CN108767642A - The method for generating low repetition high energy pulse from mode-locked laser - Google Patents

The method for generating low repetition high energy pulse from mode-locked laser Download PDF

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Publication number
CN108767642A
CN108767642A CN201810191924.2A CN201810191924A CN108767642A CN 108767642 A CN108767642 A CN 108767642A CN 201810191924 A CN201810191924 A CN 201810191924A CN 108767642 A CN108767642 A CN 108767642A
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mode
laser
locked laser
pulse
transverse modes
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CN201810191924.2A
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CN108767642B (en
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谢国强
陈迎安
乔桢
钱列加
袁鹏
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Shanghai Jiaotong University
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Shanghai Jiaotong University
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
    • H01S3/1106—Mode locking
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/086—One or more reflectors having variable properties or positions for initial adjustment of the resonator

Abstract

A method of generating low repetition high energy pulse from mode-locked laser, in mode-locked laser, using more transverse mode phase lockings come periodic modulation mode locking pulse sequence, when the frequency interval of adjacent transverse mode is the M/N of intermode beat note, (M/N is positive rational number, M and N is positive integer and relatively prime), mode-locked laser repetition rate can become fundamental frequency, and (c/2L, c are the lighies velocity, L is that chamber is long) 1/N, to realize low-repetition-frequency, high pulse energy mode-locked laser output.It is long that the present invention does not increase chamber, so that it may which that realizes repetition rate is greatly reduced (1/N for falling to fundamental frequency), and to play the effect for generating high pulse energy from mode-locked laser, and above-mentioned N values can be adjusted as needed.

Description

The method for generating low repetition high energy pulse from mode-locked laser
Technical field
The invention belongs to technical field of ultrafast laser, especially a kind of to generate low repetition high energy pulse from mode-locked laser Method.
Background technology
The ultrashort pulse duration that mode-locked laser generates is short, and peak power is high, each field such as manufacturing industry, medicine all It has a wide range of applications.
The pulse recurrence frequency of mode-locked laser is an important parameter, in the certain feelings of mode-locked laser mean power Under condition, it determines the pulse energy of mode-locked laser.Usually, the repetition rate of laser pulse is long depending on chamber, such as The repetition rate of a length of 1.5 meters of the laser of chamber is 100 megahertzs, i.e., the laser pulse number of output per second is 108It is a.Therefore High pulse energy is realized in mode-locked laser, can be realized by reducing repetition rate.It is usual to reduce repetition rate It can only be realized by increasing chamber length, but this can have problem in actual laser：Make repetition rate from 100 megahertzs It is reduced to 1 megahertz, chamber length just needs to increase to 150 meters from 1.5 meters, and the volume of such solid state laser will become very huge Greatly, multiple optical elements is needed to carry out light path foldings to realize, but optical fiber laser can cause after using long optical fiber it is non- Linearly equal limitation.
Invention content
The present invention provides a kind of method generating low repetition high energy pulse from mode-locked laser.This method does not increase chamber It is long, so that it may which that realizes repetition rate is greatly reduced (1/N for falling to fundamental frequency), and high arteries and veins is generated from mode-locked laser to play The effect of energy is rushed, and above-mentioned N values can be adjusted as needed.
Technical solution of the invention is as follows：
A method of generate low repetition high energy pulse from mode-locked laser, what feature was to coexist in more transverse modes In mode-locked laser, by the phase locking of multiple transverse modes, and when the Gouy phase shifts of intracavitary are M π/N, the repetition of output laser pulse Frequency will become the 1/N of fundamental frequency c/2L, wherein M/N is positive rational number, and M and N are positive integer and relatively prime, and c is the light velocity, and L is chamber It is long.By adjusting laser mirror position, the size of N can be changed.
A method of it generating low repetition high energy pulse from mode-locked laser, specifically includes the following steps：
1) more transverse modes are excited to vibrate simultaneously：CCD is set in the output end of mode-locked laser, for solid state laser, is being swashed After light device light extraction, the position of concave mirror is finely tuned, increasing the pattern size of pump light and laser, exciting more transverse modes while shaking It swings；For optical fiber laser, using multimode fibre to excite more transverse modes while vibrate, while hot spot is observed by the CCD Figure, to judge to produce multiple transverse modes；
2) more transverse modes while mode locking：The output end of CCD is connected with the input terminal of oscillograph, then finely tunes the position of concave mirror It sets, pulse train is observed on the oscillograph, be to have been modulated when observing stable pulse train on oscillograph Pulse train；
3) size of N values is adjusted：Since the pulse train on oscillograph can reflect the size of N values, each hysteroscope is finely tuned Position, while the pulse train on observation oscilloscope, to obtain desired low repetition high energy pulse, the repetition rate of the pulse It is reduced to the 1/N of fundamental frequency.
In mode-locked laser in the case of the phase locking of each transverse mode, the expression formula of the optical electric field of mode locking pulse in time domain For：
Wherein, Am,nIt is the amplitude of each transverse mode, natural number q is longitudinal mode ordinal number, and natural number m and n are transverse mode ordinal number, Δ νL= C/2L is intermode beat note, Δ νTIt is transverse mode frequency interval, Δ νTWith Δ νLRatio be equal to intracavitary Gouy phase shifts and constant The ratio of π, Gouy phase shifts are determined and adjustable by cavity configuration.The first item of above-mentioned optical electric field represents what more transverse mode phase lockings generated Modulation function, Section 2 represent the fundamental frequency pulse train of longitudinal mode mode locking generation.When the phase locking and Δ ν of different transverse modesTWith Δ νLRatio when being M/N (M/N is positive rational number, and M and N are positive integer and relatively prime, and ratio can indicate a positive rational number), The least common multiple for the pulse period that the modulation function period of transverse mode phase locking and longitudinal mode mode locking generate is to export pulse Period, to expect in this week it is reciprocal obtain the repetition rate of output pulse, the repetition rate be fundamental frequency 1/N (with the value of M without It closes).
Beneficial effects of the present invention can be summarized as：
1) present invention realizes low-repetition-frequency, high pulse energy in mode-locked laser using the phase locking of more transverse modes Mode locking pulse output；
2) it is not necessarily to achieve that being greatly lowered for repetition rate by changing chamber length, maintains the compact of mode-locked laser Property.
Description of the drawings
Fig. 1 is the schematic diagram of the present invention.(a) traditional single transverse mode mode-locked laser：It is the chamber period to export the pulse period (T)；(b) it is low-repetition-frequency mode-locked laser of the present invention：Meet M by the Gouy phase shifts of more transverse mode phase lockings and intracavitary π/N (M/N is positive rational number, and M and N are positive integer and relatively prime, and ratio can indicate a positive rational number), exports the week of pulse Phase is NT, i.e., repetition rate becomes the 1/N of fundamental frequency.
Fig. 2 is that low repetition pulse generates principle.(a) pulse train of longitudinal mode mode locking；(b) strong caused by transverse mode phase locking Spend modulation function；(c) low repetition (repetition rate becomes the 1/N of fundamental frequency) pulse train that mode-locked laser generates.
Fig. 3 is a calculated examples for realizing low-repetition-frequency.(a) a length of 1.5 meters corresponding fundamental frequency pulse trains of chamber； (b) when intracavitary Gouy phase shifts are π/5, (repetition rate becomes base for the low repetition that more transverse mode phase locking mode-locked lasers generate The 1/5 of frequency) mode locking pulse.
Fig. 4 is low-repetition-frequency mode-locked laser embodiment of the present invention.
Specific implementation mode
By taking a length of 1.5 meters of the mode-locked laser of a chamber as an example, pulse train such as Fig. 3 (a) institutes of single transverse mode mode locking generation Show, fundamental frequency repetition rate is 100 megahertzs.If 10 transverse modes (00 mould, 01 mould ..., 09 mould) position it is identical when lock, when When intracavitary Gouy phase shifts are π/5, then repetition rate becomes 20 megahertzs, i.e. the 1/5 of fundamental frequency at this time, as shown in Fig. 3 (b).
We are further described in conjunction with experimental example.Referring to Fig. 4, Fig. 4 is low-repetition-frequency mode locking of the present invention Laser embodiments.
Fig. 4 (a) is the index path of mode-locked laser.Wherein LD is pumping source, L1And L2For two panels condenser lens, M1、M2With M3For three pieces concave mirror, SESAM is semiconductor saturable absorber, and OC is output coupling mirror.Realize the reduction of repetition rate, Concrete operations include the following steps：
1) more transverse modes are excited to vibrate simultaneously：CCD is set in the output of the output coupling mirror OC of mode-locked laser, for solid Laser, after laser light extraction, the position of fine tuning concave mirror M1, M2 or M3, to increase the pattern size of pump light and laser Ratio excites more transverse modes while vibrating；Hot spot figure is observed by the CCD simultaneously, to judge to produce multiple transverse modes；
2) more transverse modes while mode locking：The output end of CCD is connected with the input terminal of oscillograph, then finely tunes the position of concave mirror It sets, pulse train is observed on the oscillograph, be to have been modulated when observing stable pulse train on oscillograph Pulse train；
3) size of N values is adjusted：Since the pulse train on oscillograph can reflect the size of N values, each hysteroscope is finely tuned Position, while the pulse train on observation oscilloscope, to obtain desired low repetition high energy pulse, the repetition rate of the pulse It is reduced to the 1/N of fundamental frequency.
(b) the hot spot pattern that more transverse mode phase lockings obtain in mode-locked laser；(c) repetition rate obtained in experiment is The pulse train of fundamental frequency 1/5.It is a length of 1.39 meters of mode-locked laser (the fundamental frequency c/2L=107.6 of a chamber as shown in Fig. 4 (a) Megahertz), concave mirror M after the adjustment2And M3Afterwards, the transverse mode (00 mould, 02 mould and 04 mould) of three phase lockings shakes in the laser It swings, as shown in Fig. 4 (b).Hysteroscope after the adjustment, we have obtained the pulse train as shown in Fig. 4 (c), and the pulse period is 46.5 Nanosecond, repetition rate are 21.5 megahertzs, are equal to the 1/5 of fundamental frequency.At this time from N=5 known to repetition rate, and can be by calculating Know that the Gouy phase shifts of intracavitary are 13 π/5.
It should be noted that example above is only lifted more preferably to illustrate the present invention, not limit.The common skill of this field Art personnel should be appreciated that every technical solution to invention is modified or replaced equivalently, without departing from the technology of the present invention The spirit and scope of scheme should all cover in scope of the presently claimed invention.

Claims (3)

1. a kind of method generating low repetition high energy pulse from mode-locked laser, it is characterised in that in the lock that more transverse modes coexist In mode laser, by the phase locking of multiple transverse modes, and when the Gouy phase shifts of intracavitary are M π/N, the repetition frequency of output laser pulse Rate will become the 1/N of fundamental frequency c/2L, wherein M/N is positive rational number, and M and N are positive integer and relatively prime, and c is the light velocity, and L is chamber It is long.
2. a kind of method generating low repetition high energy pulse from mode-locked laser according to claim 1, feature It is by adjusting laser mirror position, to change the size of N.
3. a kind of method generating low repetition high energy pulse from mode-locked laser according to claim 1 or 2, special Sign is that this method includes the following steps：
1) more transverse modes are excited to vibrate simultaneously：CCD is set in the output end of mode-locked laser, for solid state laser, in laser After light extraction, the position of concave mirror is finely tuned, to increase the pattern size of pump light and laser, to excite more transverse modes while shake It swings；For optical fiber laser, using multimode fibre to excite more transverse modes while vibrate, while hot spot is observed by the CCD Figure, to judge to produce multiple transverse modes；
2) more transverse modes while mode locking：The output end of CCD is connected with the input terminal of oscillograph, finely tunes the same of the position of concave mirror When, pulse train is observed on oscillograph, is the arteries and veins modulated when observing stable pulse train on oscillograph Rush sequence；
3) size of N values is adjusted：Since the pulse train on oscillograph can reflect the size of N values, the position of each hysteroscope is finely tuned, Pulse train on observation oscilloscope simultaneously, can obtain desired low repetition high energy pulse, and repetition rate is reduced to fundamental frequency 1/N。
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112688155A (en) * 2020-12-25 2021-04-20 武汉奇致激光技术股份有限公司 Control method and control system for laser light intensity

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CN103036137A (en) * 2012-12-30 2013-04-10 山东大学 Method for generating subnanosecond mode-locked pulse laser with high stability and low repetition frequency
CN105261920A (en) * 2015-09-25 2016-01-20 厦门彼格科技有限公司 Low repetition frequency short pulse optical fiber amplifier based on special phase-shifting fiber Bragg grating control loop
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Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20110140009A1 (en) * 2009-12-14 2011-06-16 Massachusetts Institute Of Technology Efficient High-Harmonic-Generation-Based EUV Source Driven by Short Wavelength Light
US9837786B2 (en) * 2011-08-18 2017-12-05 University Of Pécs Short period undulator
CN103036137A (en) * 2012-12-30 2013-04-10 山东大学 Method for generating subnanosecond mode-locked pulse laser with high stability and low repetition frequency
CN105261920A (en) * 2015-09-25 2016-01-20 厦门彼格科技有限公司 Low repetition frequency short pulse optical fiber amplifier based on special phase-shifting fiber Bragg grating control loop

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