Designed for the medical products industry, a new scanner is finding applications in materials processing
For decades lasers have been employed successfully to combat the ravages of chronological and sun-induced aging of the skin. Common ablative skin resurfacing techniques using CO2 or erbium:YAG lasers, for example, offer dramatic results. However the procedure and recovery period are both quite painful, the healing process takes weeks, and the risk of infection lurks constantly.
Patient shown at left before treatment and at right after five Fraxel laser treatments. (Dr. S. Wall, Jr.)
The development of less ablative or non-ablative laser skin rejuvenation therapies is rapidly resurfacing the face of aesthetic medicine. Although the cosmetic outcome is not nearly as remarkable, treatment is much easier to tolerate, the risk of infection is low or non-existent, and downtime is drastically reduced in both length and severity.
The deep penetration of 1550nm laser energy gradually heats water molecules in the skin.
Medical device company Reliant Technologies (Mountain View, CA; www.fraxel.com), introduced non-ablative fractional resurfacing (NFR) in 2005 with its enormously successful flagship platform, the Fraxel® SR. Fraxel laser, as it is known, provides efficacy closer to ablative techniques with safety and downtime in line with non-ablative techniques. The device is designed around a 30-watt, 1550nm erbium-doped glass fiber laser optimal for deep, controlled penetration of the skin surface. Instead of vaporizing skin from the surface on down, the energy coagulates subsurface tissue without removing the outermost layers of skin, preserving barrier function and stimulating new collagen growth. More importantly, however, NFR does not rely on the massive thermal wounding of the entire treatment area in the way that ablative techniques do. Fraxel laser’s scanner technology rapidly lays down a uniform pattern of laser spots 70-100 microns in diameter (called Microscopic Treatment Zones or MTZs), spaced 200-300 microns apart within the treatment area. By leaving the surrounding tissue healthy, healing is rapid and higher treatment energies may be used. The delivered energy and the density of MTZs may be adjusted by the operator to maximize results and minimize discomfort.
To the industrial world, the unique scanner used in the Fraxel laser device is its most outstanding feature. In order to make Fraxel laser work, Reliant developed a software-controlled, motor-driven scanning wheel (named the Broome Wheel Scanner, after its inventor) that is shaped almost like a gear. Its 29 “teeth” are facets that focus laser energy in different directions, depending on which facet is currently in the path of the laser light, with minimal impact on efficiency. The scanner has applications beyond the medical products industry, especially in materials processing where microscopic holes or welds must be created rapidly and accurately, or where heat management is a serious issue.
Advantages of the Broome Wheel Scanner include:
- Fast, accurate processing
- No setting time
- High optical efficiency
- Heat management
- Better overall process control
The Broome Wheel Scanner currently can be configured to lay down up to 5000 spots per second while harnessing approximately 90 percent of laser output power. There is no settling time, as there is with other technologies. The scanner is designed for a long life with minimum downtime; the unit can withstand a 6G shock without pattern distortion, and is designed for constant use. Reliability has been outstanding-a handful of field service engineers has been able to keep up with service demand for the more than 1000 Fraxel laser units currently in the field. This means faster, more accurate production and better process control, which in turn leads to higher yields.
There are 29 facets around the Broome Wheel, but it could be designed with more. Control may be Ethernet- or PC-based with the user interface customized for the specific application to set up, monitor, and adjust the process. Laser power, as well as timing, for each facet window can be individually controlled, allowing for spots of different diameters to be created across the linear array. The unit is designed to handle multiple beams of any wavelength, and can utilize lasers with M2 approaching 1.1.
Technologies such as linear motors, acoustic optical modulators, galvanometer scanners, polygon scanners, and other optomechanical schemes are sensitive in the manufacturing environment. Settling times are longer, and they are less efficient and precise. Moreover, other scanning technologies are relatively high maintenance, and the associated downtime reduces overall production.
The Broome Wheel Scanner will never totally replace galvanometer-based or other scanner technologies, but will have a strong advantage for applications that are sensitive to thermal effects or require high-speed processing and accurate spot location. With this technology laser welding or drilling can be performed in an adjustable, non-sequential pattern that distributes heat without losing speed or accuracy. Laser removal of paint for various applications could be done in this manner to prevent heat buildup. This capability qualifies the device for a range of current applications as well as for use with emerging applications.
A persistent problem in high-speed laser drilling is thermal management. In many cases the laser/scanner combination has the capability to drill accurately and quickly, but the material reacts adversely to the rapid application of heat to nearby areas in succession, and becomes distorted. When drilling combustors for the jet engine industry, for example, multiple shots may be required to drill the hole as the combustor is rotated. The laser fires on the fly, with the number of rotations equal to the shots required. With the Broome Wheel Scanner, multiple rows can be processed during each revolution. Therefore, users can take advantage of the high-speed firing capability of fiber lasers. As a result the scanner is compatible with on-axis nozzles in a way not possible with galvanometer-based products. YAG lasers typically fire at 10-15 pulses per second at 20 J, whereas fiber lasers can produce 20 J at 10,000-20,000 pulses per second. Other drilling applications where this technology may successfully be applied include: hydraulic filter screens, filters for the food processing industry, holes in the leading edge of aircraft wings, or via holes in circuit boards.
Laser micro-welds in stainless-steel optical flexure mount.
Many potential applications for the Broome Wheel Scanner will take advantage of the accurate, high-speed laser welding capability that minimizes heat-induced materials distortion. An ideal application for a scanner integrated to a fiber laser is the welding of the flexures used on the read-write heads of computer hard disc drives, which requires very rapid welding with thermal management to ensure a lack of distortion on the resulting assembly. These devices are currently welded with conventional scanners, which are rapid but cannot compete with the speed and accuracy of the Broome Wheel Scanner. Other potential applications include medical device manufacturing, battery or fuel cell manufacturing, electronic packaging, or high-speed tack welding.
Scan head for high-speed hole drilling.
Although not poised to completely replace many technologies in current use, the Broome Wheel Scanner may revolutionize manufacturing and materials processing in the same way Fraxel laser is revolutionizing skin rejuvenation. Galvanometers, linear motors, polygon scanners, and AOMs may be rendered obsolete for some specialized applications because they are not as fast, accurate, durable, reliable, or efficient. Moreover, the scanner will make possible applications that have yet to come to fruition merely because of the lack of access to the capabilities of the Broome Wheel Scanner. The limits of the old technologies are obvious, while the possibilities of this device appear to be endless.
Joe Dallarosa (email@example.com) is director of special projects at Reliant Technologies Inc. (Mountain View, CA). For more information, visit www.fraxel.com.