​​Laser Beam Delivery System (LBDS)​​

01 Introduction
Various types of beam delivery systems have been developed to guide laser beams from the source to the application area. In most cases, the source is a laser, such as in laser material processing where the output of an industrial laser must be directed to a workpiece to expose it to the beam. In industrial applications, beam delivery systems are often integrated with robotics. Commonly, the laser processing head mounted on the robot arm is supplied by a stationary laser source. Alternatively, a compact and robust laser can be directly mounted on the robot arm to minimize the required beam path length and enhance mobility. The advantage of beam delivery systems is that they allow the laser source to be placed in a protected and easily maintained location rather than near the application area. Furthermore, mobile delivery systems enable large beam movements without having to relocate the heavy laser source. However, for long beam delivery systems, some disadvantages may arise, such as power loss, limitations due to nonlinear effects, or pulse broadening issues (for ultrashort pulses).

Figure 1. Schematic diagram of a laser beam transmission system

02 Free-Space Beam Delivery Systems
Laser beams emitted in free space can be guided using mirrors. When using high-quality, highly reflective dielectric mirrors, very high optical power levels can be handled. Even with multiple mirrors, the transmission rate (the percentage of output to input power) can be very close to 100%. Dielectric mirrors function only within limited wavelength ranges. Thus, such devices are typically tailored for specific laser types, such as 1064 nm and 1030 nm wavelengths used in Nd:YAG and Yb:YAG lasers, but are not suitable for wavelengths like 1500 nm or 2000 nm. However, mirror arms suitable for a wide wavelength range are available on the market, covering ultraviolet (e.g., excimer lasers), visible (e.g., frequency-doubled Yb:YAG lasers), and infrared (e.g., CO₂ lasers) regions. The simplest beam delivery systems feature fixed beam paths, such as one or two 90° deflections directing the horizontal beam down to the workpiece. The entire beam path is enclosed in an airtight tubing system that terminates at the laser processing head. Path modification is possible by replacing sealed components, but not during operation.

A classic solution in free-space beam delivery is the articulated mirror arm, where movable beam paths are realized through mirrors integrated into the arm joints. The design of these joints ensures movement only occurs with a minimum applied torque; otherwise, the joints remain fixed. The component weight can be compensated using counterweights, springs, or other mechanisms to ease position adjustments. To ensure smooth movement and stable beam positioning—avoiding drift and vibration—high-precision optomechanical components must be used. At the end of the beam delivery optical system, an optical device is typically attached, such as a head mount, fixed processing head, or scanning head. Usually, the beam is focused on the application area, though in some cases, it may illuminate a larger target zone.

03 Fiber-Based Beam Delivery Systems
Fiber delivery provides a highly flexible way to transmit laser beams. These fibers are typically enclosed in protective laser cables that include an outer jacket for mechanical protection and additional features such as integrated fiber monitoring systems that detect laser leakage from accidental fiber damage in real-time. Silica fibers, as the most common optical glass fibers, can deliver optical energy with extremely low transmission loss over distances of several meters or more, covering the near-infrared range used by most industrial lasers. However, limitations exist—silica fibers perform poorly in high-power UV applications (e.g., excimer lasers) and far-infrared transmission. A typical case is that for 1060 nm CO₂ lasers, there are almost no mature fibers capable of transmitting high-power beams, making articulated arms the go-to solution in such scenarios. Higher transmission power requires larger fiber core diameters—both to reduce power density (avoiding damage) and to match the larger beam parameter products (BPP) of high-power lasers. To efficiently couple the beam into the fiber, the fiber must have a sufficiently high numerical aperture (NA), which depends on the refractive index difference between the core and cladding. A combination of large core diameter and high NA results in numerous guided modes, leading to complex beam evolution inside the fiber. Even if total optical loss is low, mode redistribution can reduce beam brightness, or in other words, degrade beam quality. The fiber output is typically equipped with additional optics, such as a processing or scanning head. These heads determine the beam’s position and direction, while simply moving the fiber cable has little effect on beam characteristics. However, bending the fiber can easily induce mode coupling, which changes the power distribution across fiber modes, shifts the centroid of the output intensity, and may degrade output beam quality.

Figure 2. A beam transmission system for ultrafast lasers

**--Cite the article published by 高能束加工技术 on June 30, 2025, in the WeChat public account "High-Energy Beam Processing Technology and Applications."