7A and 7B show the driving of the laser generator of FIG. 2, respectively, showing the optical paths in which the Pockels cell is turned off and on.

Referring to the laser pulse generation method with reference to FIGS. 5 and 6, first, the mode switching timing of the Pockels cell is set (S10). This step is a step of setting the timing at which the Pockels cell operates in a mode that maintains the phase of incident light and then switches to a mode that delays the phase of incident light, as described with reference to FIG. 4.

To this end, the Pockels cell is turned off to drive the laser generator (S11), the current discharge curve and timing jitter of the excitation light source are measured (S13), and then, a threshold time is set from the measured result (S15). . For example, by matching the measured timing jitter with the current discharge curve, the elapsed time from the current discharge time point at which the timing jitter is less than or equal to a predetermined value may be set as the threshold time (Δt _c ). In addition, in this case, a plurality of threshold times determined according to the number of pulses to be generated may be set. For example, within the number of pulses (N) that can be generated during one period (t _p ) of the current discharge curve, one or more timing jitter reference values determined according to the desired number of pulses (k) are set, and the set timing With reference to the jitter reference value, N threshold times (Δt _c _k) (1≦k≦N) corresponding to the number of pulses k may be set. The information set in this way is stored in the memory of the laser pulse generator.

Next, the number of pulses k (1≦k≦N) to be generated by the laser generator is selected (S20). The selection of the number of pulses k may be, for example, a user input or an input by executing another device or program.

The laser generator is driven by reflecting the threshold time (Δt _c _k) corresponding to the selected number of pulses (k) as the critical time point of the Pockels cell control (S30).

At this time, the Pockels cell 170 operates in a mode in which the phase of the incident light is maintained from the initial time point (t ₁ ) at which the current discharge of the excitation light source 132 starts to the critical time point (t ₁ +Δt _c _k). Control the cell 170 (S32).

Looking at the optical path shown in FIG. 7A, the excitation light L _E emitted from the pump chamber 130 is unpolarized light, passes through the polarizer 150 and is linearly polarized with S polarization. Here, S polarization is exemplary, and may be linearly polarized with P polarization perpendicular thereto. The Pockels cell 170 is in an off state and transmits incident light without affecting the polarization of the incident light. Here, the off state represents a state that does not affect the polarization of the incident light, and is not limited to the meaning that an electric signal is not applied. For example, a predetermined electric signal for allowing the Pockels cell 170 to transmit incident light without affecting the polarization of the incident light may be applied to the Pockels cell 170. Even after the S-polarized light passes through the Pockels cell 170 in the off state, the S-polarized light is maintained as it is, and the S-polarized light, which is reflected by the second mirror 180, is maintained as it is. S-polarized light may pass through the polarizer 150, and therefore, the excitation light L _E emitted from the pump chamber 130 may reciprocate the resonance path between the first mirror 110 and the second mirror 180. I can. In this way, resonance in which light can reciprocate between the first mirror 110 and the second mirror 180 while the Pockels cell 170 is in the off state, that is, for a time of t ₁ to t1 + Δt _c _k A path is formed, and a plurality of pulses may be output through the first mirror 110 at a predetermined time interval by the action of the saturation absorber 120.

Next, after the threshold point (t ₁ +Δt _c _k), the Pockels cell 170 is driven in an ON state to operate in a mode that delays the phase of incident light. An electric signal for causing the Pockels cell 170 to operate as a 1/4 wavelength plate may be applied to the Pockels cell 170. For example, from t ₁ +Δt _c _k to t ₁ +t _p , the Pockels cell 170 is controlled to be ON.

Looking at the optical path illustrated in FIG. 7B, the excitation light L _E emitted from the pump chamber 130 is unpolarized light, passes through the polarizer 150 and is linearly polarized with S polarization. The Pockels cell 170 is in an ON state and operates in a mode that delays polarization of incident light. The Pockels cell 170 may operate as a 1/4 wavelength plate. The S-polarized light changes to a right-handed circular polarization (RC) state after passing through the Pockels cell 170 in a state of operating as a quarter-wave plate. The light of the right circular polarization RC is reflected by the second mirror 180 and changes to a left-handed circular polarization (LC) state. Next, the left circular polarized light (LC) passes through the Pockels cell 170 operating as a 1/4 wavelength plate, and is converted into S polarization and P polarization, which is linearly polarized light in the vertical direction. Since the polarizer 150 transmits only S polarized light, light of P polarized light does not pass through the polarizer 150. In this way, a resonance path capable of reciprocating between the first mirror 110 and the second mirror 180 is not formed by the action of the Pockels cell 170, and a pulse is not output. Since the timing at which the Pockels cell 170 is controlled in this state is based on a preset threshold time so that an unstable pulse is not generated, the laser pulse generator 1000 can maintain a stable output while implementing a multi-pulse.

8 is a block diagram showing a schematic configuration of a laser pulse generator according to another embodiment, and FIG. 9 is a cross-sectional view showing a schematic structure of a laser generator used in the laser pulse generator of FIG. 8.

The laser pulse generating device 1001 includes a laser generating unit 101 and a control unit 301 that controls the laser generating unit 101. The laser pulse generating device 1001 may further include a memory 501 in which information used for controlling the laser generating unit 101 is stored, and information used for controlling the laser generating unit 101 It may further include an input unit 401 to which is input.

Unlike the laser generator 100 shown in FIG. 2, the laser generator 101 shown in FIG. 9 may be positioned in and out of the resonance path, and the saturation absorber 121 may be positioned to resonate on the resonance path. It further includes a phase retarder 161 that can be positioned in or out of the path. The phase retarder 161 may be a 1/4 wavelength plate. In addition, the laser generator 101 has a first position driving unit 125 and a phase retarder 161 that drive the position of the saturation absorber 121 so that the saturation absorber 121 can move in and out of the resonance path. It may further include a second position driving unit 165 for driving the position of the phase retarder 161 so as to move inside and out.

The laser generator 100 may be selectively operated in a single pulse mode or a multiple pulse mode. For example, whether the laser generator 101 operates in a single pulse mode or a multi-pulse mode may be input through the input unit 401, and the control unit 301 includes the laser generator 101 in the single pulse mode or The first position driver 125, the second position driver 165, and the Pockels cell 170 may be controlled to operate in a multi-pulse mode.

First, a single pulse mode operation will be described with reference to FIGS. 10, 11A, and 11B.

When the single pulse mode is selected in the mode selection step (S20), the first position driving unit 125 and the second position driving unit 125 so that the saturation absorber 121 deviates from the resonance path and the phase retarder 161 is located within the resonance path. 165) is controlled.

11A shows an optical path in which the Pockels cell 170 is controlled in an ON state.

The unpolarized excitation light L _E emitted from the pump chamber 130 is linearly polarized with S polarization by the polarizer 150. Next, passing through the phase retarder 161, which is a 1/4 wavelength plate, polarization is converted into right-circular polarization (RC), and passing through the Pockels cell 170 operating as a 1/4 wavelength plate by being controlled to be ON. Polarization is converted back to S polarization. When the S polarized light, which is linearly polarized light, is reflected by the second mirror 180, the S polarized light is maintained and passes through the Pockels cell 170 operating as the next quarter-wave plate and enters a right-circular polarization (RC) state. Light of the right-circular polarized light (RC) passes through the phase retarder 161 that is a 1/4 wavelength plate and changes to the S-polarized state again, and the light of S-polarized light may pass through the polarizer 150 that transmits the S-polarized component. According to this path, a resonance path through which light can reciprocate between the first mirror 110 and the second mirror 180 is formed, and the amplified laser light is output through the first mirror 110.

11B shows an optical path in which the Pockels cell 170 is controlled in an ON state.

The unpolarized excitation light L _E emitted from the pump chamber 130 is linearly polarized with S polarization by the polarizer 150. Next, it passes through the phase retarder 161, which is a 1/4 wavelength plate, is converted into right-circular polarization (RC), and passes through the Pockels cell 170 controlled in an OFF state, and the right-circular polarization (RC) is maintained. . The right circularly polarized light RC is reflected by the second mirror 180, is changed to the left circularly polarized light LC, passes through the Pockels cell 170 controlled in an OFF state, and maintains the left circularly polarized light LC state. Next, it passes through the phase retarder 161, which is a 1/4 wavelength plate, and is polarized into P polarized light. The light in the P polarization state cannot pass through the polarizer 150 that transmits only the S polarization component. In this way, a resonance path capable of reciprocating between the first mirror 110 and the second mirror 180 is not formed by the action of the Pockels cell 170, and a pulse is not output.

Therefore, according to the selection of the single pulse mode, after the saturation absorber is positioned out of the resonance path and the phase retarder is positioned in the resonance path (S21), the laser generating unit ( When 100) is driven (S23), the output path of FIG. 11A is temporarily formed and a single pulse may be output.

Next, a multi-pulse mode operation will be described with reference to FIGS. 10, 12A, and 12B.

When the multi-pulse mode is selected in the mode selection step (S20), the saturation absorber 121 is disposed on the resonance path and the phase retarder 161 is located outside the resonance path, so that the first position driver 125 and the second position driver (165) is controlled (S31). In addition, the number of pulses k to be generated in the multi-pulse mode is selected (S33). The order of step S31 and step S33 is exemplary, and may be performed at the same time or may be reversed.

12A is an optical path in which the Pockels cell 170 is controlled in an OFF state, and FIG. 12B shows an optical path in which the Pockels cell 170 is controlled in an ON state, and in FIGS. 7A and 7B They are substantially the same as the optical paths described respectively.

That is, the threshold point (Δtc_k) is set according to the selected number of pulses (k), and the Pockels cell 170 during t ₁ to t ₁ +Δtc_k based on the current discharge start point (t ₁ ) of the excitation light source 132 As shown in FIG. 12A, a reciprocating resonance path is formed to output multiple pulses (S32). Next, during t ₁ +Δtc_k ~ t ₁ +t _p , the Pockels cell 170 is turned on to form an optical path as shown in FIG. 12B, so that a pulse that causes unstable output is not generated. do.

As described above, the present invention has been described with reference to an embodiment shown in the drawings, but this is only exemplary, and those of ordinary skill in the art will understand that various modifications and variations of the embodiment are possible therefrom. Therefore, the true technical scope of the present invention should be determined by the technical spirit of the appended claims.

Claims

A laser medium, an excitation light source supplying light to the laser medium, a first mirror and a second mirror forming a resonance path through which the light excited by the laser medium is amplified, and a saturation absorber disposed on the resonance path, A laser generator including a polarizer and a Pockels cell; And

Including, a laser pulse generator for controlling the saturation absorber or the Pockels cell so that the laser generator operates in a single pulse mode or a multiple pulse mode.
The method of claim 1,

The control unit in the multi-pulse mode,

The Pockels cell operates in a mode in which the phase of the incident light is maintained from the initial time point (t 1 ) at which the current discharge of the excitation light source starts to the critical time point (t 1 +Δt c ) after a predetermined threshold time (Δt c ) has elapsed. And controlling the Pockels cell to operate in a mode in which the Pockels cell delays the phase of the incident light after the threshold point in time (t 1 +Δt c ).
The method of claim 2,

The polarizer is a linear polarizer that transmits only a predetermined linearly polarized component of incident light,

The Pockels cell operates as a 1/4 wave plate according to a control signal.
The method of claim 2,

The critical time (Δt c ) is

In a state in which the Pockels cell operates in a mode that maintains the phase of incident light, timing jitter of multiple pulses generated by the laser generator is measured,

The laser pulse generator, wherein the measured timing jitter is matched with the current discharge curve of the excitation light source, and is a value set in advance as an elapsed time from the current discharge time point at which the timing jitter of a predetermined value or less is indicated.
The method of claim 2,

The critical time (Δt c ) is

A laser pulse generator comprising a plurality of threshold times (Δt c _k) determined according to the number of pulses (k) to be generated.
The method of claim 5,

An input unit for inputting the number of pulses generated by the laser generator; And

The laser pulse generator further comprises a memory for storing information of the plurality of threshold times (Δt c _k) determined according to the number of pulses (k).
The method of claim 1,

The saturation absorber is configured to be movable to a position within or outside the resonance path.
The method of claim 7,

The laser pulse generator further comprises a; first position driving unit for driving the position of the saturation absorber.
The method of claim 8,

A phase retarder disposed on the resonance path and configured to move to a position within or outside the resonance path; further comprising, a laser pulse generator.
The method of claim 9,

The polarizer is a linear polarizer that transmits only a predetermined linearly polarized component of incident light,

The phase retarder is a 1/4 wave plate, laser pulse generator.
The method of claim 9,

A second position driving unit for driving the position of the phase retarder so that the phase retarder deviates from the resonance path; further comprising, a laser pulse generator.
The method of claim 11,

The control unit

In the single pulse mode, the first position driving unit and the second position driving unit are controlled so that the saturation absorber deviates from the resonance path and the phase retarder is located on the resonance path,

In the multi-pulse mode, the saturation absorber is positioned on the resonance path and the first position driver and the second position driver are controlled so that the phase retarder deviates from the resonance path.
A laser medium, an excitation light source supplying excitation light to the laser medium, first and second mirrors forming a resonance path through which the light excited by the laser medium is amplified, and a saturated absorber disposed on the resonance path In a method of generating a laser pulse using a laser generator including a polarizer and a Pockels cell,

Selecting whether the laser generator operates in a single pulse mode or a multiple pulse mode;

Controlling the saturation absorber or the Pockels cell according to the selection.
The method of claim 13,

For the multi-pulse mode operation, setting a timing at which the Pockels cell operates in a mode that maintains the phase of incident light and then switches to a mode that delays the phase of incident light.
The method of claim 14,

When the multi-pulse mode is selected, the Pockels cell maintains the phase of the incident light from the initial time point (t 1 ) at which the current discharge of the excitation light source starts to a predetermined threshold time point (t 1 +Δt c ) determined by the timing. And controlling the Pockels cell to operate in a mode and to operate in a mode in which the Pockels cell delays the phase of incident light after the threshold point in time (t 1 +Δt c ).
The method of claim 15,

The setting step

Operating the Pockels cell in a mode for maintaining the phase of incident light and measuring timing jitter of multiple pulses generated by the laser generator;

Measuring a current discharge curve of the excitation light source;

The method comprising: matching the measured timing jitter with the current discharge curve, and setting an elapsed time from the current discharge time point to a threshold time (Δt c ) at a time point indicating the timing jitter less than or equal to a predetermined value.
The method of claim 15,

The setting step

Setting a reference value for timing jitter determined according to the desired number of pulses k (k is a natural number greater than or equal to 1);

Setting a threshold time (Δt c _k) corresponding to the number of pulses (k) with reference to the timing jitter reference value; further comprising.
The method of claim 17,

When the multi-pulse mode is selected, receiving the number of pulses (k) to be generated in the laser generator; further comprising,

A method of controlling the Pockels cell by reflecting a threshold time (Δt c _k) corresponding to the number of pulses (k) to the threshold time point.