1.15 µm正交偏振He-Ne激光位移传感器：一种新型方法

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"这篇文章是关于基于正交偏振He-Ne激光器在1.15微米波长的位移传感器的研究。该研究提出了一种新的位移传感方法，利用了激光的偏振混合和腔调谐技术。由于1.15微米波长的He-Ne激光功率调谐曲线的不规则性，传统的测量方法难以准确地检测到腔体长度的变化。这种不规则性的原因在于与633纳米波长的He-Ne激光相比，其相对激发度更高。为了扩大位移测量范围，研究人员开发了这种方法，并进行了实验验证。" 在光学领域，位移传感器是至关重要的工具，用于精确测量微小的物体移动或变形。这篇论文中提到的基于正交偏振He-Ne激光的位移传感器，是一种利用激光特性的创新设计。He-Ne激光因其稳定性好、光束质量高而常被用于精密测量。在1.15微米波长的He-Ne激光器中，激光的两个正交偏振态可以通过混合来感知位移变化。传统的位移测量方法，如干涉仪，依赖于激光的频率或相位变化来反映位移。然而，描述中指出，在1.15微米波长的He-Ne激光中，功率调谐曲线并非线性，这使得通过直接监测功率变化来测量腔体长度变化变得困难。曲线的扭曲是由更高的相对激发度导致的，这意味着激光的动态行为更加复杂。为了解决这个问题，研究者提出了一种新的方法，该方法结合了偏振混合和腔调谐的概念。偏振混合涉及激光的两个正交偏振态之间的相互作用，而腔调谐则是改变激光谐振腔的长度，从而影响激光的频率。通过巧妙地利用这两个特性，可以更灵敏地探测到位移，即使在功率曲线非线性的情况下。实验部分可能包括设置和操作这种新型传感器的具体步骤，以及收集和分析数据的过程。实验结果可能证明了这种方法的有效性，展示出在较宽的位移范围内能够实现高精度的测量，这是传统的633纳米He-Ne激光器难以做到的。这项工作为位移测量提供了一种新的策略，特别是在1.15微米波长的He-Ne激光器中，它克服了传统方法的局限性，扩大了测量范围，并提高了测量精度。这对于需要精确位移测量的诸多应用，如精密机械、航空航天、光学仪器校准等领域具有重要意义。

COL 10(3), 032801(2012) CHINESE OPTICS LETTERS March 10, 2012

Displacement sensor based on polarization mixture of

orthogonal polarized He-Ne laser at 1.15 µm

Zhengqi Zhao (

ëëë



ééé

), Shulian Zhang (

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ööö

)

∗

, Peng Zhang (

ÜÜÜ

+++

), Zhaoli Zeng (

QQQððð

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Yidong Tan (

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), and Yan Li (

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)

State Key Laboratory of Precision Measurement Technology and Instruments, Department of

Precision Instruments and Mechanology, Tsinghua University, Beijing 100084, China

∗

Corresponding author: zsl-dpi@mail.tsinghua.edu.cn

Received July 15, 2011; accepted S eptember 23, 2011; posted online November 18

2011

Displacement sensor based on the polarization mixture and t he cavity tu ning of the orthogonal polarized

He-Ne laser 1.15 µm is p resented. The power tuning curves of He-Ne laser are irregular, and it is difficult to

measure the change in cavity length. The distortion of the curves is caused by the higher relative excitation

compared with the He-Ne laser at 633 nm. In view of its potential for the wider displacement measuring

range, a new method of d isplacement sensing is developed. Experiments show that displacement measuring

stability based on the method of the polarization mixture is better than that of the power tuning curves.

The displacement sensor achieves the measuring range of 100 mm, resolution of 144 nm, and linearity of

7×10

−6

OCIS codes: 280.3420, 140.1340, 260.5430

doi: 10.3788/COL201210.032801.

The applications of laser technology are widely used

in metrology because of the traceability to the

wavelength

[1,2]

. Many characteristics and applications

of laser, such as spectrum, wavelength, beat frequency,

intensity, laser line, and fringes , are used in different

measurement areas

[3−7]

. In most of these applications,

laser is regarded as a source of light with excellent per-

formance, including having high intensity, stability, and

directionality. Another importa nt factor in displace-

ment measurement is the stability of frequency because

frequency is directly related to result of measurement.

Hence, the frequency stabilization system is necessary

in a high-precision measuring system, which results in a

complex structure.

Intracavity tuning displacement sens ing is the appli-

cation of the intracavity laser method in the field of

displacement measurement. Du et al.

[8]

utilized a dual-

frequency He-Ne laser at 633 nm a s a displacement sen-

sor, with the measuring range being 12 mm. It has the

merits of linearity, self-calibra tion, and traceability to the

wavelength. The simple structure also has stability. The

frequency stabilization system is not necessary and the

cost is much lower. However, the measuring range can

hardly be increased because the meas uring method re-

quires the operation of a single longitudinal mode. Dur-

ing the process of measur ement, the vibration of the cav-

ity mirror may lead to the detuning of the laser cavity,

and the output light disappears when the loss surpasses

the gain. Research shows that He-Ne laser at 1.15 µm

is more promising for the intracavity laser method, be-

cause the active medium gain of the laser is more than

that of He- Ne la ser at 633 nm. Therefore, in theory, the

adoption of He-Ne laser at 1.15 µm can enlarge the mea-

surement range.

The active medium of He- Ne laser is mainly Doppler

broadened. The laser line function g

(v, v

) is in the

form of a Gaussian shape. When v e quals v

, g

(v, v

)

reaches the maximum

[9]

Dmax

= λ



2πk



, (1)

where v

is the central frequency, λ is the wave le ngth

of the laser, m is the atomic mass, k

is the Boltzmann

constant, and T is the temperature. The corresponding

gain fac tor G can be expressed as

G = ∆n

8πc



2πk



1/2

, (2)

where ∆n is the inverted population density, υ is the

velocity of atoms , and A

is the spontaneous emission

rate. Equation (2) shows that G is proportional to λ

This means that the gain of the laser will be higher for

a lo nger wavelength with the same a ctive medium and

conditions. Higher gain promises a wider displacement

measurement range and stability, thus He-Ne laser a t

1.15 µm is more suitable to be a displacement sensor.

After inserting a birefringence element (such as a

quartz plate, a stress-birefring e nce glass, etc.) into the

laser cavity, one geometric cavity length becomes a cav-

ity with two physical lengths. One laser beam then

splits into two orthogonal linear polarized beams with a

certain frequency difference

[10,11]

. They can be called o-

light and e-light, respectively, according to crystal optics.

The cavity tuning characteristics of the orthogonally po-

larized dual-frequency He-Ne laser a t 1.15 µm have been

discussed in detail

[12]

The schematic structure of the experimental setup is

shown in Fig. 1. A half-intracavity cavity laser is com-

posed of a concave output mirror M, a ca t’s eye reﬂector

(CER), and a He-Ne laser discharge tube T. W refers to

the window plate with an anti-reﬂection co ating on bo th

surfaces; Q is a quartz plate, which is obliquely placed

to keep a certain angle between the crystal axis and the

laser axis, and the frequency difference is a djusted by the

1671-7694/2012/032801(4) 032801-1

 2012 Chinese Optics Letters

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