THORLABS MC2000 User manual

MC2000, MC2000-EC
Optical Chopper
Operating Manual

Optical Chopper System
18488-D02 Rev G, September 24, 2012 Page 2 www.thorlabs.com
Table of Contents
ePart 1.Safety Warnings...........................................................................................................................5
Part 2.Product Overview.........................................................................................................................6
Front Panel Description .............................................................................................................................................7
Rear Panel Description ..............................................................................................................................................7
Part 3.Setup.............................................................................................................................................8
Part 4.Basic Operation............................................................................................................................9
4.1.Internal Reference Operating Mode ......................................................................................................9
4.2.External Reference Mode........................................................................................................................9
4.3.Reference-Out Signal.............................................................................................................................10
Part 5.Advanced Operating Instructions..............................................................................................11
5.1.Internal Frequency Synthesizer............................................................................................................11
Setup for Internal Reference Frequency ..................................................................................................................11
Selecting the REFERENCE OUT signal .................................................................................................................11
5.2.External Reference Mode......................................................................................................................11
Setup for External Reference Frequency .................................................................................................................11
Selecting the REFERENCE OUT signal .................................................................................................................11
5.3.Harmonic Reference Generation..........................................................................................................12
Setup for External Reference Frequency .................................................................................................................12
Setting the Reference Harmonic..............................................................................................................................12
Setting the Sub-Harmonic........................................................................................................................................12
Combining the Harmonic and Sub-Harmonic Modes..............................................................................................12
Selecting the REFERENCE OUT signal .................................................................................................................12
5.4.Two-Frequency Chopping.....................................................................................................................12
Selecting the REFERENCE OUT signal .................................................................................................................12
Setting the Chopping Speed in the Two Frequency Mode.......................................................................................13
5.5.Two-Slot Blade .......................................................................................................................................13
Setup for Two-Slot Blade Reference Frequency......................................................................................................13
Selecting the REFERENCE OUT signal .................................................................................................................14
Part 6.Remote Communications...........................................................................................................15
6.1.Installing the USB Drivers.....................................................................................................................15
6.2.Command Line Interface ......................................................................................................................15
6.3.Commands..............................................................................................................................................16
6.4.Blade Indexes..........................................................................................................................................18
Part 7.Maintenance and Troubleshooting...........................................................................................19
7.1.Cleaning ..................................................................................................................................................19
7.2.Diagnostic Messages...............................................................................................................................19
Part 8.Fuse Replacement and Line Voltage Selection ........................................................................20
8.1.Materials Needed....................................................................................................................................20
8.2.Fuse Replacement and Line Voltage Selection....................................................................................20

Optical Chopper System
18488-D02 Rev G, September 24, 2012 Page 3 www.thorlabs.com
Part 9.Visual Menu Structure...............................................................................................................22
Part 10.Specifications .............................................................................................................................23
Part 11.Drawings.....................................................................................................................................26
Part 12.Regulatory ..................................................................................................................................28
12.1.Waste Treatment is Your Own Responsibility....................................................................................28
12.2.Ecological Background..........................................................................................................................28
Part 13.Certificate of Conformity...........................................................................................................29
Part 14.Thorlabs Worldwide Contacts ...................................................................................................31

Optical Chopper System
18488-D02 Rev G, September 24, 2012 Page 4 www.thorlabs.com
Table of Figures
Figure 1:Front Panel............................................................................................................................. 7
Figure 2:Rear Panel.............................................................................................................................. 7
Figure 3:Circuit Board Layout with 110/220 VAC Switch................................................................ 21
Figure 4:Console Dimensional Drawing............................................................................................ 26
Figure 5:Chopper Head Dimensional Drawing.................................................................................. 27

Optical Chopper System
18488-D02 Rev G, September 24, 2012 Page 5 www.thorlabs.com
Part 1. Safety Warnings
Warning Electrical Shock
To avoid electrical shock the power cord protective grounding conductor must be
connected to ground. Refer servicing to qualified personnel.
The unit must be powered off, unplugged from the AC input power source,
and disconnected from all external devices before removing the cover and
replacing the fuse. Failure to do so may cause serious injury to the user since high
voltages exist within the unit.
Thorlabs provides the proper 120 VAC power input cable with each MC2000 for use in the United
States and the appropriate 230 VAC input cable with each MC2000-EC for use in Europe. If using this
unit anywhere else, the user will need to supply a properly grounded power cable to power the unit. If
something should go wrong with the unit, do not attempt to fix. Call a Thorlabs representative and
arrange for repair. The unit should never be opened unless changing the fuse or line voltage as described
in Section 5.
Thorlabs ships all units configured to operate in the United States (i.e. line voltage 115 VAC, 60 Hz and
250 mA fuse installed). It may be necessary to change the line voltage to 230 VAC and replace the fuse
with a 125 mA Slow Blo fuse. Care must be taken when configuring the unit. See Section 5 for complete
details.
Warning Rotating Blade!
Keep hands clear while the blade is spinning. Turn power off before servicing.

Optical Chopper System
18488-D02 Rev G, September 24, 2012 Page 6 www.thorlabs.com
Part 2. Product Overview
The MC2000 Optical Chopper is a precision instrument utilizing advanced features to meet the most
demanding applications. The MC2000 uses a phased-locked loop (PLL) motor speed control design to
precisely maintain the chopping speed and phase to a reference signal. An internal, crystal-stabilized,
frequency synthesizer provides an accurate and stable reference frequency for long-term stable
performance.
Unlike conventional, open-loop speed control designs, the PLL speed control circuit also allows the
MC2000 chopper to be synchronized to external reference signals, including other MC2000 choppers
and reference sources such as DSP lock-in amplifiers.
For more advanced measurements, the MC2000 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.
The MC2000 also supports 2-frequency chopping from a single chopper blade. A special blade is
available with 7 outer slots and 5 inner slots. This slot combination allows a single beam to be split and
individually modulated for ratio metric 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 MC2000 provides the sum and difference frequencies of the 2-frequency blade
for accurate lock-in detection of the frequency-mixed response.
A high quality, rare earth magnet, DC motor and a photo-etched optical chopper wheel are the top two
design elements responsible for this device’s high precision. The compact optical head has a wide base
for extra stability. The base is slotted for two 1/4"-20 mounting screws on 3" centers. The interface cable
uses circular snap-on connectors for easy setup.
The MC2000 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 MC2000.
Thorlabs offers a number of different blades to extend the range of the
chopping frequency. A standard 10-slot blade is included with the
MC2000. 2-slot, 15-slot, 30-slot, 60-slot, and 2-frequency blades are
also available.

Optical Chopper System
18488-D02 Rev G, September 24, 2012 Page 7 www.thorlabs.com
Front Panel Description
Figure 1: Front Panel
Rear Panel Description
Figure 2: Rear Panel
Control Knob
This knob is used to highlight and select menu items.
LCD Display
The controller menus are displaye
d
h
e
r
e.
Power
Press to toggle
p
owe
r
Ext Input
The external reference signal is connected to this
input BNC (TTL / CMOS logic level).
Ref Output
The reference
output signal
selected by the
reference out menu
(CMOS logic
level
)
.
Cooling Fan
Do not block when the
unit is operating.
Modular Interface
Connector for the
optical hea
d
AC input receptacle
Requires an IEC compatible
plug with ground terminal.
Cord supplied for US
o
p
eration.
Fuse Holder
The system fuse is
installed here.
USB 2.0 Por
t

Optical Chopper System
18488-D02 Rev G, September 24, 2012 Page 8 www.thorlabs.com
Part 3. Setup
1. Carefully unpack the MC2000 controller, optical head, and accessories. See below for a
complete list of parts. If any of the items appear damaged or missing, do not use the MC2000.
Call Thorlabs, or email [email protected]om and arrange for a replacement.
Parts List:
•MC2000 Control Box
•MC2000 Optical Chopping Head
•MC1F10: 10-slot chopping blade
•2 meter mini circular cable for optical head / control box interface
•This Operating Manual
•Power Supply Line Cord: 120 VAC with the MC2000 or 230 VAC with the MC2000-EC
•125 mA Fuse for use at 230 VAC operation (250 mA fuse installed in unit)
•1/16" Allen Key for blade replacement
•0.05" Allen Key for hub alignment.
•(3X) 4-40 x 1/8" Phillips Pan Head Screws with Internal Tooth Washers
2. Remove the 3 mounting screws and lock washers from the chopper blade hub using the 1/16"
hex key provided.
3. Unpack the 10-slot blade and install onto chopper blade hub using the 3 screws and washers
removed in the previous step. Tighten the screws securely with the hex wrench.
4. Attach the modular cord into the circular connector labeled ‘OPTICAL HEAD’ on the back of
the MC2000 controller and plug the other end into the circular connector on the optical head.
5. Mount the optical head on a sturdy surface in an area free of obstructions. Make sure the blade
can spin freely.
6. Attach the AC line cord to the MC2000 and plug into an AC outlet.
Note: the MC2000 can be operated from 100/115 VAC or 230 VAC. A voltage selector switch is located
inside of the MC2000 controller. If you are not sure what operating voltage your unit is set to, proceed
immediately to Part 8. Fuse Replacement and Line Voltage Selection on page 20 for instructions on
setting the operating voltage.

Optical Chopper System
18488-D02 Rev G, September 24, 2012 Page 9 www.thorlabs.com
Part 4. Basic Operation
4.1. Internal Reference Operating Mode
The MC2000 is most often used in the internal reference mode where the chopping speed is set
internally.
1. Turn the MC2000 power on. The LCD display will show the Thorlabs logo and firmware
revision number before changing to the top-level menu list. The display will then show the
current menu, menu options, and operating status of the unit. By turning the front panel control
knob, different menu items can be highlighted. Push the control knob to select the highlighted
item.
2. Set the MC2000 parameters to the following for quick internal operation:
•Blade – (MC1F10)
•Ref. In – (INTERNAL)
•Freq. – Set to the desired frequency
•Phase – Set to the desired phase
•Harm N – Set the N harmonic to 1
•Harm D – Set the D harmonic to 1
3. Highlight and select Run Mode. The unit will adjust its speed and lock onto the set speed within
a few seconds.
Note that all menu parameters can be changed in standby mode, while only frequency, phase and N/D
harmonic parameters can be changed in run mode. The unit always powers up in standby mode.
4.2. External Reference Mode
This mode allows the user to control the chopper blade with a logic-level external reference signal.
1. To enable external reference mode, attach a TTL or CMOS logic level reference signal to the
‘EXT REF INPUT’ BNC on the front panel. Turn the MC2000 power on.
2. Set the MC2000 parameters to the following for quick external operation:
•Blade – (MC1F10)
•Ref. In – (EXTERNAL)
•Freq. – Set to the desired frequency
•Phase – Set to the desired phase
•Harm N – Set the N harmonic to 1
•Harm D – Set the D harmonic to 1

Optical Chopper System
18488-D02 Rev G, September 24, 2012 Page 10 www.thorlabs.com
3. Highlight and select Run Mode. The unit will adjust its speed and lock onto the external
reference speed within a few seconds.
4.3. Reference-Out Signal
The MC2000 supports a number of different reference out signals. For reference output selection,
highlight and select the external reference out signal from the following menu list. This list is described
in more detail in the following sections.
•TARGET – The reference out signal synthesized internally from a unit’s crystal clock
•ACTUAL – The reference out signal obtained from the feedback sensor reading the outer slots
on a chopper wheel
•INNER – Reference out signal obtained from the feedback sensors reading the inner slots of a
two slotted chopper wheel. (Note: This menu item is only displayed when a two-slot blade is
selected.)
•OUTER – Reference out signal obtained from the feedback sensor reading the outer slots of a
two slotted chopper wheel. (Note: This menu item is only displayed when a two slot blade is
selected.)
•SUM – The reference out signal obtained from the two frequency blade 5/7 sum
•DIFF – The reference out signal obtained from the two frequency blade 5/7 difference