JP2009252824A - Laser pulse compression device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser pulse compression device compensating phase dispersion even if change occurs in dispersion of an amplified output laser pulse with a change of the number of pulse reciprocating times and that of a pulse repetition frequency, and obtaining optimum pulse width. <P>SOLUTION: The laser pulse compression device includes a first diffraction grating reflecting laser pulse light, a second diffraction grating receiving incident diffraction light reflected by the first diffraction grating, a prism which repetitively reflects diffraction light reflected by the second diffraction grating and makes it incident on the second diffraction grating, and a total reflection mirror outputting repetitive reflection light which is made incident on the second diffraction grating to an external part through the first diffraction grating as repetitive laser pulse light. The device further includes a sliding mechanism part moving in parallel to an optical axis of incident diffraction light reflected on the first diffraction grating, a movable stand fixing the second diffraction grating to the sliding mechanism part, a cabinet storing them, and an adjusting means varying a distance between the first diffraction grating and the second diffraction grating from outside the cabinet. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a laser pulse compression apparatus mounted on a short pulse laser apparatus using a diffraction grating.

  Chirped pulse amplification (CPA) is known as a method for generating (ultra-short) laser pulses having a high peak output and a pulse width on the order of femtoseconds (fs) to picoseconds (ps). For example, in FIG. 2 of Japanese Patent Application Laid-Open No. 2004-48020 (see Patent Document 1), the output of the injection source 1 containing the transmitter 5, the expander 15, and the amplifier 25 is connected to an amplifier 55 via an optical frequency converter. A CPA system of a hybrid device equipped with a high energy bulk amplifier 2 containing a compressor 65 is disclosed. In this CPA, an optical pulse having a wide pulse width in which the wavelength of the chirped optical pulse changes with time is generated, amplified, and then compressed by a pulse compressor to obtain a short optical pulse with a high peak output. .

  Further, in FIG. 1 of Japanese Patent Laid-Open No. 9-211154 (see Patent Document 2), the laser pulse that has passed through the diffraction gratings 5-1, 5-2 is reflected by the total reflection mirror 7, and again, the diffraction grating 5- A laser pulse compression device that takes out a laser pulse via 1 and 5-2 is disclosed.

  FIG. 1 (see Patent Document 3) of Japanese Patent Application Laid-Open No. 2007-109962 includes diffraction grating pairs 1 and 3 and one diffraction grating 1 of diffraction grating pairs 1 and 3 including the normal line of diffraction grating 1 and diffraction. An incident means 2 for making incident a laser pulse having an incident surface perpendicular to the incident surface of the grating 1 and a predetermined angle, and the laser pulse passing through the diffraction grating pairs 1 and 3 are reflected to reflect the diffraction grating pair. A laser pulse compression device is disclosed that includes a reflecting mirror 4 that is arranged so as to be incident again in 1 and 3.

Japanese Patent Laid-Open No. 2004-48020 (FIG. 2)

Japanese Patent Application Laid-Open No. 9-2111504 (FIG. 1) “Paragraph 0032”

JP 2007-109962 (FIG. 1)

  However, the one described in Patent Document 1 has a problem in using a fiber compressor because the pulse compressor has optical damage and nonlinearity due to high peak output, and a bulk diffraction element compressor is required. There was a problem of being.

  Patent Document 2 discloses that the laser pulse 2-3 reflected by the total reflection mirror 7 passes through the diffraction grating pair 5 having negative dispersion characteristics again, so that the pulse can be obtained even if the diffraction grating interval is short. Although compression is possible and suitable for downsizing of the apparatus, there is no description about adjusting the distance of the diffraction grating to compensate for phase dispersion and configuring an optimum optical path length.

  The one described in Patent Document 3 can increase the diffraction efficiency of the diffraction grating by changing the incident angle in the plane perpendicular to the grating including the normal line of the diffraction grating of the laser pulse incident on the diffraction grating. Although it is possible to increase the transmittance of the compression device, there is no description about adjusting the distance between the diffraction gratings to compensate for phase dispersion and configuring an optimum optical path length.

  The present invention has been made to solve the above-described problems, and compensates for phase dispersion even when a change in dispersion of the amplified output laser pulse due to a change in the number of times of pulse reciprocation and pulse repetition frequency occurs. An object of the present invention is to provide a laser pulse compression device capable of obtaining a pulse width.

  According to a first aspect of the present invention, there is provided a laser pulse compression device including a first diffraction grating that causes laser pulse light incident from an input window to be incident through a first total reflection mirror and reflected as diffraction light, and the first diffraction grating. A second diffraction grating having an incident / reflecting surface arranged in parallel with a distance from the incident / reflecting surface of the first diffractive grating for receiving the reflected incident diffracted light, and the diffracted light reflected by the second diffractive grating. And a repetitive laser pulse that is repeatedly reflected from the output window directly through the first diffraction grating. A second total reflection mirror that outputs light to the outside, a slide mechanism portion provided with a slide region that is movable in parallel with the optical axis of the incident diffraction light reflected by the first diffraction grating, and the slide mechanism The second diffraction grating is fixed to the slide area of the section A movable base that moves along the slide region, the first total reflection mirror, the second total reflection mirror, the first diffraction grating, the movable base to which the second diffraction grating is fixed, and the slide mechanism section A housing having an outer wall that forms a sealed space for housing the housing, and an adjustment rod that is provided outside the housing and passes through a through-hole provided in the outer wall of the housing and is connected to the movable base. And adjusting means for varying the distance between the first diffraction grating and the second diffraction grating.

  According to a second aspect of the present invention, there is provided a laser pulse compression device including a first diffraction grating that causes laser pulse light incident from an input window to be incident through a first total reflection mirror and reflected as diffracted light, and the first diffraction grating. A second diffraction grating having an incident / reflecting surface arranged in parallel with a distance from the incident / reflecting surface of the first diffractive grating for receiving the reflected incident diffracted light, and the diffracted light reflected by the second diffractive grating. And a repetitive laser pulse that is repeatedly reflected from the output window directly through the first diffraction grating. A second total reflection mirror that outputs light to the outside, a slide mechanism portion provided with a slide region that is movable in parallel with the optical axis of the incident diffraction light reflected by the first diffraction grating, and the slide mechanism The first diffraction grating is fixed to the slide area of the part A movable base that moves along the slide region, the first total reflection mirror, the second total reflection mirror, the first diffraction grating, the movable base to which the first diffraction grating is fixed, and the slide mechanism section A housing having an outer wall that forms a sealed space for housing the housing, and an adjustment rod that is provided outside the housing and passes through a through-hole provided in the outer wall of the housing and is connected to the movable base. And adjusting means for varying the distance between the first diffraction grating and the second diffraction grating.

  According to a third aspect of the present invention, there is provided the laser pulse compression device according to the first or second aspect, wherein the adjusting means includes a position control circuit section for sending a pulse signal for moving the adjusting rod based on an input signal.

  In the laser pulse compression device according to claim 4, the position control circuit unit includes a memory circuit unit and a CPU, and the count number of the pulse signal is stored in a memory element of the memory circuit unit. The display signal for displaying distance information between the first diffraction grating and the second diffraction grating is sent to a display unit installed outside the housing.

  According to the laser pulse compression device of the present invention, even when a change in dispersion caused by a change in the number of reciprocating pulses occurs in a regenerative amplifier or the like of a short pulse laser device, the short pulse laser device is optimally compensated for the dispersion. There is an effect that the interval of the diffraction grating can be adjusted.

  Further, since the distance (interval) between the first diffraction grating and the second diffraction grating can be adjusted without opening the housing of the laser pulse compression device, the cleanliness in the housing can be maintained.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be described below with reference to FIG. FIG. 1 is a configuration diagram of a laser pulse compression apparatus according to the first embodiment. In FIG. 1, 1 is an input window (incident window) for receiving laser pulse light from a laser pulse light source, 2 is a first total reflection mirror for reflecting laser pulse light incident from the input window 1, and 3 is first total reflection. A first diffractive grating fixedly arranged to receive laser light reflected by the mirror 2 and irradiate reflected light as incident diffracted light, 4 is a movable second diffractive grating arranged in parallel with the first diffractive grating 3, 5 is a prism that reflects the laser pulse light that has passed through the first diffraction grating 3 and the second diffraction grating 4 so as to increase its height (perpendicular to the paper surface), and 6 is a laser pulse that is reflected back by the prism 5. A second total reflection mirror that allows light to enter through the second diffraction grating 4 and the first diffraction grating 3, and an output window (outgoing) that emits laser pulse light reflected by the second total reflection mirror 6 to the outside. Window).

  8 is a movable table (movable part) for moving the second diffraction grating 4, and 9 is a guide for sliding the movable table 8 to change the parallel distance between the second diffraction grating 4 and the first diffraction grating 3. Rail (sliding mechanism) 10 is a holder for fixing the second diffraction grating 4 and the movable base 8, 11 is a first total reflection mirror 2, a second total reflection mirror 6, a first diffraction grating 3, a second A housing for storing the diffraction grating 4 and the prism 5, etc., 12 is connected to the movable base 8 with an adjusting rod extending from the outer wall of the housing 11 to the inside of the housing 11, and the movable base 8 is slid to the second time. An adjusting means using a micrometer or the like for moving the diffraction grating, 12a is a distance display section (display section) of the adjusting means 12, and 12b is an adjusting means 12 for sliding the movable base 8 by rotating the adjusting rod. It is a knob part. The adjusting means 12 is installed outside the housing 11.

  Next, the operation will be described. Laser pulse light incident from the input window 1 is incident on the first total reflection mirror 2, and the reflected light is incident on the first diffraction grating 3. The first diffraction grating 3 is provided with a grating on an aluminum vapor deposition film or the like on a flat plate and reflects laser pulse light incident between the gratings as diffraction light. The diffracted laser pulse light has an incident surface parallel to the first diffractive grating 3 disposed at a fixed distance, and is incident on the second diffractive grating 4 having the same configuration as the first diffractive grating 3. This reflected light is incident on the prism 5 (indicated by solid arrows). Next, the laser pulse light repeatedly reflected by the prism 5 returns via the second diffraction grating 4 and the first diffraction grating 3, but the optical path propagating through the return path so as not to be blocked by the first total reflection mirror 2. The light is changed and directly incident on the second total reflection mirror 6, and the reflected light is taken out from the output window 2 (indicated by a broken line arrow). In this way, pulse compression is performed by reciprocating the laser pulse light.

  In order to be able to change the distance (interval) between the first diffraction grating 3 and the second diffraction grating 4 in which the entrance and reflection surfaces are arranged in parallel to each other, the second diffraction grating 4 is used as the first diffraction grating. 3 is fixed to a movable base 8 via a holder 10 on a rail (sliding mechanism portion) 9 that is movable while being parallel to 3. The movable table 8 is connected to an adjustment rod extending from the micrometer 12 and is configured to check the amount of movement of the second diffraction grating 4 by a distance display unit (display unit) 12 a of the micrometer 12. The movement amount of the distance is adjusted by the knob portion 12b of the micrometer 12.

  Since the distance adjustment of the second diffraction grating 4 is determined by the amount of movement of the adjustment bar, the adjustment bar may be combined with coarse adjustment by the knob portion 12b and fine adjustment by the micrometer 12 body.

  In the first embodiment, the second diffractive grating 4 side is moved by using the movable base 8, but the incident and outgoing surfaces of the first diffractive grating 3 and the second diffractive grating 4 are parallel to each other. The first diffraction grating 3 side may be moved by keeping the first diffraction grating 3 so as to be relatively movable while both the first diffraction grating 3 and the second diffraction grating 4 are kept parallel. Anyway.

  FIG. 2 is a block diagram of a short pulse laser device equipped with the laser pulse compression device according to the first embodiment of the present invention. In FIG. 2, 20 is a fiber laser light source with chirped pulse output, 21 is a pulse stretcher, 22 is a regenerative amplifier that amplifies the pulse width of a relatively short output ultrashort pulse, and 23 is amplified by the regenerative amplifier 22. This is a laser pulse compression device that converts laser light into long and short pulses with a short time width.

  Next, the operation of the short pulse laser device will be described. In FIG. 2, in the chirp pulse amplification method, a regenerative amplifier 22 is used as the amplification method. The regenerative amplifier 22 is a kind of laser pulse amplifier, and includes a resonator composed of two total reflection mirrors and a laser gain medium, and an electro-optic element that controls the incident / exit timing of laser amplified light. The laser pulse from the oscillator incident on the resonator is confined in the resonator and reciprocates in the resonator. While the laser pulse reciprocates in the resonator, amplification is gradually performed, and the laser pulse amplified by an appropriate number of reciprocations is emitted to the laser pulse compression device 23. The output power and phase dispersion characteristics of the amplified laser pulse depend on the number of reciprocations in the resonator and the pulse repetition frequency. The amplified laser pulse is incident on the laser pulse compression device 23, and the pulse width is compressed to become a high peak pulse. The average output and pulse repetition frequency of the ultrashort laser pulse can be changed by changing the environment or changing the specifications of the apparatus.

  The output of the regenerative amplifier 22 can be changed by appropriately setting the number of reciprocations in the regenerative amplifier 22 as described above. When the number of reciprocations is changed, the dispersion of the output pulse of the regenerative amplifier 22 also changes accordingly. However, the first diffraction grating 3 and the second diffraction grating 3 installed in the laser pulse compression device for obtaining the optimum pulse time width at the set number of reciprocations It is possible to measure the distance (interval) with the diffraction grating 4 in advance, set a desired diffraction grating interval, and adjust it with the adjusting means 12.

  Next, a method of setting a desired diffraction grating interval in place of the adjusting unit 12 shown in FIG. 1 and automatically adjusting by the adjusting unit will be further described with reference to FIG. 120 is an automatic adjustment means, 120a is a display unit for displaying distance information between the first diffraction grating 3 and the second diffraction grating 4, 120b is a servo motor driven by a pulse signal, and 120c is a servo. It is a rotating shaft of the motor 120b.

  120d is equipped with a CPU, a storage circuit including a storage element, and the like, and based on a control input signal from the outside, a position for sending the forward / reverse rotation amount or movement amount of the rotating shaft 120c of the servo motor 120b to the servo motor 120b as a pulse count signal It is a control circuit unit. Further, the pulse number signal is stored in the storage element of the position control circuit 120d, and a CPU that incorporates a position display signal for displaying the distance between the first diffraction grating 3 and the second diffraction grating 4 in the position control circuit 120d. To send out.

  From the above, even when dispersion changes due to changes in the number of reciprocating pulses of the short pulse laser device, the diffraction grating interval can be adjusted by the laser pulse compression device so as to optimally compensate for the dispersion.

  Further, since the distance (interval) between the first diffraction grating 3 and the second diffraction grating 4 can be adjusted without opening the casing 11 of the laser pulse compression device, the cleanliness in the casing 11 can be maintained. .

It is a block diagram of the laser pulse compression apparatus by Embodiment 1 of this invention. It is a block block diagram of the short pulse laser apparatus carrying the laser pulse compression apparatus by Embodiment 1 of this invention.

Explanation of symbols

1..Input window 2..First total reflection mirror 3..First diffraction grating 4..Second diffraction grating 5..Prism 6..Second total reflection mirror 7..Output window 8..Movable Stand (moving part)
9 .. Slide mechanism part (rail) 10 .. Holder 11 .. Housing 12 .. Adjustment means 12 a .. Display part (distance display part) 12 b .. Knob part 20 .. Laser light source (fiber laser light source) 21.・ Pulse stretcher 22 ・ ・ Regenerative amplifier 23 ・ ・ Laser pulse compressor 120 ・ ・ Adjustment means 120a ・ ・ Display (distance display)
120b ... Servo motor 120c ... Rotary shaft (shaft)
120d..Position control circuit section

Claims (4)

A first diffraction grating that makes laser pulse light incident from the input window incident through the first total reflection mirror and reflects it as diffraction light, and the first diffraction light that receives the incident diffraction light reflected by the first diffraction grating. A second diffraction grating having an incident / reflecting surface arranged in parallel and spaced apart from the incident / reflecting surface of the first diffraction grating; and the reflected light reflected by the second diffraction grating is re-routed and repetitively reflected to change the first diffraction grating. A prism that is incident on the second diffraction grating, and a second total reflection mirror that outputs the repetitively reflected light incident on the second diffraction grating to the outside as repetitive laser pulse light directly from the output window via the first diffraction grating A slide mechanism part provided with a slide region that can be translated with respect to the optical axis of the incident diffraction light reflected by the first diffraction grating, and the second diffraction in the slide region of the slide mechanism part A movable base that moves along the slide area while fixing the lattice. The first total reflection mirror, the second total reflection mirror, the first diffraction grating, the movable base to which the second diffraction grating is fixed, and an outer wall that forms a sealed space for housing the slide mechanism. A housing and an adjustment rod provided outside the housing and penetrating through a through hole provided in the outer wall of the housing and coupled to the movable base are moved, and the first diffraction grating and the first diffraction grating are moved. A laser pulse compression device comprising adjusting means for varying the distance from the two diffraction gratings. A first diffraction grating that makes laser pulse light incident from the input window incident through the first total reflection mirror and reflects it as diffraction light, and the first diffraction light that receives the incident diffraction light reflected by the first diffraction grating. A second diffraction grating having an incident / reflecting surface arranged in parallel and spaced apart from the incident / reflecting surface of the first diffraction grating; and the reflected light reflected by the second diffraction grating is re-routed and repetitively reflected to change the first diffraction grating. A prism that is incident on the second diffraction grating, and a second total reflection mirror that outputs the repetitively reflected light incident on the second diffraction grating to the outside as repetitive laser pulse light directly from the output window via the first diffraction grating A slide mechanism portion provided with a slide region movable in parallel with the optical axis of the incident diffraction light reflected by the first diffraction grating, and the first diffraction in the slide region of the slide mechanism portion A movable base that moves along the slide area while fixing the lattice. The first total reflection mirror, the second total reflection mirror, the first diffraction grating, the movable base to which the first diffraction grating is fixed, and an outer wall that forms a sealed space for housing the slide mechanism portion. A housing and an adjustment rod provided outside the housing and penetrating through a through hole provided in the outer wall of the housing and coupled to the movable base are moved, and the first diffraction grating and the first diffraction grating are moved. A laser pulse compression device comprising adjusting means for varying the distance from the two diffraction gratings. 3. The laser pulse compression device according to claim 1, wherein the adjustment unit includes a position control circuit unit that transmits a pulse signal for moving the adjustment rod based on an input signal. The position control circuit unit includes a memory circuit unit and a CPU, and the count number of the pulse signal is stored in a memory element of the memory circuit unit. According to the count information, the CPU detects the first diffraction grating and the second time. 4. The laser pulse compression device according to claim 3, wherein a display signal for displaying distance information with respect to the diffraction grating is sent to a display unit installed outside the casing.

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