Laser Systems and Processing: Laser Classification
Laser systems are devices capable of generating high-intensity, monochromatic, coherent light beams, widely used in various industrial and scientific fields. Based on their operational principles, wavelength ranges, and application requirements, lasers can be classified into several types. Below are the common classifications of lasers and their characteristics:
1. Basic Laser Classifications
a. Classification by Operational Principles:
Gas Lasers: These utilize excited gases to generate laser beams, such as the CO2 laser and argon ion laser. CO2 lasers are extensively used for cutting, welding, and engraving, while argon ion lasers find applications in scientific research and optical measurements.
Solid-state Lasers: These lasers excite solid materials (e.g., crystals or glasses) to produce laser light, examples include Nd
lasers (neodymium-doped yttrium aluminum garnet) and Nd
lasers. Solid-state lasers are known for their efficiency and stability, suitable for medical, precision machining, and scientific research applications.
Semiconductor Lasers: These directly generate laser light using semiconductor materials (e.g., gallium nitride, gallium arsenide). Semiconductor lasers are widely used in communications, information technology, and optoelectronics, as well as industrial processing.
b. Classification by Wavelength:
Infrared Lasers: Typically operate within the wavelength range of 800 nanometers to 1 millimeter, used for processing metals, plastics, and other materials.
Visible Light Lasers: Operate within the wavelength range of 400 to 800 nanometers, commonly used in microscopy, display technologies, and specific material processing applications.
Ultraviolet Lasers: Wavelengths shorter than 400 nanometers, characterized by high energy and resolution, suitable for fine machining and semiconductor manufacturing.
2. Applications of Lasers
a. Industrial Laser Applications:
Laser Cutting and Welding: CO2 lasers, fiber lasers, and solid-state lasers are extensively used for metal cutting, welding, and surface treatment.
Laser Marking: Infrared and ultraviolet lasers are employed for marking, labeling, and tracking items.
Laser Engraving and Micromachining: Visible and ultraviolet lasers are used for precise engraving and micromachining of materials.
b. Scientific and Medical Applications:
Scientific Research: Solid-state lasers are used for spectroscopy, optical experiments, and quantum research.
Medical Lasers: Used in ophthalmic surgeries, dermatological treatments, and dental procedures.
3. Laser Processing Systems
A laser processing system includes not only the laser source itself but also optical systems, control systems, and auxiliary equipment such as cooling systems and gas supply systems. The combination and optimization of these systems enable efficient handling of various complex processing requirements.
Conclusion
As crucial tools in modern manufacturing and scientific research, lasers in their diverse types and wide application areas demonstrate their indispensable role in improving production efficiency, enhancing material processing precision, and fostering innovation in scientific research. With technological advancements and increasing demand, laser technology will continue to evolve and expand into new application domains.
Laser devices can be classified based on five aspects: gain medium, pumping method, output wavelength, output power, and operational mode. The specific classification methods are as follows:
According to the pumping method, lasers can be categorized as optical-pumped lasers, electrical-pumped lasers, chemical pump lasers, thermal pump lasers, and nuclear pump lasers. Generally, different types of pump sources are adapted to different absorption wavelengths of laser crystals.
Based on the output wavelength, lasers can be classified into infrared lasers, visible lasers, ultraviolet lasers, and deep ultraviolet lasers. Different materials have different absorption wavelength ranges, thus requiring lasers of different wavelengths to meet the demands of various materials in precision processing or different application scenarios.
According to the output power, lasers can be divided into low-power lasers, medium-power lasers, and high-power lasers. Lasers of different powers are suitable for different application scenarios.
Depending on the operating mode, lasers can be continuous-wave lasers or pulsed lasers. Pulsed lasers can further be categorized into millisecond lasers, microsecond lasers, nanosecond lasers, picosecond lasers, and femtosecond lasers. The operation of lasers can be continuous or pulsed, depending on whether their power output is essentially continuous over time or presented in the form of optical pulses at a certain time scale.
Based on the gain medium, lasers can be classified into solid-state lasers, gas lasers, liquid lasers, and free electron lasers. Solid-state lasers can further be categorized into fiber lasers, semiconductor lasers, all-solid-state lasers, and hybrid lasers.
In this article, several major types of lasers are detailed based on different gain media: disk lasers, fiber lasers, semiconductor lasers, and YAG lasers.
I. Disk Lasers [1]. Brief Introduction to the Principle and Advantages of Disk Lasers (laserfair.com)
Disk lasers are diode-pumped solid-state lasers, initially demonstrated in the early 1990s by Adolf Giesen at the University of Stuttgart. The gain medium in thin disks is typically a crystal such as Yb
, Nd
, and ytterbium-doped media used for wide wavelength tuning.
Currently, disk lasers are represented by TRUMPF products.
The design concept of disk lasers effectively addresses the thermal effects in solid-state lasers, achieving a perfect combination of high average power, peak power, efficiency, and beam quality. Disk lasers have become an indispensable new type of laser light source for machining applications in industries such as automotive, marine, railway, aviation, and energy. Currently, TRUMPF in Germany is the only company worldwide with the technology to produce high-power disk lasers, achieving up to 16 kW of power and beam quality of 8 mm*mrad, enabling remote laser welding with robotic arms and high-speed cutting of large surfaces, thereby opening up broad applications in high-power laser processing fields.
Advantages of Disk Lasers:
Modular structure Disk lasers adopt a modular structure, allowing rapid on-site replacement of each module. The cooling system and beam guidance system are integrated with the laser source, compact in structure, occupying a small footprint, and quick to install and commission.
Excellent beam quality and standardization For all TRUMPF disk lasers exceeding 2 kW, the beam parameter product (BPP) is standardized to 8 mm*mrad. The laser does not vary with operational modes and is compatible with all TRUMPF optical components.
Due to the large spot size inside disk lasers, the optical components endure lower optical power density. The damage threshold of optical component coatings is typically around 500 MW/cm², and for quartz, it is 2-3 GW/cm². The power density inside TRUMPF disk laser resonators is usually less than 0.5 MW/cm², and on coupled fibers, it is less than 30 MW/cm². Such low power densities prevent damage to optical components and avoid nonlinear effects, ensuring operational reliability.
Utilizes real-time laser power feedback control system. The real-time feedback control system maintains stable power reaching the workpiece, ensuring excellent repeatability of machining results. Disk lasers have almost zero preheating time, with an adjustable power range from 1% to 100%. Due to the complete resolution of thermal lensing effects, laser power, spot size, and beam divergence are stable across the entire power range, without wavefront distortion.
Fiber can be hot-swapped while the laser is running. In case of a fiber failure, simply close the fiber's optical path without shutting down, allowing other fibers to continue laser output. Fiber replacement is straightforward, plug-and-play, requiring no tools or alignment adjustments. Dust-proofing at the interface prevents dust or fiber contamination in the optical component area.
Safe and reliable operation. Even if the processed material has a high emission rate causing laser back-reflection into the laser, it does not affect the laser itself or the machining effect. There are no restrictions on material processing or fiber length. Laser operation safety is certified by German safety standards.
Pumping diode module replacement is quick and simple. Diode arrays installed in pumping modules are also modular. These modules have a long lifespan with a warranty period of 3 years or 20,000 hours. Whether for planned replacement or immediate replacement due to unexpected failures, there is no need to shut down operations. When one module fails, the control system alerts and automatically adjusts the current of other modules to maintain constant laser output power, allowing users to continue working for several hours or even tens of hours. On-site replacement of pumping diode modules during production is straightforward, requiring no training for operators.
II. Fiber Lasers
Fiber lasers are represented by IPG.
Principle: Fiber lasers, like other lasers, consist of three parts: a gain medium capable of generating photons (doped fiber), an optical resonator for resonant amplification of photons within the gain medium, and a pump source that excites photon transitions. See the diagram below.
Fiber Lasers:
Working Principle: Pump light is coupled into a gain medium (typically doped with rare-earth elements like erbium, neodymium) via a reflective mirror. The rare-earth ions absorb the pump light, undergo energy level transitions, achieve population inversion, and emit photons as they return to their ground state. This emission forms stable laser output.
Characteristics: High surface area-to-volume ratio for efficient cooling without forced cooling systems, high power density due to small core diameter, high efficiency, low threshold, narrow linewidth, and low coupling losses. Flexible and compact due to the flexibility of fiber optics.
Working Principle: Operate by injecting carriers (electrons and holes) into a semiconductor material. These carriers recombine and emit photons, generating light amplification when placed in a resonant cavity formed by two parallel mirrors.
Advantages: Small size, lightweight, reliable operation, low power consumption, high efficiency. Continuous wave and pulsed output available across a wide range of wavelengths from infrared to visible light.
Applications: Widely used in fiber optics, laser printing, laser pointers, optical discs, and various sensing applications.
YAG Lasers (Yttrium Aluminum Garnet):
Composition: YAG crystal (Y3Al5O12) serves as the laser medium. Pumped by a light source, typically a flashlamp or a laser diode, within a resonant cavity.
Types: Continuous wave YAG lasers, Q-switched YAG lasers (for short and ultrashort pulses), frequency-doubled YAG lasers, Raman shifted YAG lasers, and tunable YAG lasers.
Applications: Cutting, welding, drilling of metals and other materials due to precise control and high beam quality. Used in industries like aerospace, automotive, medical, and microelectronics.
