As a high-precision measuring instrument, laser interferometers play a crucial role in modern scientific research and industrial production. Through in-depth analysis of their principles and elaboration of their technical characteristics, their outstanding performance in measuring physical quantities such as length, displacement, and angle is demonstrated. Meanwhile, combined with a wealth of application examples, their wide use in fields including mechanical manufacturing, optical processing, and the semiconductor industry is revealed. Finally, the future development directions of laser interferometers are discussed, covering innovations and breakthroughs in areas such as higher precision, further miniaturization, and multi-parameter measurement. In today’s highly precise fields of scientific research and industrial production, the accurate measurement of various physical quantities is key to achieving high-quality products and advanced technologies. As a high-precision measuring instrument based on laser technology, laser interferometers, with their unparalleled measurement precision, high resolution, and non-contact measurement characteristics, have become indispensable measuring tools in numerous fields. From nanoscale measurements on the microscale to kilometer-scale measurements on the macroscale, and from precision control in mechanical manufacturing to precision assembly in aerospace, laser interferometers all play an important role. ### 1. Working Principle of Laser Interferometers The working principle of laser interferometers is based on the phenomenon of light interference. When two laser beams with the same frequency, constant phase difference, and consistent vibration direction meet, interference fringes are produced. By measuring changes in these interference fringes, physical quantities of the measured object—such as displacement, length, and angle—can be accurately obtained. A laser interferometer typically consists of a laser source, a beam splitter, a reflector, and a detector. The laser beam emitted by the laser source is split into two beams by the beam splitter: one serves as the reference beam, and the other as the measurement beam. The measurement beam irradiates the measured object, is reflected, and then meets the reference beam at the detector, where interference occurs. After receiving the interference signal, the detector converts it into an electrical signal for processing and analysis. Displacement of the measured object can be calculated based on changes in the interference fringes. When the measured object moves, the optical path of the measurement beam changes, leading to a change in the phase of the interference fringes. By measuring this phase change, the displacement of the object can be accurately calculated. The relationship between displacement and the phase change of the interference fringes can be expressed by the following formula: [Note: The original text omitted specific symbols in the formula. In standard expressions, the formula is usually written as: ΔL = (λ/2π)·Δφ, where ΔL represents displacement, λ represents the laser wavelength, and Δφ represents the phase change of the interference fringes.] ### 2. Key Technologies of Laser Interferometers #### Laser Source Technology A high-quality laser source is the foundation for laser interferometers to achieve high-precision measurement. Laser sources need to have characteristics such as high stability, narrow linewidth, and low noise. Currently, commonly used laser sources include helium-neon lasers and semiconductor lasers. Among them, semiconductor lasers are increasingly widely used in laser interferometers due to their advantages of small size, long service life, and ease of integration. #### Beam Splitting and Combining Technology Beam splitters and beam combiners are key components for realizing optical path separation and interference in laser interferometers. Beam splitters need to evenly split a laser beam into two, while beam combiners need to accurately combine two beams into one. To achieve high-precision beam splitting and combining, high-precision optical coating technology and optical processing techniques are usually adopted. #### Interference Fringe Detection Technology The detection of interference fringes is a key link in obtaining measurement information. Common interference fringe detection technologies include photodetector detection, CCD detection, and CMOS detection. Among these, photodetectors have the advantages of fast response speed and high sensitivity, making them suitable for high-speed measurement; CCD and CMOS detection technologies, with their high resolution and intuitive imaging, are suitable for high-precision static measurement. #### Signal Processing and Error Compensation Technology The measurement precision of laser interferometers is affected by various factors, such as ambient temperature, humidity, and vibration. Therefore, advanced signal processing and error compensation technologies are needed to improve measurement precision. Common signal processing methods include digital filtering, phase demodulation, and lock-in amplification. Error compensation technologies include environmental error compensation, optical path error compensation, and nonlinear error compensation. ### 3. Types of Laser Interferometers #### Michelson Interferometer The Michelson interferometer is one of the most common types of laser interferometers. It consists of two mutually perpendicular plane mirrors and a beam splitter. By moving one of the plane mirrors, the optical path difference between the measurement beam and the reference beam can be changed, thereby generating interference fringes. With the advantages of simple structure and high measurement precision, Michelson interferometers are widely used in measuring physical quantities such as length, displacement, and refractive index. #### Fabry-Perot Interferometer The Fabry-Perot interferometer is composed of two parallel plane mirrors with high reflectivity. When a laser beam is reflected multiple times between the two plane mirrors, multi-beam interference is produced. Fabry-Perot interferometers have extremely high resolution and measurement precision, making them suitable for measuring physical quantities such as micro-displacement and vibration. #### Mach-Zehnder Interferometer The Mach-Zehnder interferometer consists of two beam splitters and two reflectors. The measurement beam and reference beam are separated and combined at the two beam splitters to form interference fringes. Mach-Zehnder interferometers have the advantages of strong anti-interference ability and large measurement range, and are suitable for measuring displacement and deformation of large-sized objects. ### 4. Common Issues and Solutions in the Use of Laser Interferometers Laser interferometers often encounter some problems during use. The following are common issues and corresponding solutions: - **Unstable or blurred interference fringes**: Manifested as jitter, flicker, or indistinctness of fringes. Possible causes include environmental interference (such as vibration, temperature changes, and air flow), unstable laser sources, or dirt and damage on the surface of optical components. Corresponding solutions include improving the measurement environment (reducing vibration sources, controlling ambient temperature and air flow), checking and stabilizing the laser source (replacing it if necessary), and cleaning or replacing problematic optical components. - **Large measurement errors**: The measured data deviates significantly from the expected value. Causes may include incorrect instrument calibration, external interference during measurement, or improper optical path adjustment. To address this, strictly calibrate the instrument in accordance with the operation manual, eliminate external interference factors (such as electromagnetic interference), and re-adjust the optical path to ensure its accuracy. - **Signal loss or interruption**: The interference signal suddenly disappears or is intermittent during measurement. This may be due to loose or damaged connecting lines, detector failure, or insufficient laser intensity. In such cases, check and fasten the connecting lines (replacing damaged ones promptly), inspect and replace faulty detectors, and check the laser source to adjust its output intensity. - **Limited measurement range**: Inability to measure sizes or displacements beyond the instrument’s specified range. The cause may be that the measurement range of the selected laser interferometer does not meet actual needs, or the optical path setup is unreasonable, limiting the measurement range. The solution is to select a laser interferometer with an appropriate measurement range and optimize the optical path setup to fully utilize the instrument’s measurement capabilities. - **Poor data repeatability**: Significant differences in results from multiple measurements of the same object. This may be due to non-standard measurement operations (failure to maintain consistent measurement conditions) or instrument stability issues. It is necessary to conduct measurements in strict accordance with standard operating procedures, maintain consistency in measurement conditions, and perform maintenance and inspection on the instrument to ensure its stability. - **Low interference fringe contrast**: The light-dark contrast of interference fringes is not obvious. Causes may include large differences in light intensity between the two beams or stray light in the optical path. The solution is to adjust the light intensity of the two beams to make them as close as possible, while checking and eliminating stray light in the optical path. When using a laser interferometer, one should calmly analyze the causes of problems and take corresponding solutions to ensure the accuracy of measurement results. ### 5. Development Trends of Laser Interferometers As the demand for measurement precision in scientific research and industrial production continues to increase, the precision of laser interferometers is also constantly improving. In the future, by adopting more advanced laser sources, optical components, and signal processing technologies, laser interferometers are expected to achieve higher measurement precision, reaching the sub-nanometer or even picometer level. To meet the needs of on-site measurement and portable applications, laser interferometers will develop toward further miniaturization. Through the use of micro-nano processing technology and integrated optics technology, the optical path and electronic components of laser interferometers will be integrated into a small-sized chip, realizing the miniaturization and portability of the instrument. To meet the needs of complex measurement tasks, laser interferometers will gain the ability to measure multiple physical quantities simultaneously. For example, in addition to measuring basic physical quantities such as length, displacement, and angle, they will also be able to measure dynamic parameters (such as speed, acceleration, and vibration) and environmental parameters (such as temperature and pressure). With the development of artificial intelligence and automation technology, laser interferometers will be equipped with intelligent and automated measurement functions. By combining with computer technology and robot technology, they will realize automatic control of the measurement process, automatic data collection and processing, and automatic analysis of measurement results and report generation, thereby improving measurement efficiency and accuracy. As a high-precision measuring instrument, laser interferometers play an irreplaceable role in modern scientific research and industrial production. Research on their working principle, key technologies, types, application fields, and development trends shows that laser interferometers are constantly innovating and developing to adapt to the ever-increasing measurement demands. With the continuous advancement of technology, it is believed that laser interferometers will demonstrate their powerful measurement capabilities in more fields and make greater contributions to promoting the development of science and technology and the progress of industrial production.