Open or Closed Chopper?
We offer two types of Chopper Systems: open and closed. Both chopper systems use the same controller, and most of the same wheels.
Open chopper system
The 75159 Open Chopper is economical and versatile. Because you have complete access to the wheel, you can chop various beams simultaneously. Wheel interchange is quick and easy. You can mount the 75159 on an optical rod, or directly to an optical table. It is useful for chopping laser beams. Dual aperture blades allow sum and difference frequency explanation of physical parameters.
Enclosed Chopper System
- Chopper blade is enclosed; provides safer operation
- Safeguards against hazardous scattered light from high intensity sources
- Has 1.5 Inch Series flanges for direct coupling to Oriel Light Sources or Detectors
- Offers on/off “shutter” frequency
The 75158 Enclosed Chopper System is a better choice if you're mounting the chopper in an optical system; you can couple the chopper head directly to other instruments via the 1.5 Inch Series male flange. When chopping lasers or UV beams, you can reduce potential hazards by enclosing the beam path. Additionally, you can ensure that unchopped ambient light does not saturate a detector when you enclose the optical path, after the chopper. This model includes various apertures from 0.18 to 1.26 inches (4.6 to 32 mm) in diameter, to match the beam size to wheel aperture size. The 75158 also has a 1/4-20 tapped hole in its base, for rod mounting. Note, you cannot use the dual aperture chopper wheels with the enclosed chopper.
Chopper Wheels
We offer two types of chopper wheels: single and dual aperture. Both are 5 inch (128 mm) diameter wheels with standard aperture patterns. The single aperture models fit in either chopper head; the dual aperture models are only usable in the open chopper head. Use the dual aperture models to chop multiple beams simultaneously. The wheels are precision etched, and coated with a broadband absorber to minimize retroreflections. You can vary the chopping frequency with the controller. In any situation, the maximum chopping rate depends upon:
1. Beam diameter, which determines the maximum number of apertures you can use (see Fig. 1)
2. Maximum rotation rate of the motor: 80 rps for continuous duty operation.
The Chopper Wheels Table shows the number of apertures, maximum chopping frequency and beam diameter limit for each wheel, at full modulation. If the beam size is limiting the chop rate, consider focusing the beam at the chopper to reduce the beam size. This allows you to use a wheel with more apertures, and therefore get a higher chop rate.
Fig. 1 The largest beam fits just inside the aperture with its edge at the aperture edge. This is the largest beam which is fully blocked by the blade. With two blades, you can use the slots to rotate one blade with respect to the other, to choose the duty cycle.
