KR102210160B1 - Pulse laser apparatus - Google Patents

Abstract

The pulsed laser device according to the present invention includes an oscillator for generating a laser, an enlarger for expanding a pulse width of a laser incident from the oscillator, and a compressor for compressing the pulse width of a laser incident from the enlarger, wherein the compressor is optical It includes gratings, reflective mirrors that change the path of the laser, and a dispersion control unit that adjusts the distance between the optical gratings by changing a position.

Description

Pulse laser apparatus {Pulse laser apparatus}

The present invention relates to a pulsed laser device, and more particularly, to an ultrashort pulse laser device capable of adjusting the pulse width of an output laser.

The development of industrial technology has demanded precision and high productivity in the field using lasers, and in recent years, ultrashort lasers have been used in various fields to meet this demand. Ultrashort lasers show different characteristics from conventional lasers. For example, in the ultrashort laser, since the laser light is irradiated to the medium for a short period of time, it is possible to avoid thermal effects or thermal deformation caused by conventional laser processing. In addition, the ultra-short laser can process the inside of the medium without damaging the surface. Therefore, ultra-short lasers are used in fields that require precise and fine processing (semiconductors, electronic chips, medical care, etc.).

An object of the present invention is to provide a pulsed laser device capable of adjusting the pulse width of an output laser.

The problem to be solved by the present invention is not limited to the problems mentioned above, and other problems that are not mentioned will be clearly understood by those of ordinary skill in the relevant technical field from the following description.

The present invention includes an oscillator for generating a laser, an enlarger for expanding a pulse width of a laser incident from the oscillator, and a compressor for compressing the pulse width of a laser incident from the enlarger, wherein the compressor includes optical gratings and It provides a pulsed laser device including reflecting mirrors for changing a path and a dispersion adjusting unit for adjusting a distance between the optical gratings by changing a position.

It may further include a pulse picker between the oscillator and the expander, and an amplifier between the expander and the compressor.

The oscillator may include a pump light source and an optical fiber, and the optical fiber may include a core and a cladding surrounding the core.

The core may be doped with ytterbium (Yb).

The dispersion control unit includes at least two or more mirrors, and the mirrors may move in a first direction in which the laser is incident or in a second direction opposite to the first direction.

Each of the mirrors may move in the first direction or the second direction by the same distance.

The dispersion control unit may be provided on the moving path of the laser between the optical gratings.

The optical gratings include a groove, and the compressor may control dispersion by adjusting the density of the groove, an angle at which a laser is incident on the optical gratings, and a distance between the optical gratings.

The compressor may further include an active mirror whose shape is deformable and an image sensor that transmits laser pulse information to the active mirror.

The image sensor may be a Shack-Hartmann Wavefront Sensor.

The pulsed laser device according to the present invention can adjust the pulse width of the output laser by adjusting the moving distance of the laser between the optical gratings by moving the dispersion control unit of the compressor.

1 is a conceptual diagram illustrating a pulsed laser device according to embodiments of the present invention.
2, 4, and 5 are diagrams for describing compressors according to embodiments of the present invention.
3A and 3B are graphs showing a time pulse shape of a laser pulse passing through a compressor according to an embodiment of the present invention.

In order to fully understand the configuration and effects of the present invention, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The present invention is not limited to the embodiments disclosed below, but may be implemented in various forms, and various modifications and changes may be added. However, it is provided to complete the disclosure of the present invention through the description of the present embodiment, and to fully inform the scope of the invention to those of ordinary skill in the art to which the present invention belongs. In the accompanying drawings, the size of the constituent elements is enlarged compared to the actual size for convenience of description, and the ratio of each constituent element may be exaggerated or reduced.

The terms used in this specification are for explaining examples and are not intended to limit the present invention. In addition, terms used in the present specification may be interpreted as meanings commonly known to those of ordinary skill in the art, unless otherwise defined.

In this specification, the singular form also includes the plural form unless specifically stated in the phrase. As used in the specification,'comprises' and/or'comprising' refers to the presence of one or more other elements, steps, actions and/or elements, and/or elements, steps, actions and/or elements mentioned. Or does not exclude additions.

In the present specification, terms such as first and second are used to describe various areas, concepts, and the like, but these areas and concepts should not be limited by these terms. These terms are only used to distinguish certain domains or concepts from other domains or concepts. Accordingly, a portion referred to as a first portion in one embodiment may be referred to as a second portion in another embodiment. The embodiments described and illustrated herein also include complementary embodiments thereof. Parts indicated by the same reference numerals throughout the specification represent the same elements.

Hereinafter, embodiments of the pulsed laser device according to the present invention will be described in detail with reference to FIGS. 1 to 5.

1 is a conceptual diagram illustrating a pulsed laser device according to embodiments of the present invention.

Referring to FIG. 1, the pulsed laser device according to the present invention includes an oscillator (Oscillator) 110, a pulse-picker (120), a stretcher (130), an amplifier (140), and a compressor (150). ) And a diagnostic device 160.

The oscillator 110 may include a pump light source 111 and a first optical fiber 112. The pump light source 111 may be a laser diode. For example, the pump light source 111 may generate a laser having a center wavelength of about 976 nm. The laser generated by the pump light source 111 may be incident on the first optical fiber 112. The first optical fiber 112 may include a core and a cladding surrounding the core. The first optical fiber 112 may be doped with a rare earth element in its core. Rare earth elements can be doped into the core as a gain medium. For example, the first optical fiber 112 may be doped with ytterbium (Yb) in its core. For example, the first optical fiber 112 may generate a laser having a center wavelength of about 1035 nm using the incident laser. In conclusion, the oscillator 110 may generate a laser having a center wavelength of about 1035 nm. The laser generated by the oscillator 110 may be a pulsed laser. For example, the repetition rate of the laser generated by the oscillator 110 may be about 1 MHz to 100 MHz. For example, the full-width at half maximum of the laser generated by the oscillator 110 may be about 0.1 nm to 100 nm. For example, the pulse width of the laser generated by the oscillator 110 may be about 0.01ps to 100ps. For example, the output of the laser generated by the oscillator 110 may be about 1mW to 1W.

The laser generated by the oscillator 110 may be incident on the pulse picker 120. The pulse picker 120 may include an acousto-optic modulator (AOM) or an electro-optic modulator (EOM). The pulse picker 120 may adjust the repetition rate of the laser using an acousto-optic modulator or an electro-optic modulator. For example, the repetition rate of the laser passing through the pulse picker 120 may be about 1 Hz to 50 MHz.

The laser passing through the pulse picker 120 may be incident on the enlarger 130. The expander 130 may include a second optical fiber (not shown). The expander 130 may adjust positive dispersion by using the material and length of the second optical fiber (not shown). The pulse width of the laser may be stretched through the expander 130 having positive dispersion. For example, the pulse width of the laser passing through the enlarger 130 may be about 100ps to 1ns.

The laser that has passed through the enlarger 130 may be incident on the amplifier 140. The amplifier 140 may amplify the output of the laser. For example, the output of the laser passing through the amplifier 140 may be several mW to hundreds of kW.

The laser passing through the amplifier 140 may be incident on the compressor 150. The compressor 150 may include optical gratings 151 in FIG. 2. The compressor 150 may adjust negative dispersion using optical gratings (151 in FIG. 2). The pulse width of the laser may be compressed through the compressor 150 having negative dispersion. For example, the pulse width of the laser passing through the compressor 150 may be about 0.05ps to 100ps. That is, the laser passing through the compressor 150 may be an ultrashort laser.

In this case, the positive dispersion and the negative dispersion may be determined according to the sign of the group delay dispersion parameter defined as in [Equation 1] below.

In [Equation 1], D is the group delay dispersion parameter, c is the speed of light, n is the refractive index of the material through which the laser passes, and λ is the wavelength of the laser. If D is positive, it indicates positive variance, and if D is negative, it indicates negative variance.

The laser passing through the compressor 150 may pass through the diagnostic device 160. The diagnostic device 160 may measure the pulse width of the laser. The laser passing through the diagnostic device 160 may be output to the outside of the pulsed laser device.

2 is a view for explaining a compressor according to an embodiment of the present invention. 3A and 3B are graphs showing a time pulse shape of a laser pulse passing through a compressor according to an embodiment of the present invention. In FIGS. 3A and 3B, the x-axis of the graphs represents time in units of fs (10 ^-15 s), and the y-axis represents the relative intensity of the laser pulse. 3A and 3B, the laser pulses are Gaussian pulses having a spectral half width of about 4 mm.

Referring to FIG. 2, the compressor 150 may include optical gratings 151, a dispersion control unit 152, and reflection mirrors 153. The compressor 150 may adjust dispersion according to a groove density, a brazed angle of the optical gratings 151, and a distance a laser moves between the optical gratings 151. Accordingly, the compressor 150 may cancel dispersion of the expander (130 in FIG. 1). A dispersion control unit 152 may be provided between the optical gratings 151. The dispersion control unit 152 may include, for example, two mirrors. The position of the dispersion control unit 152 may change in the first direction D1 and the second direction D2. The first direction D1 and the second direction D2 may be opposite to each other. The first direction D1 and the second direction D2 may be substantially parallel to the direction in which the laser is incident on the dispersion control unit 152. The two mirrors of the dispersion adjusting unit 152 may move by the same length in the first direction D1 or the second direction D2 by one length adjusting device. The laser moving between the optical gratings 151 may change its path through the reflective mirrors 153. The reflective mirrors 153 may increase the path of the laser between the optical gratings 151.

에 대한 파수 함수(wavenumber function)

를 중심 주파수

에 대하여 테일러 전개(Taylor expansion)하면 아래의 [수학식 2]와 같다. 이때, [수학식 2]의 2차항의 계수는 아래의 [수학식 3]과 같이 군속도 분산(Group Velocity Dispersion, GVD)을 의미한다. 군속도 분산(GVD)은 단위 길이당 군지연 분산(Group Delay Dispersion, GDD) 및 단위 길이당 2차 분산(second-order dispersion)과 같다. L은 레이저의 이동 거리이다. 또한, [수학식 2]의 3차항의 계수는 아래의 [수학식 4]와 같이 단위 길이당 3차 분산(third-order dispersion)을 의미한다.In the laser pulse passing through the compressor 150, the angular frequency (angular frequency)

Wavenumber function for

Center frequency

For Taylor expansion, it is as shown in [Equation 2] below. In this case, the coefficient of the quadratic term in [Equation 2] means group velocity dispersion (GVD) as shown in [Equation 3] below. Group Velocity Dispersion (GVD) is equal to Group Delay Dispersion (GDD) per unit length and second-order dispersion per unit length. L is the moving distance of the laser. In addition, the coefficient of the third order term in [Equation 2] means third-order dispersion per unit length as shown in [Equation 4] below.

Hereinafter, the second-order dispersion and the third-order dispersion mean values obtained by multiplying the values of [Equation 3] and [Equation 4] by the moving distance L of the laser. At this time, the unit of the second variance is ps ² and the unit of the ^third variance is ps ³ .

In the pulsed laser device according to an embodiment of the present invention, the laser pulse passing through the enlarger (130 in FIG. 1) may have a positive second order dispersion and a negative third order dispersion. In addition, the laser pulse passing through the compressor 150 may have a negative secondary dispersion and a positive third dispersion.

As an example, the laser pulse passing through the enlarger (130 of FIG. 1) may have a second variance of about +58.56ps ² and a third variance of about -0.96ps ³ . Further, the laser pulse passing through the compressor 150 may have a secondary dispersion of about -58.56ps ² and a ^third dispersion of about +0.96ps ³ . That is, ideally, the laser pulses passing through both the expander (130 of FIG. 1) and the compressor 150 may have a value of 0 because the second and third dispersions are canceled. Assuming that the groove density of the optical gratings 151 is about 1739 grooves/mm, the incident angle is about 63.6 degrees, and the moving distance of the laser between the optical gratings 151 is about 900 mm, the second dispersion of the compressor 150 and The third order variance can be calculated. That is, the second-order dispersion, third-order dispersion, and half-width values of the graphs calculated in this specification may vary as the groove density of the optical gratings 151, the angle of incidence, and the moving distance of the laser between the optical gratings 151 vary. have.

2 and 3A, the first pulse G1 may be a Gaussian pulse having a first half width FWHM1. The first half width (FWHM1) is about 390 fs. The first pulse G1 is a theoretical pulse that can be obtained when the dispersion is canceled from each other in the enlarger (130 in FIG. 1) and the compressor 150 and becomes zero.

Meanwhile, when the position of the dispersion control unit 152 of the compressor 150 is moved, the moving distance of the laser may vary. When the dispersion control unit 152 is moved by a certain length, the moving distance of the laser between the optical gratings 151 may increase or decrease by twice the length of the movement of the dispersion control unit 152. For example, when the dispersion control unit 152 is moved about 25 mm in the first direction D1, the moving distance of the laser may increase by about 50 mm. As another example, when the dispersion control unit 152 is moved about 25 mm in the second direction D2, the moving distance of the laser may decrease by about 50 mm.

In an example, when the moving distance of the laser increases by about 50 mm, the laser pulse passing through the compressor 150 may have a second order dispersion of about -61.81ps ² and a third order dispersion of about +1.02ps ³ . Compared to before moving the position of the dispersion control unit 152 of the compressor 150, the second dispersion may decrease by about 3.25ps ² and the third dispersion may increase by about 0.06ps ³ . Accordingly, the laser pulse passing through both the expander (130 in FIG. 1) and the compressor 150 may have a second order dispersion of about -3.25ps ² and a third order dispersion of about +0.06ps ³ .

2 and 3B, the second pulse G2 may be a Gaussian pulse having a second half width FWHM2. The second half width (FWHM) is about 23ps. The second pulse G2 is a pulse that can be obtained when the dispersion control unit 152 is moved about 25 mm in the first direction D1 (when the moving distance of the laser increases by about 50 mm).

On the other hand, in another example, when the moving distance of the laser is reduced by about 50 mm, the laser pulse passing through the compressor 150 may have a secondary dispersion of about -55.31ps ² and a ^third dispersion of about +0.90ps ³ . Compared to before moving the position of the dispersion control unit 152 of the compressor 150, the second dispersion may increase by about 3.25ps ² and the third dispersion may decrease by about 0.06ps ³ . Accordingly, the laser pulse passing through both the expander (130 of FIG. 1) and the compressor 150 may have a second order dispersion of about +3.25ps ² and a third order dispersion of about -0.06ps ³ .

In conclusion, by adjusting the position of the dispersion control unit 152 of the compressor 150, the second and third dispersion of the laser pulse can be adjusted. 3A and 3B mean that the half width of the pulsed laser can be changed by adjusting the position of the dispersion adjusting unit 152.

4 is a view for explaining a compressor according to another embodiment of the present invention. Hereinafter, contents overlapping with those described with reference to FIG. 2 will be omitted.

Referring to FIG. 4, the dispersion control unit 152 of the compressor 150 may include four mirrors. The four mirrors of the dispersion adjusting unit 152 may move by the same length in the first direction D1 or the second direction D2 by one length adjusting device. When the dispersion control unit 152 is moved by a predetermined length, the moving distance of the laser between the optical gratings 151 may increase or decrease by four times the length of the movement of the dispersion control unit 152. For example, when the dispersion control unit 152 is moved about 12.5 mm in the first direction D1, the moving distance of the laser may increase by about 50 mm. As another example, when the dispersion control unit 152 is moved by about 12.5 mm in the second direction D2, the moving distance of the laser may decrease by about 50 mm. However, this is only exemplary, and the present invention is not limited thereto, and unlike shown, the dispersion control unit 152 may include more than four mirrors, and the mirrors are in the first direction by one length adjusting device. It can move the same length in (D1) or in the second direction (D2).

When comparing the case of FIG. 4 with the case of FIG. 2, even if the dispersion control unit 152 is slightly moved, the moving distance of the laser between the optical gratings 151 may be increased or decreased to the same degree. Accordingly, it is possible to greatly adjust the dispersion by using the smaller sized compressor 150. That is, it is possible to change the pulse width of the laser to a larger size with the compressor 150 having a smaller size.

5 is a view for explaining a compressor according to another embodiment of the present invention. Hereinafter, contents overlapping with those described with reference to FIG. 2 will be omitted.

Referring to FIG. 5, the compressor 150 may include optical gratings 151, a dispersion controller 152, reflective mirrors 153, an active mirror 154, and an image sensor 155. The optical gratings 151 may include a first optical grating 151a and a second optical grating 151b. The laser pulse entering the compressor 150 may be first incident on the first optical grating 151a and later incident on the second optical grating 151b. Compared with the case of FIG. 2, the compressor 150 may further include an image sensor 155 in which a reflective mirror 153 for incidence of a laser into the first optical grating 151a is replaced with an active mirror 154 have.

The active mirror 154 may include cell mirrors. Each of the cell mirrors may move so that the shape of the active mirror 154 may be deformable. For example, the active mirror 154 may include cell mirrors connected to piezo sensors. Piezo sensors may change the shape or position of the cell mirrors of the active mirror 154 when voltage is applied. Each of the piezo sensors may change the shape or position of each of the cell mirrors according to the applied voltage.

The image sensor 155 may include, for example, a Shack-Hartmann Wavefront Sensor (SHWFS). The image sensor 155 may receive the laser pulse diffracted by the first optical grating 151a by the 0th order and transmit the laser pulse information to the active mirror 154. Wavefront aberration of the laser pulse passing through the compressor 150 may be corrected due to feedback from the active mirror 154 and the image sensor 155.

In the above, embodiments of the present invention have been described with reference to the accompanying drawings, but those of ordinary skill in the art to which the present invention pertains can be implemented in other specific forms without changing the technical spirit or essential features. You can understand that there is. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not limiting.

110: oscillator
120: pulse picker
130: enlarger
140: amplifier
150: compressor
160: diagnostic device

Claims (10)

An oscillator that generates a laser;
An enlarger to enlarge the pulse width of the laser incident from the oscillator; And
Comprising a compressor for compressing the pulse width of the laser incident from the enlarger,
The compressor includes optical gratings, reflective mirrors for changing a path of the laser, and a dispersion adjusting unit for adjusting a distance between the optical gratings by changing a position,
The dispersion control unit includes at least two or more mirrors,
The mirrors move in a first direction in which the laser is incident or a second direction opposite to the first direction by one length adjusting device,
The dispersion control unit is a pulsed laser device provided on a moving path of the laser between the optical gratings inside the compressor. The method of claim 1,
A pulse picker between the oscillator and the expander; And
Pulsed laser device further comprising an amplifier between the expander and the compressor. The method of claim 1,
The oscillator includes a pump light source and an optical fiber,
The optical fiber is a pulsed laser device comprising a core and a cladding surrounding the core. The method of claim 3,
A pulsed laser device in which the core is doped with ytterbium (Yb). delete The method of claim 1,
Each of the mirrors moves in the first direction or the second direction by the same distance.
delete The method of claim 1,
The optical gratings comprise a groove,
The compressor controls dispersion by adjusting the density of the groove, the angle at which the laser is incident on the optical gratings, and the distance between the optical gratings. The method of claim 1,
The compressor further comprises an active mirror whose shape is deformable and an image sensor that transmits laser pulse information to the active mirror. The method of claim 9,
The image sensor is a shock-Hartmann wavefront sensor (Shack-Hartmann Wavefront Sensor) pulse laser device.

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