What is high reflection ?
Generally speaking, high reflection refers to the low resistance of processed materials, the smooth surface and the low absorption rate of near-infrared lasers. The figure shows the absorption coefficient of common metallic elements, which results in the emission of a large number of lasers.
Furthermore, in most laser usage scenarios, the material is perpendicular to the laser or at a small tilt angle.
As a result, the returned laser re-enters the output head and even a part of the returned light is coupled to the power transfer fiber and transmitted back to the laser, leading to continuous high temperatures in the laser's main components.
Specific anti-high reflection implementation scheme
In the process of processing high-reflection materials, the high-reflection laser may cause damage to the cutting or welding head and the laser source if it enters the laser source. This is especially true for high-power fiber laser products, where the laser return power is significantly higher and the risk of damage is greater. If the material is not penetrated during cutting, the high-power return light can return into the laser and cause damage.
To solve these problems, the R&D team of Raycus laser designed a four-level anti-high reflection light protection design and added multiple return light monitoring functions to ensure real-time protection of the laser in case of abnormal processing.
01 C lass IV anti-high reflection light design
Anti-high reflection design of optical cable output head
Raycus laser designed QBH, QD and QP fiber optic output heads are designed to effectively convert uncontrollable return light into absorbable light and heat, improving the heat absorption and dissipation capacity of the output head and minimizing the impact of return light on internal components.
In the laser processing system, the feedback laser may impact the output optical cable head and cause heating or damage. To ensure the safety of the output optical cable, a primary return light removal device was integrated into the output optical cable, as shown in the figure at the top of the original design.
The anti-high reflection design added to the end of the optical cable helps reduce damage to the laser's internal optical structure by immediately removing most of the returned laser. This design, combined with a water cooling system, effectively absorbs the returned stripped laser and eliminates its thermal impact on the optical cable output head.
Two-stage anti-glare design in beam combining module
High-power multi-module laser products are mainly constructed using multiple unitary modules in a beam combination.
When cutting high-reflection materials, some light may still be transmitted back into the beam combination through the output optical cable, even after passing through the primary anti-high-reflection design in the cable.
Therefore, to ensure the safety and reliability of the optical devices and optical path design within the beam combination, a two-stage anti-high reflection shielding design is added, as illustrated in the figure.
Step-by-step removal of the homing laser ensures the safety of optical anti-high reflection protection devices and reduces the impact of the homing laser on the laser optical path structure.
Anti-glare design on the unit module
Due to the presence of an optical resonator inside the drive module, when the low-power feedback laser enters and is repeatedly amplified by the resonator, it can seriously impact the optical stability of the laser and increase the likelihood of damage to the laser.
To increase the stability and reliability of the laser during high-power reverse cutting, the drive module includes a high anti-reflection device in conjunction with its optical path design, as illustrated in the figure.
02 High anti-glare multiple software monitoring design (imported successively)
High-reflection software protection refers to the monitoring and protection mechanism that is activated when strong backreflection generated by the laser enters the laser optical system during the processing of high-reflection materials, leading to instability of laser operation or damage to optical devices.
Although the anti-high reflection device can ensure that the laser continues to operate without damage within a specific return laser power limit, there is still a risk of damage if this limit is exceeded. To ensure timely protection of the laser in case of excessive laser return power, various high anti-software protection designs have been added into multi-module high-power laser products.
High anti-interference protection design for output optical cable
When the return optical power is high, part of the returned laser will return to the output optical cable along its original path, while the remainder will directly impact the front of the output optical cable.
While carrying out research on return laser transmission and monitoring function integration technology, we have integrated multiple detection functions, such as laser monitoring and return light monitoring, into optical cable temperature monitoring for real-time monitoring of the return laser. return.
If the power of the homing laser exceeds the laser's capability, the laser will shut down and an alarm will sound immediately to prevent damage. This also serves as a reminder to the customer that there is a problem with processing.
Combination of beam and optical module with high protection design
Since there are two types of return laser: center laser and cladding laser, in addition to the high anti-protection design of the output optical cable, we also incorporate a high anti-detection module within the beam combination to monitor the reverse transmission laser power and track return laser power in real time.
This high-reflection detection module can detect both core and cladding lasers, effectively reducing the risk of laser damage caused by the core-return laser, which could go unnoticed if only the cladding-return laser was being monitored.
In the case of a high-return laser, the module will turn off the laser and trigger an alarm, ensuring the safety and reliability of the laser.
03 Cutting test
Due to the low laser absorption and high thermal conductivity of red copper, the red copper surface remains in a mirrored state, causing a constant stream of laser to return to the optical fiber output head. This allows evaluation of the anti-high reflection capabilities of the new fiber optic output head.
Aluminum Cutting
Red copper cutting and abnormal cutting
With proper operation, the Raycus laser can effectively cut high-reflection materials such as aluminum, brass and red copper plates, resulting in efficient cuts and desirable cross-sectional effects.
The high reflection abnormal processing test is conducted to evaluate the anti-high reflection capabilities of the laser.
When marking back and forth on a red copper plate, the laser does not penetrate the plate, resulting in a high light return. Despite this, the laser continues to function normally, demonstrating the strong anti-high reflection capabilities of the Raycus laser.
Signal display
The high reflection test demonstrates that the high reflection monitoring signal can be transmitted to the screen in real time during the cutting process.
In case of abnormal processing, the high reflection signal can be monitored and its value remains within the laser limit.
If the high reflection exceeds a certain threshold, the machine alarm will be activated to alert staff to check the operation for errors.
The following suggestions are provided by the process engineer for cutting high-reflection materials:
(1) When cutting brass, red copper and other materials, it is advisable to maintain a moderate speed and leave some space, avoiding extremes.
(2) Red copper must be cut with oxygen, not nitrogen or air.
In case of the following problems, the machine must be stopped immediately for inspection:
(1) Contamination of the lower protective mirror.
(2) Failure of material penetration during high reflection cutting.
(3) Material penetration during high reflection cutting, but failure in complete cutting.
