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Portable Optical Tweezers Kit

Chapter 7: Teaching Tips

Page 82

MTN024417-D02

In essence, a single laser beam can create an ideal three-dimensional optical trap. One

thing is crucial for functioning optical tweezers: in order to trap an object in a three-

dimensional trap, a highly focused laser beam with a suitable intensity profile is required.

The object is always pushed in direction towards the point with highest intensity:

•

Radially into the middle of the laser beam due to the (Gaussian) intensity profile

•

Vertically into the direction of the focus

As soon as a particle moves away from the focus, a restoring force acts on it to push it

back into the focus.

Summary of Contents for EDU-OT3

Page 1: ...EDU OT3 EDU OT3 M Portable Optical Tweezers User Guide...

Page 2: ...Laser Source 16 4 2 Beam Expander 17 4 3 Right Angle Mirrors 18 4 4 Sample Positioning System 19 4 5 Microscope 20 4 6 Additional Components 22 4 7 Included Hardware 23 4 7 1 Imperial Kit 23 4 7 2 Met...

Page 3: ...6 3 Arranging the Silica Beads 65 6 4 Manipulating a Dairy Cream Particle in a Cream Water Emulsion 66 6 5 The Holding Force of the Optical Trap 68 6 5 1 Brownian Motion 68 6 5 2 The Maximum Holding...

Page 4: ...ice Warning Laser Radiation 1 2 Laser Radiation Warning The class 3B laser diode used in this kit can emit more than 50 mW of optical power which can cause damage to the eyes if viewed directly The la...

Page 5: ...erimental setup with which particles on the order of microns can be trapped and moved The beam path is schematically depicted in Figure 1 It is possible to perform a variety of experiments using a num...

Page 6: ...e Optical Tweezers Kit Chapter 2 Product Description Rev B February 15 2022 Page 3 The light path through the optical tweezers experiment LED Sample Position Laser Camera Microscope Beam Path Laser Be...

Page 7: ...is greater than the scattering force which pushes the particle in the direction of the beam away from the focus The various theoretical approaches to describe optical trapping can roughly be divided...

Page 8: ...tional to Therefore according to equation 3 is proportional to 2 and thus to intensity 2 of the incident field The force exerted on the particle by the incident field is proportional to the gradient o...

Page 9: ...be taken into account namely that light can transfer momentum to an object in the form of photons The force action of a beam on a particle can be explained using Newton s second law the force on a pa...

Page 10: ...d remains in the sphere while the rest exits the sphere again through transmission The beams which exit the sphere again were thus subject to a change in momentum The force on the sphere is equal to t...

Page 11: ...om the equations This angle becomes larger the more heavily the beam is focused which occurs when a higher numerical aperture objective is used The component of the beam that points in the incident di...

Page 12: ...he sphere always moves into the focus or the point of highest intensity In order to ultimately achieve a stable optical trap the following must be true 18 In the following we ll discuss these forces i...

Page 13: ...xpressed in terms of and Figure 5 shows a partial beam incident on the sphere with angle from the side The following statements hold true sin sin 19 and sin 2 2 20 roughly corresponds to the focal len...

Page 14: ...lts in mirrored force vectors and in the right part of the sphere which were not drawn to avoid an overcrowded figure The Contribution of One Ray to the Total Force5 6 When you consider all of the par...

Page 15: ...ly want to discuss the curve s general form Therefore the forces are given in arbitrary units a u On the horizontal axis 1 corresponds to the focus position on the sphere s outer surface right above t...

Page 16: ...ot the occurring forces as a function of the focus distance to the sphere s center in units of the sphere s radius Figure 8 shows the gradient force and the scattering force Plotting the sum of both f...

Page 17: ...hat scattering and gradient force are strongest when the laser focus is at near the sphere s surface i e 1 So for a stable trap we can assume the condition7 1 1 1 28 Absolute values are used since is...

Page 18: ...l tweezing ocurrs or not remains the same see Equation 28 Combining what we know about the numerical aperture and laser power we can note that the increase in trapping strength can be achieved through...

Page 19: ...able 1 x L658P040 S 658 nm 40 mW 5 6 mm A Pin Code Laser Diode8 1 x LTN330 A Adjustable Collimator for 5 6 mm Laser Diodes AR Coated 350 700 nm 1 x KLD101 K Cube Laser Diode Driver 1 x TPS002 15 V 5 V...

Page 20: ...6 Long 2 x CP45 M 30 mm Removable Segment Cage Plate 2 x CP45T M 30 mm Removable Segment Cage Plate Thick 1 x LA1509 A 1 N BK7 Plano Convex Lens f 100 mm AR Coating 350 700 nm 1 x SM1A6 Adapter with...

Page 21: ...mping Fork 1 x BE1 M Pedestal Base Adapter 4 3 Right Angle Mirrors 2 x KCB1C M Right Angle Kinematic Mirror Mount 30 mm Cage Compatible 2 x PF10 03 P01 1 Protected Silver Mirror 2 x SM1L05 1 Lens Tube...

Page 22: ...Travel9 2 x KDC101 K Cube DC Servo Motor Module 2 x KPS201 K Cube Power Supply 1 x MT402 Right Angle Bracket 1 x MT401 M Mounting Base for Translation Stages 2 x MT405 Side Mounted Actuator Adapter fo...

Page 23: ...M Slip On 1 5 Post Clamps 1 x LB1676 1 N BK7 Bi Convex Lens f 100 mm 1 x CP33T M SM1 Threaded Cage Plate 0 5 Thick 1 x FES0650 IC 1 Shortpass Filter 650 nm Cut Off10 1 x CM1 DCH M 30 mm Cage Cube wit...

Page 24: ...mm Cage Assembly Rod 3 Long 4 x ER1 5 6 mm Cage Assembly Rod 1 5 Long 1 x MCWHL7 Cold White Mounted LED 1300 mA11 Max 1 x SM1L10 1 Lens Tube 1 Long 1 x DG10 600 1 N BK7 Ground Glass Diffuser 600 Grit...

Page 25: ...s 1 x MB1224 MB3060 M Aluminum Breadboard 12 x 24 x 1 2 300 mm x 600 mm x 12 7 mm 1 x RDF1 Rubber Dampening Breadboard Feet 1 x CPA1 30 mm Cage System Alignment Plate with 1 mm Aperture 1 x BBH1 Bread...

Page 26: ...ong 2 1 4 20 Cap Screw 3 8 Long 10 8 32 Cap Screw 1 2 Long 3 1 4 20 Cap Screw 1 2 Long 12 8 Washer 2 1 4 20 Cap Screw 5 8 Long 8 8 32 Setscrew 1 2 Long 1 1 4 20 Cap Screw 3 4 Long 4 1 8 x 1 4 Steel Do...

Page 27: ...M6 x 10 mm Cap Screw 10 M4 x 12 mm Cap Screw 3 M6 x 12 mm Cap Screw 12 M4 Washer 2 M6 x 16 mm Cap Screw 8 M4 x 12 mm Set Screw 1 M6 x 20 mm Cap Screw 4 1 8 x 1 4 Steel Dowel Pin 8 M6 Washer 22 SD1 M6...

Page 28: ...Use the threaded hole in the breadboard and not the counterbored holes Positions of Components on the Breadboard Teaching Note In the previous version of this kit EDU OT1 M the laser segment had to b...

Page 29: ...he orientation depicted to the right note the position of the tip tilt adjusters This orientation is critical because you will not be able to access the cage rod locking screws if the KC1 T M is in a...

Page 30: ...ssembly in the LTN330 A using the black retaining ring the retaining ring can be tightened using a thin screwdriver Make sure to use the thick retaining ring and not the one you unscrewed in the previ...

Page 31: ...s PF10 03 P01 in the right angle mirror mounts KCB1C M with the reflective surface facing away from the knobs Figure 12 Mirror and Right Angle Mount Base Screw the BE1 M base into the PH3 PH75 M post...

Page 32: ...A1509 A must be attached to the CP45 M cage plate using two SM1 retaining rings Beam Expander Lens 2 Components Cage Assembly The cage assembly features a removable segment that comprises the two lens...

Page 33: ...h respect to the cage rods until the ER1 fill half of the CP45T M s flexure locks Tighten the two side located 2 mm 5 64 setscrews the smaller lower ones on the CP45T M using a 5 64 2 mm hex key The a...

Page 34: ...t of the flexure locks You may want to leave a small gap between the adjacent cage rods Fix all of the KC1 T s cage rod locking screws You may fix the CP45 M s and CP45T M s flexure locks However in o...

Page 35: ...s that there is sufficient space for manual adjustment between the stage assembly and the mirrors Remove the retaining rings from all four lens tubes Screw an SM1L05 lens tube into the KCB1C M of the...

Page 36: ...using To do so remove the small black screws on the side of the housing with the included hex key and pull off the top of the housing Next install the DMSP605R dichroic mirror such that the part numbe...

Page 37: ...12 mm cap screw Make sure not to mistake the thick SD1 adapter with a thin washer Also the C1498 M s label should face upwards Ensure that you do not touch the bottom of the objective with your finge...

Page 38: ...er SM1T2 Connect the SM1L10 lens tube to the CP33 M cage plate Mount the cage plate to the C1498 M post clamp using an SD1 counterbore adapter and an 8 32 1 2 long M4 x 12 mm cap screw Finally install...

Page 39: ...om the SM1T2 lens tube coupler Next screw the SM1L15 lens tube to the coupler and tighten the locking ring Screw the SM1NT1 slotted locking ring onto the coupler do not tighten it Second screw the SM1...

Page 40: ...ake sure that the upper locking screws fix the cage rods to the thick cage plate The lower locking screws need to be left free so the camera segment can be attached to the beamsplitter assembly The fu...

Page 41: ...tom of the objective should be about 11 5 cm Use a level at the beamsplitter cube to make sure the assembly is vertical If not you have to adjust the angle in which the C1498 M clamp is screwed to the...

Page 42: ...posts supporting the cage segment and the laser to the breadboard using the two CF125 clamps and two 1 4 20 3 8 long M6 x 10 mm cap screws with washers Note If the objective microscope was assembled w...

Page 43: ...3 32 hex key from the MT405 Remove the end mount adapter by removing the two inner screws Do not remove the locking plate and attempt to mount an actuator on that side of the stage First screw the two...

Page 44: ...of the stage Screw the second MT1 M Z8 with side mounted motor onto the first one in the orientation shown in the image to the right using two 1 4 20 3 8 long M6 x 10 mm cap screws Add 2 dowel pins t...

Page 45: ...washers Screw the adapter assembly to the stage using two 1 4 20 0 315 long M6 x 8 mm cap screws with washers and 4 dowel pins you may need to use the screws to pull the stages together once you have...

Page 46: ...d washers should be used with the following controllers as well Then place the two KDC101 K Cube Stage controller cubes in their positions mount them to the breadboard and connect them to the computer...

Page 47: ...en the newly installed program Kinesis Laser Controller Panel In the Kinesis control panel see Figure 29 press Settings To operate the laser properly the polarity setting of the diode will need to be...

Page 48: ...mW of output power Set the operating current just below 100 mA According to our test measurements this will result in an output power above 50 mW The advantage is a stronger optical trap the downside...

Page 49: ...m the Thorlabs website13 or use the installation CD included with the camera then follow the installation guide After finishing the installation reboot and connect the camera to your computer After th...

Page 50: ...to check the signal coming from the camera A helpful feature is the Draw Circle option You can use it to mark the location of your laser spot This can be helpful when you move out of the trapping pla...

Page 51: ...the general settings tab you can set the frame rate and the exposure time Also you can activate the Autoexposure feature However please note that this function results in frame rates of about 10 FPS W...

Page 52: ...ufacturing lot This will affect the Red Gain settings you have to choose for your setup To do so vary the Red Gain during the adjustment process and choose the optimal setting that allows to observe b...

Page 53: ...Furthermore select Joystick Mode in the menu and chose Velocity Control This corresponds to a continuous motion of the stage when the wheel is actuated Confirm with the menu button Method 2 Configurat...

Page 54: ...Note By clicking OK the settings are sent to the device By checking the Persist Settings to the Device checkbox the settings are stored in the device and loaded after each restart of the controllers...

Page 55: ...Portable Optical Tweezers Kit Chapter 5 Setup and Adjustment Page 52 MTN024417 D02 Kinesis KDC101 Settings Kinesis Drive Array Velocity...

Page 56: ...startup This option can be activated via the dropdown menu File Options by checking the box Use device persisted settings see Figure 42 Use Device Persisted Settings In most cases for the optical twee...

Page 57: ...the microscope that includes all parts starting from the camera until the cage plate above the beamsplitter For that unscrew the cage locking screws from the CP33T M and loosen the screw on the C1498...

Page 58: ...late Screw in the collimation lens retaining ring as far as possible Screw in the collimation lens as far as possible as close to the diode as possible see image to the right Step 2 Collimation Turn t...

Page 59: ...aser Mount Alignment Turn the tip and tilt screws on the KC1 T mount until the brightest spot of the laser light distribution hits the hole in the alignment plate Turn off the laser Remove the alignme...

Page 60: ...mode laser that enters the objective as centered and vertical as possible Also the laser beam should be as parallel as possible with a small divergence angle In our setup this is not the case After fo...

Page 61: ...older Place the sample in the holder with the selected well under the objective Step 3 Approach Raise the sample positioning table with the micrometer screw and pay close attention to the camera image...

Page 62: ...Portable Optical Tweezers Kit Chapter 5 Setup and Adjustment Rev B February 15 2022 Page 59 Focus Level Settings The camera image should look similar to Figure 44 TOP of Cover Glass...

Page 63: ...Portable Optical Tweezers Kit Chapter 5 Setup and Adjustment Page 60 MTN024417 D02 Camera Images During the Approach 2 m Beads BOTTOM of Cover Glass IN Sample...

Page 64: ...the slip plate with the attached lens tube camera and fix the screws again In rare cases you may initially not see a laser spot in the camera image at all In these cases you may find it within the tra...

Page 65: ...s do not coincide If you want the movement in Z direction to be smoother a hex key can be inserted in the adjuster of the MT1B This allows you to move the stage up and down with less vibration in the...

Page 66: ...optimized for the sample slides and the cover glasses provided with the OTKBTK Content of the OTKBTK Preparation Kit with tools for glass bead sample preparation green highlighting Do not use immersio...

Page 67: ...nt to temporarily set the maximum velocity of the KDC101 controllers to a higher value see Section 5 2 4 Now raise the sample positioning table once again using the micrometer screw and pay close atte...

Page 68: ...bad adjustment and can be ignored At this point if the trapped beads move out of the focal plane it indicates that the focal planes of the laser and camera system are not aligned See Section 5 5 abov...

Page 69: ...observed that they disappear from the focus and can no longer be clearly seen on the monitor see Figure 51 The explanation for this observation can be found by examining more closely the cream water...

Page 70: ...he optical trap and thus to move upward once again to the surface of the water This procedure can be observed again with the aid of the z axis screw Cream particles collect on the surface of the water...

Page 71: ...nd what role it plays in the experiments with the optical tweezers Solution Brownian motion is the statistic vibrating motion translation and rotation of microscopic free particles Under the microscop...

Page 72: ...uation possible and is offered for free is Viana available at http www viananet de en Note Before taking the video sequence make sure that the beads do not show a drift in any direction which can be c...

Page 73: ...For that it is important to note that the objective magnification always depends on the tube lens The objective used in this setup is made by Zeiss and is labeled as a 63x objective However Zeiss stan...

Page 74: ...ich the spheres move and can be described by the following equation 6 32 Here describes the radius of the bead and describes the effect of viscosity of the suspension The latter indicates how thick th...

Page 75: ...force of the optical tweezers Solution If the PS bead is in the optical trap two forces act on it First of all the frictional force which is caused by the suspension in which the PS bead is located an...

Page 76: ...were able to trap and move toothpaste matter we are not sure whether or not this is microplastic To prepare a sample mix a small bit of toothpaste with destilled water Yeast cultures can be trapped L...

Page 77: ...rticle is trapped in a focused laser beam and how a three dimensional optical trap works For keeping an object in place a restoring force has to act as soon as the object leaves its equilibrium positi...

Page 78: ...simplicity we will only consider two rays in the following which are symmetrical around the beam axis The insights we gain with these two rays can be transferred to the entire beam First we have a lo...

Page 79: ...direction and intensity since they both have the same radial distance to the beam center with highest intensity and carry the same momentum In Figure 56 the momentum vectors of the beams are depicted...

Page 80: ...ot change However the direction changes In Figure 57 the vectors before the entry of the beam into the sphere position 1 and after the exit position 3 are subtracted to see how the momentum changes Th...

Page 81: ...hed away by the beam along the optical axis The beam experiences no momentum change orthogonal to the optical axis so it stays in the center of the beam Unfocused Laser Beam Particle is not on the Bea...

Page 82: ...th partial beams then exhibit the momentum change displayed in Figure 61 Unfocused Off Axis Laser Beam Momentum Changes As shown the partial beams exhibit momentum changes that differ in magnitude Fig...

Page 83: ...e Beam s Main Axis Below the Laser Focus We will next consider a focused laser beam The particle is assumed to be in the center of the beam but below the focus of the laser The laser is assumed to be...

Page 84: ...entum Changes The net momentum change of the entire beam is depicted in Figure 66 Focused Laser Beam Change in Momentum The laser beam exhibits a momentum change downwards Hence the bead s momentum is...

Page 85: ...p an object in a three dimensional trap a highly focused laser beam with a suitable intensity profile is required The object is always pushed in direction towards the point with highest intensity Radi...

Page 86: ...1 that is responsible for a movement of the camera image on the screen in vertical direction Choose the other KDC101 in the Target dropdown menu of Left Analog X 6 In the Action dropdown menus of both...

Page 87: ...Portable Optical Tweezers Kit Chapter 8 Control via Game Controller Page 84 MTN024417 D02 Input Devices Settings in Kinesis Software...

Page 88: ...Portable Optical Tweezers Kit Chapter 8 Control via Game Controller Rev B February 15 2022 Page 85 Recommended Controller Calibration Settings Homing the KDC101 controllers...

Page 89: ...PC turn the power of the KLD101 off and back on again All settings are correct but the laser diode still doesn t emit light Switch of the KLD101 then remove the laser diode from its mount and reinsert...

Page 90: ...er o Is the objective clean Are you able to find the plane with the beads in their solution If not you may need to carefully clean the objective o Have you used immersion oil Please note that this set...

Page 91: ...to other Thorlabs products such as Pure OEM products that means assemblies to be built into a unit by the user e g OEM laser driver cards Components Mechanics and optics Left over parts of units disa...

Page 92: ...rmation USA Canada and South America Thorlabs Inc sales thorlabs com techsupport thorlabs com UK and Ireland Thorlabs Ltd sales uk thorlabs com techsupport uk thorlabs com Europe Thorlabs GmbH europe...

Page 93: ......

Page 94: ...www thorlabs com...

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