In the previous article, we detailed the M² factor, the "gold standard" for beam quality, and how to accurately measure and optimize the M² value in practical applications. The answer is actually quite simple—the practical value of the M² factor relies heavily on the seamless integration of a beam analyzer. This article focuses on the combined application of these two components, from equipment setup to industry practice, adapting to the needs of R&D, production, and application fields.

I. Basic Definitions of M² Factor and Spot Analyzer

The M² factor (beam quality factor) is an internationally recognized parameter for quantifying the spatial quality of a laser beam. It measures the degree of deviation between the actual laser beam and the ideal fundamental Gaussian beam (TEM00 mode) and is a key indicator for judging laser performance.

As a core supporting device for M² factor measurement, the laser spot analyzer can not only capture real-time images of laser spots, but also calculate M² values ​​in conjunction with them. Furthermore, it can locate beam quality problems through data analysis, serving as a key bridge for transforming the M² factor from an "abstract parameter" into a "practical indicator".

II. The M² factor comprehensively reflects four major characteristics

The M² factor, while seemingly a numerical value, actually comprehensively reflects multiple key properties of the laser and directly determines the application effect of laser equipment:

• Focusing capability: The smaller the M² value, the smaller the laser spot size that can be focused, and the higher the power density, making it suitable for high-precision processing and other scenarios;

• Transmission efficiency: The high-quality beam with low M² has less energy loss during long-distance transmission, making it suitable for applications such as laser communication and remote processing.

• Mode purity: M² > 1 means that there are higher-order mode components in the beam. The larger the value, the higher the proportion of higher-order modes and the worse the beam quality.

• System compatibility: Especially in fiber optic coupling scenarios, single-mode fiber has extremely high requirements for beam size, and usually requires an M² value close to 1 to ensure good coupling efficiency.

III. Measurement Device Setup and Optical Path Adjustment

Accurate measurement of the M² factor requires standardized setup and optical path calibration. The core equipment and adjustment methods are as follows:

(I) Core measuring device

1. Focusing lens (focal length known)

2. Slit-type or camera-type spot analyzer

3. Precision displacement platform (scanning along the optical axis)

4. Attenuator (optional, to prevent detector saturation)

(II) Techniques for Adjusting the Optical Path

The optical path is constructed and aligned using two mirrors (usually plane mirrors). The alignment principle is based on the dual-mirror method of adjusting the optical path, that is, by precisely adjusting the angle and position of the two mirrors, the incident light and the target optical path are matched coaxially (or in a specified direction).

IV. Industry Applications and Laser Optimization Value of the M² Factor

(I) Laser R&D and parameter iteration (core requirements for technical positions)

1. Application objective: To improve beam quality and shorten the research and development cycle by optimizing the core parameters of the laser through real-time monitoring.

2. Specific scenario: In the research and development of fiber lasers, when adjusting key indicators such as pump power, fiber core diameter, and grating parameters, a spot analyzer is used to track the changes in the M² value in real time to avoid parameter redundancy caused by adjusting based on experience.

3. Core Value: Provides data support for parameter adjustments, significantly reduces ineffective R&D attempts, and accelerates product iteration.

(II) Laser production and outgoing quality inspection (core requirements for production/quality inspection positions)

1. Application Objective: To establish a standardized quality inspection process to ensure that the M² value of lasers leaving the factory meets the standards and reduce after-sales risks.

2. Specific scenario: During mass production, samples are taken at a rate of 10%-20% of each batch, and the M² value is quickly measured using a spot analyzer (the common industry standard for acceptance is M² ≤ 1.5). Non-conforming products are promptly intercepted.

3. Core Value: Unified quality inspection standards prevent substandard products from entering the market and maintain brand reputation.

(III) Optimization of laser processing technology (core requirement for application positions)

1. Application objective: To match optimal processing parameters, reduce debugging time, and improve processing yield.

2. Specific scenarios: During laser cutting and welding, fluctuations in the M² value can lead to problems such as burrs on the cutting edge and incomplete welds. By using a spot analyzer to monitor the stability of M² in real time, we can ensure that the beam quality always meets the standards during the processing.

3. Core Value: Reduce process trial and error costs, improve production efficiency, and ensure product processing accuracy.

(iv) High-tech fields such as medical care and scientific research (special needs scenarios)

1. Application objective: To meet stringent beam quality requirements and ensure safety and experimental accuracy.

2. Specific scenario: Medical equipment such as femtosecond lasers in ophthalmology have extremely high requirements for beam quality, which must meet the requirements of M²≤ 1.3 and long-term stability error<2%. Continuous monitoring through a beam analyzer can avoid surgical risks caused by beam quality deterioration.

3. Core Values: Compliance with industry regulations ensures medical safety and the reproducibility of scientific research results.

V. The Optimization Effect of the Spot Analyzer on the M² Factor

The spot analyzer is not merely a tool for "measuring M²", but its core value lies in its ability to pinpoint the root cause of M² degradation through a closed-loop "measurement-analysis-feedback" process, thereby guiding M² optimization. Its specific functions can be categorized into three main types:

1. Precisely pinpoint the physical root cause of M² degradation: An increase in the M² value essentially indicates that the beam deviates from the ideal Gaussian distribution, but the cause cannot be determined solely by the numerical value. The analyzer can quickly pinpoint the problem through beam spot visualization and multi-parameter linkage analysis;

2. Parameter iteration closed loop supporting M² optimization: Provides real-time data feedback during R&D or process debugging, helping staff quickly identify the optimal parameters without repeated trial and error;

3. Long-term monitoring of M² stability to prevent performance degradation: After long-term use of laser equipment, aging of optical components, vibration, temperature drift and other factors will cause the M² value to rise slowly. The analyzer can achieve long-term stable monitoring and provide early warning of potential faults.