Method for determining laser incident angle in radial resonance mode of photoacoustic cell
A technology of laser incident angle and photoacoustic pool, which is applied in the direction of material analysis, measuring devices, instruments, etc. through optical means, can solve the problems of unclear quantitative relationship, inability to effectively excite low-order radial resonance modes, etc., and achieve great guidance Significance, effect of improving signal amplitude and detection sensitivity
Inactive Publication Date: 2011-09-28
SOUTHWEAT UNIV OF SCI & TECH +1
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Problems solved by technology
The longitudinal or angular resonant modes of the cavity can be excited by pulsed light incident along the axial direction, but the low-order radial resonant modes cannot be effectively excited, because the mode coupling coefficient at this time is zero
Experiments have found that the angle of the incident light off the cavity axis has a significant effect on the amplitude of the acoustic signal of the low-order radial resonance mode, but the quantitative relationship between the two has not been clarified so far.
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[0009] All features disclosed in this specification, or steps in all methods or processes disclosed, may be combined in any manner, except for mutually exclusive features and / or steps.
[0010] Any feature disclosed in this specification (including any appended claims, abstract and drawings), unless expressly stated otherwise, may be replaced by alternative features which are equivalent or serve a similar purpose. That is, unless expressly stated otherwise, each feature is one example only of a series of equivalent or similar features.
[0011] Such as figure 1 As shown, a method for determining the laser incident angle in the radial resonance mode of the photoacoustic cell, let the incident point A of the laser be located at the end face of the cylindrical cavity of the photoacoustic cell, and the angle between the incident light and the central axis z Satisfy , where: R is the radius of the cylindrical cavity, L is the longitudinal length of the cylindrical cavity, is ...
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The invention discloses a method for determining a laser incident angle in a radial resonance mode of a photoacoustic cell. An incidence point of a laser is positioned on the end face of a cylindrical cavity of the photoacoustic cell; the distance from the incidence point to the center of the end face is 0.5568 times radius of the cylindrical cavity; an included angle theta 0 between the incidentlight and a central axis z meets a formula, wherein R is the radius of the cylindrical cavity, L is the longitudinal length of the cylindrical cavity, alpha01 is a value of a first extreme point of abessel function of order zero, and xi is approximate to 2.133; and the distance from the incidence point to the center of the end face can also be equal to the radius of the cylindrical cavity, and at the moment, xi is approximate to 3.832. The method has the advantages that: according to the position and the incident angle of the laser incidence point determined, the resonance mode of the photoacoustic cell can be excited furthest, and signal amplitude and detection sensitivity of a photoacoustic method for detecting trace gas devices can be effectively improved; in addition, the method has great guidance signification for optimal structural design and installation and debugging for the photoacoustic cell.
Description
technical field [0001] The invention relates to the field of photoacoustic spectrum gas analysis, in particular to a method for determining the incident angle of laser light in the radial resonance mode of a photoacoustic cell. Background technique [0002] There are three basic structural forms of resonant cavities widely used in existing photoacoustic gas detection devices: (1) Helmholtz resonant cavity; (2) one-dimensional cylindrical resonant tube; (3) three-dimensional cavity structure. The Helmholtz resonator can be compared to a simple harmonic oscillator composed of springs and particles, and its resonance enhancement factor generally does not exceed 10. For a one-dimensional cylindrical resonant tube, if the cross-sectional size of the cavity is much smaller than the longitudinal length, the excited sound field only changes in the length direction, and works in the pure longitudinal resonance mode. In gas photoacoustic detection devices, the three-dimensional photo...
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IPC IPC(8): G01N21/00
Inventor 刘先勇郭锋王寿全袁长迎余玉江张阳胡文乐莉
Owner SOUTHWEAT UNIV OF SCI & TECH