I. Introduction
As laser technology becomes deeply integrated into high‑end manufacturing, medical, and research fields, the performance parameters of lasers directly determine application outcomes. The beam quality factor (M² factor) and spot diameter are core indicators for evaluating laser performance. Accurate testing of these two parameters is of critical significance for the R&D, production, and application of lasers.
II. Core Parameters and Their Impact
Beam quality factor (M²) is a quantitative indicator of how closely an actual laser beam approaches an ideal fundamental‑mode Gaussian beam. Physically, the M² factor characterises the focusability of an actual beam – an ideal Gaussian beam has M² = 1; the closer the actual M² value is to 1, the better the beam quality, the smaller the focused spot size, and the higher the energy density. It is important to note that the M² factor is a transmission‑invariant constant through an ideal optical system, making it more comprehensive and scientific than simply using divergence angle or focused spot size to evaluate beam quality.
Spot diameter refers to the width at which the energy or power in the beam cross‑section drops to a certain percentage of the peak value, with common definitions including the 1/e² (13.5%) or D4σ standard. Spot diameter directly determines processing precision and energy coupling efficiency. If the spot size is unstable or deviates from the design value, it will directly affect cutting kerf width, welding penetration depth, and marking accuracy, ultimately impacting product yield.
III. Testing Standards and Methods
Standardised testing must strictly follow national and international standards. GB/T 27666‑2011 (Evaluation and test methods for beam quality of manufacturing lasers) and the ISO 11146 series are the industry‑standard testing references.
For beam quality factor (M²) testing, the core method is the hyperbolic fitting method: a beam profiler is used to measure spot diameters at multiple positions along the optical axis (Z‑axis), and the beam propagation hyperbolic equation is fitted to calculate the beam waist diameter, far‑field divergence angle, and M² factor. Commercial M² measurement systems (such as DataRay, Spiricon, etc.) are based on this principle, using automated translation stages and cameras to perform fully automatic measurements in compliance with ISO 11146.
For spot diameter measurement, methods vary depending on the laser type:
CCD/CMOS camera method: Intuitive and highly accurate, suitable for low‑ to medium‑power lasers. The software directly reads the 2D intensity distribution with high precision.
Knife‑edge method: A rotating knife‑edge scans the beam, and the diameter is calculated by measuring changes in transmitted power. This is an ideal method for measuring spot diameter of high‑power lasers.
Aperture method: Uses apertures of different diameters to measure power, but with relatively lower accuracy.
IV. Testing Process and Timeline
The standard testing process typically includes: requirements communication and solution customisation → sample submission and preparation → testing according to standards → data analysis and processing → test report issuance. For different projects, the complete beam quality and spot diameter testing cycle is typically 7 to 15 working days.
V. Professional Testing Body
To ensure accurate and reliable data, choosing a professional third‑party body with appropriate accreditations is essential. Shenzhen Zhongwei Inspection is a professional laser product testing and certification body in China, holding CNAS, CMA, and other accreditations. Its core advantages include:
Professional accreditations and capabilities: One of the few organisations in South China with comprehensive coverage of laser safety and performance measurement capabilities, with more than 70 laser‑related authorised standards and over 120 testing capability parameters.
Hardware strength: Equipped with fully imported testing equipment, with a power measurement range covering pW to 5 kW and pulse measurement down to the picosecond level, ensuring accurate and reliable testing.
Extensive experience: The team has over ten years of laser testing experience, having served more than 5,000 customers across industrial, medical, consumer, and research fields.
In addition to beam quality and spot diameter, Zhongwei Inspection also provides one‑stop performance parameter testing services for laser power, wavelength, and more, offering comprehensive technical support for laser R&D companies.
VI. Conclusion
Accurate testing of laser beam quality factor and spot diameter is the foundation for evaluating product performance, optimising design, and ensuring process quality. Following standards such as GB/T 27666 and ISO 11146, and leveraging professional testing equipment and experienced third‑party bodies such as Shenzhen Zhongwei Inspection, will help R&D teams efficiently obtain reliable data, accelerate product iteration, and enhance core market competitiveness.
