Nonlinear pulse width compression device based on spectral broadening, and femtosecond fiber laser system including same

Abstract

According to the present disclosure, a second mirror and a third mirror are disposed to face each other with a nonlinear crystal interposed therebetween. The second mirror and the third mirror reflect a laser beam multiple times therebetween, and respectively include a plurality of first points formed at equal intervals along an edge portion of the second mirror, and a plurality of second points formed at equal intervals along an edge portion of the third mirror, the plurality of first points and the plurality of second points being configured to cause reflections to occur between the second mirror and the third mirror in a preset sequence. The third mirror includes a hole through which a laser beam finally reflected via the second mirror is transmitted to the outside, wherein the laser beam forms a reciprocating path by alternately passing through the plurality of first points and the plurality of second points one by one while rotating in the clockwise direction or the counterclockwise direction.

Description

Nonlinear pulse width compression device based on spectrum broadening, femtosecond fiber laser system including the same

[0001] The present disclosure relates to a laser system. More specifically, the present disclosure relates to a nonlinear pulse width compression device for spectral expansion and a femtosecond fiber laser system including the same.

[0002] Generally, femtosecond laser light has been used in industrial settings to reduce cutting defects in semiconductor wafers and secondary battery electrodes.

[0003] Here, the femtosecond laser light was modulated by a pulse control signal to control the repetition rate as well as by a laser light formed by a pulse train of the femtosecond laser.

[0004] For example, laser light could be generated by a femtosecond fiber laser system.

[0005] However, conventional femtosecond fiber laser systems had limitations in increasing beam intensity by expanding the spectrum of laser light.

[0006] Therefore, recently, there is a demand for the development of improved technology capable of increasing beam intensity by expanding the spectrum of laser light.

[0007] The purpose of the embodiment according to the present disclosure is to provide a method for increasing beam intensity by expanding the spectrum of laser light.

[0008] The problems that this disclosure aims to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by a person skilled in the art from the description below.

[0009] A nonlinear pulse width compression device for spectrum expansion according to one aspect of the present disclosure for achieving the above-described technical problem comprises: a first mirror that reflects incident laser light; a second mirror that receives and reflects laser light incident through the first mirror; and a third mirror that reflects laser light incident through the second mirror. The apparatus may include a nonlinear crystal that expands the spectrum of laser light traveling back and forth through the second mirror and the third mirror, wherein the second mirror and the third mirror are positioned opposite each other with the nonlinear crystal in between, and the second mirror and the third mirror each include a plurality of first points formed at equal intervals on the edge portion of the second mirror and a plurality of second points formed at equal intervals on the edge portion of the third mirror for reflection of a plurality of laser lights between them in a predetermined order, and the third mirror includes a hole that transmits the laser light finally reflected through the second mirror to the outside, wherein the laser light forms a back-and-forth path by alternating one by one through the plurality of first points and the plurality of second points in a clockwise or counterclockwise rotation.

[0010] In addition, it may further include a lens that is positioned in the same line as the first mirror and focuses the laser light.

[0011] In addition, the beam intensity in the nonlinear crystal can be determined according to the focal length of the lens.

[0012] In addition, the beam intensity may be characterized as becoming stronger as the number of reciprocating paths formed alternately by the laser light passing through the plurality of first points formed at 10 equal intervals and the plurality of second points formed at 9 equal intervals in a clockwise or counterclockwise rotation increases.

[0013] In addition, the nonlinear crystal may be characterized by moving horizontally between the second mirror and the third mirror to control the magnification amount of the spectrum.

[0014] In addition, the distance between the second mirror and the third mirror may be characterized by being calculated based on the radius of curvature of the second mirror and the radius of curvature of the third mirror.

[0015] In addition, the above nonlinear crystal may include any one of SF10, SF11, Fused silica, BK7, CaF2, Sapphire glass, and Birefringent crystal corresponding to the glass series, any one of water and alcohol corresponding to the liquid, and may include argon and nitrogen corresponding to the gas.

[0016] A femtosecond fiber laser system including a nonlinear pulse width compression device for spectrum expansion according to another aspect of the present disclosure may be provided.

[0017] According to the above-described means for solving the problem of the present disclosure, the effect of expanding the spectrum of laser light to increase beam intensity is provided.

[0018] FIG. 1 illustrates a femtosecond fiber laser system according to the present disclosure.

[0019] Figure 2 illustrates a detailed configuration of the femtosecond fiber laser system of Figure 1 as an example.

[0020] FIG. 3 shows the wavelength of the pulsed laser light of FIG. 2, the wavelength of the first continuous wave laser light, and the wavelength of the second continuous wave laser light.

[0021] Figures 4 and 5 illustrate the configuration of the nonlinear pulse width compression device of Figure 2.

[0022] Figure 6 illustrates the laser spectrum at different positions according to the intensity of the laser beam by the nonlinear pulse width compression device of Figures 4 and 5.

[0023] Throughout this disclosure, the same reference numerals denote the same components. This disclosure does not describe all elements of the embodiments, and general content in the art to which this disclosure pertains or content that overlaps between embodiments is omitted. The terms 'part, module, component, block' as used in the specification may be implemented in software or hardware, and depending on the embodiments, a plurality of 'parts, modules, components, blocks' may be implemented as a single component, or a single 'part, module, component, block' may include a plurality of components.

[0024] Throughout the specification, when a part is described as being "connected" to another part, this includes not only cases where they are directly connected but also cases where they are indirectly connected, and indirect connections include connections made via a wireless communication network.

[0025] Furthermore, when it is stated that a part "includes" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0026] Throughout the specification, when it is stated that a component is located "on" another component, this includes not only cases where a component is in contact with another component, but also cases where another component exists between the two components.

[0027] Terms such as "first," "second," etc., are used to distinguish one component from another, and the components are not limited by the aforementioned terms.

[0028] Singular expressions include plural expressions unless there is an obvious exception in the context.

[0029] In each step, identification codes are used for convenience of explanation and do not describe the order of the steps; the steps may be performed differently from the specified order unless a specific order is clearly indicated in the context.

[0030] The operating principles and embodiments of the present disclosure will be described below with reference to the attached drawings.

[0031] FIG. 1 illustrates a femtosecond fiber laser system according to the present disclosure. FIG. 2 illustrates a detailed configuration of the femtosecond fiber laser system of FIG. 1 as an example.

[0032] FIG. 3 shows the wavelength of the pulsed laser light of FIG. 2, the wavelength of the first continuous wave laser light, and the wavelength of the second continuous wave laser light.

[0033] Referring to FIGS. 1 to 3, a femtosecond fiber laser system (100) according to the present disclosure may include a femtosecond light source (10), a preamplifier (20), a pulse picker (30), a first continuous wave light source (40), a main amplifier (50), a nonlinear pulse width compression device (60), a polarizing plate (65), a control module (70), and a second continuous wave light source (80).

[0034] The femtosecond light source (10) can generate femtosecond laser light (12). Here, the femtosecond laser light (12) can have a frequency of about 10 MHz to about 1000 MHz.

[0035] A preamplifier (20) can be connected to a femtosecond light source (10). Here, the preamplifier (20) can amplify femtosecond laser light (12).

[0036] The pulse speaker (30) can be connected to a preamplifier (20). Here, the pulse speaker (30) can generate pulsed laser light (32) by modulating femtosecond laser light (12). Here, pulsed laser light (32) refers to femtosecond laser light having any pulse train.

[0037] The first continuous wave light source (40) may be connected to a pulse speaker (30) and a main amplifier (50) by an optical fiber (11). Here, the first continuous wave light source (40) may provide a first continuous wave laser light (42) to the main amplifier (50). For example, the first continuous wave light source (40) may include a laser diode, but the present disclosure is not limited thereto.

[0038] Here, the first continuous wave light source (40) may include a first pump light source (41) and a first ring resonator (43). Here, the first pump light source (41) may generate a first pump light (45). For example, the first pump light source (41) may include a laser diode. Additionally, the first ring resonator (43) may be provided between the first pump light source (41) and the coupler (44). Here, the first ring resonator (43) may have a first radius (R1). Here, the first ring resonator (43) may resonate the first pump light (45) to generate a first continuous wave laser light (42).

[0039] The second continuous wave light source (80) can be connected to the coupler (44). Here, the second continuous wave light source (80) can generate a second continuous wave laser light (82) that is longer than the wavelength of the first continuous wave laser light (42) of the first continuous wave light source (40). Here, the second continuous wave light source (80) may include a second pump light source (81) and a second ring resonator (83). Here, the second pump light source (81) may generate a second pump light (85). For example, the second pump light source (81) may include a laser diode. Additionally, the second ring resonator (83) may be provided between the second pump light source (81) and the coupler (44). Here, the second ring resonator (83) may have a second radius (R2) that is larger than the first radius (R1). Here, the second ring resonator (83) can resonate the second pump light source (85) to generate the second continuous wave laser light (82).

[0040] The first continuous wave laser light (42) and the second continuous wave laser light (82) can prevent damage to the main amplifier (50) during the idle period of the pulsed laser light (32). In this case, the first continuous wave laser light (42) and the second continuous wave laser light (82) can prevent damage to the main amplifier (50) because, at the moment when the pulsed laser light (32) is turned off, the first pump light source (40) and the second pump light source (80) are turned on, and the first continuous wave laser light (42) and the second continuous wave laser light (82) are oscillated and input to the main amplifier (50).

[0041] Additionally, the first continuous wave laser light (42) and the second continuous wave laser light (82) may have the same polarization. Here, the pulsed laser light (32) may have a polarization perpendicular to the first continuous wave laser light (42) and the second continuous wave laser light (82).

[0042] As illustrated in FIG. 3, the wavelength peak of the first continuous wave laser light (42) may overlap with one side of the wavelength band of the pulsed laser light (32), and the wavelength peak of the second continuous wave laser light (82) may overlap with the other side of the wavelength band of the pulsed laser light (32). For example, the wavelength peak of the first continuous wave laser light (42) may overlap with the short wavelength of the pulsed laser light (32), and the wavelength peak of the second continuous wave laser light (82) may overlap with the long wavelength of the pulsed laser light (32). Additionally, the wavelength peak of the first continuous wave laser light (42) may overlap with or touch either end of the wavelength band of the pulsed laser light (32).

[0043] A polarizing plate (65) is provided between the main amplifier (50) and the non-linear pulse width compression device (60) and can eliminate the first continuous wave laser light (42) and the second continuous wave laser light (82). In one example, a first continuous wave light source (40) provided perpendicular to the polarization axis of the pulsed laser light (32) generates the first continuous wave laser light (42) polarized in one direction, and the polarizing plate (65) can eliminate the first continuous wave laser light (42). In another example, a second continuous wave light source (80) provided perpendicular to the polarization axis of the pulsed laser light (32) generates the second continuous wave laser light (82) polarized in one direction, and the polarizing plate (65) can eliminate the second continuous wave laser light (82).

[0044] Here, the polarizing plate (65) may have a polarizer perpendicular to the polarization direction of the first continuous wave laser light (42) and the second continuous wave laser light (82). For example, if the first continuous wave laser light (42) and the second continuous wave laser light (82) are polarized in a horizontal direction, the polarizing plate (65) may have a vertical polarizer. For another example, if the first continuous wave laser light (42) and the second continuous wave laser light (82) are polarized in a vertical direction, the polarizing plate (65) may have a horizontal polarizer. For yet another example, if the first continuous wave laser light (42) and the second continuous wave laser light (82) are right-circle polarized, the polarizing plate (65) may have a left-circle polarizer. For yet another example, if the first continuous wave laser light (42) and the second continuous wave laser light (82) are left-circle polarized, the polarizing plate (65) may have a right-circle polarizer.

[0045] The control module (70) may include a memory that stores data for an algorithm or a program that reproduces the algorithm for controlling the operation of components within the system, and at least one processor that performs the aforementioned operation using the data stored in the memory. Here, the memory and the processor may each be provided as separate chips. Additionally, the memory and the processor may be provided as a single chip.

[0046] The memory can store data supporting various functions of the system and programs for the operation of the control module, as well as input or output data. Additionally, the memory can store multiple application programs (or applications) running on the system, data for the operation of the system, and instructions. At least some of these application programs may be downloaded from an external server via wireless communication.

[0047] Here, the memory may include at least one storage medium among Flash Memory type, Hard Disk type, Solid State Disk (SSD) type, Silicon Disk Drive (SSD) type, Multimedia Card Micro type, card type memory (e.g., SD or XD memory, etc.), Random Access Memory (RAM), Static Random Access Memory (SRAM), Read Only Memory (ROM), Electrically Erasable Programmable Read Only Memory (EEPROM), Programmable Read Only Memory (PROM), magnetic memory, magnetic disk, and optical disk. Additionally, the memory may be a database that is separated from the system and connected via wired or wireless connection.

[0048] Memory can store data related to the femtosecond fiber laser. The processor can control operations related to the femtosecond fiber laser.

[0049] The control module (70) can control the pre-amplifier (20), the pulse speaker (30), and the main amplifier (50). Additionally, the control module (70) can control the pre-amplifier (20) and the pulse speaker (30) to control the generation of femtosecond laser light (12) and pulse laser light (32). Here, when femtosecond laser light (12) and pulse laser light (32) are not generated, the first continuous wave light source (40) can provide the first continuous wave laser light (42) to the main amplifier (50) to prevent burning and damage to the main amplifier (50).

[0050] The femtosecond fiber laser system (100) according to the present disclosure may further include a pulse width expander (15), an isolator (16), a picker control module (34), and a coupler (44).

[0051] A pulse width expander (15) may be provided between the femtosecond light source (10) and the preamplifier (20). Such a pulse width expander (15) can expand the pulse width of the femtosecond laser light (12).

[0052] For example, the pulse width expander (15) may include a circulator (13) and a chirp fiber Bragg grating (14). Here, the circulator (13) may be provided between the femtosecond light source (10) and the preamplifier (20). Here, the circulator (13) may include at least one port. Additionally, the chirp fiber Bragg grating (14) may be connected to the port of the circulator (13). Such a chirp fiber Bragg grating (14) can expand the pulse width of the femtosecond laser light (12).

[0053] The isolator (16) may be connected by an optical fiber (11) between the preamplifier (20) and the pulse picker (30). Such an isolator (16) can protect the preamplifier (20) and the femtosecond light source (10) by blocking the return of the femtosecond laser light (12). Here, the optical fiber (11) located between the preamplifier (20) and the isolator (16) may include a gain medium optical fiber, such as a Yb-doped, Nd-doped, or Er-doped Polarization Maintaining Fiber. For example, the preamplifier (20) may include a laser diode.

[0054] A picker control module (34) can be connected to a pulse picker (30). Such a picker control module (34) can control the pulse repetition rate and the pulse train. Here, an optical fiber coupling device (18) may be provided in the optical fiber (11) adjacent to the picker control unit (34).

[0055] Here, the picker control module (34) provides a pulse control signal to the pulse picker (30), and the pulse picker (30) can generate a pulse laser light (32) by modulating the femtosecond laser light (12) based on the pulse control signal. Here, the pulse control signal and the pulse laser light (32) may have a modulated frequency between about 0 Hz and about 1 GHz.

[0056] A coupler (44) may be provided between a pulse speaker (30) and a main amplifier (50). Additionally, a coupler (44) may be provided between a first continuous wave light source (40) and a main amplifier (50). Here, the coupler (44) may connect the pulse speaker (30) and the first continuous wave light source (40) to the main amplifier (50). For example, the coupler (44) may include a Y-branch coupler.

[0057] Additionally, the coupler (44) can couple optical fibers (11) connected to the first continuous wave light source (40) and the pulse speaker (30). Here, the optical fibers (11) may include single-mode optical fibers. Additionally, the optical fibers (11) may include multi-mode optical fibers, and the present disclosure is not limited thereto.

[0058] A main amplifier (50) may be provided between a pulse speaker (30) and a non-linear pulse width compression device (60). Here, the main amplifier (50) may be provided between a first continuous wave light source (40) and a non-linear pulse width compression device (60). Here, the main amplifier (50) may amplify pulsed laser light (32). Additionally, the main amplifier (50) may amplify the first continuous wave laser light (42). Additionally, the main amplifier (50) may amplify the second continuous wave laser light (82). For example, the main amplifier (50) may include a plurality of laser diodes. Here, the main amplifier (50) may include a first main amplifier (52), a second main amplifier (54), and a third main amplifier (56).

[0059] The first main amplifier (52) may be connected to the coupler (44) and the second main amplifier (54) via an optical fiber (11). Here, the first main amplifier (52) may include a laser diode and a gain medium optical fiber. Here, the gain medium optical fiber of the first main amplifier (52) may include a Yb-doped, Nd-doped, or Er-doped Polarization-Maintaining Fiber. Additionally, the first filter (51) may be connected to the first main amplifier (52) and the second main amplifier (54) via an optical fiber (11). Here, the first filter (51) may remove noise from the pulsed laser light (32) amplified by the first main amplifier (52). Additionally, an isolator (16) may be provided between the first filter (51) and the gain medium optical fiber. Here, the isolator (16) can increase the amplification efficiency of the first main amplifier (52) by blocking reverse flow for the pulsed laser light (32) and the first continuous wave laser light (42).

[0060] The second main amplifier (54) may be connected by an optical fiber (11) between the first main amplifier (52) and the third main amplifier (56). Here, the second main amplifier (54) may include a laser diode and a gain medium optical fiber. Here, the gain medium optical fiber of the second main amplifier (54) may include a Yb-doped, Nd-doped, or Er-doped Polarization-Maintaining Fiber. Additionally, the second filter (53) may be connected by an optical fiber (11) between the second main amplifier (54) and the third main amplifiers (56). Here, the second filter (53) may remove noise from the pulsed laser light (32) amplified by the second main amplifier (54). Additionally, the first cladding mode stripper (55) may be provided between the gain medium optical fiber of the second main amplifier (54) and the second filter (53). Here, the first cladding mode stripper (55) can remove residual pumps within the cladding of the gain medium optical fiber. Additionally, an isolator (16) can be provided between the first cladding mode stripper (55) and the second filter (53). Here, the isolator (16) can increase the amplification efficiency of the second main amplifier (54) by blocking reverse flow for the pulsed laser light (32) and the first continuous wave laser light (42).

[0061] The third main amplifier (56) may be connected via an optical fiber (11) between the second main amplifier (54) and the nonlinear pulse width compression device (60). Here, the third main amplifier (56) may include a laser diode and a gain medium optical fiber. Here, the gain medium optical fiber provided between the third main amplifier (56) and the lens (58) may include a Yb-doped, Nd-doped, or Er-doped Polarization-Maintaining Fiber. Additionally, an end cap (59) may be provided at the end of the gain medium optical fiber. Here, the end cap (59) may prevent the end of the optical fiber (11) from being damaged by the amplified pulsed laser light (32) and the first continuous wave laser light (42). Additionally, the lens (58) may be provided between the third main amplifier (56) and the nonlinear pulse width compression device (60). Here, the lens (58) can collimate the pulsed laser light (32) and the first continuous wave laser light (42) to the pulse width compression device (60).

[0062] A nonlinear pulse width compression device (60) can be connected to a main amplifier (50). Here, the nonlinear pulse width compression device (60) can compress the pulse width of the pulse laser light (32) and block or remove the first continuous wave laser light (42) and the second continuous wave laser light (82).

[0063] FIGS. 4 and 5 illustrate the configuration of the nonlinear pulse width compression device of FIG. 2. FIG. 6 illustrates the laser spectrum at different positions according to the intensity of the laser beam by the nonlinear pulse width compression device of FIGS. 4 and 5.

[0064] Referring to FIGS. 4 to 6, the nonlinear pulse width compression device (60) may include a lens (61), a first mirror (62), a second mirror (63), a third mirror (64), and a nonlinear crystal (65).

[0065] The lens (61) is positioned in alignment with the first mirror (62) and can focus the laser light (66). Here, the first mirror (62) can reflect the laser light (66). For example, the first mirror (62) may be a planar reflective mirror. Additionally, the laser light (66) may be an ultrafast laser light.

[0066] The second mirror (63) may include a groove (g1) that receives and reflects the laser light (66) reflected through the first mirror (62), and may include a plurality of first points (P11 to P19) that reflect the reflected laser light (66). For example, the second mirror (63) may be a radius of curvature mirror. Here, the groove (g1) and the plurality of first points (P11 to P19) may be formed at equal intervals of 10 on the edge portion of the second mirror (63). Not limited thereto, the plurality of first points may be formed at equal intervals of 4, 6, 8, 10, or 12 or more.

[0067] The third mirror (64) includes a groove (g1) and a plurality of second points (P21 to P29) that reflect laser light (66) reflected through a plurality of first points (P11 to P19), and may include a hole (h1) that outputs the laser light (66) reflected through the groove (g1), the plurality of first points (P11 to P19), and the plurality of second points (P21 to P29) to the outside. For example, the third mirror (64) may be a radius of curvature mirror. Here, the plurality of second points (P21 to P29) may be formed at 9 equal intervals on the edge portion of the third mirror (64). Not limited thereto, the plurality of second points may be formed at 4, 6, 8, 10, or 12 or more equal intervals.

[0068] Here, the laser light (66) can form a reciprocating path by alternating one by one in a clockwise or counterclockwise rotation through 10 equally spaced grooves (g1) and a plurality of first points (P11 to P19) and a plurality of second points (P21 to P29) formed at 9 equally spaced intervals.

[0069] A nonlinear crystal (65) can expand the spectrum of laser light (66) that travels back and forth through a second mirror (63) and a third mirror (64). Here, the nonlinear crystal (65) can move horizontally between the second mirror (63) and the third mirror (64) to adjust the amount of spectrum expansion. Here, the nonlinear crystal (65) may include any one of SF10, SF11, Fused silica, and Sapphire glass corresponding to the glass series, any one of water and alcohol corresponding to the liquid, and stable gases such as argon and nitrogen corresponding to the gas.

[0070] Here, when the nonlinear crystal (65) is made of N-SF11 material, the reference output must exceed approximately Pc = 0.8 MW @ 1064 nm to expand the spectrum of the laser light (66) (this is called Self-Phase Modulation, SPM phenomenon).

[0071] In the present disclosure, the distance (d) between the second mirror (63) and the third mirror (64) can be calculated based on the following [Equation 1] and [Equation 2].

[0072] [Mathematical Formula 1]

[0073]

[0074] [Mathematical Formula 2]

[0075]

[0076] Here, frep is the focal length of the lens, Lfc is the distance between the second mirror and the third mirror when the second mirror has curvature (the third mirror is a flat mirror), Lcc is the distance between the second mirror and the third mirror when both the second mirror and the third mirror have curvature, n is the number of times the laser beam travels back and forth between the two mirrors, and m is the shape of the beam formed by the laser beam traveling back and forth between the two mirrors. For example, when n=5 times, when m=1, the shape of the beam (a) between the two mirrors is 180 degrees and the angle between the two consecutive beams is 36 degrees, when m=2, the shape of the beam (b) between the two mirrors is 360 degrees and the angle between the two consecutive beams is 72 degrees, and when m=3, the shape of the beam between the two mirrors is 540 degrees and the angle between the two consecutive beams is 108 degrees. R is the radius of curvature of the second mirror and the third mirror. c can be a concave mirror, which is a curvature mirror.

[0077] Therefore, if the radius of curvature of the second mirror is R=1m, the third mirror is flat, and m=2 and n=10, Lfc can be calculated as 9.54915cm. As another example, if the radius of curvature of both the second and third mirrors is R=1m, and m=2 and n=10, Lcc can be calculated as 4.89435cm.

[0078] The nonlinear pulse width compression device (60) according to the present disclosure can focus a laser light (66) through a lens (61), reflect the focused laser light (66) through a first mirror (62), receive and reflect the reflected laser light (66) through a groove (g1) of a second mirror (63), reflect the received and reflected laser light (66) through P21 among a plurality of second points (P21 to P29) of a third mirror (64), and reflect the reflected laser light (66) through P11 among a plurality of first points (P11 to P19) of the second mirror (63).

[0079] Thereafter, the nonlinear pulse width compression device (60) according to the present disclosure may reflect the reflected laser light (66) through P22 among a plurality of second points (P21 to P29) of the third mirror (64), reflect the reflected laser light (66) through P12 among a plurality of first points (P11 to P19) of the second mirror (63), reflect the reflected laser light (66) through P23 among a plurality of second points (P21 to P29) of the third mirror (64), and reflect the reflected laser light (66) through P13 among a plurality of first points (P11 to P19) of the second mirror (63).

[0080] Thereafter, the nonlinear pulse width compression device (60) according to the present disclosure may reflect the reflected laser light (66) through P24 among a plurality of second points (P21 to P29) of the third mirror (64), reflect the reflected laser light (66) through P14 among a plurality of first points (P11 to P19) of the second mirror (63), reflect the reflected laser light (66) through P25 among a plurality of second points (P21 to P29) of the third mirror (64), and reflect the reflected laser light (66) through P15 among a plurality of first points (P11 to P19) of the second mirror (63).

[0081] Thereafter, the nonlinear pulse width compression device (60) according to the present disclosure may reflect the reflected laser light (66) through P26 among a plurality of second points (P21 to P29) of the third mirror (64), reflect the reflected laser light (66) through P16 among a plurality of first points (P11 to P19) of the second mirror (63), reflect the reflected laser light (66) through P27 among a plurality of second points (P21 to P29) of the third mirror (64), and reflect the reflected laser light (66) through P17 among a plurality of first points (P11 to P19) of the second mirror (63).

[0082] Afterwards, the nonlinear pulse width compression device (60) according to the present disclosure can reflect the reflected laser light (66) through P28 among a plurality of second points (P21 to P29) of the third mirror (64), reflect the reflected laser light (66) through P18 among a plurality of first points (P11 to P19) of the second mirror (63), reflect the reflected laser light (66) through P29 among a plurality of second points (P21 to P29) of the third mirror (64), reflect the reflected laser light (66) through P19 among a plurality of first points (P11 to P19) of the second mirror (63), and output the reflected laser light (66) to the outside through the hole (h1) of the third mirror (64).

[0083] As shown in FIG. 6, the beam intensity in the nonlinear crystal (65) can be determined by the focal length of the lens (L).

[0084] Here, the beam intensity can be increased as the number of reciprocating paths formed alternately by the laser light (66) through 10 equally spaced grooves (g1), a plurality of first points (P11 to P19), and a plurality of 9 equally spaced second points (P11 to P19) increases, with one by one, in a clockwise or counterclockwise rotation.

[0085] For example, when the reflected laser light (66) travels from P19 of the second mirror (63) through the nonlinear crystal (65) to the hole (h1) of the third mirror (64), the beam intensity (I1, I2, I3) in the nonlinear crystal (65) can be stronger than the beam intensity (I1, I2) in the nonlinear crystal (65) when it travels from P14 of the second mirror (63) through the nonlinear crystal (65) to P25 of the third mirror (64).

[0086] Additionally, when moving from P14 of the second mirror (63) to P25 of the third mirror (64) through the non-linear crystal (65), the beam intensity (I1, I2) in the non-linear crystal (65) can be stronger than the beam intensity (I1) in the non-linear crystal (65) when passing from the groove (g1) of the second mirror (63) to P21 of the third mirror (64) through the non-linear crystal (65).

[0087] As described above, the disclosed embodiments have been explained with reference to the attached drawings. Those skilled in the art will understand that the present disclosure may be practiced in forms different from the disclosed embodiments without changing the technical spirit or essential features of the present disclosure. The disclosed embodiments are illustrative and should not be interpreted restrictively.

Claims

1. A first mirror that reflects incident laser light; A second mirror that receives and reflects laser light incident through the first mirror; A third mirror that reflects laser light incident through the second mirror; and It includes a nonlinear crystal that expands the spectrum of laser light traveling back and forth through the second mirror and the third mirror, and The second mirror and the third mirror are arranged facing each other with the non-linear crystal in between, and The second mirror and the third mirror each include a plurality of first points formed at equal intervals on the edge portion of the second mirror and a plurality of second points formed at equal intervals on the edge portion of the third mirror for reflection of a plurality of laser lights between the two, in order for reflection between the two to occur in a predetermined order. The third mirror includes a hole that transmits the laser light finally reflected through the second mirror to the outside, The above laser light is, A non-linear pulse width compression device for spectrum expansion, characterized by forming a round-trip path by alternating clockwise or counterclockwise rotation through the plurality of first points and the plurality of second points.

2. In Paragraph 1, A non-linear pulse width compression device for spectrum expansion, further comprising a lens provided in alignment with the first mirror and focusing the laser light.

3. In Paragraph 2, A nonlinear pulse width compression device based on spectrum expansion, characterized in that the beam intensity in the nonlinear crystal is determined according to the focal length of the lens.

4. In Paragraph 3, The above beam intensity is, A non-linear pulse width compression device for spectrum expansion, characterized in that the laser light becomes stronger as the number of reciprocating paths formed alternately one by one in a clockwise or counterclockwise rotation through a plurality of first points formed at 10 equal intervals and a plurality of second points formed at 9 equal intervals increases.

5. In Paragraph 3, The above nonlinear crystal is, A non-linear pulse width compression device for spectrum expansion, characterized by horizontal movement between the second mirror and the third mirror to adjust the amount of spectrum expansion.

6. In Paragraph 3, The distance between the second mirror and the third mirror is, A nonlinear pulse width compression device based on spectrum expansion, characterized by being calculated based on the radius of curvature of the second mirror and the radius of curvature of the third mirror.

7. In Paragraph 1, The above nonlinear crystal is, It includes any one of SF10, SF11, Fused silica, BK7, CaF2, Sapphire glass, and Birefringent crystal, which belong to the glass series, and It includes either water or alcohol corresponding to a liquid, and A non-linear pulse width compression device for spectrum expansion, comprising argon and nitrogen corresponding to gases.

8. A femtosecond fiber laser system comprising a nonlinear pulse width compression device according to spectrum expansion as described in any one of claims 1 to 7.

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