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Optical Chopper, Phase Locked, Includes 6 Wheels
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Optical Chopper, Phase Locked, No Wheels Included


  • Type
    Phase Locked Optical Chopper
  • Chopper Wheel
    2 slot, 7/5 slot, 42/30 slot, 60 slot, 100 slot, and 60/2 slot
  • Chopping Frequency
    4 Hz to 10.65 kHz
  • Phase Jitter
    0.4° rms typical
    Wheel and frequency dependent, see manual for more details
  • Phase Shifter Range
    -180° to +179°
  • Weight
    6.4 kg
  • Dimensions
    102 x 216 x 368 mm


Complete Chopper System

The 3502 optical chopper comes complete with six chopper wheels, a chopper head motor with built-in wheel cover, and a controller with a USB interface.  The 3502-BASE model excludes the six standard chopper wheels, providing a lower cost alternative with wheels ordered separately.

Six Broadband Absorber Coated Chopper Wheels Included

Six chopper wheels are included with the 3502 optical chopper system allowing for chopping frequencies from 4 Hz to 10.65 kHz (not included in the 3502-BASE model). Shown in the top row are the 60/2-slot, 7/5-slot, and 2-slot wheels, and the bottom row shows the 100-slot, 42/30-slot, and 60-slot wheels. All chopper wheels are 4.50 inch (114.3 mm) diameter.  These high quality chopper wheels are made of a beryllium copper alloy, which offer superior performance compared to lower cost steel alternatives.  This material choice allows for better thermal conductivity, higher strength, tighter machine tolerances, and are non-magnetic, non-sparking, and corrosion resistant.  If a wheel becomes lost or bent, replacement models are available.

Advanced Optical Chopper Controller

The front panel display of the controller allows monitoring of the chopping frequency, as well as a number of other operating parameters. Easy-to-use cursor keys provide easy adjustment of operating parameters. The chopping rate may be set from 4 Hz to 2.00 kHz, using either the internal frequency synthesizer or an external source as the reference. Chopping mode options are selectable at the fundamental, a harmonic (2 to 15), or even a sub-harmonic (1/2 to 1/15) of the reference.

Chopper Head Features and Benefits

The 3502 optical chopper head features a high-quality DC motor with a built-in photo-sensor, providing persistent feedback to provide superior drift and jitter parameters during operation.  The wheel cover allows for operator safety while in use, and also provides additional blocking of stray light to the photo-sensor element for improved performance.  Two mounting options are available for end use: mounted directly to an optical table on its base, or at elevated positions on a 1/2"-diameter post.  When mounted by its base, two set screws can be utilized for complete 360° rotation and position locking.  For replacement or stand alone ordering of this chopper head, contact your Newport sales representative for part number 90083484.

Stable and Reliable Phase Locking

For stable chopping with minimum jitter and drift, the Model 3502 optical chopper uses precision photo-etched wheels mounted on a high-quality DC motor. In addition, the chopper controller has its own internal crystal-controlled frequency synthesizer and phase-locked loop for precisely locking the chopping frequency. A photo-interrupter on the chopper head monitors the chopping frequency, and the chopper controller actively stabilizes the motor speed to ensure stable chopping with a minimum of frequency drift. In internal-reference mode, the chopper controller uses its internal frequency synthesizer as the reference. When the Model 3502 is operated in external-reference mode, the chopping rate is locked to the user-provided reference from another chopper or signal source. The chopper may also be run asynchronously with the rear-panel analog-control-voltage input. In all cases, the frequency-synthesizer output is available on the front panel for use in your measurement setup. The reference signal can be divided and multiplied by the sub-harmonic and harmonic generators before being processed by the phase shifter.

Unique Chopper Features

Unique features of the Model 3502 include outputs at the sum and difference of the inner and outer wheels’ chopping frequencies for nonlinear-optics experiments, and a high-stability phase shifter that can lock two choppers together for long fluorescence-decay measurements.