CN104184026A - Femto second laser with adjustable time domain pulse width, and method - Google Patents

Abstract

The invention relates to the technical field of a laser, and discloses a femto second laser with an adjustable time domain pulse width, and a method. The femto second laser employed by the method comprises a pumped laser, an optical coupler and a segment of photonic crystal fibers. The output end of the pumped laser is packaged with the segment of photonic crystal fibers through the optical coupler, and the segment of photonic crystal fibers are photonic crystal fibers which has a length of 1m and a range of 1fs to 1ps. According to the femto second laser provided by the invention, by use of the modulation instability of the photonic crystal fibers, the cross section structures of the photonic crystal fibers are designed, initial long pulses are split to form femto second pulses, and the femto second pulses whose time domain period is adjustable within a range of 1fs to 1ps are output. The structure is simple, the cost is low, and the operation is stable; and besides, the femto second laser has wide application prospects in such fields as ultrafast dynamics, microstructure material science, life science and the like.

Description

Femto-second laser and method that a kind of time domain pulsewidth is adjustable

Technical field

The present invention relates to laser technique field, relate in particular to a kind of adjustable femto-second laser and the method for time domain pulsewidth for generation of the femtosecond pulse of different time domain pulsewidth.

Background technology

Femtosecond pulse has extremely short pulse duration, high peak power and extremely wide spectral region, in various fields extensive application such as high field laser physics, ultrafast chemical kinetics, fine structure material science and life sciences.Within 1981, the first generation femto-second laser taking dye laser as representative is succeeded in developing, and makes the mankind successfully enter into the femtosecond epoch; But dye laser power output is low, it is unstable to turn round, maintenance management is complicated etc., shortcoming makes its range of application be subject to great restriction.Within 1991, the second generation femto-second laser taking titanium-doped sapphire solid state laser as representative is born, because it has the advantage such as stability of material, operating reliability, make dyestuff femto-second laser be on the brink of to eliminate, but femto-second solid laser system is made up of hundreds of mechanical component and optical elements that separate, must be placed on ultra-clean, shockproof, constant temperature special laboratory guarantee its normally work.Third generation table femto-second laser is taking fiber laser as representative, the special geometry of optical fiber makes it can obtain high single by gain, and there is fabulous radiating effect, but aspect the technical indicator such as single pulse energy, average output power, be difficult to compare favourably with solid state laser.

Summary of the invention

Technical problem to be solved by this invention: for the uncontrollable state of the art of current femto-second laser output pulse time domain pulsewidth, proposed a kind of time domain pulsewidth adjustable femto-second laser and method.This femto-second laser adopts common nanosecoud pulse laser or continuous light laser pumping photonic crystal fiber to be made, simple in structure, with low cost, the more important thing is, by the cross-sectional structure parameter of design photonic crystal fiber, this laser can the output time-domain cycle from 1fs to 1ps within the scope of adjustable femtosecond pulse flexibly.

For achieving the above object, the technical solution used in the present invention is:

The femto-second laser that time domain pulsewidth is adjustable, includes pump laser, optically coupled device, one section of photonic crystal fiber, and described pump laser output forms by coupling device and one section of photonic crystal fiber encapsulation; Described one section of photonic crystal fiber is the photonic crystal fiber of the long 1fs to 1ps of 1m.

The femto-second laser that time domain pulsewidth is adjustable, described pump laser is the long-pulse laser that output pulse width is exported initial long pulse more than hundred picosecond magnitudes.

The femto-second laser that time domain pulsewidth is adjustable,

Described optically coupled device is condenser lens optically coupled device, for the initial long pulse of pump laser output is washed off and assembled the fibre core that is coupled into photonic crystal fiber; Condenser lens optically coupled device is connected to form by condenser lens and optical fiber splicing device.

The femto-second laser that time domain pulsewidth is adjustable, described optical fiber splicing device is only son and heir's sonet card connection device.

The femto-second laser that time domain pulsewidth is adjustable, described optical fiber splicing device is several sonet card connection devices.

The femto-second laser that time domain pulsewidth is adjustable, described photonic crystal fiber is the corresponding femtosecond pulse photonic crystal fiber of output 1fs to 1ps; Comprise: the femtosecond pulse photonic crystal fiber of the femtosecond pulse photonic crystal fiber of 1fs to 5.5fs, the femtosecond pulse photonic crystal fiber of 5.5fs to 10.9fs, 10.9fs to 50.2fs, the femtosecond pulse photonic crystal fiber of 50.2fs to 101.9fs, the femtosecond pulse photonic crystal fiber of 101.9fs to 546.7fs, the femtosecond pulse photonic crystal fiber of 546.7fs to 1000.2fs;

(a) photonic crystals optical fiber structure of femtosecond pulse 1000.2fs is: bore dia and pitch of holes ratio d/ Λ=0.88, and pitch of holes is 4.0 μ m;

(b) photonic crystals optical fiber structure of femtosecond pulse 546.7fs is: corresponding aperture diameter and pitch of holes ratio d/ Λ=0.87, and pitch of holes is 3.0 μ m;

(c) photonic crystals optical fiber structure of femtosecond pulse 101.9fs is: corresponding aperture diameter and pitch of holes ratio d/ Λ=0.55, and pitch of holes is 3.0 μ m;

(d) photonic crystals optical fiber structure of femtosecond pulse 50.2fs is: corresponding aperture diameter and pitch of holes ratio d/ Λ=0.39, and pitch of holes is 3.0 μ m;

(e) photonic crystals optical fiber structure of femtosecond pulse 10.9fs is: corresponding aperture diameter and pitch of holes ratio d/ Λ=0.59, and pitch of holes is 4.0 μ m;

(f) photonic crystals optical fiber structure of femtosecond pulse 5.5fs is: corresponding aperture diameter and pitch of holes ratio d/ Λ=0.80, pitch of holes is 5.0 μ m.

The femto-second laser that time domain pulsewidth is adjustable, described pump laser or replace with based on adjusting the nanosecond laser of Q, or the laser of washing off for the initial long pulse of continuous wave output.

A kind of method of utilizing the adjustable femto-second laser of described time domain pulsewidth to produce femtosecond pulse, that the laser of the initial long pulse of continuous wave output is transmitted to photonic crystal fiber by optically coupled device, when transmission, the pulsing division by the modulational instability in photonic crystal fiber of initial long pulse, produces extremely narrow ultrashort femtosecond pulse; By changing the cross-sectional structure of photonic crystal fiber, can obtain from 1fs to 1ps within the scope of the femtosecond pulse in different time domain cycle;

Modulational instability in described optical fiber is in non linear system, and the interaction of nonlinear effect and effect of dispersion and cause the modulation to systematic steady state shows as continuous or quasi-continuous radiation modulation is split into ultrashort radiation;

Modulational instability in optical fiber occurs under anomalous dispersion condition, first ensures that the operation wavelength of pump laser is in the anomalous dispersion region of photonic crystal fiber, and the time domain cycle that modulation splits into ultrashort pulse is:

$T=\frac{2\mathrm{\π}}{{\mathrm{\Ω}}_{\max }}---\left(1\right)$

In formula, Ω _maxbe two maximum gain secondary lobes producing of modulational instability with respect to the angular frequency interval of pump light frequency, its expression formula is:

${\mathrm{\Ω}}_{\max }={\left(\frac{2\mathrm{\γ}{P}_0}{\left|{\mathrm{\β}}_2\right|}\right)}^{1/2}---\left(2\right)$

In formula, γ is the non linear coefficient of optical fiber, P ₀the peak power of incident pulse, β ₂it is 2nd order chromatic dispersion coefficient; As angular frequency interval Ω _maxwhile reaching tens Terahertzs, modulational instability can split into ultrashort femtosecond pulse by initial long pulse;

It is mainly the cross-sectional structure of design photonic crystal fiber, by diameter d and the pitch of holes Λ of design covering airport, the operation wavelength that makes pump laser is all the time under the prerequisite in photonic crystal fiber the anomalous dispersion region, changes the 2nd order chromatic dispersion factor beta of photonic crystal fiber in pumping wave strong point in very on a large scale ₂thereby, change angular frequency interval Ω _maxwith the cycle T of ultrashort pulse, obtain the femtosecond pulse of different time domain pulsewidth; Comprise:

1) design covering airport diameter and pitch of holes ratio, adopt self adaptation step Fourier method numerical solution laser in photonic crystal fiber, to transmit satisfied general non-linear Schrodinger equation, the long pulse that the complete works of pulsewidth of emulation half-shadow is 100ps, peak power 1400W transmits in the photonic crystal fiber of the long Different structural parameters of 1m, obtains the femtosecond pulse waveform under the different time domain cycle;

When pitch of holes Λ=3.0 of photonic crystal fiber, μ m is constant, reduce gradually the ratio d/ Λ of bore dia and pitch of holes, ratio d/ Λ by bore dia and pitch of holes is reduced to 0.35 gradually from 0.90, calculate abbe number and non linear coefficient under each cross-sectional structure parameter, substitution general non-linear Schrodinger equation numerical solution carries out emulation, obtain along with the reducing of the ratio d/ Λ of bore dia and pitch of holes, under different cycles, division formation is reduced to the femtosecond pulse of 3fs gradually from 1031.6fs;

Get corresponding airport diameter and pitch of holes ratio d/ Λ=0.87, obtain T=546.7fs femtosecond pulse waveform;

Get corresponding airport diameter and pitch of holes ratio d/ Λ=0.55, obtain T=101.9fs femtosecond pulse waveform;

Get corresponding airport diameter and pitch of holes ratio d/ Λ=0.39, obtain T=50.2fs femtosecond pulse waveform;

When pitch of holes is 4.0 μ m, get airport diameter and pitch of holes ratio d/ Λ=0.88 of corresponding photonic crystals optical fiber structure, obtain T=1000.2fs femtosecond pulse waveform; Get airport diameter and pitch of holes ratio d/ Λ=0.59 of corresponding photonic crystals optical fiber structure, obtain T=10.9fs femtosecond pulse waveform;

When pitch of holes is 5.0 μ m, get airport diameter and pitch of holes ratio d/ Λ=0.80 of corresponding photonic crystals optical fiber structure, obtain T=5.5fs femtosecond pulse waveform;

The ratio d/ Λ of its median pore diameter and pitch of holes generally should be less than 0.90, and the excessive airport that easily causes subsides; Meanwhile, the ratio d/ Λ of bore dia and pitch of holes should be greater than 0.35, can cause pumping wavelength 1064nm to fall into the normal dispersion district of optical fiber when being less than 0.35, and modulational instability can not occur;

2) design pitch of holes, constant when ratio d/ Λ=0.80 of airport diameter and pitch of holes, increases gradually pitch of holes Λ, the femtosecond pulse under the different time domain cycle of acquisition;

Adopt the pitch of holes of photonic crystal fiber is increased to 5 μ m gradually from 2 μ m, calculate abbe number and non linear coefficient under each cross-sectional structure parameter, substitution general non-linear Schrodinger equation carries out numerical simulation, and the cycle that can obtain is reduced to the femtosecond pulse of 1.1fs gradually from 140.5fs; Wherein pitch of holes should be less than 5 μ m, can cause pumping wavelength 1064nm to fall into the normal dispersion district of optical fiber when being greater than 5 μ m, and modulational instability can not occur.

Owing to adopting technical scheme as above, the present invention has following superiority:

The femto-second laser that a kind of pulsewidth is adjustable and method, this femto-second laser adopts common nanosecoud pulse laser or continuous light laser pumping photonic crystal fiber to be made, simple in structure, with low cost, the more important thing is, by the cross-sectional structure parameter of design photonic crystal fiber, this laser can the output time-domain cycle from 1fs to 1ps within the scope of adjustable femtosecond pulse flexibly.

The present invention is compared with common silica fiber, photonic crystal fiber claims again microstructured optical fibers, the airport of wavelength magnitude evenly arranged along the axial in its covering, thus the refractive index of covering can effectively be reduced, and light is limited in transmitting according to total internal reflection principle in fibre core.Can flexible due to size, shape and the arrangement mode of its airport, make people can in very large range change mould field distribution, dispersion characteristics and the nonlinear characteristic of photonic crystal fiber.Therefore, photonic crystal fiber becomes the preferred material of the technical indicators such as Recent study raising femtosecond pulse single pulse energy, average output power very soon.

The present invention is compared with existing femto-second laser, and its advantage comprises:

The first, this femto-second laser only needs a conventional long-pulse laser and the long photonic crystal fiber of one section of rice magnitude, based on adjust the nanosecond laser of Q or continuous light laser all can, cost reduces greatly;

The second, divide initial long pulse by the modulational instability of photonic crystal fiber, form femtosecond pulse, simple in structure, running is stable;

The 3rd, due to photonic crystal fiber adjustable dispersion characteristics flexibly, by the structural parameters of design photonic crystal fiber, this femto-second laser can be exported the femtosecond pulse of different time domain pulsewidth.In view of these advantages, this femto-second laser has broad application prospects in various fields such as ultrafast chemical kinetics, fine structure material science and life sciences.

Brief description of the drawings

Fig. 1 is the structural representation of the adjustable femto-second laser of time domain pulsewidth.

Fig. 2 is the inceptive impulse waveform of pump laser output, the complete works of pulsewidth 100ps of half-shadow oscillogram.

Fig. 3 a is that emulation obtains T=1000.2fs femtosecond pulse oscillogram; Fig. 3 b is that emulation obtains T=546.7fs femtosecond pulse oscillogram; Fig. 3 c is that emulation obtains T=101.9fs femtosecond pulse oscillogram; Fig. 3 d is that emulation obtains T=50.2fs femtosecond pulse oscillogram; Fig. 3 e is that emulation obtains T=10.9fs femtosecond pulse oscillogram; Fig. 3 f is that emulation obtains T=5.5fs femtosecond pulse oscillogram.

Fig. 4 is that pitch of holes Λ is set to 3.0 μ m, the femtosecond pulse periodogram obtaining under different bore dias and pitch of holes ratio d/ Λ.

Fig. 5 is that the ratio d/ Λ of bore dia and pitch of holes is set to 0.80, the femtosecond pulse periodogram obtaining under different pitchs of holes.

Embodiment

Below in conjunction with accompanying drawing and instantiation, the present invention is further illustrated, and accompanying drawing is only for example object, instead of limit the scope of application of the present invention.

Fig. 1 is the structural representation of the adjustable femto-second laser of a kind of time domain pulsewidth provided by the invention, include pump laser 1, optically coupled device 2, one section of photonic crystal fiber 3, described pump laser 1 output forms by coupling device 2 and one section of photonic crystal fiber 3 encapsulation; Described one section of photonic crystal fiber is the photonic crystal fiber of the long 1fs to 1ps of 1m.

As specific embodiment, pump laser selects the Nd:YAG that Teem Phononics company produces to adjust Q microchip laser, operation wavelength 1064nm, the inceptive impulse waveform of output as shown in Figure 2, the complete works of pulsewidth of half-shadow is 100ps, peak power in the time that repetition rate is 7.2kHz can reach 15kW, it is to be noted, also can select other operation wavelengths, the long-pulse laser of pulsewidth more than hundred picosecond magnitudes, or replace with the nanosecond laser based on adjusting Q, or the laser of washing off for the initial long pulse of continuous wave output.

Optically coupled device adopts the condenser lens optically coupled device of convergent lens mode that laser beam is coupled into photonic crystal fiber.For the initial long pulse of pump laser output is washed off and is assembled the fibre core that is coupled into photonic crystal fiber.Condenser lens optically coupled device is connected to form by condenser lens and optical fiber splicing device.

Described optical fiber splicing device is only son and heir's sonet card connection device, for quick only son and heir's optical fiber and pump laser are fixed together and obtain a kind of femtosecond pulse, when the another kind of femtosecond pulse of needs, another only son and heir's optical fiber of fast replacing, the other end of this optical fiber just obtains the femtosecond pulse of another kind of time domain pulsewidth.

Described optical fiber splicing device is several sonet card connection devices, and for quick several optical fiber and pump laser are fixed together, these several optical fiber other ends just can obtain several femtosecond pulses.

Described photonic crystal fiber is the corresponding femtosecond pulse photonic crystal fiber of output 1fs to 1ps, for avoiding interpulse walk-off effect, the length of photonic crystal fiber is elected 1m as, its cross-sectional structure parameter is designed definite by the femtosecond pulse cycle producing, concrete making adopts and froths and draw cone technology to realize.As adopted: Chen Zilun on 2010,47,020602:1-7. laser and optoelectronics progress periodical, Hou Jing, the post-processing technology of the photonic crystal fiber of Jiang Zongfu work realizes.Each photonic crystal fiber comprises: the femtosecond pulse photonic crystal fiber of the femtosecond pulse photonic crystal fiber of 1fs to 5.5fs, the femtosecond pulse photonic crystal fiber of 5.5fs to 10.9fs, 10.9fs to 50.2fs, the femtosecond pulse photonic crystal fiber of 50.2fs to 101.9fs, the femtosecond pulse photonic crystal fiber of 101.9fs to 546.7fs, the femtosecond pulse photonic crystal fiber of 546.7fs to 1000.2fs;

To adopt self adaptation step Fourier method numerical solution laser in photonic crystal fiber, to transmit satisfied general non-linear Schrodinger equation as shown in Figure 3, the long pulse that the complete works of pulsewidth of emulation half-shadow is 100ps, peak power 1400W transmits in the photonic crystal fiber of the long Different structural parameters of 1m, femtosecond pulse waveform under the several different cycles that obtain

(a) photonic crystals optical fiber structure of femtosecond pulse T=1000.2fs is: bore dia and pitch of holes ratio d/ Λ=0.88, and pitch of holes is 4.0 μ m;

(b) photonic crystals optical fiber structure of femtosecond pulse T=546.7fs is: corresponding aperture diameter and pitch of holes ratio d/ Λ=0.87, and pitch of holes is 3.0 μ m;

(c) photonic crystals optical fiber structure of femtosecond pulse T=101.9fs is: corresponding aperture diameter and pitch of holes ratio d/ Λ=0.55, and pitch of holes is 3.0 μ m;

(d) photonic crystals optical fiber structure of femtosecond pulse T=50.2fs is: corresponding aperture diameter and pitch of holes ratio d/ Λ=0.39, and pitch of holes is 3.0 μ m;

(e) photonic crystals optical fiber structure of femtosecond pulse T=10.9fs is: corresponding aperture diameter and pitch of holes ratio d/ Λ=0.59, and pitch of holes is 4.0 μ m;

(f) photonic crystals optical fiber structure of femtosecond pulse T=5.5fs is: corresponding aperture diameter and pitch of holes ratio d/ Λ=0.80, pitch of holes is 5.0 μ m.

A kind of method of utilizing the adjustable femto-second laser of described time domain pulsewidth to produce femtosecond pulse, that the laser of the initial long pulse of continuous wave output is transmitted to photonic crystal fiber by optically coupled device, when transmission, the pulsing division by the modulational instability in photonic crystal fiber of initial long pulse, produces extremely narrow ultrashort femtosecond pulse; By changing the cross-sectional structure of photonic crystal fiber, can obtain from 1fs to 1ps within the scope of the femtosecond pulse in different time domain cycle;

Modulational instability in described optical fiber is in non linear system, and the interaction of nonlinear effect and effect of dispersion and cause the modulation to systematic steady state shows as continuous or quasi-continuous radiation modulation is split into ultrashort radiation;

Modulational instability in optical fiber occurs under anomalous dispersion condition, first ensures that the operation wavelength of pump laser is in the anomalous dispersion region of photonic crystal fiber, and the time domain cycle that modulation splits into ultrashort pulse is:

$T=\frac{2\mathrm{\π}}{{\mathrm{\Ω}}_{\max }}---\left(1\right)$

In formula, Ω _maxbe two maximum gain secondary lobes producing of modulational instability with respect to the angular frequency interval of pump light frequency, its expression formula is:

${\mathrm{\Ω}}_{\max }={\left(\frac{2\mathrm{\γ}{P}_0}{\left|{\mathrm{\β}}_2\right|}\right)}^{1/2}---\left(2\right)$

In formula, γ is the non linear coefficient of optical fiber, P ₀the peak power of incident pulse, β ₂be 2nd order chromatic dispersion coefficient, calculate by empirical equation; As angular frequency interval Ω _maxwhile reaching tens Terahertzs, modulational instability can split into ultrashort femtosecond pulse by initial long pulse; Empirical equation adopts S.Kunimasa and K.Masanori.Empirical relations for simple design of photonic crystal fibers[J] .Opt.Express, 2005,13 (1): 267-274. document.

It is mainly the cross-sectional structure of design photonic crystal fiber, by diameter d and the pitch of holes Λ of design covering airport, the operation wavelength that makes pump laser is all the time under the prerequisite in photonic crystal fiber the anomalous dispersion region, changes the 2nd order chromatic dispersion factor beta of photonic crystal fiber in pumping wave strong point in very on a large scale ₂thereby, change angular frequency interval Ω _maxwith the cycle T of ultrashort pulse, obtain the femtosecond pulse of different time domain pulsewidth; Comprise:

1) design covering airport diameter and pitch of holes ratio, adopt self adaptation step Fourier method numerical solution laser in photonic crystal fiber, to transmit satisfied general non-linear Schrodinger equation, the long pulse that the complete works of pulsewidth of emulation half-shadow is 100ps, peak power 1400W transmits in the photonic crystal fiber of the long Different structural parameters of 1m, obtains the femtosecond pulse waveform under the different time domain cycle;

Fig. 4 keeps the pitch of holes Λ=3.0 μ m of photonic crystal fiber constant, reduces gradually the ratio d/ Λ of bore dia and pitch of holes, and the femtosecond pulse under the different cycles of acquisition, marks with little triangle in figure.Ratio d/ Λ by bore dia and pitch of holes is reduced to 0.35 gradually from 0.90, calculate abbe number and non linear coefficient under each cross-sectional structure parameter, substitution general non-linear Schrodinger equation numerical solution carries out emulation, as shown in Figure 3, can observe the femtosecond pulse waveform that division forms.

Get corresponding airport diameter and pitch of holes ratio d/ Λ=0.87, obtain T=546.7fs femtosecond pulse waveform;

Get corresponding airport diameter and pitch of holes ratio d/ Λ=0.55, obtain T=101.9fs femtosecond pulse waveform;

Get corresponding airport diameter and pitch of holes ratio d/ Λ=0.39, obtain T=50.2fs femtosecond pulse waveform;

When pitch of holes is 4.0 μ m, get airport diameter and pitch of holes ratio d/ Λ=0.88 of corresponding photonic crystals optical fiber structure, obtain T=1000.2fs femtosecond pulse waveform; Get airport diameter and pitch of holes ratio d/ Λ=0.59 of corresponding photonic crystals optical fiber structure, obtain T=10.9fs femtosecond pulse waveform;

When pitch of holes is 5.0 μ m, get airport diameter and pitch of holes ratio d/ Λ=0.80 of corresponding photonic crystals optical fiber structure, obtain T=5.5fs femtosecond pulse waveform;

Fig. 4 has drawn along with the reducing of the ratio d/ Λ of bore dia and pitch of holes, and what emulation obtained under different cycles that division forms is reduced to the femtosecond pulse of 3fs gradually from 1031.6fs.It should be noted that, the ratio d/ Λ of bore dia and pitch of holes is generally no more than 0.90, and the excessive airport that easily causes subsides; Meanwhile, the ratio d/ Λ of bore dia and pitch of holes can not be less than 0.35, and too small meeting causes pumping wavelength 1064nm to fall into the normal dispersion district of optical fiber and modulational instability can not occur.

2) design pitch of holes, Fig. 5 keeps ratio d/ Λ=0.80 of airport diameter and pitch of holes constant, increases gradually pitch of holes Λ, and the femtosecond pulse under the different time domain cycle of acquisition, marks with small circle in figure.

Adopt the pitch of holes of photonic crystal fiber is increased to 5 μ m gradually from 2 μ m, calculate abbe number and non linear coefficient under each cross-sectional structure parameter, substitution general non-linear Schrodinger equation carries out numerical simulation, and the cycle that can obtain is reduced to the femtosecond pulse of 1.1fs gradually from 140.5fs; It should be noted that, pitch of holes can not exceed 5 μ m, excessively can cause equally pumping wavelength 1064nm to fall into the normal dispersion district of optical fiber and modulational instability can not occur.

Claims (8)

1. the femto-second laser that time domain pulsewidth is adjustable, it is characterized in that: include pump laser (1), optically coupled device (2), one section of photonic crystal fiber (3), described pump laser (1) output forms by coupling device (2) and one section of photonic crystal fiber (3) encapsulation; Described one section of photonic crystal fiber (3) is the photonic crystal fiber of the long 1fs to 1ps of 1m.

2. the adjustable femto-second laser of a kind of time domain pulsewidth according to claim 1, is characterized in that: described pump laser (1) is the long-pulse laser that output pulse width is exported initial long pulse more than hundred picosecond magnitudes.

3. the adjustable femto-second laser of a kind of time domain pulsewidth according to claim 1, it is characterized in that: described optically coupled device (2) is condenser lens optically coupled device, for the initial long pulse of pump laser output is washed off and assembled the fibre core that is coupled into photonic crystal fiber; Condenser lens optically coupled device is connected to form by condenser lens and optical fiber splicing device.

4. the adjustable femto-second laser of a kind of time domain pulsewidth according to claim 3, is characterized in that: described optical fiber splicing device is only son and heir's sonet card connection device.

5. the adjustable femto-second laser of a kind of time domain pulsewidth according to claim 3, is characterized in that: described optical fiber splicing device is several sonet card connection devices.

6. the adjustable femto-second laser of a kind of time domain pulsewidth according to claim 1, is characterized in that: described photonic crystal fiber (3) is the corresponding femtosecond pulse photonic crystal fiber of output 1fs to 1ps; Comprise: the femtosecond pulse photonic crystal fiber of the femtosecond pulse photonic crystal fiber of 1fs to 5.5fs, the femtosecond pulse photonic crystal fiber of 5.5fs to 10.9fs, 10.9fs to 50.2fs, the femtosecond pulse photonic crystal fiber of 50.2fs to 101.9fs, the femtosecond pulse photonic crystal fiber of 101.9fs to 546.7fs, the femtosecond pulse photonic crystal fiber of 546.7fs to 1000.2fs;

(a) photonic crystals optical fiber structure of femtosecond pulse 1000.2fs is: bore dia and pitch of holes ratio d/ Λ=0.88, and pitch of holes is 4.0 μ m;

(b) photonic crystals optical fiber structure of femtosecond pulse 546.7fs is: corresponding aperture diameter and pitch of holes ratio d/ Λ=0.87, and pitch of holes is 3.0 μ m;

(c) photonic crystals optical fiber structure of femtosecond pulse 101.9fs is: corresponding aperture diameter and pitch of holes ratio d/ Λ=0.55, and pitch of holes is 3.0 μ m;

(d) photonic crystals optical fiber structure of femtosecond pulse 50.2fs is: corresponding aperture diameter and pitch of holes ratio d/ Λ=0.39, and pitch of holes is 3.0 μ m;

(e) photonic crystals optical fiber structure of femtosecond pulse 10.9fs is: corresponding aperture diameter and pitch of holes ratio d/ Λ=0.59, and pitch of holes is 4.0 μ m;

(f) photonic crystals optical fiber structure of femtosecond pulse 5.5fs is: corresponding aperture diameter and pitch of holes ratio d/ Λ=0.80, pitch of holes is 5.0 μ m.

7. the adjustable femto-second laser of a kind of time domain pulsewidth according to claim 1, is characterized in that: described pump laser (1) or replace with based on adjusting the nanosecond laser of Q, or the laser of washing off for the initial long pulse of continuous wave output.

8. a method of utilizing the adjustable femto-second laser of time domain pulsewidth described in claim 1 to produce femtosecond pulse, it is characterized in that: be that the laser of the initial long pulse of continuous wave output is transmitted to photonic crystal fiber by optically coupled device, when transmission, the pulsing division by the modulational instability in photonic crystal fiber of initial long pulse, produces extremely narrow ultrashort femtosecond pulse; By changing the cross-sectional structure of photonic crystal fiber, can obtain from 1fs to 1ps within the scope of the femtosecond pulse in different time domain cycle;

Modulational instability in described optical fiber is in non linear system, and the interaction of nonlinear effect and effect of dispersion and cause the modulation to systematic steady state shows as continuous or quasi-continuous radiation modulation is split into ultrashort radiation;

Modulational instability in optical fiber occurs under anomalous dispersion condition, first ensures that the operation wavelength of pump laser is in the anomalous dispersion region of photonic crystal fiber, and the time domain cycle that modulation splits into ultrashort pulse is:

$T=\frac{2\mathrm{\π}}{{\mathrm{\Ω}}_{\max }}---\left(1\right)$

In formula, Ω _maxbe two maximum gain secondary lobes producing of modulational instability with respect to the angular frequency interval of pump light frequency, its expression formula is:

${\mathrm{\Ω}}_{\max }={\left(\frac{2\mathrm{\γ}{P}_0}{\left|{\mathrm{\β}}_2\right|}\right)}^{1/2}---\left(2\right)$

In formula, γ is the non linear coefficient of optical fiber, P ₀the peak power of incident pulse, β ₂it is 2nd order chromatic dispersion coefficient; As angular frequency interval Ω _maxwhile reaching tens Terahertzs, modulational instability can split into ultrashort femtosecond pulse by initial long pulse;

It is mainly the cross-sectional structure of design photonic crystal fiber, by diameter d and the pitch of holes Λ of design covering airport, the operation wavelength that makes pump laser is all the time under the prerequisite in photonic crystal fiber the anomalous dispersion region, changes the 2nd order chromatic dispersion factor beta of photonic crystal fiber in pumping wave strong point in very on a large scale ₂thereby, change angular frequency interval Ω _maxwith the cycle T of ultrashort pulse, obtain the femtosecond pulse of different time domain pulsewidth; Comprise:

1) design covering airport diameter and pitch of holes ratio, adopt self adaptation step Fourier method numerical solution laser in photonic crystal fiber, to transmit satisfied general non-linear Schrodinger equation, the long pulse that the complete works of pulsewidth of emulation half-shadow is 100ps, peak power 1400W transmits in the photonic crystal fiber of the long Different structural parameters of 1m, obtains the femtosecond pulse waveform under the different time domain cycle;

When pitch of holes Λ=3.0 of photonic crystal fiber, μ m is constant, reduce gradually the ratio d/ Λ of bore dia and pitch of holes, ratio d/ Λ by bore dia and pitch of holes is reduced to 0.35 gradually from 0.90, calculate abbe number and non linear coefficient under each cross-sectional structure parameter, substitution general non-linear Schrodinger equation numerical solution carries out emulation, obtain along with the reducing of the ratio d/ Λ of bore dia and pitch of holes, under different cycles, division formation is reduced to the femtosecond pulse of 3fs gradually from 1031.6fs;

Get corresponding airport diameter and pitch of holes ratio d/ Λ=0.87, obtain T=546.7fs femtosecond pulse waveform;

Get corresponding airport diameter and pitch of holes ratio d/ Λ=0.55, obtain T=101.9fs femtosecond pulse waveform;

Get corresponding airport diameter and pitch of holes ratio d/ Λ=0.39, obtain T=50.2fs femtosecond pulse waveform;

When pitch of holes is 4.0 μ m, get airport diameter and pitch of holes ratio d/ Λ=0.88 of corresponding photonic crystals optical fiber structure, obtain T=1000.2fs femtosecond pulse waveform; Get airport diameter and pitch of holes ratio d/ Λ=0.59 of corresponding photonic crystals optical fiber structure, obtain T=10.9fs femtosecond pulse waveform;

When pitch of holes is 5.0 μ m, get airport diameter and pitch of holes ratio d/ Λ=0.80 of corresponding photonic crystals optical fiber structure, obtain T=5.5fs femtosecond pulse waveform;

The ratio d/ Λ of its median pore diameter and pitch of holes generally should be less than 0.90, and the excessive airport that easily causes subsides; Meanwhile, the ratio d/ Λ of bore dia and pitch of holes should be greater than 0.35, can cause pumping wavelength 1064nm to fall into the normal dispersion district of optical fiber when being less than 0.35, and modulational instability can not occur;

2) design pitch of holes, constant when ratio d/ Λ=0.80 of airport diameter and pitch of holes, increases gradually pitch of holes Λ, the femtosecond pulse under the different time domain cycle of acquisition;

Adopt the pitch of holes of photonic crystal fiber is increased to 5 μ m gradually from 2 μ m, calculate abbe number and non linear coefficient under each cross-sectional structure parameter, substitution general non-linear Schrodinger equation carries out numerical simulation, and the cycle that can obtain is reduced to the femtosecond pulse of 1.1fs gradually from 140.5fs; Wherein pitch of holes should be less than 5 μ m, can cause pumping wavelength 1064nm to fall into the normal dispersion district of optical fiber when being greater than 5 μ m, and modulational instability can not occur.