Biophysics Tutorial Week 7: Lasers in Medicine

Biophysics Tutorial (Week 7)

• The tutorial focuses on lasers
• The presentation covers lasers in medicine, including their history, components, types, and applications

Introduction to Laser and its Applications

• Lasers use Light Amplification by Stimulated Emission of Radiation (LASER)
• The acronym LASER represents the process of light amplification.

Laser in Medicine

• Lasers are used in a wide range of medical disciplines
• These include diagnosis, therapy, surgery, and medical instrumentation.

History of Laser

• The word "laser" is an acronym for light amplification by stimulated emission of radiation
• Its applications in medicine are significant

Basic Components of Laser

• Laser systems have three main parts
• Active medium (laser medium)
• Energy source (pump)
• Optical resonator (mirrors)

Laser Principles

• Spontaneous absorption – light absorption by atoms
• Spontaneous emission – light emission by excited atoms
• Stimulated emission – light emission by excited atoms upon interaction with photons

Types of Lasers

• Lasers can be categorized by their active medium
• The different types are solid-state, gas, liquid, and semiconductor.

Unique Properties of Laser Light

• Laser light is monochromatic (single wavelength)
• Laser light is coherent (with consistent phase and polarization). This creates strong intensity, a narrow and collimated ray.
• A laser ray is very powerful.

Differences between Laser and Ordinary Light

• Laser light is monochromatic, collimated, and coherent. Ordinary light is not
• The presentation uses diagrams illustrating these differences in appearance.

Laser Power and Classification

• Laser power is measured in watts or milliwatts, and power density in milliwatts per centimeter squared (mW/cm²)
• It can be classified into four groups according to their power ranges

Laser Classifications

• The classification table details the power range, and effect of each level
• Class 1 lasers pose no hazard
• Class 4 lasers can cause serious burns to skin and clothing, and injury to eyes and require extreme caution.

Types of Laser

• The different types include laser diode, gas lasers, dye lasers, and solid-state lasers.

Solid-State Laser

• A solid-state laser typically consists of a laser medium (ruby or Nd:YAG) within a flashtube
• A fully reflecting mirror, a partially reflecting mirror, and the laser output component are visible in the diagram.

Laser Medium

• The medium can be either a glass or crystalline material.
• Ruby is an example of a typical solid-state laser medium.
• Neodymium-doped yttrium aluminum garnet (Nd:YAG) is highly common.

Gas Laser

• Gas lasers use a mixture of gases (Helium-Neon, Argon, CO2) as the laser medium
• Gas lasers usually output in the IR spectrum range.

Liquid Laser

• Dye lasers are a type of liquid laser
• They utilize liquid dyes as the active medium
• They generate a light beam ranging from the near-ultraviolet (UV) to the near-infrared (IR) region.

Semiconductor (Diode) Laser

• A p-n junction in a semiconductor diode functions as the laser medium
• These lasers are very compact, cheap, and consume low power which don't need external mirrors.
• Electrical energy is used as the pump source in this type.

This tutorial explores the role of lasers in medicine, covering their history, key components, and applications across various medical disciplines. Gain insights into how lasers function and their importance in diagnosis, therapy, and surgical procedures.