CN103439218B - Pressure-broadening-based alkali metal stream atomic density measuring method - Google Patents

Abstract

The invention discloses a pressure-broadening-based alkali metal stream atomic density measuring method, relating to an alkali metal atomicity density measuring method. The method comprises the following steps of: firstly, producing an alkali metal air chamber filled with positive pressure gas and uniformly heating; secondly, radiating the air chamber by utilizing stable-powder laser and carrying out frequency sweeping so as to measure an absorption curve of the alkali metal, and carrying out negative logarithm taking processing to obtain an optical depth curve; finally, carrying out lorentz nonlinear fitting on the obtained data, acquiring the overall width of a half peak value of a lorentz curve, thus obtaining pressure broadening parameters and further obtaining the air pressure of the filled gas; obtaining the atomicity density of alkali metal steam according to a peak value of the lorentz curve, thereby realizing the measurement of the atomic density and gas pressure intensity of the alkali metal air chamber.

Description

A kind of alkali metal vapour atomic density measuring method based on pressure broadening

Technical field

The present invention relates to a kind of atomic density measuring method, particularly a kind of alkali metal vapour atomic density measuring method based on pressure broadening, can be used for the physical characteristics experiment of qualitative and quantitative analysis alkali metal atom.

Background technology

The number density of atomic vapour has great importance for application such as explanation atomic collision experiment, the experiments of measuring of atomic physics characteristic and the optical pumpings of atom.Particularly alkali metal atom, because its outermost layer only has the simple structure of an electronics, becomes the primary study object of physics and even optics.Traditional alkali metal vapour density measuring method measures the temperature of alkali metal vapour, and rule of thumb density formula obtains then, simple but error is very large.Measure the atomic density of alkali metal vapour according to the absorption line integral method of non-broadening, because under low temperature, dopplerbroadening coefficient is less, curve live width is very narrow, high to the performance requirement of laser instrument; If to its high-temperature heating, the temperature of alkali metal vapour is difficult to precise and stable control and prediction, and error is larger.Based on the atomic density measuring method of Faraday effect, need to carry out Faraday modulation when extracting the rotation angle of first polarisation, and carry out the easy temperature influence of faraday's crystal modulated and produce drift, and experiment is comparatively complicated.

Summary of the invention

Technology of the present invention is dealt with problems and is: overcome the deficiencies in the prior art, a kind of alkali metal vapour atomic density measuring method based on pressure broadening is proposed, several atmospheric gas is filled with in the air chamber measured, utilize the principle of pressure broadening, change spectral absorption curve, avoid light absorption line line width and the problem that causes measuring error large, improve the measuring accuracy of atomic density.

Technical solution of the present invention is: a kind of alkali metal vapour atomic density measuring method based on pressure broadening, is characterized in that: first, make the alkaline metal air chamber being filled with the gas of malleation, and homogeneous heating is saturated to alkali metal vapour; Secondly, irradiate air chamber and frequency sweep with the laser of firm power, measure alkali-metal absorption curve, row relax of going forward side by side obtains optical depth; Finally, Lorentz nonlinear fitting is carried out to the data obtained, get its half peak value whole-line width, obtain the parameter of pressure broadening, then obtain air pressure, then according to the peak value of Lorentz curve, obtain the atomicity density of alkali metal vapour.Implementation step is as follows:

(1) make and be filled with the alkaline metal air chamber of barotropic gas and homogeneous heating, irradiate air chamber and frequency sweep with the laser of firm power, measure alkali-metal absorption curve, get negative logarithm process and obtain optical depth curve;

(2) Lorentz nonlinear fitting is carried out to the optical depth data that step (1) obtains, get half peak value overall with of the Lorentz curve of matching, obtain the parameter of pressure broadening, then obtain the air pressure of insufflation gas;

(3) Lorentz curve obtained step (2) and the parameter of pressure broadening, obtain the atomic density of alkali metal vapour according to the peak value of the Lorentz curve of matching.

In described step (3), to the parameter of Lorentz curve and pressure broadening, the method obtaining the atomicity density n of alkali metal vapour according to its peak value is:

$n=\frac{{\mathrm{OD}}_{\max }}{{\mathrm{\σ}}_{\max }}$

Wherein, optical depth OD=n σ (v) l, l are the optical length of alkaline metal air chamber; The photon absorption cross sections that σ (v) is alkali metal atom amasss, the peak value of its standard Lorentz curve

Wherein, r _efor electron radius, c is the light velocity, and f is resonant intensity, Γ _lfor the parameter Γ of pressure broadening _l=v ₊-v _-;

ν _-, ν ₊by the frequency that half peak value of the Lorentzian of matching is right;

Described Lorentzian is:

Wherein, ν ₀for the jump frequency of alkali metal atom, K is scale-up factor.

Principle of the present invention is: the absorption spectrum of atom is under the impact of temperature and pressure, and its live width can broaden.When pressure broadening broadening is far longer than the dopplerbroadening that temperature causes, spectrum is Lorentz distribution.Accordingly, to the alkaline metal air chamber being filled with barotropic gas, carry out irradiation and frequency sweep with laser, measure alkali-metal absorption spectrum; Then carry out Lorentz fit, draw half peak value overall with, and then obtain the atmospheric pressure value of insufflation gas; According to peak value and the air pressure of Lorentz curve, draw the atomic density of alkali metal vapour.

The present invention's advantage is compared with prior art: the present invention utilizes pressure broadening effect, be filled with the gas of malleation, pressure broadening is made to be far longer than dopplerbroadening, under overcoming vacuum condition, dopplerbroadening parameter estimation is forbidden, line width causes the problem that atomic density measuring error is large, avoid and directly contact measurement temperature and temperature error cannot bring the problem of density measure error, method is simple and reliable.

Accompanying drawing explanation

Fig. 1 is the process flow diagram of a kind of alkali metal vapour atomic density measuring method based on pressure broadening of the present invention;

Fig. 2 is the system schematic of absorption spectrum experiments of measuring in the present invention.

Embodiment

As shown in Figure 1, specific embodiment of the invention step is as follows:

1, make be filled with the gas of malleation and vacuum condition include alkali-metal glass air chamber and vacuum room, and use baking box homogeneous heating.

2, glass air chamber step 1 made is placed in experimental provision as shown in Figure 2, wherein 1 is Distributed Feedback Laser, 2 is collimation lens, 3,5 is 1/2 wave plate, 4,6 is PBS, and 7 is glass air chamber, and 3 in figure are respectively vacuum room, vacuum alkaline metal air chamber, are filled with the alkaline metal air chamber of barotropic gas, 8 is photodetector, 9 data acquisition board.

Irradiate air chamber and frequency sweep with the laser of firm power, measure alkali-metal absorption curve.Concrete steps are:

1) laser is passed twice through Amici prism, be divided into the light beam that three beams light intensity is identical; A branch of irradiation vacuum alkaline metal air chamber, a branch of irradiation is filled with the alkaline metal air chamber of barotropic gas in addition, the vacuum room that a branch of irradiation scale is identical, accesses 3 photodetectors respectively;

2) by step 1) described in the photo detector signal of front two-beam poor with the work of three-beam respectively, obtain the alkaline metal absorption curve under vacuum condition and positive air pressure condition;

3) by step 2) described in alkaline metal absorption curve carry out getting negative logarithm process,

I＝I(0)exp(-OD) (1)

I (0) is initial beam intensity, obtains optical depth OD;

4) according to step 2) in alkaline metal absorption curve under the vacuum condition that obtains, obtain resonance frequency ν ₀.

3, carry out Lorentz nonlinear fitting to the optical depth data that step 2 obtains, the Lorentzian adopted is:

Wherein, Γ _lfor the parameter of pressure broadening, ν ₀for the jump frequency of alkali metal atom, K is scale-up factor.

Get half peak value overall with Γ of the Lorentz curve of matching _l=v ₊-v _-, ν _-, ν ₊by the frequency that half peak value is right, obtain the parameter of pressure broadening, obtain the air pressure of insufflation gas divided by the pressure broadening coefficient under unit atmospheric pressure.

4, according to the Lorentz curve that step 3 obtains, peak value OD is got _max, then the atomic density of alkali metal vapour:

$n=\frac{{\mathrm{OD}}_{\max }}{{\mathrm{\σ}}_{\max }}---\left(3\right)$

Wherein, optical depth OD=n σ (v) l, l are the optical length of alkaline metal air chamber; The photon absorption cross sections that σ (v) is alkali metal atom amasss, the peak value of its standard Lorentz curve:

${\mathrm{\σ}}_{\max }=\mathrm{\σ}\left(v_0\right)=\frac{{2r}_e\mathrm{cf}}{{\mathrm{\Γ}}_L}---\left(4\right)$

Wherein, r _efor electron radius, c is the light velocity, and f is resonant intensity.

The content be not described in detail in instructions of the present invention belongs to the known prior art of professional and technical personnel in the field.

Claims (1)

1., based on an alkali metal vapour atomic density measuring method for pressure broadening, it is characterized in that comprising the following steps:

(1) make and be filled with the alkaline metal air chamber of barotropic gas and homogeneous heating, irradiate air chamber and frequency sweep with the laser of firm power, measure alkali-metal absorption curve, get negative logarithm process and obtain optical depth data;

Describedly measure alkali-metal absorption curve and be specially:

(11) laser is passed twice through Amici prism, be divided into the light beam that three beams light intensity is identical; A branch of irradiation vacuum alkaline metal air chamber, a branch of irradiation is filled with the alkaline metal air chamber of barotropic gas in addition, the vacuum room that a branch of irradiation scale is identical, accesses 3 photodetectors respectively;

(12) by poor with the work of three-beam respectively for the photo detector signal of two-beam front in step (11), the alkaline metal absorption curve under vacuum condition and positive air pressure condition is obtained;

(2) carry out Lorentz nonlinear fitting to the optical depth data that step (1) obtains, the Lorentzian adopted is:

Wherein, Γ _lfor the parameter of pressure broadening, ν ₀for the jump frequency of alkali metal atom, K is scale-up factor;

Get half peak value overall with Γ of the Lorentz curve of matching _l=v ₊-v _-, ν _-, ν ₊by the frequency that half peak value is right, obtain the parameter of pressure broadening, then obtain the air pressure of insufflation gas;

(3) Lorentz curve obtained step (2) and the parameter of pressure broadening, obtain the atomic density of alkali metal vapour according to the peak value of the Lorentz curve of matching;

In described step (3), to the parameter of Lorentz curve and pressure broadening, the method obtaining the atomicity density n of alkali metal vapour according to the peak value of the Lorentz curve of matching is:

Wherein, optical depth OD=n σ (v) l, l are the optical length of alkaline metal air chamber; The photon absorption cross sections that σ (v) is alkali metal atom amasss, the peak value of its standard Lorentz curve

Wherein, r _efor electron radius, c is the light velocity, and f is resonant intensity, Γ _lfor the parameter Γ of pressure broadening _l=v ₊-v _-;

ν _-, ν ₊by the frequency that half peak value of the Lorentzian of matching is right;

Described Lorentzian is:

Wherein, ν ₀for the jump frequency of alkali metal atom, K is scale-up factor.