We present a mechanical laser shutter design that utilizes a DC electric
motor to rotate a blade which blocks and unblocks a light beam. The blade and
the main body of the shutter are modeled with computer aided design (CAD) and
are produced by 3D printing. Rubber flaps are used to limit the blade's range
of motion, reducing vibrations and preventing undesirable blade oscillations.
At its nominal operating voltage, the shutter achieves a switching speed of
(1.22 $\pm$ 0.02) m/s with 1 ms activation delay and 10 $\mu$s jitter in its
timing performance. The shutter design is simple, easy to replicate, and highly
reliable, showing no failure or degradation in performance over more than
$10^8$ cycles.Comment: 4 pages, 6 figures; supplementary materials for shutter replication
  added under "Ancillary files

Braverman, Boris

Kawasaki, Akio

Vuletić, Vladan

Zhang, Grace H.

Review of Scientific Instruments

English

arXiv

We present a mechanical laser shutter design that utilizes a direct current electric motor to rotate a blade which blocks and unblocks a light beam. The blade and the main body of the shutter are modeled with computer aided design (CAD) and are produced by 3D printing. Rubber flaps are used to limit the blade’s range of motion, reducing vibrations and preventing undesirable blade oscillations. At its nominal operating voltage, the shutter achieves a switching speed of (1.22 ± 0.02) m/s with 1 ms activation delay and 10 μs jitter in its timing performance. The shutter design is simple, easy to replicate, and highly reliable, showing no failure or degradation in performance over more than 10⁸ cycles

Vuletic, Vladan

DSpace@MIT

REVIEW OF SCIENTIFIC INSTRUMENTS 86, 126105 (2015)Note: Fast compact laser shutter using a direct current motorand three-dimensional printingGrace H. Zhang,a) Boris Braverman, Akio Kawasaki, and Vladan VuletićDepartment of Physics, MIT-Harvard Center for Ultracold Atoms and Research Laboratory of Electronics,Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA(Received 4 September 2015; accepted 28 November 2015; published online 14 December 2015)We present a mechanical laser shutter design that utilizes a direct current electric motor to rotatea blade which blocks and unblocks a light beam. The blade and the main body of the shutter aremodeled with computer aided design (CAD) and are produced by 3D printing. Rubber flaps are usedto limit the blade’s range of motion, reducing vibrations and preventing undesirable blade oscillations.At its nominal operating voltage, the shutter achieves a switching speed of (1.22 ± 0.02) m/s with1 ms activation delay and 10 µs jitter in its timing performance. The shutter design is simple, easy toreplicate, and highly reliable, showing no failure or degradation in performance over more than 108cycles. C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4937614]Fast and robust optical shutters are essential to manylaser-based experiments, as well as technological applications.These experiments, spanning a wide range of research areasin science and engineering, require the shutter to have thefollowing performance characteristics: short switching time,small activation delay, high timing precision or low jitter, lowvibration and heat dissipation, an aperture size capable ofaccommodating the relevant beam sizes, high extinction ratio,laser power handling sufficient for the blocked beam, and along operation lifetime.To be useful for precise laser experiments, shutters requireexcellent timing performance, with short activation delays,fast switching times, and low timing jitters. A short activationdelay allows for the generation of short light pulses, and afast switching time allows for generating pulses with well-defined edges. A small timing jitter allows precise timing con-trol and synchronization with other parts of the experimentalapparatus. These three qualities are necessary for the shutter toquickly and accurately realize a desired laser intensity profileover time.A shutter can be operated based on a large variety of mech-anisms. Shutters based on electro-optical and acousto-opticalmodulators are very fast and hence have excellent timingperformance, but require careful alignment. Most importantly,these types of shutters are unable to provide full extinctionand transmission of the incident light, which can only beachieved by mechanical shutters. Many commercial lasersafety interlock and diaphragm shutters exist,1,2 but they aretypically not designed for precise timing applications inoptics experiments; these shutters do not possess thedesired timing performance and produce high noiseand vibrations during operation. Commercial shutters withthe requisite high performance3,4 have costs that areimpractical for typical laboratories, which can require tens ofshutters.a)ghzhang0@mit.eduLacking satisfactory commercial options, various labora-tories have developed custom-made mechanical shutter sys-tems.5–11 However, we find that these designs have drawbacksthat limit their usability. Systems that utilize piezo-actuatorsprovide fast switching times and low timing jitter,5 but haveinsufficient extinction ratios and small sweep ranges. A designbased on the modification of voice-coil motors in computerhard disk drives achieves both high speeds and a large aperturediameter,8 but is too bulky in size for flexible placement in mostoptical setups. Another design, based on the thermal expansionof NiCr wire, achieves activation delay of less than 300 µs,11but cannot operate at repetition rates with switching intervalsshorter than 5 s due to the long relaxation time required for thethermal recovery of the wire.Most importantly, the aforementioned shutter designscapable of high speed and precision all require complicatedand delicate assembly. This leads to three major disadvan-tages that severely restrict the large-scale application of theseshutter designs. The difficult assembly process makes it hard toconstruct and maintain the shutters in the quantities typicallyrequired by a laboratory. Higher complexity decreases thereliability of the shutter as the overall shutter system containsmore elements vulnerable to mechanical or electrical mal-functioning; this is especially important for applications thatFIG. 1. CAD rendering of the shutter design. There is an upper apertureand a lower aperture, symmetric about the height of the motor axle, throughwhich the laser beam can travel. The motor axle rotates the shutter blade toalternately block and unblock each aperture.0034-6748/2015/86(12)/126105/3/$30.00 86, 126105-1 ©2015 AIP Publishing LLC This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP:18.62.19.190 On: Mon, 21 Dec 2015 17:30:09126105-2 Zhang et al. Rev. Sci. Instrum. 86, 126105 (2015)require long-term operation. Finally, the high sensitivity ofeach shutter to fine variations in its construction process causesperformance inconsistency among separate shutter units.In this article, we present a compact and high-performingshutter system that is easy to construct and replicate consis-tently. The main components of the shutter are the 3D printedplastic mount and shutter blade, a direct current (DC) electricmotor, and an electrical driver circuit. Detailed proceduresfor assembly are described in the supplementary material.12Assembly of the shutter and driver takes under an hour whenprovided the required materials, which consist of easily obtain-able electrical components and 3D printed ABS plastic struc-tures that can be produced in any desired quantity in oneoperation. Testing of the design shows both high speed andhigh reliability; the shutter has operated with sub-millisecondswitching time for over 108 cycles without degradation.The shutter design is presented in Fig. 1. The DC motorrotates the shutter blade which blocks and unblocks the laserbeam. The motor axle and the hole in the blade through whichit is inserted are flattened to prevent slipping between duringoperation. Two neoprene rubber flaps, attached to the supportby adhesive, act as physical stops to halt the motion of theblade and to dampen vibrations from the blade that wouldotherwise cause it to bounce back and lead to undesirabletransient blocking or unblocking of the beam. Laser beams cantravel through the upper or lower aperture, both of 2.5 mmwidth, which are alternately blocked and unblocked duringoperation. The shutter can be secured to an optical post throughthe mounting hole, as shown in Fig. 2, and is compact enoughto be inserted into any optical setup.The electrical circuit of a single shutter driver, presented inFig. 2, primarily consists of a H bridge and a pulse-generatingRC circuit similar to another reported design.9 The circuit al-lows for bipolar driving of the motor with a unipolar electricalsupply. The timing sequence of the opening and closing of theshutter is controlled by the transistor-transistor logic (TTL)input signal.This shutter design demonstrates excellent timing perfor-mance through its short activation delay, fast switching time,and low timing jitter. A fast avalanche photodiode (APD) wasFIG. 2. Shutter units stacked on an optical post (left), side view of shutterwith plastic blade (bottom right), and the circuit schematic for a single shutterdriving circuit, with part numbers indicated (top right).used to measure the transmission of a laser beam through theaperture during repeated blade transitions, giving the activa-tion delay and the switching time of the shutter. Opening andclosing delay times are between 1 and 2 ms, depending on thealignment of the laser beam through the shutter aperture. Thespeed of the shutter blade, measured by clipping an expandedlaser beam with a metal sheet and determining the delay timetaken by the shutter to provide complete extinction of theincident laser beam, was found to be (1.22 ± 0.02) m/s atthe nominal operating voltage of 9 V. The activation delayand switching time decrease with the operating voltage, asshown in Fig. 3. The typical jitter ranges in activation delayand switching time were measured to be about 20 µs and10 µs, respectively, also decreasing with increased operatingvoltage. The jitter of the shutter’s timing response over 1000measurements in a sample period of 14 h is shown in Fig. 4,illustrating the high mechanical stability provided by rubberflaps in arresting the motion of the shutter blade.The shutter shows high consistency in the timing perfor-mance between each unit. The performance variation betweendifferent shutter units is smaller than the performance variationcaused by removing the shutter from the setup and placing itback in the same position.The shutter operates under low power, thereby extend-ing its functional lifetime. Its mechanical motion is bistable,requiring only 2-3 mA of current to keep the blade in its raisedor lowered position, in contrast to the 100 mA required by un-stable shutters.6,8 Its operating voltage range is 4–15 V. Below4 V, the motor cannot overcome static friction to actuate theblade motion, while above 15 V, excessive driving force causesthe blade to bounce back from the rubber flap and produceFIG. 3. Distribution of 100 measurements of activation delay, the timeinterval between the application of the TTL signal and 50% transmission,and switching time, the time interval between 80% transmission and 20%transmission, at different operating voltages VCC. This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP:18.62.19.190 On: Mon, 21 Dec 2015 17:30:09126105-3 Zhang et al. Rev. Sci. Instrum. 86, 126105 (2015)FIG. 4. Jitter range of delay times (top) and switching times (bottom) over14 h at operating voltage VCC= 9 V.transient blockage or opening of the aperture. Operation at 9 Vonly dissipates 13 mJ of energy in the shutter motor duringeach transition.The shutter has maximum short-term and long-term repe-tition rates of 110 Hz and 20 Hz, respectively. These limi-tations are due to the ABS plastic softening from high heatdissipation by the motor and could be solved by adding a heatsink to the mounting structure or by fabrication of the shuttercomponents from more heat-resistant materials. The plasticblade has a laser power-handling of 50 mW for a beam sizeof 1 mm, but can be replaced by metal, as shown in Fig. 2, thesurface of which could be painted black to absorb and dissipateenergy from the laser. We estimate that this would increase thepower-handling limit to above 1 W.The shutters produce minimal noise and vibrations. Atan operating voltage of 4 V, operation is not detectable byear. Noise and vibration could be further reduced by addingelectronic braking to the driver circuit.Applications of this shutter design can be extended byreplacing the opaque blade with an optical component. In thisway, one can remotely place components such as a polarizingelement or a wave plate in and out of the path of a laser beam.The low timing jitter is equivalent to a high repeatability of theblade position during each shutter cycle, suggesting that evenalignment-sensitive elements such as lenses or prisms couldreplace the blade for control over the aligning or focusing ofthe laser beam.In conclusion, we have designed and implemented asimple, compact, robust, low-noise, high-performance lasershutter, based on a small commercial DC motor, 3D printedshutter body and blade, and rubber motion stops. The shutterhas a lifetime and timing performance comparable to commer-cial shutters with both very low cost and construction time.Most importantly, this shutter is easy to reproduce in largenumbers with high consistency, as the mechanical structureis fixed by the computer aided design (CAD) file used for 3Dprinting, requires no extra tinkering during assembly, and ishighly reliable due to the elimination of variations in assemblyand the simplicity of the mechanism. We expect this design tobe highly useful in laser experiments across many disciplines,where it could fill a niche where commercial options arecurrently limited.This research was supported by NSF, DARPA QuASAR,and by MURIs through AFOSR and ARO. B.B. acknowledgessupport from the National Science and Engineering ResearchCouncil of Canada and G.Z. from the Undergraduate ResearchOpportunity Program at MIT.1Thorlabs, “Optical shutter,” https://www.thorlabs.us/newgrouppage9.cfm?objectgroup_id=927.2RT Technologies, “Laser beam shutters,” http://www.rtlasersafety.com/laser-beam-shutters.php.3Stanford Research Systems, “Laser shutter systems SR470 & SR474 - lasershutters & controllers,” http://www.thinksrs.com/products/SR470474.htm.4Vincent Associates, “LS2 2 mm uni-stable shutters,” https://www.uniblitz.com/product/ls2-shutter-system/.5C. Adams, Rev. Sci. Instrum. 71, 59 (2000).6K. Singer, S. Jochim, M. Mudrich, A. Mosk, and M. Weidemüller, Rev. Sci.Instrum. 73, 4402 (2002).7T. P. Meyrath, “Inexpensive mechanical shutter and driver for optics experi-ments,” http://george.ph.utexas.edu/∼meyrath/informal/shutter.pdf (2003).8L. Maguire, S. Szilagyi, and R. Scholten, Rev. Sci. Instrum. 75, 3077 (2004).9D. Mitchell and P. Lebel, “Ultrafast mechanical shutters for laser cool-ing applications: The ishutter system,” http://www.phas.ubc.ca/∼qdg/publications/InternalReports/LM-APSC479.pdf (2008).10S. Martinez, L. Hernandez, D. Reyes, E. Gomez, M. Ivory, C. Davison, andS. Aubin, Rev. Sci. Instrum. 82, 046102 (2011).11M. Ye, D. Jiang, and C. Wong, Rev. Sci. Instrum. 61, 2003 (1990).12See supplementary material at http://dx.doi.org/10.1063/1.4937614 fordetailed instructions on the assembly of the shutter. This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP:18.62.19.190 On: Mon, 21 Dec 2015 17:30:09

Fast Compact Laser Shutter Using a Direct Current Motor and 3D Printing

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