Building the oscillating stage

Fast movement of a retro-reflecting mirror and syncing of this movement to a 4 colour laser and camera is critical to our experimental setup

The laser, camera and oscillating mirror are all connected via an oscillating stage mechanism and circuit built in house.  This allows the focal planes being imaged to be illuminated and captured simultaneously.

Oscillating cam mechanism

The cam mechanism converts rotary motion of a DC motor to linear reciprocating motion, to move the mirror and thus the imaging focus backward and forward.  The plane separation adjuster is designed to with micrometer bushings to alter the eccentricity of the motion and increase or decrease the distance the mirror moves. 

A slotted plate is attached to the mirror mechanism.  These slots are designed to block and unblock two optical switches when the mirror is at the two extremes of its motion.  

Circuit diagram

The circuit uses two optical switches (U2 and U3) to determine which focal plane is in focus.  These switches output a TTL voltage whenever they are uncovered.  The voltages pass to two versalase control box inputs (in this case shown as A and C, corresponding to 405nm and 532nm, although they can be connected to any inputs necessary).  The voltages are also connected to the OR gate U1.  This outputs a TTL signal whenever it receives a TTL signal; the output signal is then connected to the camera, which is triggered whenever it receives a signal.  This signal is monitored by an oscilloscope.

Parts list


Globe motors DC motor, 22.4W, 12VDC, 5200rpm max

(discontinued by RS components - available from ebay


Toshiba TC74HC32AP(F) 14 pin OR gate

(RS components)


Honeywell HOA-2001 thru-hole slotted optical switch, inverter with 10K pull up resistor output

(discontinued by RS components - substitute


MR6322 miniature bearing 2.5mm x2



Plastic sheeting for flexure

(ebay listing)


M3 bushings and extremely fine adjusters

(Thorlabs F3ES12)

(Thorlabs F3ESN1P)


Nikon 60x oil objective


Nikon 60x ELWD air objective

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Prof. John McCarron

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Glasgow, G4 0RE



Prof. John Girkin

Durham University South Road,

Durham, DH1 3LE