MultiWave Hybrid Technology* combines multiple laser beams with various wavelengths into a single coaxial laser beam. There are existing systems using two different laser wavelengths independently, but this is the first technology capable of combining multiple wavelengths into a single beam, providing a valuable tool for the development of novel material processing technologies.
One example of an existing application using two wavelengths independently is stainless steel cutting. In this application, a 1.06μm laser beam is used to heat the steel locally, thereby increasing its optical absorptivity. Once the material is heated, the 1.06μm laser beam is switched off, and a 10.6μm laser, which is much less expensive to operate, is used to complete the material processing operation. This allows one laser wavelength to modify the properties of the material so the second laser wavelength can carry out the material processing operation much more efficiently.
MultiWave Hybrid Technology takes this capability to a new realm. It allows multiple laser beams with various wavelengths to be combined into a single coaxial beam. Each component of this hybrid laser beam is independently controlled to allow optimum laser processing flexibility for an unlimited number of organic and inorganic materials. Moreover, the unique design of the optical system allows all wavelengths to focus into the same plane simultaneously. This allows the different wavelengths to work together to provide material processing capabilities that have never before been possible.
Interaction of Laser Energy with Materials
A laser beam is an electromagnetic wave with a characteristic wavelength. The wavelength is dependent upon the type of laser used to generate the beam. Figure 1 shows a portion of the electromagnetic spectrum extending from the ultraviolet region at the left, through the visible region in the center and into the infrared region at the right. Various types of lasers are depicted on the spectrum, each at its characteristic wavelength. These individual lasers have applications ranging from microelectronics, to optical storage to laser processing of materials. MultiWave Hybrid Technology combines several of these wavelengths into a single beam to add a new dimension to the way laser energy interacts with materials.
When a laser beam (like any electromagnetic wave) passes through a material, it will interact with the material in some way. The electric field associated with the laser beam causes any charged particle in the material to move. There are two types of charged particles in the atomic structure of any material: electrons and protons. The protons have a relatively high mass and are difficult to move. The electrons have a much lower mass; therefore, they can move more easily in response to the force exerted by the electric field component of the laser beam. This movement is a regular oscillation with a period determined by the wavelength of the laser beam.
After being set in motion by the laser beam, the moving electrons need to return to their equilibrium state. This is achieved through one of two mechanisms. The electrons can re-emit electromagnetic energy in random directions, where the laser beam is said to be reflected or transmitted depending upon the direction. Alternatively, a population of electrons all oscillating with the same period can transfer their energy to the chemical lattice of the material. In this case, the energy of the laser beam is said to be absorbed.
Interaction of Laser Energy with Organic Materials
Generally speaking, organic materials are chains of carbon atoms with hydrogen atoms bonded at regular intervals (Figure 2). For organic solids, these chains can be thousands of carbon atoms long.
Because of the regular molecular structures of these organic materials, they can only oscillate in certain modes. For example, carbon-carbon bonds can stretch and relax with a certain characteristic period, or they can rotate back and forth, again with a characteristic period. The implication for laser processing is that only lasers with wavelengths that match the natural oscillation periods of the organic material are absorbed. If the laser wavelength does not match the characteristic oscillation periods, then the laser energy will be reflected or transmitted.
This point is illustrated by the absorption spectrum for acrylic, a common organic material (Figure 3). The chart shows that for a 10.6μm laser, nearly 100% of the laser energy is absorbed. In contrast, the energy absorption for a 1.06μm laser is nearly zero.
Most organic solids, being made up of long chain hydrocarbons, have optical absorption spectra similar to acrylic. They tend to absorb very strongly in the mid- to far-range infrared region, from about 3μm to 15μm wavelength. This explains why CO2 lasers with a wavelength of 10.6μm are so effective for organic materials.
* Universal Laser Systems’ MultiWave Hybrid Technology is U.S. Patent Pending.