Optical Tweezers

Created by: Maryam Badakhshi, Shannon O’Keefe, Laura Poloni, Hasmita Singh

Overview1) Background & Applications2) Apparatus3) Laser Safety

1. Background & Applications

Optical Tweezers

Public image by RockyRoccon 2007

• Highly focused laser beam is used to physically hold and move microscopic dielectric objects

• Can manipulate objects with noncontact and direct trapping

• Advanced Physics Laboratory for the Optical Tweezers apparatus involves the determination of optical trap stiffness of silica beads through various methods

Manipulation of Nanodevices

(Tong et. al., Nano Letters, 2010)

• Alignment and rotation of a silver nanowire

(Nam et. al., IJPEM, 2009)

• Four spheres trapped and rotated by linearly scanning with laser light

(Gross et. al., Methods in Enzymology, 2010)

Isolation and Visualization of DNA

Trapping of two beads

“Catching” a Single DNA Molecule

Force-Extension analysis of the trapped DNA

Staining with Fluorescent Dye

Protein-coated DNA region

Fluctuations in DNA molecule

(Gross et. al., Methods in Enzymology, 2010)

2. Apparatus

Main Components

Very Dangerou

s!Safe!

Main Components

3. Laser Safety

Optical Trap Laser Characteristics980 nm Infrared range330mW maximum powerCollimated beamClass 3B laser

Optical Trapping Kit, Thorlabs. 2009.

Laser Classification

Class 3B Laser

Safety Interlocks

Class 1 working environment

• Hazardous under direct and specular reflection, but not diffuse reflection• Direct exposure to beam is an eye hazard• Maximum power 500mW

• Considered incapable of causing injury

Hazards

Diffuse reflectionsInvisible

Most dangerous procedure, contact your TA/Instructor

Eye injuries without laser safety glasses

Stray Beams

Beam Alignment

Biological Effects

Biological EffectsCornea

Focussing elementLens

Fine focusVitreous HumorRetina

Image is projected from the cornea and lensConnection to brain through optic nerve

FoveaSharp vision

Vitreous Humor

Schematic of the eye by SurferSam Online.

Biological EffectsLaser Light 400-1400nm

Focussed beam on retinaAmplification of light by human eye: 10,000Extremely large irradiance Dependent on exposure time

Retinal Hazard Region

Thermal Effects

• Overheating• Retina burns• Scars / blind spots in the field of vision• Invisible light: damage may only be detected post-injury• Severe damage may require surgery or transplant•Depending on location of the burn, could permanently lose:• Central vision• Peripheral vision

Elements of Laser Safety, Gary E. Myers. 1998.

Laser Hazards Control

• Remove wristwatches or reflective jewellery

• Close and lock the room door

• Place “Laser Work in Progress” warning sign on door

• In case of an emergency, contact your TA/Instructor or UofT Campus Police 416-978-2222

• Return the laser controller key when completed

• Turn off laser when changing samples

• Wear laser safety glasses AT ALL TIMES

- Wavelength and Optical Density

• If someone unexpectedly enters, turn laser off

Thorlabs. 2010.

Laser Safety Industries. 2010.

Questions?