Ytterbium (Yb) doped glass fiber is the media for the fiber la- ser. Te process used to generate the beams from the Nd:YAG and fiber laser is largely responsible for the differences in the properties of the laser beam, primarily related to thermal management. Tose properties are defined in terms of beam quality, average power, and peak power. Beam Quality: Fiber laser is delivered using a fiber-optic
cable. In a fiber-laser system, the focus diameter is indepen- dent of the laser parameters and dependent only on the fiber diameter and the collimator/focus lens combination. Nd:YAG lasers for welding of medical devices, in most ap-
plications, are also delivered to the laser system using a fiber- optic cable. In fact, fiber delivery for pulsed Nd:YAG laser welding is a ‘must have’ and virtually all welding with this type of laser involves fiber delivery. Te reason for this is inher- ent to the laser itself. With a typical pulsed Nd:YAG welding laser, every small change to the laser parameters, required to compensate for flashlamp aging, changes the thermal input to the system which, in turn, changes the beam divergence, producing a different focus diameter. Tis generates different weld diameter and weld penetration. Since the laser output of the fiber-optic cable is divergent,
the output must first be collimated. A lens, called the collimat- ing lens, is used to capture and collimate the laser energy. Te collimated laser beam is then focused onto the workpiece.
Since the beam from the Nd:YAG laser is more di-
vergent that that of the fiber laser as a result of thermal effects, the diameter of the fiber through which the laser beam is delivered is two to three times greater. For the same focal lengths of the collimating and focusing optics, this would mean a two to three times larger focused beam at the workpiece. In the past, pulsed Nd:YAG lasers used relatively large
diameter fibers of 600 or even 1000 µm. Te resulting focused beams were useful for welding but not for cutting. Today’s pulsed Nd:YAG lasers, use smaller fibers, 100 to 300 µm, so are much better for cutting. But they have a disadvantage of low average power and, hence, low cut speed. Average and Peak Power: Te average power of fiber lasers
(to several kW) can be considerably higher than that of pulsed Nd:YAG lasers (hundreds of Watts). As is discussed later, this provides opportunity for new and more cost-effective manu- facturing processes. Te main disadvantage of fiber lasers compared to pulsed
Nd:YAG is lower peak power. High peak power is required for deep penetration (several mm’s) cutting (for piercing), drilling, and welding (for keyhole generation). However, since medical device manufacturing typically involves weld- ing, cutting, and drilling of thin materials, high peak power is not required.
Laser welded feed-through feature in a pacemaker cover. The latest fiber-laser technology provides for increasingly smaller welds which allow designers to reduce size of their devices.