A laser interferometer based on a non-stabilized light source

Abstract

The application discloses a kind of laser interferometer based on non-stable frequency light source, its characteristics are that the laser interferometer is composed of non-stable frequency narrow linewidth laser, first beam splitter and reference module and detection module, the non-stable frequency narrow linewidth laser 1 is divided into two laser light sources by first beam splitter, one laser light source is used for frequency detection of laser wavelength by reference module, another laser light source is used for target displacement detection by detection module;The laser wavelength measured and obtained by the reference module is used to correct the measurement result of detection module, to realize high-precision displacement detection.Compared with prior art, the application does not need to lock the laser frequency, can meet the premise of industrial application, reduce the volume and cost of laser interferometer, and the selection of laser interferometer operating wavelength and device is no longer affected by frequency reference device, so that the use of interferometer is more flexible and convenient, simple structure, high stability, further broaden the application scenario of laser interferometer in industrial environment.

Description

Technical Field

[0001] The present invention relates to the technical field of laser interferometers, in particular to a laser interferometer based on a non-stable frequency light source. Background Art

[0002] An interferometer is a precision instrument that uses the principle of interference to measure length and minute changes in length. It is currently the most accurate precision measurement method and is widely used in displacement detection, optical component testing, spectral detection, deep space exploration, and other fields. With the continuous advancement of science and technology and manufacturing processes, people have placed higher demands on measurement. Laser interferometry technology is a typical representative of the highest level of precision measurement, with measurement accuracy reaching nanometers or even higher, playing a vital role in precision machining and scientific research.

[0003] The premise for the laser interferometer in the existing technology to achieve high-precision measurement is that a frequency-stable laser light source is required. In order to obtain a frequency-stable light source, a frequency reference device is usually required as a comparison standard for frequency locking. This not only increases the complexity and size of the laser interferometer, but also increases the development cost. In addition, during the long-term operation of the laser interferometer, the light source is easily affected by the environment, resulting in frequency unlocking and the need to relock the frequency. The laser interferometer is large in size and has poor stability, which greatly limits the promotion and application of laser interferometers in industry. Summary of the Invention

[0004] The purpose of the present invention is to provide a laser interferometer based on a non-stable light source in response to the deficiencies in the prior art. The laser interferometer adopts a non-stable narrow-linewidth laser diode as the light source of the interferometer, utilizes a reference module with a fixed optical path difference for laser wavelength detection, and uses the laser wavelength obtained by combining the detection module with the reference module to measure the target displacement. While meeting the measurement accuracy requirements of industrial applications, it does not require a frequency-stable light source, greatly reducing the complexity of the laser interferometer, reducing the size, and reducing the cost. In addition, the selection of the working wavelength and devices of the laser interferometer is no longer affected by the frequency reference device (such as the atomic gas chamber), making the use of the interferometer more flexible and convenient, with a simple structure, greatly meeting the needs of the laser interferometer, and having a small size and high stability, further broadening the application scenarios of the laser interferometer in industrial environments.

[0005] The purpose of the present invention is achieved as follows: a laser interferometer based on a non-stable frequency light source, characterized in that the light source used by the laser interferometer is generated by a narrow linewidth laser, and the generated light source does not need to be frequency locked. The laser is divided into two parts by a first beam splitter, one part is provided to a reference module for frequency detection, and the other part is provided to a measurement module for target displacement detection.

[0006] The reference module is used to detect the laser wavelength in real time and correct the measurement results of the detection module. It specifically includes: a second beam splitter, a first corner reflector, a second corner reflector, a first optical window and a first photodetector. The above devices are all installed on quartz glass to reduce the impact of the environment on the measurement results and increase the accuracy of laser wavelength measurement; the first optical window changes the optical path of the half-beam spot to generate two orthogonal interference signals in the detection module; two linear detectors are installed side by side on the first photodetector to realize the simultaneous detection of the two interference signals; the optical path difference L of the reference module ref is a constant value, and the interference phase is obtained by measuring The laser wavelength can be obtained and satisfies the following formula (a):

[0007]

[0008] Where M is an integer number of cycles. ref = is a constant value, while the laser wavelength is a gradual variable that fluctuates within a small range, so M is also a constant value. The laser wavelength can be calculated in real time using formula (a).

[0009] The detection module, used for detecting target displacement, specifically includes a third beam splitter, a third corner reflector, a fourth corner reflector, a second optical window, and a second photodetector. The third beam splitter, third corner reflector, second optical window, and second photodetector are mounted on quartz glass to minimize environmental influences on target displacement measurements. The fourth corner reflector is mounted on the target to be measured and moves with the target.

[0010] The second optical window changes the optical path of the half-beam light spot, generating two orthogonal interference signals in the detection module.

[0011] Two linear detectors are installed in parallel on the second photoelectric detector to realize the simultaneous detection of two interference signals. The target movement direction can be determined by combining the two orthogonal interference signals. The target displacement L satisfies the following formula (b):

[0012]

[0013] Wherein, m is the integer part of the phase change of the interference signal, n is the decimal part of the phase change of the interference signal, and the laser wavelength λ is obtained by detection of the reference module.

[0014] In a specific application of the present invention, a series of wavelengths λ can be obtained by performing k wavelength detections in combination with the reference module (a). i (i=1,2,3,…,k-1,k). The displacement calculation can also be divided into k segments. The displacement Li (i=1,2,3,…,k-1,k) is obtained from formula (b). The final displacement L satisfies the following formula (c):

[0015] L=L1+L2++L k-1 +L k (c).

[0016] Compared with the existing technology, the present invention has the advantages of reducing the size and cost of the laser interferometer without locking the laser frequency, which can meet the requirements of industrial applications. In addition, the selection of the working wavelength and device of the laser interferometer is no longer affected by the frequency reference device (such as the atomic gas chamber), making the use of the interferometer more flexible and convenient, and the structure is simple, which greatly meets the needs of the laser interferometer. In addition, the present invention has a small size and high stability, which further broadens the application scenarios of the laser interferometer in the industrial environment and improves the competitiveness of the laser interferometer in the field of industrial precision measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of the present invention. DETAILED DESCRIPTION

[0018] The features of the present invention and other related features are further described in detail below through embodiments in conjunction with the accompanying drawings to facilitate understanding by those skilled in the art:

[0019] See Figure 1 The present invention consists of a non-stable narrow-linewidth laser 1, a first beam splitter 2.1, a reference module I and a detection module II. The reference module I includes: a second beam splitter 2.2, a first corner reflector 3.1, a second corner reflector 3.2, a first optical window 4.1 and a first photodetector 5.1; the detection module II includes: a third beam splitter 2.3, a third corner reflector 3.3, a fourth corner reflector 3.4, a second optical window 4.2 and a second photodetector 5.2.

[0020] The laser light emitted by the non-stable narrow-linewidth laser 1 is split into two parts by a first splitter 2.1 and provided to a reference module I and a detection module II, respectively. The laser light incident on the reference module I is split into two laser beams by a second beam splitter 2.2. One laser beam passes through a first corner reflector 3.1 and a first optical window 4.1, then transmits through the second beam splitter 2.2 and is incident on a first photodetector 5.1, where the first optical window 4.1 changes the optical path length of the half-beam spot. The other laser beam passes through the second corner reflector 3.2, is reflected by the second beam splitter 2.2, and is incident on the first photodetector 5.1. The two light beams arriving at the first photodetector 5.1 interfere with each other to form two orthogonal interference signals, which are detected by the first photodetector 5.1 and used to calculate the laser wavelength.

[0021] The laser beam incident on detection module II is split into two laser beams by the third beam splitter 2.3. One laser beam passes through the third corner reflector 3.3 and the second optical window 4.2, is reflected by the third beam splitter 2.3, and is incident on the second photodetector 5.2, where the second optical window 4.2 changes the optical path of half the beam spot. The other laser beam is reflected by the fourth corner reflector 3.4 mounted on the target, passes through the third beam splitter 2.3, and is incident on the second photodetector 5.2. The two light beams arriving at the second photodetector 5.2 interfere with each other to form two orthogonal interference signals, which are detected by the second photodetector 5.2 and used to calculate the target displacement.

[0022] In this embodiment, the wavelength of the light source of the non-stable narrow linewidth laser 1 is about 780 nm, and the optical path difference L of the reference module I is about 100 nm. ref The sampling frequency of reference module I is 10kHz. The sampling frequency of detection module II is 1MHz. Combined with the interference signal, the target displacement is calculated using the following formulas (a) to (c):

[0023]

[0024]

[0025] L=L1+L2++L k-1 +L k (c).

[0026] The measurement results are shown in Table 1 below:

[0027] Table 1 Summary of measurement results

[0028] Group Actual displacement (mm) Measurement displacement (mm) Absolute value of error (nm) 1 500.000213 500.000157 56 2 500.000756 500.001099 343 3 500.000078 499.999791 287

[0029] In this embodiment, three tests were conducted, with a target displacement of approximately 500 mm and a maximum measurement error of 343 nm, which can meet the needs of industrial applications.

[0030] The above embodiments are only for further explanation of the present invention and are not intended to limit the present invention. Any equivalent implementation of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A laser interferometer based on a non-stable frequency light source, characterized in that: The laser interferometer is composed of a non-stable narrow linewidth laser, a first beam splitter, a reference module and a detection module. The reference module includes: a second beam splitter, a first corner reflector, a second corner reflector, a first optical window and a first photodetector; the detection module includes: a third beam splitter, a third corner reflector, a fourth corner reflector, a second optical window and a second photodetector; the laser emitted by the non-stable narrow linewidth laser is divided into two beams by the first beam splitter, one laser is incident on the reference module for laser wavelength calculation, and the other laser is incident on the detection module for target displacement detection, the laser incident on the reference module is divided into two beams by the second beam splitter, one laser is transmitted through the first corner reflector and the first optical window, and then is incident on the first photodetector; the other laser is incident on the second corner reflector. The laser beam incident on the detection module is divided into two beams by the third beam splitter, one laser beam is reflected by the third beam splitter after passing through the third corner reflector and the second optical window, and is incident on the second photodetector; the other laser beam is reflected by the fourth corner reflector installed on the target, and is incident on the second photodetector after passing through the third beam splitter. The two beams of light arriving at the second photodetector interfere with each other to form two orthogonal interference signals, which are detected by the second photodetector and are used to calculate the target displacement; the laser wavelength measured by the reference module is used to correct the measurement result of the detection module to realize displacement detection.

2. The laser interferometer based on a non-stable frequency light source according to claim 1, characterized in that: The optical path difference of the reference module L ref is a constant value, and the interference phase is obtained by measuring φ ref The laser wavelength can be obtained. Except for the fourth corner reflector installed on the target, the other components of the reference module and the detection module are all installed on a bottom plate with a low thermal expansion coefficient.

3. The laser interferometer based on a non-stable frequency light source according to claim 1, characterized in that: The first optical window changes the optical path of half the beam spot to generate two orthogonal interference signals in the reference module; the second optical window changes the optical path of half the beam spot to generate two orthogonal interference signals in the detection module.

4. The laser interferometer based on a non-stable frequency light source according to claim 1, characterized in that: Two linear detectors are installed in parallel on the first and second photoelectric detectors to achieve simultaneous detection of two interference signals.

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