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

Overview 1) Introduction 2) Background & Applications 3) Apparatus 4) Laser Safety

1. Introduction

Experiment Context Optical Tweezers are a brand new experiment Not currently part of Advanced Physics Labs Purpose of presentation: TA/Instructor to deliver a brief presentation to students Apparatus Applications Hazards Safety procedures Students can make an informed decision regarding choosing an experiment

Relevant Courses Theory behind Experiment: Energy Equipartition theory Relates to courses in both Engineering and Arts and Science: Phy293  Engineering PHY256H1  Arts and Science This lab is designed for the Advanced Physics Labs: PHY424/426/428/429 (A&S) and PHY327/427/428/429 (Engineering)

Experiment Learning Objectives Students will have the opportunity to : Work on interesting and challenging experiments Deepen their understanding of the underlying Physics Further develop laboratory, analysis and communication skills Gain familiarity with the Optical Trapping apparatus and its various applications

2. 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)

3. Apparatus

Main Components Very Dangerous! Safe!

4. Laser Safety

Optical Trap Laser Characteristics 980 nm  Infrared range 330mW maximum power Collimated beam Class 3B laser

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 reflections Invisible Most dangerous procedure, contact your TA/Instructor Eye injuries without laser safety glasses Stray Beams Beam Alignment Biological Effects

Cornea Focussing element Lens Fine focus Vitreous Humor Retina Image is projected from the cornea and lens Connection to brain through optic nerve Fovea Sharp vision

Biological Effects Laser Light nm Focussed beam on retina Amplification of light by human eye: 10,000 Extremely 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

Laser Hazards Control Wear laser safety glasses AT ALL TIMES - Wavelength and Optical Density Remove wristwatches or reflective jewellery Close and lock the room door Place “Laser Work in Progress” warning sign on door If someone unexpectedly enters, turn laser off In case of an emergency, contact your TA/Instructor or UofT Campus Police Return the laser controller key when completed Turn off laser when changing samples