Corrections to Laser Beam Emission Angle (Pointing Angle) May Be Required

Corrections to Laser Beam Emission Angle (Pointing Angle) May Be Required

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Are collimated beams always emitted parallel to the laser's axis?



A laser may not emit its beam parallel to the long axis of the laser package. This angular deviation is called the pointing angle (θp) and is described in Clip 1. Compensating for an angular deviation can be achieved when a kinematic mount with pitch (tip) and yaw (tilt) adjustments is used to position the laser.

Video Clip 1: The pointing angle (θp) is the angular deviation between the direction of the collimated laser beam (red arrow) and the long axis of the laser housing (dotted line). This axis is perpendicular to the front face of the collimator or collimated laser package.

Video Clip 2: Fitting a PL202 collimated laser package with an AD11NT adapter makes it possible to secure the laser in a KM100 mount that provides pitch (tip) and yaw (tilt) adjustment capability.

Angular Deviation
Several factors can result in angular deviation of the beam, including non-optimal seating of the laser in a mount, the laser cavity not being perfectly centered in the housing, and the deflection of the beam as it travels through optics integrated within the laser package. The compounded tolerances (tolerance stack up) result in a non-zero pointing angle.

When the laser has a cylindrical housing, this deviation can be measured by placing the laser in a V-groove mount, rotating the laser around its long axis, and recording the diameter of the circle traced by the laser spot. Maximum angular deviation is often specified for collimated laser packages.

Using a Kinematic Mount to Correct the Angle
One method to correct the angle of a laser beam is to secure the laser in a kinematic mount and use the mount's adjusters to tune the pitch and yaw of the laser. 

In some cases, the kinematic mount is directly compatible with the outer diameter of the laser housing. Kinematic V-mounts, including those compatible with Ø1.5" posts, can be configured to accept a range of different housing diameters without the use of an adapter.

Other kinematic mounts have an inner bore with a fixed diameter. A variety of adapters, including some designed for cylindrical or SM-threaded components, are available to create compatibility between the outer diameter of the laser housing and the mounts' inner bore.

Attaching an Adapter 
The procedure for using an AD11NT adapter to install a PL202 collimated laser package into a KM100 kinematic mount is demonstrated in Clip 2. Before attaching the adapter, pass the laser head through the bore of the kinematic mount, from back to front.

Because there is a stop integrated into the back plane of the mount's inner bore, it is necessary to attach the adapter on the side of the mount opposite the adjusters. The stop helps secure 1" diameter optics in the bore, but it also prevents the 1" diameter adapter from being inserted into the bore from the back of the mount.

The adapter includes nylon-tipped setscrews to secure the laser, and the mount also includes a nylon-tipped setscrew to secure the adapter. Nylon-tipped setscrews are chosen to securely grip the installed component without scratching or otherwise marring its surface.

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Date of Last Edit: Oct. 12, 2020

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