part1-lasers-01-slides

Electromagnetic Waves

  • Definition and Properties

    • Electromagnetic waves are waves of electric and magnetic fields that propagate through space.

    • The characteristics of electromagnetic waves include frequency, wavelength, energy, and amplitude.

    • Frequency refers to the number of oscillations of the wave per second (measured in Hertz).

    • Wavelength is defined as the distance between two consecutive crests or troughs of the wave.

    • Higher frequency correlates with more energy, while lower frequency results in less energy.

    • The speed of light is a constant (C) at approximately 3 x 10^8 m/s, and is related to wavelength and frequency by the equation:[ \text{wavelength} = \frac{C}{\text{frequency}} ]

The Electromagnetic Spectrum

  • Overview

    • The electromagnetic spectrum encompasses all types of electromagnetic radiation, which can be categorized based on their frequency and wavelength.

    • Ranges from extremely low frequency (ELF) to gamma rays.

  • Categories of Frequency

    • Extremely Low Frequency (ELF): 3 Hz – 3 kHz

    • Very Low Frequency (VLF): 3 kHz – 30 kHz

    • Low Frequency (LF): 30 kHz – 300 kHz

    • Medium Frequency (MF): 300 kHz – 3 MHz

    • High Frequency (HF): 3 MHz – 30 MHz

    • Very High Frequency (VHF): 30 MHz – 300 MHz

    • Ultra High Frequency (UHF): 300 MHz – 3 GHz

    • Super High Frequency (SHF): 3 GHz – 30 GHz

    • Extremely High Frequency (EHF): 30 GHz – 300 GHz

  • Non-Ionizing vs. Ionizing Radiation

    • Non-ionizing radiation (e.g. radio waves, microwaves) does not carry enough energy to ionize atoms.

    • Ionizing radiation (e.g. X-rays, gamma rays) has sufficient energy to cause ionization in matter.

  • Sources of EMF

    • Includes natural and man-made sources such as:

      • Cosmic sources (sunlight)

      • Radio signals (AM/FM radio, mobile phones)

      • Medical equipment (X-rays, MRI)

Applications of the EM Spectrum in Medicine

  • Treatment Requirements

    • Different forms of electromagnetic radiation are used for treatment at varying depths:

      • Surface Sculpting: UV, mid-IR with µm depth

      • Sub-Dermal Treatment: Visible, near IR, Terahertz with mm to cm depth

      • Whole Body Treatment: RF, X-ray, Gamma at 10 cm depth

  • Imaging Requirements

    • Depth and resolution are crucial for effective imaging. Key considerations include:

      • Resolution is diffraction limited, meaning it is affected by beam size and wavelength.

      • The relationship between imaging depth and resolution limits must be understood for accurate diagnostics.

Propagation and Interaction of EM Waves

  • How EM Waves Propagate

    • The propagation of EM waves interacts with matter based on properties such as the ionization potential of the material.

    • Photon energy above a material's ionization potential can liberate electrons. For example:

      • Hydrogen's ionization potential is 13.6 eV, which can be ionized by extreme ultraviolet (EUV), X-rays, and gamma rays.

Mathematical Foundations

  • Maxwell’s Equations

    • Fundamental equations that describe how electric and magnetic fields propagate and interact in free space.

    • Describe the behavior of electromagnetic fields in the presence of charge and current.

  • Wave Equation Solutions

    • Solutions address wave propagation in different mediums:

      • In a non-conducting medium (σ = 0), there is no attenuation (transparent). Properties depend on permittivity (ε) and permeability (μ).

      • Biophysical tissue properties make most of the body opaque at optical frequencies due to electrolytes present within tissues.

    • The wave equation can yield complex wave numbers for various media characteristics.