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Interferometry
A laser interferometer is an instrument that performs high-precision measurements based on the principle of optical interference. Its core working principle involves the superposition of two or more beams of coherent light to form interference fringes; by analyzing changes in these fringes, physical quantities such as length, displacement, surface topography, and refractive index can be measured.
1. The Basic Principles of Laser Interference
Interference conditions:
Two light beams must satisfy coherence (temporal coherence and spatial coherence).The optical path difference must be less than the coherence length of the laser (ΔL < Lc), where ΔL denotes the optical path difference and Lc denotes the coherence length.
Interference formula:
Light intensity distribution I = 
(∆ф) where ∆ф = 
ΔL represents the phase difference. Each movement of the interference fringes corresponds to a change in optical path difference by one wavelength. 
) .
2. Classification of Laser Interferometers
2.1 Classification by Optical Path Structure
(1) Michelson Interferometer
Principle: A beam splitter divides the laser into a reference beam and a measurement beam. After being reflected, the two beams recombine to produce interference. Featuring a simple structure, this setup is suitable for displacement measurement (e.g., LIGO gravitational wave detection).
Michael Interferometer Schematic
(2) Mach-Zehnder Interferometer
Principle: Two beams of light travel along independent paths without using mirrors, making it ideal for measuring changes in refractive index (such as fluid flow velocity or plasma diagnostics).
Principle Diagram of a Mach-Zehnder Interferometer
(3) Fabry-Perot Interferometer
Principle: Multi-beam interference, high finesse, used for spectral analysis or laser cavity length control.
Principle Diagram of a Fabry-Perot Interferometer
(4) Fizeau Interferometer
Principle: This method utilizes direct light interference between the surface under test and a reference plane, making it suitable for optical surface flatness inspection.
Fizeau Interferometer Schematic
2.2 Categorized by Measurement Object
(1) Displacement/Length Interferometer
Measure target displacement with nanometer-level precision, such as for machine tool guide rail calibration.
(2) Wavefront/Shape Interferometer
Detect surface errors of optical components (such as lenses and mirrors with λ/10 accuracy).
(3) Refractive Index/Gas Interferometer
By inverting the medium's refractive index based on changes in optical path difference, such as air refractive index compensation.
2.3 Classification by Signal Processing Method
(1) Zero-Offset Interferometer
Directly detecting the interference light intensity is structurally simple but easily affected by noise.
(2) Heterodyne Interferometer
By introducing a frequency difference (such as in acousto-optic modulation), the anti-interference capability can be enhanced through beat-frequency signals—for example, in precision positioning applications within semiconductor manufacturing.
3. Typical Application Areas
3.1 Industrial Manufacturing and Metrology
Position feedback for CNC machines and lithography equipment (nanometer-level repeat positioning accuracy).
Optical component surface shape inspection (e.g., telescope lenses, smartphone camera modules).
CNC machine tool repeat positioning with a laser interferometer
3.2 Scientific Research
Gravitational wave detection (Michelson interferometer).
Plasma Density Measurement (Mach-Zehnder Interferometer).
Laser Interferometer Gravitational-Wave Observatory (LIGO)
3.3 Biomedical
Optical Coherence Tomography (OCT) uses low-coherence light interference to achieve micrometer-level imaging of biological tissues.
Laser Interference Optical Coherence Tomography
3.4 Environmental Monitoring
Atmospheric turbulence analysis, gas concentration detection (via refractive index changes).
Research on Laser Transmission Against Atmospheric Turbulence
3.5 Semiconductor Industry
Wafer thickness measurement, lithography alignment (dual-frequency laser interferometer).
Research on Lithographic Alignment Using Laser Interferometers
4. CNI's Typical Interference Laser System
CNI offers highly reliable, narrow-linewidth, single-longitudinal-mode (single-frequency) lasers that feature stable mode operation, long coherence length, low noise, and excellent beam quality—making them the ideal choice for interference applications.
For detailed information, please visit www.cnilaser.com.
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UV Band | Blue Light | Green Light | Yellow Light | Red Light | IR Band |
266, 320,349, 355, 360nm, etc. | 405,450,457,473, | 509,515,520,532,543, 550nm, etc. | 552,556,561,577, 589nm, etc. | 607,633,639, | 720,1030,1064,1342,1550nm, etc. |
Laser interferometers, with their ingenious optical path design and advanced signal processing techniques, achieve ultra-precise measurements spanning from macroscopic to microscopic scales. Their applications extend across high-end fields such as industry, scientific research, and healthcare, and they are poised for further advancements toward higher precision, enhanced anti-interference capabilities, and multifunctional versatility in the future.
Changchun New Industries Optoelectronics Technology Co., Ltd.
Address: No. 888 Jinhu Road, High-Tech Zone, Changchun, 130103, P.R.China
International Tel:+86-431-85603799
Email: sales@cnilaser.com
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