50 results about "Ultrashort pulse" patented technology

According to the large-depth-diameter-ratio micropore laser rotary-cutting precision machining system and method, light beam self-rotation and light beam scanning are achieved through a compact rotating assembly integrating a Dove prism and double reflectors, the off-axis angle and the off-axis amount are precisely regulated and controlled through deflection and movement of the reflectors, light beams are subjected to off-axis focusing through a focusing assembly, and the precision of laser rotary-cutting precision machining is achieved. Finally, a light path focusing mode of first converging and then off-axis focusing is formed, large-depth-diameter-ratio micropore machining is achieved, the aperture range is dozens of micrometers to several millimeters, and the maximum depth-diameter ratio can reach 15: 1 or above; the device is compact in structure, a complex adjusting system is not needed, the control mode is simple, high rotating speed can be achieved, ultra-short pulse time domain broadening is reduced through the double-reflector system, and machining of hole patterns such as steep straight holes and taper holes can be achieved.

The invention relates to the technical field of battery materials, in particular to a method for manufacturing a lithium-loving microstructure on the surface of a copper foil current collector for a metal lithium negative electrode through femtosecond laser additive manufacturing. Based on the characteristics of ultrashort pulse, ultrahigh peak power and high precision of femtosecond laser, the femtosecond laser is focused on the surface of a copper foil current collector coated with a metal salt solution, and the power and repetition frequency of the femtosecond laser are regulated and controlled, so that the metal salt is decomposed into nano metal particles which are locally sintered and fused on the surface of the copper foil current collector; the moving path of the femtosecond laser micro-nano moving table is controlled, the lithium-loving metal microstructure is manufactured on the surface of the copper foil current collector in an additive mode, ordered and compact deposition of metal lithium can be guided, growth of lithium dendrites can be remarkably inhibited, and the reversible capacity and cycling stability of the metal lithium negative electrode can be improved. The method is simple in technological process, high in preparation efficiency and high in repeatability, and wide application prospects are provided for practicability of the high-energy-density metal lithium battery.

The present invention relates to a device for measuring the damage limit of a laser amplification medium and a method for measuring the damage limit. A device for measuring the damage limit of a laser amplification medium according to one embodiment of the present invention may include: an ultrashort pulse generator that generates laser light having an ultrashort pulse; an amplification unit that irradiates the laser light onto a laser amplification medium to amplify the output of the laser light; and a beam measurement unit that generates a beam profile of the laser light output from the amplification unit and measures a damage threshold of the laser amplification medium by utilizing a change in the beam profile according to a Kerr lens phenomenon.

This invention discloses a wavelength-tunable dual-cavity ultrafast fiber laser based on rotating optical fibers and its control method, relating to the field of laser technology. The dual-cavity ultrafast fiber laser of this invention integrates a wavelength division multiplexer within a dual-ring resonant cavity, structurally integrating two wavelength channels, each containing an independent gain fiber, to achieve dual-color soliton output and reduce gain competition. By setting an adjustable rotating fiber filter, consisting of a polarization controller, rotating optical fibers, and a polarization-dependent isolator, in the multiplexing section, the center wavelength of both wavelengths is tunable. Simultaneously, the two sub-cavities share the same saturable absorber to achieve passive synchronous mode-locking, and a delay line is introduced into one of the channels to adjust the equivalent cavity length, achieving repetition frequency matching and timing alignment between the two sub-cavities, thereby obtaining stable, tunable, and synchronous dual-wavelength ultrashort pulse output.

The invention provides a non-Gaussian ultrashort pulse-oriented multi-channel feature inversion method and device, and the method comprises the steps: obtaining a first FROG trace graph, carrying out the multi-channel feature extraction of the first FROG trace graph, and generating a three-channel input feature graph; inputting the three-channel input feature map into an intensity prediction network, outputting a predicted pulse intensity envelope, inputting the first FROG trace map into a phase prediction network, outputting predicted pulse phase distribution, and filtering the predicted pulse intensity envelope and pulse phase distribution to smooth noise; and reconstructing a complex electric field based on the filtered intensity and phase, regenerating to obtain a second FROG trace graph, and calculating an error index between the first FROG trace graph and the second FROG trace graph, the error index comprising an FROG error and an intensity correlation coefficient. According to the invention, the requirement of an advanced ultrafast laser system for high-precision online diagnosis of non-ideal pulses is met, and key technical support is provided for online diagnosis and closed-loop control of the advanced ultrafast laser system.

The application relates to the field of optical information technology, and particularly relates to a high-energy thulium-doped fiber laser based on self-locking mode and dispersion management technology, wherein a pump laser is connected with one end of a pump protector, the other end of the pump protector is connected with an a end of a wavelength division multiplexer, a b end and a c end of the wavelength division multiplexer are respectively connected with an i end of a three-port circulator and one end of a thulium-doped gain fiber, the other end of the thulium-doped gain fiber is connected with a d end of an optical coupler, an e end of the optical coupler is connected with one end of a polarization controller, the other end of the polarization controller is connected with one end of a single-mode optical fiber, the other end of the single-mode optical fiber is connected with a g end of the three-port circulator, an h end of the three-port circulator is connected with one end of a collimator, and the other end of the collimator is provided with a dispersion compensation assembly, high-energy ultrashort pulses can be generated, the structure is optimized, and the manufacturing cost is reduced.

The invention discloses an ultrashort pulse dynamic regulation and control device and method based on double acousto-optic deflectors, and belongs to the technical field related to laser. The device comprises an acousto-optic deflector group and a 4f optical system, the 4f optical system is formed by biconvex lenses with two times of focal length, and the optical axis is parallel to the horizontal plane; the 4f optical system changes the positive and negative of the symbols of acousto-optic effect group delay dispersion and improves the range of group delay dispersion; the acousto-optic deflector group is composed of two acousto-optic deflectors which are arranged in parallel and in opposite directions, and the two acousto-optic deflectors are located on the two sides of the 4f optical system respectively and are both perpendicular to the optical axis. First polarized light of an input light beam is converted into second polarized light through the first acousto-optic deflector, the second polarized light is converted into first polarized parallel light beams through the 4f optical system and the second acousto-optic deflector, and an output light beam is obtained. The acousto-optic deflector group provides continuously adjustable group delay dispersion and regulates and controls the pulse width of an output light beam. The device is low in cost, is simple to operate, and dynamically regulates and controls the pulse width of the output light beam.

This invention discloses a neutron analysis physics testing system and method, belonging to the field of nuclear physics testing technology. The system includes: a high-speed synchronous pulse generator for generating pulse signals with multiple modulation sequences; an ultrashort pulse neutron generator for emitting short pulse neutron rays with specified parameters onto a sample; a neutron detector for acquiring secondary neutron signals; a gamma detector for acquiring characteristic gamma signals generated by neutron-excited probes of the sample; a safety control module for controlling the operating state of the ultrashort pulse neutron generator; and a data processing device for real-time collection and summarization of neutron signals and characteristic gamma signals based on the timing of the pulse signals with multiple modulation sequences. This system reduces time window drift and measurement errors, and activates the ultrashort pulse neutron generator only when a gate signal allows, improving the accuracy, safety, and stability of geological physics parameter measurements.

A real-time vector analysis method for detecting an optical signal with a bandwidth greater than 1 THz includes: mapping, by a time-lens focusing system, a spectrum of a signal under test to different temporal location information; obtaining, by fully broadening an ultrashort pulse by a dispersion, a time domain spectrum of the ultrashort pulse to form a chirped swept frequency source; inputting an out of the signal under test after passing through the time-lens and the chirped swept frequency source to a coherent receiver to realize an interference process and a conversion of an optical signal to an electrical signal, and recovering an intensity information and a phase information of frequency domain of the signal under test from the electrical signal by data acquisition and processing; then recovering a full-field information of time domain of the signal under test by a Fourier inverse transform.

The application discloses a kind of based on ultrafast laser liquid area impact regulation and control's molten pool pore inhibition method, belong to additive manufacturing and welding technical field.The method first establishes the three-dimensional space coordinates of ultrafast laser focus and molten pool liquid area servo correlation;After dynamic molten pool is formed by heat source, ultrafast laser is accurately focused in the molten pool liquid area pore prone position, and plasma shock wave induced by ultrafast laser ultrashort pulse acts on liquid metal.The method breaks through the inherent convection state of molten pool by shock wave and increases local flow rate, while high-frequency impact shears large-volume bubble into micro-nano bubble, and promotes micro-nano bubble collision and rapid floating, realizes the multi-mechanism synergistic exhaust of active interference-flow field-large bubble shear crushing-micro-nano bubble merging and floating, and completely drives away bubble from molten pool liquid area before solidification front arrives.The application significantly improves the density and mechanical properties of formed piece and welded joint.

An optoelectronic oscillator (100) and a signal processing method, which relate to the technical field of optoelectronics. In the optoelectronic oscillator (100), an electro-optical modulator (110), an optoelectronic detector (120), a first filter (130) and a power divider (140) form an optoelectronic oscillation loop. Compared with a conventional single-passband filter, the first filter (130) in the optoelectronic oscillation loop has an additional low-frequency passband, and thus can excite a pulse train of the low-frequency passband and a pulse train of a bandpass band in the optoelectronic oscillation loop. Since the oscillation of a pulse signal can automatically narrow a pulse train to form an ultrashort pulse train, when the pulse train excited by the bandpass band has undergone pulse narrowing by means of an oscillation mechanism in the optoelectronic oscillation loop, the pulse train excited by the low-frequency passband may further undergo pulse narrowing, such that the optoelectronic oscillator (100) can generate a microwave pulse train which is shorter than that of a conventional optoelectronic oscillator, that is, an ultrashort microwave pulse train.

The invention discloses a uranium mine logging instrument based on ultrashort pulse neutrons and a working method thereof, and relates to the field of uranium mine exploration logging. The logging instrument comprises a control communication short section, an ultrashort pulse neutron generator used for emitting fast neutron pulses with the pulse width smaller than 1 microsecond to a stratum, a shielding body and a double-thermal-neutron detection assembly used for detecting thermal neutrons and epithermal neutrons on measuring points consistent in space, all of which are sequentially arranged in the axial direction of the logging instrument. The gamma detector is used for detecting inelastic scattering gamma rays emitted by stratum elements and capturing gamma rays, and the fast neutron detector is used for detecting and outputting source intensity monitoring signals of fast neutron pulses in real time. According to the logging instrument, the ultra-short fast neutron pulse is emitted, the neutron yield is detected in real time, the neutron time spectrum and gamma-ray energy spectrum multi-dimensional information with an accurate timestamp are obtained in a combined mode, high-precision and anti-interference inversion is conducted on the stratum uranium content, and stratum information is obtained efficiently and accurately.

The invention discloses an ultra-short pulse optical parametric oscillator based on a bicrystal structure, and relates to a laser and an assembly, and the oscillator comprises a first beam shaper (2) which is used for shaping idler frequency light (1); a second beam shaper (4) for shaping the pump light (3); a dichroscope (5); the first nonlinear crystal (6) is arranged on a light emitting path of the dichroscope (5), and the first nonlinear crystal (6) is used as an input coupling mirror of the optical parametric oscillator; the second nonlinear crystal (7) is arranged on a light emitting path of the first nonlinear crystal (6), and the first nonlinear crystal (6) and the second nonlinear crystal (7) form a resonant cavity; and the three-direction color mirror (9) is arranged on a light emitting path of the second nonlinear crystal (7) and is used for separating the pump light, the signal light (8) generated by nonlinear frequency conversion and the amplified idle frequency light (1) and transmitting and outputting the idle frequency light. The conversion efficiency of the optical parameter amplification process is improved, and the overall amplification performance of the optical parameter amplifier is guaranteed.

A device for the generation of ultrashort pulses, wherein an oscillator is formed by: a first and a second non-overlapping transmission band-pass filter, which can serve as reflecting end element of the oscillator; optically transparent means with non-linear Kerr coefficient χ(3) different from zero configured to achieve a spectral broadening by self-phase modulation of the signal transiting through these means; an optical waveguide that produces a positive gain; a node configured to receive a trigger signal designed to activate the operation of the oscillator; a trigger signal generating device comprising: a laser source, for example a microchip, configured to generate a laser pulse, preferably with a minimum bandwidth, having a duration of hundreds of ps, up to the ns; a coupling system designed to introduce the pulse of the trigger laser into a waveguide made of an optically transparent material characterised by a non-linear Kerr coefficient χ(3) different from zero, which is configured to produce two distinct effects in order to spectrally broaden the pulse of the trigger laser, and precisely: a) self-phase modulation four-wave mixing; the output of the waveguide supplies the trigger signal to the node. The pulses produced by the oscillator typically have a duration of the order of the picosecond and are easily reduced to the Fourier limit of circa 100 femtoseconds by means of a dispersive device.

The application discloses a graphene-coated surface saturable absorber device of a multimode optical fiber with an internal microstructure, which adopts a mixed structure of graphene and a graded-index multimode optical fiber. The saturable absorber device comprises a first single-mode optical fiber, a mixed structure based on a multimode optical fiber, and a second single-mode optical fiber. The mixed structure based on the multimode optical fiber is composed of a tapered graded-index multimode optical fiber with an internal microstructure and a single-layer graphene film. The graded-index multimode optical fiber is first subjected to a micro-tapering treatment, then a microstructure is inscribed in the core inside the taper waist, then the graphene film is coated on the surface of the taper waist of the optical fiber, and finally the single-mode optical fibers are fused at both ends of the multimode optical fiber. The saturable absorber combines the nonlinear multimode interference effect in the multimode optical fiber and the saturable absorption characteristics of graphene, can perform secondary compression on the pulse width of a high-energy pulse, and thus obtains an ultrashort pulse. The application has the advantages of a solid structure, strong stability, a high damage threshold and the like, and provides an effective technical means for obtaining a stable ultrashort pulse mode locking.

Systems and methods for optical matrix multiplication are disclosed. An optical matrix multiplier includes an optical source configured to produce a sequence of optical pulses based on an input vector. The multiplier further includes a fanout module configured to receive a sequence of optical pulses and produce multiple optical pulse sequences. The multiplier further includes multiple delay lines, each delay line configured to apply a delay to an associated one of the optical pulse sequences. The multiplier further includes multiple modulators, each modulator configured to modulate one of the delayed optical pulse sequences. The multiplier further includes at least one accumulator configured to sum at least one modulated optical pulse sequence.

The invention provides an optical fiber oscillator and a homologous synchronous double-color optical fiber ultrafast seed source device and method thereof. The optical fiber oscillator, the homologous synchronous double-color optical fiber ultrafast seed source device and the homologous synchronous double-color optical fiber ultrafast seed source method can reduce system complexity and dependence on external active synchronous control, hopefully improve the synchronization precision of double-color ultrashort pulses to a sub-femtosecond magnitude, can realize a wider wavelength coverage range, reduce dependence on an external control system, and improve the synchronization precision of the double-color ultrashort pulses to the sub-femtosecond magnitude. And the laser can be applied to the fields with high requirements such as high-power laser output and long-distance laser communication.

A microscope apparatus comprises an array unit on which a sample is mounted; a beam irradiation unit for irradiating the sample mounted on the array unit with a focused ion beam; a laser output unit for emitting laser light with ultrashort pulses; a laser irradiation unit for irradiating the sample mounted on the array unit with the laser light emitted by the laser output unit; and a microscope unit for viewing the sample mounted on the array unit. The laser irradiation unit includes a spatial light modulator for modulating the laser light emitted by the laser output unit and for emitting the modulated laser light, as well as a scanning unit for irradiating the sample mounted on the array unit with the laser light emitted by the spatial light modulator while scanning the sample.

A system and a method for generating stable ultrashort pulses of XUV and soft X-ray radiation from laser-ablated plumes of a liquid target, using a laser source a pre-pulse and a laser source of a main pulse, by selecting the pre-pulse and the main pulse; directing and focusing the pre-pulse to a surface of the liquid target to ablate the surface of the liquid target, forming a plasma plume generating harmonics; the main pulse being selected for driving the harmonics.

The invention belongs to the field of wafer annealing, and particularly relates to a laser annealing system based on a neural network. According to the detected crystal defect type, parameters of secondary laser annealing are obtained by using the neural network, and then ultrashort pulse high-energy laser beams such as picosecond, femtosecond and the like are controlled to perform secondary laser annealing on the defects, so that in-situ repair is accurately and efficiently performed on an area with lattice defects on the surface of a semiconductor material, and the crystal quality of the semiconductor material is improved. The method is particularly suitable for a semiconductor process with laser annealing, the speed and the success rate of repairing crystal defects by using secondary laser annealing can be effectively improved, the process performance of a semiconductor is optimized, and the yield of a prepared semiconductor wafer material is improved.

The present disclosure can generate laser light having an ultrashort pulse and high peak power, be miniaturized, and improve light-pulse light conversion efficiency. A laser element includes: a laminated semiconductor layer that includes a first reflection layer for a first wavelength and an active layer that performs surface light emission at the first wavelength; a laser medium that is disposed on a rear side of an optical axis of the laminated semiconductor layer, and includes a second reflection layer for a second wavelength on a first surface facing the laminated semiconductor layer and a third reflection layer for the first wavelength on a second surface on an opposite side to the first surface; a fourth reflection layer for the second wavelength that is disposed further toward the rear side of the optical axis than the second surface; a first resonator that resonates light of the first wavelength between the first reflection layer and the third reflection layer; a second resonator that resonates light of the second wavelength between the second reflection layer and the fourth reflection layer; and a semiconductor saturable absorber that is disposed between the third reflection layer and the fourth reflection layer and generates the light of the second wavelength by mode-locking, and the optical axis of the laminated semiconductor layer and an optical axis of the laser medium are uniaxially arranged.

A microscope device according to the present invention is provided with: a placement unit on which a sample is placed; a beam irradiation unit for irradiating the sample disposed in the placement unit with a focused ion beam; the laser output part is used for outputting ultra-short pulse laser; a laser irradiation unit for irradiating the laser light output from the laser light output unit to the sample arranged in the arrangement unit; and a microscope unit for observing the sample arranged in the arrangement unit, the laser irradiation unit including: a spatial light modulator for modulating and emitting the laser light output from the laser light output unit; and a scanning unit for irradiating the sample disposed in the disposing unit with the laser light emitted from the spatial light modulator while scanning the sample.

The utility model belongs to the technical field of lasers, and discloses a 9-shaped hybrid mode-locked fiber laser, which comprises a pumping source, a 2 * 2 polarization-maintaining fiber coupler, a nonlinear amplification loop mirror loop connected with a first side of the polarization-maintaining fiber coupler, and a chirp fiber Bragg grating connected with a second side of the polarization-maintaining fiber coupler, the polarization maintaining optical fiber coupler is located at the connecting position of the nonlinear amplification annular mirror loop and a linear arm of the laser resonant cavity and used for coupling laser of the nonlinear amplification annular mirror loop to the linear arm, and after being reflected by the chirp fiber bragg grating, the laser is output to the nonlinear amplification annular mirror loop through the chirp fiber bragg grating. And then the laser on the linear arm is split into two beams of light which are transmitted clockwise and anticlockwise in a loop of the nonlinear amplification annular mirror. According to the utility model, two passive mode locking technologies are combined, rapid and stable mode locking can be realized, the operation state is slightly influenced by the environment, the signal-to-noise ratio of output laser pulses can be improved, and ultra-short pulses with narrower pulse width can be realized.

The present application relates to the technical field of fiber lasers, and particularly relates to a conical fiber saturable absorber based on selenium-sulfurized rhenium quantum dots and a preparation method and application thereof. The present application discloses a conical fiber saturable absorber based on selenium-sulfurized rhenium quantum dots, which comprises selenium-sulfurized rhenium quantum dots and a conical fiber, wherein the selenium-sulfurized rhenium quantum dots are deposited on a conical region of the conical fiber; in the present application, the selenium-sulfurized rhenium belongs to a triclinic system, has unique asymmetric surface characteristics and excellent nonlinear optical response, and the quantum dot form of the selenium-sulfurized rhenium has a carrier limiting effect, so that the state density is more concentrated; the conical fiber saturable absorber is made of the selenium-sulfurized rhenium quantum dots, the mode-locked pulse sequence generated by the fiber laser has higher stability, and stable ultrashort pulse output can be realized at a low starting threshold and high power.

This invention discloses a laser marking method for crystal oscillator circuits, comprising: Step 1: fixing the crystal oscillator to be marked; Step 2: obtaining the coordinates of the area to be marked on the crystal oscillator; Step 3: using a laser at a first preset power to etch and remove the marking layer on the crystal oscillator according to the obtained coordinates; Step 4: using a laser at a second preset power to etch the circuit layer on the crystal oscillator according to the obtained coordinates, and capturing the spectral / acoustic characteristics of the etching product in real time. When it is detected that the nickel layer is about to be etched through, the laser is controlled to etch intermittently in a single-pulse manner until a preset adjustment amount is reached, and then the etching is stopped to complete the marking. This invention utilizes the high absorption rate of 355nm ultraviolet light to metals and the high transmittance of quartz, combined with picosecond ultrashort pulses, to directly vaporize and sublimate the metal material, achieving coating etching without damaging the quartz substrate; the heat-affected zone is strictly controlled within 2μm, completely eliminating burrs and recast layers.

The invention discloses a method and a system for regulating and controlling interfacial properties of micro-droplets based on femtosecond laser. A micro-nano three-dimensional structure is accurately constructed on the surface of a material through the ultra-short pulse characteristic of femtosecond laser, and an electronic push-pull system can be formed on a micro-droplet interface when the inside and outside of a water-oil interface are filled with charge donors and acceptors, so that the charge transmission efficiency can be remarkably improved, the charge return rate can be inhibited, and the problem of pain points for improving the photoelectric conversion efficiency of the material is solved. Compared with the traditional photoetching technology, the processing precision is high, the heat affected zone is small, and various organic / inorganic hybrid materials and the like can be processed; by innovatively combining space selective processing of femtosecond laser with a molecular self-assembly technology, regulation and control of the charge transfer performance of a material interface are realized, the separation state charge return rate is effectively inhibited, and the charge transfer efficiency is greatly improved. The method can be widely applied to flexible photoelectric devices, micro-fluidic sensing chips and artificial photosynthetic systems, and an effective solution is provided for a new generation of efficient energy conversion devices.

A method is for manufacturing a stone, in particular for a timepiece, from a mineral body of monocrystalline or polycrystalline type. The method includes an ablation step in which the body is subjected to a material ablation by scanning on at least one face of the body using ultra-short pulse laser radiation whose duration is less than one hundred picoseconds, and whose beam is guided by a precession system having at least three axes to at least partially cancel the angle of the laser cone, which is due to the focusing of the laser. A mineral stone of monocrystalline or polycrystalline type, in particular for a horological movement, is likely to be obtained by the method. The stone includes in particular a face provided with a peripheral rim, in particular for laterally clamping an endstone in a bearing.

The invention belongs to the field of laser detection, and relates to an intracavity chiral molecule detection system based on high repetition frequency orbital angular momentum laser, which comprises a high repetition frequency laser generation part used for generating high repetition frequency pulse laser; the intra-cavity dispersion control and tuning part is used for controlling resonant wavelength, generating positive and negative chirps, realizing an intra-cavity soliton mode locking state and outputting optimized high repetition frequency ultrashort pulses; the vortex light generating part is used for receiving the high repetition frequency ultrashort pulse and loading the high repetition frequency ultrashort pulse into a high repetition frequency vortex light beam carrying orbital angular momentum; the chiral molecule detection part is positioned between the vortex light generation part and the observation and feedback part and is responsible for carrying out chiral molecule detection by utilizing the generated high-repetition-frequency vortex light beam; and the observation and feedback part is used for analyzing a detection result and feeding back the detection result to the high repetition frequency laser generation part and the intracavity dispersion control and tuning part to form closed-loop control. According to the invention, chiral molecule detection is realized by using the nonlinear effect of vortex light in the cavity.

The application relates to an ultrashort light pulse generation system based on a pulse width compression technology and belongs to the technical field of optoelectronic devices.The structure is as follows: the output end of a seed pulse source (1) is connected with the input end of a pulse width expansion module (2), the output end of the pulse width expansion module (2) is connected with the input end of an energy pre-amplification module (3), the output end of the energy pre-amplification module (3) is connected with the input end of a multi-channel pulse division module (4), the output end of the multi-channel pulse division module (4) is connected with the input end of a dispersion management module (5), the output end of the dispersion management module (5) is connected with the input end of an energy amplification module (6), the output end of the energy amplification module (6) is connected with the input end of a pulse coherent superposition module (7), and the output end of the pulse coherent superposition module (7) is connected with the input end of a pulse width compression module (8). The application has the advantages of high output pulse energy, high power, ultrashort pulse width and switchable pulse type.

According to the present disclosure, a first mirror, a second mirror, a third mirror, and a fourth mirror are arranged to face each other with a nonlinear crystal interposed therebetween, and the first mirror, the second mirror, the third mirror, and the fourth mirror respectively include a plurality of first points, a plurality of second points, a plurality of third points, and a plurality of fourth points, so as to reflect multiple laser beams between the mirrors in a predetermined sequence, wherein the second mirror may include a second hole through which the laser beam that is finally reflected from the first mirror is transmitted to the outside.