JP2019078580A - Transmission light measuring device and optical device - Google Patents

Abstract

To properly measure transmission light obtained by transmitting high-intensity laser beams through a saturable absorber to the extent that the saturable absorber is destroyed.SOLUTION: A transmission light measuring device 100 includes: a laser oscillator 110 for oscillating laser light having intensity equal to or more than 10W/cm; an optical device 130 having a saturable absorption part which includes a saturable absorber and has an irradiated surface positioned on an optical path of laser light LA oscillated from the laser oscillator 110 and has a moving part for relatively moving the irradiation surface and the optical path; and a laser power meter 140 for measuring the laser light transmitting through the saturable absorption part.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a transmitted light measurement device that measures transmitted light transmitted through a saturable absorber, and an optical device.

  Conventionally, in order to shorten the pulse width of the laser beam output by the laser output device, the laser output device is provided with a saturable absorber (SA). In the laser output device, the saturable absorber is disposed on the optical path of the laser beam oscillated by the laser oscillator. The saturable absorber absorbs incident light of intensity less than a predetermined saturation value, but transmits incident light of intensity greater than the saturation value. Therefore, the saturable absorber transmits only the central portion having a saturation value or more of the 1-pulse laser beam oscillated by the laser oscillator, and does not absorb and transmit other than the central portion. Therefore, the pulse width of the laser beam (transmitted light) transmitted through the saturable absorber becomes shorter than the incident light. As the saturable absorber, a semiconductor, a carbon nanotube, or a carbon nanowall is used (for example, Non-Patent Document 1).

  The saturation value of the saturable absorber is uniquely determined by the composition and the thickness (optical path length of light passing through the saturable absorber). For this reason, the pulse width of the output laser light (transmitted light) can not be adjusted unless the saturable absorber itself incorporated in the laser output device is replaced.

  Therefore, by making the saturable absorber into a triangular prism shape and moving the saturable absorber one-dimensionally in the direction orthogonal to the optical path, the optical path length of the laser beam passing through the saturable absorber is changed to change the pulse width. Laser output devices for tuning have been developed (e.g., Patent Document 1).

Patent No. 45 73 644

SPIE 9361, Ultrafast Phenomena and Nanophotonics XIX, 936104 (March 14, 2015) Q-switched fiber laser based on carbon nano wall saturable absorber, Proc.

When analyzing the transmitted light of the pulse laser, a laser power meter is used. However, the response time of the laser power meter is about several seconds. On the other hand, since the presence time of one pulse of transmitted light is less than one picosecond (10 ^-12 seconds), it is impossible to measure one pulse of transmitted light with a laser power meter. For this reason, in the laser power meter, transmitted light of a plurality of pulses (10 ¹¹ pulses or more) is integrated to measure the intensity, energy density, wavelength and the like.

  By the way, in recent years, the laser light of the laser output device of Patent Document 1 has higher intensity than the laser light oscillated by the laser oscillator, and transmits the laser light to the extent that the saturable absorber is broken to the saturable absorber. There is a demand to process materials. In this case, analysis of the transmitted light is required to determine the degree of processing of the material.

  However, the irradiation point of the laser light in the saturable absorber is destroyed only by irradiation with the laser light of one pulse. Therefore, in the next irradiation, since the laser light is irradiated to the broken portion, the oscillated laser light, not the transmitted light of the saturable absorber, reaches the laser power meter as it is. Therefore, there is a problem that integration of transmitted light can not be performed in the laser power meter, and only transmitted light can not be measured.

  The present disclosure provides a transmitted light measurement device and an optical device capable of appropriately measuring the transmitted light obtained by transmitting a laser beam of high intensity to the extent that the saturable absorber is destroyed to the saturable absorber. The purpose is to

In order to solve the above problems, a transmitted light measurement device according to an aspect of the present disclosure includes a laser oscillator that oscillates a laser beam with an intensity of 10 ¹³ W / cm ² or more, and a saturable absorber, Measuring a laser beam transmitted through the saturable absorber, a saturable absorber having an illuminated surface positioned on the optical path of the laser beam oscillated from the light source, a moving unit relatively moving the illuminated surface and the optical path, and And a laser power meter.

  Further, the moving portion may have the irradiation surface and the optical path in a first direction intersecting the extending direction of the optical path, and in a second direction intersecting the extending direction of the optical path and the first direction. And relative movement.

  Further, the saturable absorber is one or both of carbon nanowall and carbon nanotube, and the saturable absorbing portion is disposed in the resin of one or both of polyimide and poly (methyl methacrylate). And the saturable absorber.

In order to solve the above problems, an optical device according to an aspect of the present disclosure includes a saturable absorber and has a saturable surface having an irradiation surface positioned on the optical path of laser light with an intensity of 10 ¹³ W / cm ² or more. An absorbing unit, and a moving unit configured to relatively move the irradiation surface and the optical path.

  It is possible to appropriately measure the transmitted light obtained by transmitting the laser light of high intensity to the extent that the saturable absorber is destroyed to the saturable absorber.

It is a figure explaining a transmitted light measuring device. It is a figure explaining an optical device. It is a figure explaining a saturable absorption part. It is a figure explaining the moving direction of the saturable absorption part by a movement part. It is a figure explaining the optical apparatus of a modification.

  Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the attached drawings. The dimensions, materials, and other specific numerical values and the like shown in this embodiment are merely examples for facilitating understanding and do not limit the present disclosure unless otherwise specified. In the present specification and the drawings, elements having substantially the same functions and configurations will be denoted by the same reference numerals and redundant description will be omitted. Also, elements not directly related to the present disclosure are not shown.

(Transmitted light measuring device 100)
FIG. 1 is a diagram for explaining the transmitted light measurement device 100. As shown in FIG. As shown in FIG. 1, the transmitted light measurement device 100 includes a laser oscillator 110, a beam splitter 120, an optical device 130, a laser power meter 140, and a control unit 150. In FIG. 1, the laser beam is indicated by a solid arrow and the flow of the signal is indicated by a broken arrow.

The laser oscillator 110 oscillates a laser beam having an intensity of 10 ¹³ W / cm ² or more. Also, the laser oscillator 110 oscillates laser light (pulsed laser) with a pulse width of less than 10 ⁻¹² seconds. More preferably, the laser oscillator 110 oscillates laser light with a pulse width of femtosecond (10 ^-15 seconds) or attosecond (10 ^-18 seconds).

The intensity (W / cm ² ) of the laser beam can be calculated from the following equation (1).
Intensity = energy density (J / cm ² ) / pulse width equation (1)
Therefore, it can be said that the laser oscillator 110 oscillates a laser beam having an energy density of 10 (J / cm ² ) or more.

  The beam splitter 120 splits the laser beam oscillated by the laser oscillator 110 into two. Hereinafter, one laser beam divided and going straight is referred to as laser light LA, and the other laser light going straight is referred to as laser light LB. The laser beam LA is guided to a saturable absorber described later, and the laser beam LB is guided to a laser power meter 140 described later. When the light amount of the oscillated laser light is 1, the sum of the light amount of the laser light LA and the light amount of the laser light LB becomes 1 theoretically.

  The optical device 130 includes a saturable absorber, and positions the saturable absorber on the optical path of the laser light LA split by the beam splitter 120.

  FIG. 2 is a diagram for explaining the optical device 130. As shown in FIG. In the following drawings including FIG. 2 of this embodiment, the X-axis, Y-axis, and Z-axis perpendicular to each other are defined as illustrated. As shown in FIG. 2, the optical device 130 includes a condenser lens 132, a saturable absorber 134, and a moving unit 136. In FIG. 2, the laser beam LA is indicated by a solid arrow, and the flow of signals is indicated by a dashed arrow.

  The condenser lens 132 is disposed on the optical path (in the X-axis direction in FIG. 2) of the laser beam LA by a fixing unit (not shown). The condenser lens 132 condenses the laser light LA. The condenser lens 132 is, for example, a convex lens.

  The saturable absorber 134 has a flat plate (sheet) shape extending in the YZ plane in FIG. The saturable absorber 134 is held by a holder 136a of a moving unit 136 described later such that one surface (irradiated surface 134a) in the X-axis direction in FIG. 2 faces the condenser lens 132. That is, the saturable absorber 134 is held by the moving unit 136 such that the irradiation surface 134 a is positioned on the light path of the laser light LA collected by the collecting lens 132.

  FIG. 3 is a diagram for explaining the saturable absorber 134. As shown in FIG. Specifically, FIG. 3A is a perspective view of the saturable absorber 134. FIG. 3 (b) is a cross-sectional view of the saturable absorber 134. In FIG. 3B, the laser beam LA is indicated by a white arrow.

  As shown in FIGS. 3A and 3B, the saturable absorber 134 includes a saturable absorber 160 and a surrounding portion 162. The thickness (the length in the X-axis direction in FIG. 3A and FIG. 3B) of the saturable absorber 134 is about 1 μm to 100 μm.

  In the present embodiment, the saturable absorber 160 is made of a material having an initial permeability of less than 10% (e.g., 0%). The saturable absorber 160 is composed of, for example, a plurality of carbon nanowalls. The carbon nanowall is a stack of a plurality of graphenes. The thickness of the carbon nanowall (the length in the Z-axis direction in FIG. 3B) is, for example, 1 nm or more and 100 nm or less. Moreover, the distance between adjacent carbon nanowalls (the distance in the Z-axis direction in FIG. 3B) is, for example, 1 nm or more and 10 μm or less.

The surrounding portion 162 surrounds the saturable absorber 160. That is, the saturable absorber 160 is embedded in the surrounding portion 162. The surrounding portion 162 is a resin having transparency and heat resistance to laser light with an intensity of 10 ¹³ W / cm ² or more. The surrounding portion 162 contains, for example, one or both of polyimide and poly (methyl methacrylate) (PMMA). Heat resistance can be improved by the surrounding part 162 containing a polyimide. In addition, when the surrounding portion 162 includes PMMA, the transmittance of the laser light can be improved. That is, when the surrounding portion 162 contains polyimide and PMMA, it is possible to improve heat resistance and transmittance. Further, by having the surrounding portion 162, the saturable absorber 160 can be formed into a flat plate shape.

  Returning to FIG. 2, the moving unit 136 includes a holding unit 136a, a shaft 136b, and a driving unit 136c. The holder 136 a holds the saturable absorber 134. The holding portion 136a is formed of, for example, two frames, and the saturable absorbing portion 134 is sandwiched between the frames. The shaft 136b is connected to the holding portion 136a. The drive unit 136c is configured by an actuator. The drive unit 136c moves the saturable absorber 134 through the shaft 136b and the holding unit 136a in accordance with a control command from the control unit 150 described later.

  FIG. 4 is a diagram for explaining the moving direction of the saturable absorber 134 by the moving unit 136. As shown in FIG. In FIG. 4, the trajectory of the light path of the laser light LA is indicated by a broken arrow.

  The drive unit 136c is configured to move the irradiation surface 134a (for example, Y) in a first direction (Y-axis direction in FIG. 4) orthogonal to the extension direction (X-axis direction in FIG. 4) of the light path of the laser light LA. Axially), the saturable absorber 134 is moved. In addition, the drive unit 136c performs saturable absorption so that the irradiation surface 134a moves in a second direction (Z-axis direction in FIG. 4) orthogonal to the extending direction of the light path of the laser light LA and the first direction. The unit 134 is moved. Specifically, the drive unit 136c first holds the saturable absorber 134 such that the light path is positioned at the end of the irradiation surface 134a of the saturable absorber 134 (initial position). Subsequently, the drive unit 136c moves the saturable absorber 134 by a predetermined distance Sa toward the negative side in the Y-axis direction. The distance Sa is, for example, a distance slightly shorter than the width of the saturable absorber 134 in the Y-axis direction. Subsequently, the drive unit 136c moves the saturable absorber 134 a predetermined distance Sb toward the positive side in the Z-axis direction. The distance Sb is, for example, a distance one or more and two or less times the beam diameter of the laser light LA. Then, the moving unit 136 moves the saturable absorbing unit 134 by a predetermined distance Sa toward the positive side in the Y-axis direction. Thus, the irradiation surface 134a of the saturable absorber 134 is scanned in the first direction and the second direction with respect to the fixed optical path of the laser light LA.

  Referring back to FIG. 1, the laser power meter 140 is disposed on the back side of the irradiation surface 134 a of the saturable absorber 134. The laser power meter 140 measures the laser beam transmitted through the saturable absorber 134 (hereinafter, referred to as “transmitted light”). The laser power meter 140 also measures the laser beam LB split by the beam splitter 120. The measurement result of the transmitted light and the measurement result of the laser beam LB by the laser power meter 140 are output to the control unit 150. A power meter different from the laser power meter 140 for measuring the laser light LA through the saturable absorber 134 may be provided, and the power meter may measure the laser light LB.

  The control unit 150 is configured of a semiconductor integrated circuit including a CPU (central processing unit). The control unit 150 reads a program, parameters, and the like for operating the CPU itself from the ROM. The control unit 150 manages and controls the entire transmitted light measurement device 100 in cooperation with a RAM as a work area and other electronic circuits.

  In the present embodiment, the control unit 150 causes the laser oscillator 110 to oscillate laser light at a predetermined oscillation interval for each pulse.

  Further, the control unit 150 moves the saturable absorber 134 by a predetermined separation distance in the first direction or the second direction when a predetermined passing time has elapsed since the laser oscillator 110 oscillated one pulse of the laser light. Control the moving unit 136 (driving unit 136c). That is, the control unit 150 controls the moving unit 136 such that the saturable absorber 134 intermittently moves. The passing time is the time until the laser beam oscillated from the laser oscillator 110 passes through the saturable absorber 134. Further, the separation distance is determined by the beam diameter (for example, about 10 μm) of the laser light LA (the laser light LA collected by the condensing lens 132) irradiated to the irradiation surface 134a of the saturable absorber 134. The separation distance is a distance at which the irradiation points of the laser light LA do not overlap before and after movement by the movement unit 136.

  Further, the control unit 150 calculates the transmittance of the saturable absorber 134 based on the measurement result of the transmitted light and the measurement result of the laser light LB (reference light) by the laser power meter 140.

  As described above, since the optical device 130 of the present embodiment and the transmitted light measurement device 100 including the optical device 130 include the moving unit 136, the irradiation surface 134a of the saturable absorbing unit 134 is opposed to the optical path of the laser light LA. It can be moved. Also, the moving unit 136 moves the saturable absorbing unit 134 by the separation distance each time the laser light of one pulse is oscillated. Thereby, the part irradiated with laser beam LA in the irradiation surface 134a can always be changed. That is, it is possible to irradiate the laser light LA to a non-destructed part on the irradiation surface 134a. In other words, it is possible to avoid the situation where the laser light LA is irradiated to a portion which has already been destroyed in the irradiation surface 134a. Therefore, the transmitted light transmitted through the saturable absorber 134 can reach the laser power meter 140 for a plurality of pulses. Thereby, in the laser power meter 140, transmitted light can be integrated, and it becomes possible to measure transmitted light appropriately.

  Therefore, the saturable absorber 134 can be evaluated, and the saturable absorber 134 having a desired transmittance can be manufactured. For example, when the saturable absorber 160 is a carbon nanowall, the height and density of the carbon nanowall can be adjusted to manufacture the saturable absorber 134 having a desired transmittance.

  In addition, as described above, the moving unit 136 moves the saturable absorber 134 two-dimensionally in the first direction and the second direction. That is, the moving unit 136 moves the saturable absorbing unit 134 so that the laser light LA is evenly irradiated over the entire irradiation surface 134 a of the saturable absorbing unit 134. As a result, the saturable absorber 134 necessary for earning the integration time that can be measured by the laser power meter 140 as compared with a configuration in which the mover 136 moves the saturable absorber 134 one-dimensionally in only one direction. The size of can be reduced. Therefore, the error of the distance from the laser oscillator 110 to the irradiation surface 134a can be reduced, and the transmitted light can be measured with high accuracy.

(Modification)
In the above embodiment, the optical path of the laser light LA is fixed, and the moving unit 136 moves the saturable absorber 134 as an example. However, as long as the optical path of the laser light LA and the irradiation surface 134 a of the saturable absorber 134 can move relative to each other, the optical path may be moved.

  FIG. 5 is a diagram for explaining an optical device 230 according to a modification. In FIG. 5, the laser beam LA is indicated by a solid arrow, and the flow of signals is indicated by a dashed arrow. The same reference numerals are given to constituent elements substantially the same as the optical device 130, and the description will be omitted.

  As shown in FIG. 5, the optical device 230 includes a moving unit 240 and a saturable absorber 134. In the optical device 230, the saturable absorber 134 is fixed by a fixing unit (not shown).

  The moving unit 240 includes a mirror 242, a mirror driving unit 244, and an Fθ lens 246. The mirror 242 guides the laser light LA to the Fθ lens 246.

  The mirror drive unit 244 includes a shaft 244a and a drive unit 244b. The shaft 244 a is connected to the mirror 242. The drive unit 244b is configured by an actuator. The drive unit 244b moves the mirror 242 via the shaft 244a in accordance with a control command from the control unit 150. Specifically, the drive unit 244 b moves the mirror 242 to move the optical path of the laser light LA guided to the Fθ lens 246. The driving unit 244b moves the mirror 242 to move the optical path of the laser light LA in the first direction and the second direction. For example, the drive unit 244 b moves the optical path of the laser beam LA guided to the Fθ lens 246 from the optical path KA to the optical path KB.

  The Fθ lens 246 is a lens capable of equalizing the output angle regardless of the incident angle. Therefore, only by moving the mirror 242 and moving the light path of the laser beam LA incident on the Fθ lens 246, the driving unit 244b vertically moves the laser light LA to different positions of the saturable absorber 134 (irradiated surface 134a). It is possible to

  As described above, in the optical device 230 according to the modification, the moving unit 240 can move the optical path of the laser light LA with respect to the irradiation surface 134 a of the saturable absorber 134 fixed. Further, the moving unit 240 moves the optical path of the laser light LA by the separation distance each time the laser light of one pulse is oscillated. Thereby, the part irradiated with laser beam LA in the irradiation surface 134a can always be changed. Therefore, the transmitted light transmitted through the saturable absorber 134 can reach the laser power meter 140 for a plurality of pulses. Thereby, the transmitted light can be integrated in the laser power meter 140, and the transmitted light can be measured.

  As mentioned above, although one embodiment was described, referring to an accompanying drawing, it goes without saying that this indication is not limited to the above-mentioned embodiment. It is apparent that those skilled in the art can conceive of various modifications and alterations within the scope of the claims, and it is understood that they are naturally within the technical scope of the present disclosure. Be done.

  For example, in the embodiment and the modification described above, the case where the first direction is a direction orthogonal to the extending direction of the light path of the laser light LA has been described as an example. However, the first direction may be a direction that intersects the extending direction of the light path of the laser light LA. Similarly, the second direction may be a direction intersecting the extending direction of the light path of the laser light LA and the first direction.

  Further, in the above embodiment and the modification, the moving parts 136 and 240 move the two-dimensional relative movement of the irradiation surface 134 a of the saturable absorbing part 134 and the optical path of the laser light LA as an example. . However, the moving units 136 and 240 may relatively move the irradiation surface 134 a of the saturable absorber 134 and the light path of the laser light LA in a one-dimensional manner.

  In the above embodiment, the moving unit 136 intermittently moves the saturable absorbing unit 134 as an example. However, the moving unit 136 may move the saturable absorber 134 continuously. Similarly, the moving unit 240 may move the optical path of the laser light LA continuously.

  In the above embodiment, the moving unit 136 moves the saturable absorbing unit 134 every time the laser light oscillates one pulse. However, the moving unit 136 may move the saturable absorbing unit 134 each time a plurality of pulses (for example, double pulses) of laser light are oscillated.

  Moreover, in the said embodiment, the case where the saturable absorber 160 was a carbon nanowall was mentioned as the example, and was demonstrated. However, the saturable absorber 160 may be a carbon nanotube. When the saturable absorber 160 is a carbon nanotube, it is preferable to embed in the resin a dispersant that suppresses the aggregation of carbon nanotubes together with the carbon nanotube. In addition, the saturable absorber 160 may be a sheet made of molybdenum disulfide. The saturable absorber 160 may also be a semiconductor.

  The present disclosure can be used for a transmitted light measurement device that measures transmitted light transmitted through a saturable absorber, and an optical device.

DESCRIPTION OF SYMBOLS 110 laser oscillator 130 optical apparatus 134 saturable absorption part 134a irradiation surface 136 moving part 140 laser power meter 160 saturable absorber 230 optical apparatus 240 moving part

Claims (4)

A laser oscillator that oscillates a laser beam having an intensity of 10 ¹³ W / cm ² or more;
A saturable absorber including a saturable absorber and having an irradiated surface positioned on the optical path of laser light oscillated from the laser oscillator;
A moving unit for relatively moving the irradiation surface and the light path;
A laser power meter for measuring a laser beam transmitted through the saturable absorber;
Transmitted light measuring device comprising:   The moving unit includes the irradiation surface and the optical path in a first direction intersecting the extending direction of the optical path, and in a second direction intersecting the extending direction of the optical path and the first direction. The transmitted light measurement device according to claim 1, wherein the relative movement is performed. The saturable absorber is one or both of carbon nanowalls and carbon nanotubes,
The transmitted light measuring device according to claim 1 or 2, wherein the saturable absorber includes one or both resins of polyimide and poly (methyl methacrylate), and the saturable absorber disposed in the resin. A saturable absorber having an irradiation surface including a saturable absorber and positioned on the optical path of a laser beam having an intensity of 10 ¹³ W / cm ² or more;
A moving unit for relatively moving the irradiation surface and the light path;
An optical device comprising:

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