The last optical element that the laser beam comes in contact with is the focusing lens. In CO2 lasers, this lens is usually made of one of several materials: zinc selenide (ZnSe), gallium arsenide (GaAs), or germanium (Ge). ZnSe, a thick yellow material that is transparent to visible wavelengths, is the most common of these materials and allows low-power HeNe laser beams to align. This is a great advantage over GaA or Ge, which is opaque to light in the visible part of the spectrum.
Sun: IAG lasers almost always use rapid expansion,
usually between 2k and 5k, as it is initially small in diameter. Space filters for CO2 lasers must be external, but those for Nd: IAG lasers can be located in the laser cavity itself and there are many different sizes available to choose from.
Nd: IAG lasers use optical glasses such as BK-7 or fused silicon for lenses.
The wavelength of these 1.06 μm lasers is close enough to the visible spectrum to allow adjustment of standard AR-coated optical devices to direct laser light. For example, microscope lenses can transmit Nd: IAG laser light to the surface of a VLSI circuit for microprocessing of conductor paths. As mentioned earlier, the delivery of Nd: IAG fiber optic laser beams offers incredible advantages over fixed optical network transmission. The advantage of fibers is unique to Nd: IAG lasers and has led to a huge increase in their use in the processing of industrial materials.
Fiber optic supply for Nd: IAG
The use of IAG laser fiber delivery in industry is so widespread that it should be discussed in more detail. About 90 percent of new Nd: IAG welding equipment involves the supply of optical fibers. Because glass optics transmit a wavelength of 1.06 μm, it can be used in conventional optical fibers. Normal air delivery is extremely cumbersome, prone to non-compliance As the technology of laser marking has advanced, new markets have evolved to take advantage of increasingly faster marking speeds as well as greater marking precision and imaging capabilities. Continuing developments in laser-cavity design, beam-steering and Fiber optic component, and computer hardware and software are expanding the role of the systems.
Steering the beam
Of the available marking technologies, beam-steered laser marking systems provide users with the greatest amount of image flexibility in a fast, permanent, noncontact marking process. As manufacturing processes become more automated and after-sale tracking more prevalent, laser markers are frequently the only method available to produce individually unique, permanent images at high speed.
Beam-steered laser marking systems usually incorporate either a CO2 or Nd:YAG laser. The CO2 laser emits a continuous-wave output in the far-infrared (10.6-um wavelength) while the Nd:YAG laser emits in the near-infrared (1.06 um) in either a CW or pulsed mode (1 to 50 kHz). The Nd:YAG laser is also unique in its ability to produce very short, high-peak-power pulses when operated in the pulsed mode. For example, a typical 60-W-average-power Nd:YAG laser can produce peak powers on the order of 90 kW at 1-kHz pulse rate.
The delivery optics consist of either a simple focusing lens assembly or a combination fixed upcollimator and flat-field lens assembly. In either instance, the laser beam is directed across the work surface by mirrors mounted on two high-speed, computer-controlled galvanometers