1、 Basic principles
Heterodyne laser interferometers typically consist of two coherent lasers, referred to as signal light and reference light, respectively. These two laser beams are split into two beams by a beam splitter, with one beam passing through the sample or object under test, and the other beam serving as reference light directly reaching the detector. These two beams of light are then recombined into one beam through a beam combiner to produce an interference pattern.
The phase difference caused by the variation of optical path difference in the interference pattern is reflected as a change in light intensity on the detector. After the detector receives the signal of the intensity change of two beams of light, it will convert it into an electrical signal. By measuring the amplitude and phase of the electrical signal, the optical path difference can be calculated, thereby achieving measurement of the sample or object under test.
2、 Key technologies
Laser coherence: Heterodyne laser interferometry technology utilizes the coherence of lasers, that is, the frequency of two laser beams is the same or similar, the phase difference is constant, and a stable interference pattern can be formed.
Phase modulation: In order to improve the sensitivity and stability of measurement, heterodyne laser interferometry technology usually uses phase modulation technology. By adding a modulator, such as an acousto-optic modulator, to the reference optical path, the frequency shift of the reference light is generated in the radio frequency range, thereby changing the phase of the interference pattern and achieving phase demodulation of the measurement signal.
Differential interferometry technology: Differential interferometry technology is a measurement method based on heterodyne interferometry technology. It uses the phase difference between two laser beams to measure small deformations or displacements of objects. By comparing the phase differences at different times or positions, the deformation or displacement of an object can be calculated.
3、 Advantages
High precision: Heterodyne laser interferometry technology has extremely high measurement accuracy, usually reaching the nanometer level.
Strong anti vibration and anti modulation interference capabilities: Due to the use of phase modulation technology and differential interference technology, heterodyne laser interference technology has strong anti vibration and anti modulation interference capabilities.
Wide measurement range: Heterodyne laser interferometry technology can measure objects from small displacements to larger distances.
Non contact measurement: This technology adopts a non-contact measurement method, avoiding the errors and damages that may be caused by traditional contact measurement.
4、 Application
Heterodyne laser interferometry technology is widely used in various high-precision measurement fields, such as length measurement, displacement measurement, angle measurement, surface morphology measurement, etc. Heterodyne laser interferometry technology plays an important role in semiconductor manufacturing, optical component testing, mechanical processing, and other fields.
In summary, heterodyne laser interferometry technology is a high-precision measurement method with strong resistance to vibration and modulation interference. The principle is based on the interference of two coherent lasers, and the optical path difference is determined by measuring the phase difference. With the continuous development of technology, heterodyne laser interferometry technology will be applied and promoted in more fields.