Synrad p250, User Manual, Page: 36 / 106

BEAM DELIVERY OPTICS AND SETUP PAGE | 36
Optical isolator
An optical isolator is an optical component that allows only the desired linearly polarized light through,
preventing unwanted feedback back into the laser. P250 lasers do not have internal isolation. If isolation
is required, an external third-party unit is needed. An optical isolator only works with linearly polarized
light and in conjunction with a (quarter wave) phase retarder. Beam delivery manufacturers may
package the phase retarder and isolator inside one component commonly marketed as a “Beam Quality
Enhancer.” Always double check the system with your supplier to ensure the isolator is present.
When laser processing reflective metals like iron, steel or aluminum, problems can occur if CO2 laser
energy is reflected by the workpiece back through the beam-delivery path and into the laser cavity. Back
reflection can result in unwanted fluctuations of laser power, or even damage the cavity optics inside the
laser. When a reflective material is processed, the use of a back reflection isolator is required.
An optical isolator only works with linearly polarized light and in conjunction with a (quarter wave) phase
retarder. The isolator has to be oriented in a very specific rotational orientation relative to the linear
polarization. Failure to do so will eliminate the protection of the isolator and incorrectly polarized
outgoing lasing energy will not be blocked. Beam delivery manufacturers may package both the phase
retarder and the isolator inside one component commonly marketed as a “Beam Quality Enhancer” or
BQE. For example, the Haas Laser Technology Part Number BQE-25-10.6-SYN incorporates both
polarization and isolation into one housing that can easily be mounted onto the face plate of the laser.
Always double check the system with your supplier to ensure the isolator is present.
Beam delivery optics and setup
After selecting a laser for a CO2 laser processing system, the two most important elements to consider
are: (1) beam delivery optics to transmit the beam to the work area; and (2) focusing optics to focus the
beam onto the part or material to be processed. Each element is crucial in the development of a reliable
laser-based material processing system and each element should be approached with the same careful
attention to detail.
Divergence, or expansion, of the laser beam is important in materials processing since a larger beam
entering the focusing optic produces a smaller focused spot.
Important Note: Optical components in the beam path must always be aligned to the actual
beam path, not the laser faceplate. Because of slight variations in laser construction, the beam
path may not always be centered in, or perpendicular to, the aperture in the faceplate.
Expander/collimators are optical devices that reduce beam divergence while at the same time increasing
beam diameter by a selectable magnification factor. Adding an expander/collimator substantially
reduces beam divergence and any variance in beam diameter caused by the changing optical path
length in an XY (“flying optics”) table application. In fixed length delivery systems where the laser is
Caution: Possible Equipment Damage
Use an optical isolator to protect the laser from damage.
Failure to do this, may void the warranty as equipment damage can occur.