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Optical Chopper System and Chopper Wheels
20 Hz - 10 kHz
4 Hz - 200 Hz
120 Hz - 6 kHz
Adjustable Duty Cycle
Includes Controller, Chopper Head,
Chopper Head with MC1F10HP Blade
Click to Enlarge
Controller Interface Screenshot
The MC2000B Optical Chopper is a precision instrument that utilizes advanced features to modulate light from a continuous beam. The controller uses a phase-locked loop (PLL) motor speed control design to precisely maintain the chopping speed and phase relative to a reference signal. An internal, crystal-stabilized, frequency synthesizer provides an accurate and stable reference frequency for stable long-term performance. The MC2000B Chopper offers faster locking times, interface improvements, and a larger selection of blades than our previous-generation MC2000 Optical Chopper.
An optical switch is used to get the reference signal when the chopper blades pass through and interrupt the beam path. The switch incorporates an LED with a wavelength range of 850 nm - 940 nm that is operated at the 15 mA threshold current to minimize light output from the LED.
Unlike conventional, open-loop speed control designs, the PLL speed control circuit also allows the MC2000B chopper to be synchronized to external reference signals, including other MC2000B choppers and reference sources such as DSP lock-in amplifiers. Please see the Operations tab for more details on the MC2000B chopper and its applications.
The MC2000B design features a high quality, rare earth magnet, DC motor. The photo-etched optical chopper wheel blade is made of 0.01" thick blued clock spring steel for high precision. The compact optical head has a wide base for extra stability, and the base is slotted for two 1/4"-20 (M6) mounting screws on 3" (76.2 mm) centers. The mounting slots have a 1.5" (38.1 mm) radius. The interface cable uses circular snap-on Hirose connectors for easy setup.
The MC2000B controller includes a 240 x 128 pixel graphics display for setting and monitoring chopper functionality. All of the functions are accessible through a front panel control knob with turn and push control. Multiple user setups can be easily saved and recalled from non-volatile memory. A USB interface is included as a standard feature for remote PC control of the MC2000B. A software package with a GUI to control the MC2000B is included with each controller and can also be downloaded from the Software tab. The package also supports controlling the MC2000B via programs written in C++ or LabVIEW.
Please Note: The MC2000B should be shielded from stray light sources because light contamination in the optical sensor will cause jitter.
Controller Front Panel
Controller Back Panel
Chopper Head Back Panel
USB Type B
An optical chopper is an electromechanical instrument that periodically interrupts a beam of light. The MC2000B Optical Chopper is a rotary type composed of a benchtop controller, motor head assembly, and slotted chopper blade/wheel.
MC2F57B Dual Frequency Blade
Unlike conventional, open-loop speed control designs, the PLL speed control circuit also allows the MC2000B chopper to be synchronized to external reference signals, including other MC2000B choppers and reference sources such as DSP lock-in amplifiers.
For more advanced measurements, the MC2000B can lock to a harmonic, sub-harmonic, or fractional-harmonic of an external reference frequency. The on board microprocessor is used to multiply the external reference up to the 15th harmonic or to divide the reference down to the 15th sub-harmonic. By combining both the frequency multiplication and division together, a fractional harmonic can be obtained.
In order to maximize the slope of the signal as the blade rotates (i.e., minimize the time to fully open or closed), the beam should be focused onto the widest portion of the slot in the chopper blade.
The MC2000B also supports 2-frequency chopping from a single chopper blade (example MC2F57B blade shown at right). We offer five different dual frequency blades (see below or refer to the Specs tab for details). The combination of dual frequency slots on one blade allows a single beam to be split and individually modulated for ratiometric experiments. Another example application is a pump-probe experiment where the pump beam is modulated at the outer frequency while modulating a probe beam at the inner frequency. The MC2000B provides the sum and difference frequencies of each dual frequency blade for accurate lock-in detection of the frequency-mixed response.
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MC2000B Software Screenshot
Software with GUI for Remote Operation of the MC2000B Chopper Controller
Compatibility with Other Vendors
The MC2000B is shipped with a 120 VAC power cord for use in the United States while the MC2000B-EC is shipped with a 230 VAC power cord for use in Europe. If you require a different power cord, please contact Tech Support prior to ordering.
These blades extend the chopping frequency range of the MC2000B Optical Chopper. The MC1F10HP High Precision Dual-Frequency Blade is the default chopper blade included with the MC2000B. Our high precision blades (Item # MC1F10HP, MC1F2, and MC1F2P10) offer stable frequency chopping with low jitter (see the Specs tab for more information). The controller achieves this stability by tracking the outer slots of the high precision blades.
The MC1F10A Adjustable 10 Slot Blade is composed of two discs and has an adjustable duty cycle. The discs are mounted on the optical head with the engraved dots aligned and facing forward. Once the duty cycle is adjusted to the desired value (between 0-50%), the mounting screws must be tightened.
Note that all of the blades sold for our previous-generation MC2000 Optical Chopper are compatible with our MC2000B Chopper with the exception of the MC2F57, which has been replaced by the MC2F57B (refer to the Harmonic Frequency Optical Chopper Blades section below).
Click to Enlarge
Spot Size Reference Drawing
These harmonic frequency blades have inner and outer slots that allow a single beam to be split and individually modulated. Please see the Operation tab for more details. Our blades are manufactured from 0.01" thick blued clock spring steel. These blades are not compatible with our previous-generation MC2000 Optical Chopper.