Optical Choppers and Shutters

Optical choppers are mechanical devices which intercept a light beam on a periodic basis. Boston Electronics provides several optical chopping devices. Also available are lock-in amplifiers, often used in conjunction with optical choppers.

Boston Electronics offers several types of optical choppers: variable frequency rotating disks, fixed frequency tuning fork choppers, and optical shutters.

Rotating Choppers
Rotating choppers are appropriate for experimental settings where frequency, aperture size, or mark/space ratios (duty cycle) are variables. The variable frequency rotating disks resemble small fans: a slotted disk mounted on a motor head can be set to a variety of frequencies by adjusting the motor speed. An optoswitch senses disk position and provides a reference output monitoring the chopping frequency. An external control input permits the speed to be matched to an external signal. Numerous accessories are available. Our general purpose lab bench units with 102mm diameter disks cover the frequency range of 5 to 20,000Hz, with options extending this down to 0.01Hz and up to 45,000Hz. Miniature units with 30mm diameter disks cover the frequency range 5 to 8000Hz. OEM versions, designed to be embedded in an apparatus or instrument of customer design, lack mechanical mounts and electrical interconnections but are otherwise complete.

For more technical data on the choppers, view the following manuals.

Tuning Fork Choppers
Tuning fork choppers, or "resonant" choppers, are appropriate for optical chopping when a single known fixed frequency is desired and small size or long life is needed. Tuning fork choppers resemble musical tuning forks with small vanes mounted on the tines. They vibrate in response to an AC drive signal at their resonant frequency. Their vibration occurs at a frequency fixed by the mechanics of the structure. Small size and long life make them appropriate for dedicated use in equipment. They are extremely durable and have no wearing parts; as a result they survive high acceleration and vibration and last for years. Tuning fork choppers are versatile and can be supplied for use at high or low temperature or in vacuum. Their vanes can be blackened or shiny like mirrors. Our Tuning Fork Chopper Tutorial gives additional details about the properties of tuning fork choppers.

Optical Shutters and Laser Beam Safety Shutters
Shutters differ from choppers in that they are not limited to a simple periodic on-off cycle but will follow an arbitrary, varying pattern of openings and closings. Optical shutters are useful for low frequency chopping, particularly when slow or non-periodic behavior is desired. Our CH-50, CH-60 and CH-61 shutters respond to a TTL input waveform. A single vane mounted behind an aperture moves to block or reveal the aperture based on the signal it receives. The vane can be stopped in either the open or closed position. A related product, the laser beam safety shutter, opens when power is on and closes when it is off, and can be used as an economical though shorter life alternative to the CH-series shutters. The models that Boston Electronics offers differ principally in the time it takes to open or close the aperture, the aperture size, and the expected lifetime of the mechanism.

The laser beam safety shutters can be wired in a number of configurations, based on the desired operation use.

SH-10 and SH-20 Ways to Activate

For help on choosing among the different choppers and shutters, refer to the following page.

Questions? Comments? Suggestions? Send email to the Webmaster at Boston Electronics.