CN102156111B - Device and method for measuring nonlinear refractive index coefficient of inert gas - Google Patents

Abstract

The principle of the device is that the nonlinear refractive index coefficient of the gas at a specific central frequency is obtained by measuring the change of the nonlinear spectral broadening accumulated when femtosecond laser pulses at the specific central frequency are transmitted in a hollow waveguide filled with the inert gas to be measured along with the gas pressure of the inert gas and analyzing data. The device comprises a focusing lens, an inert gas filling tube with a built-in hollow optical fiber, a scattering screen, a spectrometer, a barometer connected with the inert gas tube, an inert gas bottle and a vacuum pump which are respectively arranged on a light path where femtosecond laser pulses travel.

Description

The measurement mechanism and the measuring method of inert gas nonlinear refraction rate coefficient

Technical field

The present invention relates to inert gas, particularly a kind of measurement mechanism and method of nonlinear refraction rate coefficient of inert gas.

Background technology

Along with chirped pulse amplifies development that (CPA) technology and optical parameter chirped pulse amplify (OPCPA) technology, modern large laser system can launch bat watts (10 ¹⁵Watt) the ultra-intense laser bundle of magnitude.The propagation of high intensity laser beam light beam receives the appreciable impact of nonlinear optical effect.The propagation that relates to the high intensity laser beam light beam and with interactional experiment of gas medium and laser system in, know the nonlinear refractive index n of medium accurately ₂Most important.Specifically, the high power laser system emitted light beams need be passed through careful design, thereby avoids n ₂Relevant effect is as from phase modulation (PM) and self-focusing.In addition, many application of modern laser also have benefited from these effects, and like atmospheric laser radar (LiDAR) experiment, the white light super continuous spectrums produces, and becomes an effect etc.

Nonlinear refractive index n ₂Originate from the third-order non-linear effect, be described to the skew of refractive index, its size is proportional to light intensity, and scale factor is n ₂For nonlinear refractive index n ₂Experimental study start from the seventies in last century, the intense laser pulse technology begins to occur nanosecond at that time.Along with the development of laser technology, the nineties in last century, the Z-scan technology of early stage invention became the technological breakthrough in this area.The method is powerful, for a large amount of nonlinear factor measurements provides experiment basis.Consider technical difficulty and necessary strong focusing, almost have only solid and liquid to be fit to measure with the method.

Nonlinear refraction rate coefficient n for measurement gas ₂, utilize other technology of various nonlinear effects to occur in succession, as utilizing the effect of " electric field brings out second harmonic and produces ", THIRD-HARMONIC GENERATION is propagated the spectrum distortion that causes, self-focusing, spectrum interference etc.Although some in these methods can provide accurately and measure, its experimental provision is very complicated, and process control and Testing requirement are very high, and data analysing method is also very loaded down with trivial details.

Summary of the invention

The technical matters that the present invention will solve provides a kind of measurement mechanism and measuring method of inert gas nonlinear refraction rate coefficient.

Thereby the essence of technical solution of the present invention is to utilize waveguiding structure evenly to prolong the nonlinear interaction distance faint nonlinear effect is amplified to the degree of being convenient to measure.Simultaneously, set up the proportionate relationship between each parameter that relates in measuring through theoretical analysis, obtained inert gas nonlinear refraction rate coefficient to be measured through quantitative proportionate relationship.

Concrete technical solution of the present invention is:

A kind of measurement mechanism of measuring inert gas nonlinear refraction rate coefficient; Characteristics are that its formation is: the inert gas tube and the diffuser screen that are coupled lens, built-in hollow optic fibre on the direction that femto-second laser pulse is advanced successively; Scattered light direction at diffuser screen is provided with spectrometer; One end of described inert gas tube links to each other with inert gas bottle to be measured, and the other end is connected with barometer with vacuum pump respectively, and described coupled lens will have certain centre frequency ω ₀Femto-second laser pulse be coupled in the hollow optic fibre in the inert gas tube.

Utilize the measurement mechanism of described measurement inert gas nonlinear refraction rate coefficient to carry out the measuring method of inert gas nonlinear refraction rate coefficient, it is characterized in that the measuring process of this method is following:

1. the valve of open vacuum pump and inert gas tube connection uses vacuum pump that the gas in the inert gas tube is drained only, and air pressure is detected by barometer, shows 0 value up to registration, breaks off the valve between vacuum pump and the inert gas tube, closes vacuum pump;

2. be ω with centre frequency ₀The incident femto-second laser pulse be coupled in the hollow optic fibre in the inert gas tube through coupled lens, by the spectrum of spectrometer measurement, and write down this data through the outgoing pulse light of diffuser screen scattering;

3. open the valve between inert gas bottle and the inert gas tube, charge into the argon gas of certain air pressure, atmospheric pressure value is detected by barometer, when air pressure reaches an initial value, closes the valve between inert gas bottle and the inert gas tube;

4. be ω with centre frequency ₀The incident femto-second laser pulse is coupled in the hollow optic fibre in the inert gas tube through coupled lens, by the spectrum of spectrometer measurement through the outgoing pulse light of diffuser screen scattering, and writes down this data;

5. 3. repeating step makes the air pressure of inert gas tube increase certain atmospheric pressure value, closes the valve between inert gas bottle and the inert gas tube;

6. 4. repeating step obtains new spectroscopic data;

5. and 6. 7. repeating step until accomplishing spectral measurement, obtains the spectrum widening data I (ω) under the different air pressure, and promptly spectral intensity is with the distribution of angular frequency;

8. use formula Calculate the spectral width ω of spectrum widening data I (ω) under each air pressure _Rms, being defined as of angle bracket wherein:

Thus and then calculate the spectrum widening factor

With the variation of air pressure, Δ ω wherein _iBe the incident light spectrum width,, obtain the spectrum widening factor through linear fit

Slope value S with the variation of air pressure _Ar(ω ₀)=0.01783;

9. change inert gas bottle (6), change another kind of inert gas to be measured into, 1.～8. repeating step obtains being all ω in centre frequency ₀Incident pulse under, the spectrum widening factor of different inert gas

Slope value S with the variation of air pressure _Kr(ω ₀)=0.0279;

10. according to formula The argon gas data κ that knows in advance _Ar(ω ₀)=9.8 * 10 ^-24m ²/ W atm, and the slope value S of the argon gas that 8. obtains of step _ArThe slope value S of=0.01783 gas to be measured that 9. obtains with step _Kr=0.0279, can calculate gas data κ to be measured _Kr(ω ₀)=1.53 * 10 ^-23m ²/ W atm, wherein data κ=n ₂/ p multiplies each other these data and certain atmospheric pressure value, has just obtained the nonlinear refraction rate coefficient n under the corresponding air pressure ₂

Step 9. in, if do not change the inert gas kind, and the centre frequency of incident pulse is changed into ω ₁, so repeating step 1.～8., obtaining in centre frequency is ω ₁Incident pulse under, the spectrum widening factor of identical inert gas (argon gas)

Slope value S with the variation of air pressure _Ar(ω ₁), the computing formula of step in 10. changed into

P wherein ₁And P ₀Be respectively to the centre frequency of incident pulse and change into ω ₁, ω ₀Peak power, calculate κ _Ar(ω ₁), these data and certain atmospheric pressure value are multiplied each other, just obtained the nonlinear refraction rate coefficient n under the corresponding air pressure ₂

Step 9. in; If not only changed the inert gas kind, also changed the centre frequency of incident pulse, also changed the kind of hollow optic fibre simultaneously; For example different hollow optic fibre length and internal diameter; 1.～8. repeating step obtains under the incident pulse of new centre frequency so, the spectrum widening factor of different inert gas

With the slope value S (ω) of the variation of air pressure, the computing formula of step in 10. changed into $\frac{S_1\left({\mathrm{\&omega;}}_1\right)}{S_{\mathrm{Ar}}\left({\mathrm{\&omega;}}_0\right)}=\frac{{\mathrm{\&kappa;}}_1\left({\mathrm{\&omega;}}_1\right)\&CenterDot;{\mathrm{\&omega;}}_1\&CenterDot;P_1\&CenterDot;L_{1\mathrm{Eff}}}{{\mathrm{\&kappa;}}_{\mathrm{Ar}}\left({\mathrm{\&omega;}}_0\right)\&CenterDot;{\mathrm{\&omega;}}_0\&CenterDot;{\mathrm{<figure-callout\; id="0"\; label="P"\; filenames="HSA00000498876400022.png"\; state="\{\{state\}\}">P</figure-callout>}}_0\&CenterDot;{\mathrm{<figure-callout\; id="0"\; label="L"\; filenames="HSA00000498876400022.png"\; state="\{\{state\}\}">L</figure-callout>}}_{0\mathrm{Eff}}}\&CenterDot;\frac{{\mathrm{<figure-callout\; id="0"\; label="A"\; filenames="HSA00000498876400022.png"\; state="\{\{state\}\}">A</figure-callout>}}_{0\mathrm{Eff}}}{A_{1\mathrm{Eff}}},$ Wherein footnote Ar and 0 corresponding amount are 1.～8. middle amounts of measuring the argon gas that calculates of step, the new measuring amount of footnote 1 correspondence, L _EffBe the effective length of hollow optic fibre, be approximately equal to the physical length of optical fiber, A _EffThe effective die face that is optical fiber is long-pending, equals 0.48 times of the hollow area of optical fiber, and P is the peak power of incident pulse.According to obtaining different inert gas at ω after the step computing method substitution analog value calculating 10. ₁The κ at place ₁(ω ₁), these data and certain atmospheric pressure value are multiplied each other, just obtained the nonlinear refraction rate coefficient n under the corresponding air pressure ₂

Measuring principle of the present invention is based on the nonlinear optical spectrum widening from phase modulation (PM), and broadening amount and incident pulse width are inversely proportional in certain limit, and when the incident pulse width reached the femtosecond magnitude, the result was best.The femtosecond laser technology of current maturation can cover the scope from the visible light wave range to the middle-infrared band, so this method can be measured the inert gas nonlinear refraction rate coefficient in this spectral range.

In sum, advantage of the present invention is summarized as follows:

(1) experimental provision of the present invention is simple, and method of operating is prone to row, only need light pulse be coupled in the hollow optic fibre that fills inert gas to be measured, and the outgoing spectrum of measuring under the different air pressure gets final product.

(2) waveguiding structure used in the present invention can amplify faint nonlinear effect.Only need the adjustment waveguide length, the amplification effect that just can obtain wanting is so be fit to measure the very little gas of nonlinear refraction rate coefficient.

(3) the present invention can measure the nonlinear refraction rate coefficient of various inert gases, and the spectral range that is fit to measurement is very wide, from the visible light wave range to the middle-infrared band.

Description of drawings

Fig. 1 is the structural representation of the measurement mechanism of inert gas nonlinear refraction rate coefficient of the present invention.

Fig. 2 is the spectrum widening of argon gas under different air pressure that measures.

Fig. 3 is the spectrum widening factor and the slope thereof of argon gas under different air pressure.

Fig. 4 is the spectrum widening factor and the slope thereof of krypton gas under different air pressure.

Embodiment

Like Fig. 1: the focal length size of coupled lens (1) depends on the optimum matching of the hollow waveguide internal diameter size in incident femtosecond laser beam sizes and the inert gas tube (2).For hollow optic fibre, optimal coupling condition is the 1/e of light beam focal spot intensity ²Radius is 0.65 times of hollow optic fibre inside radius, and at this moment light beam coupling is to hollow optic fibre basic mode EH ₁₁The energy proportion of mould is maximum, is 0.98.By diffuser screen (3) scattering, scattered light is measured its spectrum by spectrometer (4) behind the light beam process hollow optic fibre.(5) be vacuum pump, be used for extracting out the gas of inert gas tube (2).Be the inert gas air pressure that inert gas bottle (6) is used for adjusting inert gas tube (2), barometer (7) is used for measuring the inert gas air pressure of (2).

The theoretical foundation of this device principle of work is the fine optics of nonlinear optical.According to the theory of nonlinear optical fiber optics, light mainly contains 2 effects and works i.e. chromatic dispersion and optical kerr effect when in waveguide, propagating.The size of these 2 effects is characterized by corresponding characteristic length respectively, i.e. chromatic dispersion length L _DWith non-linear length L _NLWhen fiber lengths during much smaller than a certain characteristic length, corresponding effect can be ignored.The length of hollow optic fibre is mostly about 1 meter, and it is very little to charge into the chromatic dispersion of gas wherein, so chromatic dispersion length is very big, effect of dispersion can be ignored.Non-linear length then becomes and can compare with fiber lengths because of the high light intensity of incident pulse, can not ignore.Under this condition, the nonlinear phase Φ of light pulse through accumulating at the different light intensity place behind the hollow optic fibre _NLBe proportional to L _Eff/ L _NL, L wherein _EffBe the effective length that the fibre-optic waveguide loss is taken into account, for hollow optic fibre, its value equals fiber lengths.The nonlinear phase shift Φ of femtosecond pulse peak light strength _NLValue maximum, be Φ _Max=γ P ₀L _Eff, γ=n wherein ₂(ω ₀) ω ₀/ cA _Eff, c is the light velocity, ω ₀Be the centre frequency of pulse, A _EffThe effective die face that is waveguide is long-pending, and its value is 0.48 times of the hollow area of optical fiber, P ₀It is the peak power of pulse.

For the fast-changing in time femtosecond pulse of intensity, its varying strength position accumulation nonlinear phase is different, thereby causes the generation of pulse chirp and the broadening of spectrum.The degree of accuracy metering method of spectral width is root mean square spectrum width Δ ω _Rms, it is defined as

$\mathrm{\&Delta;}{\mathrm{\&omega;}}_{\mathrm{<figure-callout\; id="2"\; label="rms"\; filenames="HSA00000498876400011.png"\; state="\{\{state\}\}">rms</figure-callout>}}^2=<{(\mathrm{\&omega;}-{\mathrm{\&omega;}}_0)}^2>-{<(\mathrm{\&omega;}-{\mathrm{\&omega;}}_0)>}^2$ 【1】

ω in the formula ₀Be the spectral centroid frequency, angle bracket is represented

$\underset{\&OverBar;}{<{\left(\mathrm{\&omega;}{-\mathrm{\&omega;}}_0\right)}^n>=\frac{{\&Integral;}_{-\&infin;}^{\&infin;}{(\mathrm{\&omega;}-{\mathrm{\&omega;}}_0)}^{n}I\left(\mathrm{\&omega;}\right)\mathrm{d\&omega;}}{{\&Integral;}_{-\&infin;}^{\&infin;}I\left(\mathrm{\&omega;}\right)\mathrm{d\&omega;}}}$ 【2】

Wherein I (ω) expression spectral intensity distributes.The video stretching factor that can obtain Gauss pulse according to theoretical analysis and calculation does

$\frac{\mathrm{\&Delta;}{\mathrm{\&omega;}}_{\mathrm{rms}}}{{\mathrm{\&Delta;\&omega;}}_i}={(1+\frac{4}{3\sqrt{3}}{\mathrm{\&phi;}}_{\max }^2)}^{1/2}$ 【3】

Wherein: Δ ω _iBe the rms width of inceptive impulse spectrum, Φ _MaxIt is the maximum nonlinear phase shift of femtosecond pulse peak light strength.

For the femtosecond high intensity laser beam of incident, Φ _MaxUsually much larger than 1, so can do following being similar to

$\frac{{\mathrm{\&Delta;\&omega;}}_{\mathrm{rms}}}{\mathrm{\&Delta;}{\mathrm{\&omega;}}_i}={(1+\frac{4}{3\sqrt{3}}{\mathrm{\&phi;}}_{\max }^2)}^{1/2}\&ap;K\&CenterDot;{\mathrm{\&phi;}}_{\max }$

$=K\&CenterDot;\mathrm{\&gamma;}{P}_0{L}_{\mathrm{eff}}$

$=K\&CenterDot;\frac{n_2\left({\mathrm{\&omega;}}_0\right){\mathrm{\&omega;}}_0}{{\mathrm{cA}}_{\mathrm{eff}}}{P}_0{L}_{\mathrm{eff}}$ 【4】

$=K\&CenterDot;p\frac{n_2\left({\mathrm{\&omega;}}_0\right)}{p{A}_{\mathrm{eff}}}{\mathrm{\&omega;}}_0{P}_0{L}_{\mathrm{eff}}$

Wherein the equation left side is exactly the spectrum widening factor, and COEFFICIENT K has comprised the constant with gas medium and frequency-independent, and p is an inert gas air pressure.For specific gas in a certain frequencies omega ₀Under response, when air pressure is not very high (as less than 1 atmospheric pressure, promptly 1000 millibars), thus when the interaction between the atom can be ignored, n ₂(ω ₀)/p is a constant, is made as κ (ω ₀).Following relation is then arranged

$\mathrm{\&Delta;}\frac{\mathrm{\&Delta;}{\mathrm{\&omega;}}_{\mathrm{rms}}}{\mathrm{\&Delta;}{\mathrm{\&omega;}}_i}=K\frac{\mathrm{\&kappa;}\left({\mathrm{\&omega;}}_0\right){\mathrm{\&omega;}}_0{P}_0{L}_{\mathrm{eff}}}{A_{\mathrm{eff}}}\&CenterDot;\mathrm{\&Delta;p}$ 【5】

Wherein: Δ p is the air pressure increment, and

is spectrum widening factor increment.Making S is spectrum widening factor increment and the ratio of air pressure increment Delta p, then further has

$\frac{S_1}{{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="HSA00000498876400011.png"\; state="\{\{state\}\}">S</figure-callout>}}_2}=\frac{{\mathrm{\&kappa;}}_1\left({\mathrm{\&omega;}}_1\right)\&CenterDot;{\mathrm{\&omega;}}_1\&CenterDot;P_1\&CenterDot;L_{1\mathrm{eff}}}{{\mathrm{\&kappa;}}_2\left({\mathrm{\&omega;}}_2\right)\&CenterDot;{\mathrm{\&omega;}}_2\&CenterDot;{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="HSA00000498876400011.png"\; state="\{\{state\}\}">P</figure-callout>}}_2\&CenterDot;{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HSA00000498876400011.png"\; state="\{\{state\}\}">L</figure-callout>}}_{2\mathrm{eff}}}\&CenterDot;\frac{A_{2\mathrm{eff}}}{A_{1\mathrm{eff}}}$ 【6】

Wherein footnote 1,2 refers to different measuring combination (frequency, gaseous species, optical fiber parameter etc.).Relation needs only and has known κ in advance thus ₁, just can use this gas to be standard, measure corresponding S ₁S with gas to be measured ₂, the while pulse peak power, the pulse center frequency, the effective die face of fiber lengths and optical fiber is long-pending all to be known parameters, has just obtained κ by formula [6] formula ₂, and then obtained the nonlinear refraction rate coefficient of gas to be measured.

Be that example describes with an experiment below.Laser system is commercial ti sapphire laser (spectrum physics, Spitfire, a 1kHz repetition frequency), and through after the regenerative amplification, the basic parameter of incident pulse is pulsewidth 49fs (FWHM), pulse energy 0.47mJ, and centre wavelength is 800 nanometers.Testing used optical fiber is the standardized product of Femtolaser company, internal diameter 250 μ m, and length is 1 meter.According to the incident pulse situation, the use focal length is that 1 meter lens are coupled to pulse in the optical fiber, to realize having maximum pulse energies to pass through optical fiber under the vacuum condition.

Select argon gas in the nonlinear refractive index value of 800 nanometers as standard, according to document, argon gas has n in 800 nanometers ₂/ p=9.8 * 10 ^-24m ²/ W atm.At first measure the variation of the spectrum widening of argon gas under above-mentioned incident condition with air pressure, under the original state, inert gas tube (2) is airtight, and the vacuum pump (5) that links to each other with inert gas tube (2) and the connected state of (6) are controlled by valve.Measuring process is following:

1. the valve that is communicated with of open vacuum pump (5) and inert gas tube (2); Use vacuum pump (5) that the gas in the inert gas tube (2) is drained only, air pressure is detected by barometer (7), shows 0 value up to registration; Break off the valve between vacuum pump (5) and the inert gas tube (2), close vacuum pump (5);

2. be ω with centre frequency ₀The incident femto-second laser pulse be coupled in the hollow optic fibre in the inert gas tube (2) through coupled lens (1), measure spectrum by spectrometer (4), and write down this data through the outgoing pulse light of diffuser screen (3) scattering;

3. open the valve between inert gas bottle (6) and the inert gas tube (2); Charge into the argon gas of certain air pressure, atmospheric pressure value is detected by barometer (7), when air pressure reaches an initial value; During as 100 millibars, close the valve between inert gas bottle (6) and the inert gas tube (2);

4. be ω with centre frequency ₀The incident femto-second laser pulse is coupled in the hollow optic fibre in the inert gas tube (2) through coupled lens (1), measures the spectrum through the outgoing pulse light of diffuser screen (3) scattering by spectrometer (4), and writes down this data;

5. repeating step 3, make the air pressure of inert gas tube (2) increase certain air pressure, close the valve between inert gas bottle (6) and the inert gas tube (2);

6. repeating step 4, obtain new spectroscopic data;

7. repeating step 5 and 6 until accomplishing spectral measurement, obtains the spectrum widening data under the different air pressure, like Fig. 2;

8. with the spectral width under each air pressure in formula [1] calculating chart 2, thus and then calculate the spectrum widening factor

With the variation of air pressure, Δ ω wherein ₀Be the incident light spectrum width,,, obtain the spectrum widening factor through linear fit like Fig. 3

Slope value S with the variation of air pressure _Ar(ω ₀)=0.01783;

9. change inert gas bottle (6), change another kind of different inert gas into, like krypton gas, repeating step 1～8 obtains being all ω in centre frequency ₀Incident pulse under, the spectrum widening factor of different inert gas With the slope value of the variation of air pressure, the corresponding slope value S of krypton gas as shown in Figure 4 _Kr(ω ₀)=0.0279;

10. because the pulse peak power in the formula [6], pulse center frequency, fiber lengths and the effective die face of optical fiber amass argon gas measure with the measurement of krypton gas in all identical, so have according to formula [6] formula

$\frac{S_{\mathrm{Kr}}}{S_{\mathrm{Ar}}}=\frac{{\mathrm{\&kappa;}}_{\mathrm{Kr}}\left({\mathrm{\&omega;}}_0\right)}{{\mathrm{\&kappa;}}_{\mathrm{Ar}}\left({\mathrm{\&omega;}}_0\right)}$ 【7】

ω wherein ₀Be the angular frequency of 800 nanometers, footnote Kr and Ar refer to krypton gas and argon gas respectively, according to this formula and the argon gas data κ that knows in advance _Ar(ω ₀)=9.8 * 10 ^-24m ²/ W atm, and the slope value S of the argon gas that obtains of step 8 _ArThe slope value S of=0.01783 krypton gas that obtains with step 9 _Kr=0.0279, can calculate the data κ of krypton gas _Kr(ω ₀)=1.53 * 10 ^-23m ²/ W atm, wherein data κ=n ₂/ p multiplies each other these data and certain atmospheric pressure value, has just obtained the nonlinear refraction rate coefficient n under the corresponding air pressure ₂

10 top pacing amounts have constituted one group of complete measuring process.

In above-mentioned measuring process, ar pressure is set at 100 millibars at interval, and initial gas pressure is 100 millibars, and the air pressure of krypton gas is set at 50 millibars at interval, and initial gas pressure is 50 millibars.Spectroscopic data under 5～6 different atmospheric pressure values of general measure is just enough.

In step 9,, and the centre frequency of incident pulse is changed into ω if do not change the inert gas kind ₁, repeating step 1～8 so, and obtaining in centre frequency is ω ₁Incident pulse under, the spectrum widening factor of identical inert gas (argon gas)

Slope value S with the variation of air pressure _Ar(ω ₁), have according to formula [6] simultaneously

$\frac{S_{\mathrm{Ar}}\left({\mathrm{\&omega;}}_1\right)}{S_{\mathrm{Ar}}\left({\mathrm{\&omega;}}_0\right)}=\frac{{\mathrm{\&kappa;}}_{\mathrm{Ar}}\left({\mathrm{\&omega;}}_1\right)\&CenterDot;{\mathrm{\&omega;}}_1\&CenterDot;P_1}{{\mathrm{\&kappa;}}_{\mathrm{Ar}}\left({\mathrm{\&omega;}}_0\right)\&CenterDot;{\mathrm{\&omega;}}_0\&CenterDot;P_0}$ 【8】

Computing method substitution analog value according to step 10 calculates identical inert gas (argon gas) at ω ₁The κ at place _Ar(ω ₁), these data and certain atmospheric pressure value are multiplied each other, just obtained the nonlinear refraction rate coefficient n under the corresponding air pressure ₂

Further; In step 9,, also changed the centre frequency of incident pulse if not only changed the inert gas kind; Also changed simultaneously the kind of hollow optic fibre; For example different hollow optic fibre length and internal diameter, repeating step 1～8 so, obtains under the incident pulse of new centre frequency; The spectrum widening factor of different inert gas

has according to formula [6] with the slope value S (ω) of the variation of air pressure

$\frac{S_1\left({\mathrm{\&omega;}}_1\right)}{S_{\mathrm{Ar}}\left({\mathrm{\&omega;}}_0\right)}=\frac{{\mathrm{\&kappa;}}_1\left({\mathrm{\&omega;}}_1\right)\&CenterDot;{\mathrm{\&omega;}}_1\&CenterDot;P_1\&CenterDot;L_{1\mathrm{eff}}}{{\mathrm{\&kappa;}}_{\mathrm{Ar}}\left({\mathrm{\&omega;}}_0\right)\&CenterDot;{\mathrm{\&omega;}}_0\&CenterDot;{\mathrm{<figure-callout\; id="0"\; label="P"\; filenames="HSA00000498876400022.png"\; state="\{\{state\}\}">P</figure-callout>}}_0\&CenterDot;{\mathrm{<figure-callout\; id="0"\; label="L"\; filenames="HSA00000498876400022.png"\; state="\{\{state\}\}">L</figure-callout>}}_{0\mathrm{eff}}}\&CenterDot;\frac{A_{0\mathrm{eff}}}{A_{1\mathrm{eff}}}$ 【9】

Wherein footnote Ar and 0 corresponding amount are the amounts that measurements and calculations obtain in step 1～8, the amount that measurements and calculations obtain under the corresponding new condition of footnote 1.Can obtain different inert gas at ω behind the computing method substitution analog value according to step 10 ₁The κ at place ₁(ω ₁), these data and certain atmospheric pressure value are multiplied each other, just obtained the nonlinear refraction rate coefficient n under the corresponding air pressure ₂

Claims (1)

1. measurement mechanism of measuring inert gas nonlinear refraction rate coefficient; Be characterised in that its formation is: the inert gas tube (2) and the diffuser screen (3) that are coupled lens (1), built-in hollow optic fibre on the direction that femto-second laser pulse is advanced successively; Scattered light direction at diffuser screen (3) is provided with spectrometer (4); One end of described inert gas tube (2) links to each other with inert gas bottle (6) to be measured; The other end is connected with barometer (7) with vacuum pump (5) respectively, and described coupled lens (1) will have certain centre frequency ω ₀Femto-second laser pulse be coupled in the hollow optic fibre in the inert gas tube (2), utilize the measurement mechanism of described measurement inert gas nonlinear refraction rate coefficient to carry out the measuring method of inert gas nonlinear refraction rate coefficient, the measuring process of this method is following:

1. the valve that is communicated with of open vacuum pump (5) and inert gas tube (2); Use vacuum pump (5) that the gas in the inert gas tube (2) is drained only, air pressure is detected by barometer (7), shows 0 value up to registration; Break off the valve between vacuum pump (5) and the inert gas tube (2), close vacuum pump (5);

2. be ω with centre frequency ₀The incident femto-second laser pulse be coupled in the hollow optic fibre in the inert gas tube (2) through coupled lens (1), measure spectrum by spectrometer (4), and write down this data through the outgoing pulse light of diffuser screen (3) scattering;

3. open the valve between inert gas bottle (6) and the inert gas tube (2), charge into the inert gas A of certain air pressure, atmospheric pressure value is detected by barometer (7), when air pressure reaches an initial value, closes the valve between inert gas bottle (6) and the inert gas tube (2);

4. be ω with centre frequency ₀The incident femto-second laser pulse is coupled in the hollow optic fibre in the inert gas tube (2) through coupled lens (1), measures the spectrum through the outgoing pulse light of diffuser screen (3) scattering by spectrometer (4), and writes down this data;

5. 3. repeating step makes the air pressure of inert gas tube (2) increase certain atmospheric pressure value, closes the valve between inert gas bottle (6) and the inert gas tube (2);

6. 4. repeating step obtains new spectroscopic data;

5. and 6. 7. repeating step until accomplishing spectral measurement, obtains the spectrum widening data I (ω) under the different air pressure, and promptly spectral intensity is with the distribution of angular frequency;

8. use formula

Calculate the spectral width Δ ω of spectrum widening data I (ω) under each air pressure _Rms, being defined as of angle bracket wherein:

Thus and then calculate the spectrum widening factor

With the variation of air pressure, Δ ω wherein _iBe the incident light spectrum width,, obtain the spectrum widening factor through linear fit Slope value S with the variation of air pressure _A(ω ₀);

9. change inert gas bottle (6), change another kind of inert gas B to be measured into, 1.～8. repeating step obtains being all ω in centre frequency ₀Incident pulse under, the spectrum widening factor of inert gas B

Slope value S with the variation of air pressure _B(ω ₀);

10. according to formula

The data κ of the inert gas A that knows in advance _A(ω ₀), and the slope value S of the inert gas A that 8. obtains of step _A9. the slope value S of the inert gas gas B that obtains with step _B, can calculate the data κ of inert gas B _B(ω ₀), these data and certain atmospheric pressure value are multiplied each other, just obtained the nonlinear refraction rate coefficient n under the corresponding air pressure ₂

Step 9. in, if do not change the inert gas kind, and the centre frequency of incident pulse is changed into ω ₁, so repeating step 1.～8., obtaining in centre frequency is ω ₁Incident pulse under, the spectrum widening factor of identical inert gas

Slope value S with the variation of air pressure _A(ω ₁), the computing formula of step in 10. changed into

P wherein ₁And P ₀The centre frequency that is respectively incident pulse is ω ₁, ω ₀Peak power, calculate κ _A(ω ₁), these data and certain atmospheric pressure value are multiplied each other, just obtained the nonlinear refraction rate coefficient n under the corresponding air pressure ₂

Step 9. in, if not only changed the inert gas kind, also changed the centre frequency of incident pulse, also changed simultaneously the length and the internal diameter of hollow optic fibre, 1.～8. repeating step obtains at new centre frequency ω so ₁Incident pulse under, the spectrum widening factor of different inert gas B

Slope value S with the variation of air pressure _B(ω ₁), the computing formula of step in 10. changed into

Wherein footnote A and 0 corresponding amount are 1.～8. middle amounts that calculates of measuring of step, footnote B and the new measuring amount of 1 correspondence, L _EffBe the effective length of hollow optic fibre, be approximately equal to the physical length of optical fiber, A _EffThe effective die face that is optical fiber is long-pending, equals 0.48 times of the hollow area of optical fiber, and P is the peak power of incident pulse; According to obtaining different inert gas B at ω after the step computing method substitution analog value calculating 10. ₁The κ at place _B(ω ₁), these data and certain atmospheric pressure value are multiplied each other, just obtained the nonlinear refraction rate coefficient n under the corresponding air pressure ₂

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