Therminology from lasers
Lasers are complex technology, which can make their specifications and attributes confusing to navigate. To help you better understand key laser product details as you shop, this article will explain the most common terminology in straightforward terms with real-world examples.
Laser terminology covers the fundamental principles, components, light properties, and applications of lasers, including LASER (Light Amplification by Stimulated Emission of Radiation) itself, coherence and monochromaticity of the light, active medium, pumping, optical cavity, diodes, wavelength, power, pulse width, and terms related to applications like ablation, collimation, and beam diameter.
Fundamental Principles & Components
LASER (Light Amplification by Stimulated Emission of Radiation):
The acronym describing the process by which lasers produce their light.
Pumping:
The process of exciting the atoms or molecules in a lasing medium to a higher energy level to initiate the lasing process.
Active Medium:
The material (gas, solid, or liquid) that amplifies light through stimulated emission to produce the laser beam.
Optical Cavity / Resonator:
A system of mirrors that contains the active medium, reflecting light back and forth to stimulate further emissions and amplify the beam.
Population Inversion:
A state where more atoms in the active medium are in an excited state than in a lower energy state, necessary for lasing to occur.
Properties of Laser Light
- Coherence: A characteristic where the light waves are in phase with each other in both time and space.
- Monochromaticity: The emission of light at a single or very narrow band of wavelengths.
- Divergence / Collimation: The extent to which a laser beam spreads out. A well-collimated beam has low divergence and maintains its narrowness over long distances.
- Wavelength: The "color" of the laser light, determined by the active medium.
Applications & Related Terms
- Ablation: The removal of material from a surface by vaporization or melting using a laser.
- Laser Diode: A semiconductor device that produces a laser beam.
- Beam Diameter: The width of the laser beam.
- Laser Classification: A system for categorizing lasers based on their potential hazards.
- Nominal Hazard Zone (NHZ): An area where the maximum permissible exposure level (MPE) for laser radiation is exceeded.
- Assist Gas: Used in laser cutting and welding to clear away molten material.
Measurement & Control Terms
- Power: The amount of energy per unit time produced by the laser, measured in Watts (W).
- Pulse: A single, discrete burst of laser energy.
- Pulsewidth: The duration of a laser pulse.
- Power Density: The amount of laser output per unit area (e.g., W/cm²).
- Radiant Exposure: The radiant energy per unit area, expressed in joules per square centimeter (J/cm²), particularly relevant for pulsed lasers.
VLT-Visible Light Transmission
One Of The Most Important Indicators Of Laser Safety Glasses/Windows
Most eyewear is designed to protect your eyes from specific wavelengths of light while allowing other wavelengths in the visible spectrum to pass through so you can see clearly.
Visible Light Transmission (VLT) refers to the amount of light that can pass through the lens of a pair of glasses. Here’s a simple way to understand it:
Low VLT: Less light passes through the lens, making your vision darker. This is like wearing inexpensive sunglasses that block the sun effectively but can make everything look too dark.
- High VLT: More light passes through the lens, allowing you to see colors and details more clearly. High-quality sunglasses typically have a higher VLT, which means they block harmful rays from the sun while keeping the surroundings bright and natural.
When choosing glasses, it’s important to consider not just the amount of light being blocked, but also the range of visible light that is allowed through. This ensures that you have clear and accurate vision without unnecessary distortion.
In summary, VLT is an important factor in eyewear because it helps balance protection and clarity. Higher VLT lenses usually offer better visual comfort by maintaining natural brightness while still protecting your eyes.
OD-Optical Density
How Much Light A Lens/window Can Block
OD-Optical Density (Term used in USA but not fully legal in Europe)
How Much Light A Lens Can Block
Optical Density (OD) in laser safety measures how much light a lens can block at a specific wavelength. It's an important concept because it helps determine how well laser safety glasses can protect your eyes from harmful laser light.
Here's a simple way to understand OD:
- High OD: Means the lens blocks a lot of light. For example, an OD of 5 means only 1 out of 100,000 parts of the light gets through.
Low OD: Means the lens blocks less light.
Comparison of OD and Light Transmittance
<figure class="table" style="width:500px;">
</figure>OD
Transmission of light Attenuation Factor OD
Transmission of light Attenuation Factor 0
1
1
5
0.00001
100000
1
0.1
10
6
0.000001
1000000
2
0.01
100
7
0.0000001
10000000
3
0.001
1000
8
0.00000001
100000000
4
0.0001
10000
9
0.000000001
1000000000
The required OD is determined by laser safety standards, such as those found in ANSI Z136.1 in the USA. These standards depend on several factors:
- Wavelength of the laser: Different wavelengths (or colors) of laser light can have different effects on your eyes.
- Power of the laser: Stronger lasers need lenses with higher OD to block enough light and keep your eyes safe.
- In summary, OD is a measure of how much light a lens can block at a specific wavelength. High OD means better protection, and the required OD depends on the laser's wavelength and power, as determined by safety standards.
MPE-Maximum Permissible Exposure
The Limits of Laser Safety
Maximum Permissible Exposure (MPE) can be thought of as the "speed limit" for laser safety. It’s the highest amount of laser radiation that your eyes or skin can safely handle without causing harm.
The MPE depends on several factors:
Wavelength of the Laser: Different colors or types of laser light can have different effects on your body. MPE changes based on the specific wavelength of the laser.
Exposure Time: How long you’re exposed to the laser matters. Shorter exposure times might allow for higher levels of laser radiation, while longer exposure times require lower levels to stay safe.
Type of Laser: Whether the laser is continuous wave (CW) or pulsed energy also affects the MPE. Stronger lasers with more energy need stricter limits.