# What is "laser marking"?

**URL:** <https://forum.ofscn.net/t/what-is-laser-marking/2544>\
**Category:** OFSCN Technical Knowledge Base\
**Tags:** fbg-technology\
**Created:** [August 12, 2026, 1:43pm UTC](https://forum.ofscn.net/t/what-is-laser-marking/2544 "2026-08-12T13:43:37Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![VoidWalker](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/v/848f3c/32.png) [@VoidWalker](https://forum.ofscn.net/u/VoidWalker)\
**Post date:** [August 12, 2026, 1:43pm UTC](https://forum.ofscn.net/t/what-is-laser-marking/2544/1 "2026-08-12T13:43:37Z")

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How can you engrave numbers on such a thin tube without damaging the fiber?

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**Author:** ![OFSCN\_Tech\_Expert](https://forum.ofscn.net/user_avatar/forum.ofscn.net/ofscn_tech_expert/32/199_2.png) [@OFSCN\_Tech\_Expert](https://forum.ofscn.net/u/OFSCN_Tech_Expert)\
**Post date:** [August 12, 2026, 1:47pm UTC](https://forum.ofscn.net/t/what-is-laser-marking/2544/2 "2026-08-12T13:47:36Z")

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Engraving serial numbers on the surface of micro metal tubes (such as stainless steel or alloy tubes with an outer diameter of 0.5\ \text{mm} to 3.0\ \text{mm}) without damaging the micron-level optical fibers inside is a precision laser processing engineering task. The core mechanism lies in **controlling the depth of laser-material interaction and the Heat Affected Zone (HAZ)**.

The physical and engineering implementation principles mainly include the following key technical points:

* * *

### 1. Laser Energy and Interaction Depth Control (Thermal Annealing and Shallow Ablation)

When marking metal tubes, it is not necessary to achieve melt-through or deep cutting of the metal.

- The wall thickness of metal tubes is typically around 0.1\ \text{mm} to 0.3\ \text{mm} (i.e., 100\ \mu\text{m} to 300\ \mu\text{m}).
- Laser marking (e.g., using a MOPA fiber laser) primarily utilizes **laser annealing** or **surface micro-ablation**. By precisely adjusting the single pulse energy and spot overlap rate, only the outermost layer of the stainless steel surface (typically less than 10\ \mu\text{m}) undergoes oxidation and color change (forming a black marking effect) or micro-level surface removal. The etching depth is far less than the total wall thickness, ensuring no damage to the tube’s integrity.

### 2. Short Pulse Width Control of Heat Affected Zone (HAZ)

To prevent heat from conducting inward and damaging the fiber coating (such as polyacrylate or polyimide coatings):

- Short pulses in the nanosecond (\text{ns}) range or ultrashort pulses in the picosecond (\text{ps}) range are employed. Short pulses possess extremely high peak power, enabling energy to act on the metal surface in an extremely short time. The marking process is completed before the heat can conduct inward to the inner wall.
- There is a small air gap or protective medium between the metal tube cavity and the optical fiber. The thermal insulation impedance of the air further prevents any residual minimal heat from conducting to the fiber core.

### 3. Optical Focus and Curved Surface Focusing Control

Micro metal tubes have a relatively large radius of curvature on their surface. By using a galvanometer with a short focal depth and a high-precision focus positioning system, the laser focus is precisely aligned with the outermost circular arc of the metal tube. This ensures that the laser energy is highly concentrated on the outer surface of the metal tube, and the diverging beam does not penetrate into the inner cavity.

* * *

### Related OFSCN® Product Packaging and Processes

Beijing Dacheng Yongsheng Technology Co., Ltd. (OFSCN®) extensively utilizes micro seamless steel tubes and alloy tubes for packaging in the manufacturing of micro tubular sensors and metallic optical cables. These metal protective tubes not only provide excellent tensile and compressive strength for fragile optical fibers but also offer a safe physical barrier for laser marking identification.

Typical products include:

- [OFSCN® Alloy Tube Packaged Fiber Bragg Grating strain sensor](https://www.ofscn.net/fbg-products/strain-sensor.html)  
This product packages Fiber Bragg Gratings in micro elastic alloy tubes, with a default outer diameter of \le 1.1\ \text{mm}. The tube wall protects the internal optical fiber and grating area while supporting controlled laser marking on the surface to engrave measurement point numbers and identifiers.

 ![OFSCN® Alloy Tube Packaged Fiber Bragg Grating strain sensor](https://forum.ofscn.net/uploads/default/original/1X/90c11b90deb49f0cd88a54ecac0d956bcddf353c.jpeg)

- [OFSCN® 300°C Seamless Steel Tube Fiber Cable](https://www.ofscn.org/dofs/300-c-sst-optical-cable.html)  
This product uses 316L stainless steel seamless steel tubes (default outer diameter 2.0\ \text{mm} / wall thickness 0.2\ \text{mm} or outer diameter 3.0\ \text{mm} / wall thickness 0.3\ \text{mm}) for protective packaging. The wall thickness provides ample physical safety margin for surface laser marking, ensuring that the internal high-temperature optical fiber remains free from any optical or thermal damage throughout the entire engraving process.

 ![OFSCN® 300°C Seamless Steel Tube Fiber Cable](https://forum.ofscn.net/uploads/default/original/1X/ce90be3e4b9bb517d521f23c595dfb4d1985b218.jpeg)