Laser Module 1

Risk Management Services
www.riskmanagement.ubc.ca
Laser Safety and Program Development
Module 1: Introduction and Basics
Course Contents
Module 1: Basics of Lasers
Module 2: Laser Beam Injuries
Module 3: Laser Classification & Standards
Module 4: Laser Hazard Evaluation
Module 5: Control Measures & Safety Practices
Module 6: UBC Laser Program
Basics of Lasers
What does LASER stand for?
Light
Amplification by
Stimulated
Emission of
Radiation
Components of a Laser Design

The components of a laser are:
Lasing Medium
Excitation Mechanism
Feedback Mechanism
Output coupler
Lasing Medium
Feedback
Mechanism
Output
Coupler
Lasing Medium
The lasing medium is used to create a metastable state of
atoms long enough to create a population inversion.
Major determining factor of wavelength etc
Emits light in all directions
Can be gas, liquid, solid, semiconductor
Electron Energy States - Population Distribution
3
2
The excitation mechanism is the source of energy used to
excite the lasing medium.
It can be derived from:
- Optical pumping (i.e. xenon flashtube)
- Electron Collision (i.e. electric current through a gas)
- Chemical Process ( i.e. making and breaking of
chemical bonds)
In 1917, Albert Einstein established the theoretic foundations for the

laser and the maser in the paper Zur Quantentheorie der Strahlung
(On the Quantum Theory of Radiation); via a re-derivation of Max
Plancks law of radiation, conceptually based upon probability
coefficients for the absorption, spontaneous emission, and stimulated
emission of electromagnetic radiation.
Stimulated Emission
During emission the perturbing photon is not destroyed.

A second photon is created with the same phase and
frequency as the first.
Feedback Mechanism: Optical Cavity

A resonant cavity is used to amplify number of photons. It:
Is used to reflect light from the lasing medium back into
itself
Typically consists of two mirrors at each end of the lasing
medium
Results in amplification of the energy from the excitation
mechanism in the form of light
Output coupler
Usually a partially transparent mirror on one end of the lasing
medium that allows some of the light to leave the lasing
medium in order that the light be used for the production of
the laser beam.
The output coupler is usually part of the feedback mechanism.
Helium-Neon Gas Laser
Courtesy of Metrologic, Inc.
Gas lasers use gas atoms in a tube as an active medium. The excitation mechanism is usually an electric
current through the gas. Mirrors on each end of the tube are aligned to reflect the laser beam through the
active medium. About 2% of the light passes through the output coupler at the lower left.
This photo is a typical 5 mW HeNe laser. This was the most common type of laser until the mid 1980s when
reliable, low-cost diode lasers became available. HeNe lasers are still the second most common lasers. They
provide higher beam quality than most diode lasers. They are widely used in scientific applications where low
power, high quality beams are needed.
There are many other types of gas lasers. Argon lasers produce powerful blue beams and are used in
scientific research, medical applications, and laser light shows. Carbon dioxide lasers produce beams with
powers of thousands of watts and are used for cutting and welding metals. Other gas lasers find a wide range
of applications.
Solid State Laser

High Reflectance
Mirror (HR)
Elliptical Reflector
Output Coupler
Mirror (OC)
Solid State Rod
Arc or Flash Lamp
Power Supply
Single Lamp
Double Lamp
Solid State Laser

The active medium of a solid state laser is a solid crystalline
rod containing the lasing atoms.
The optical excitation mechanism may be a flashlamp for
pulsed output or an arc lamp for continuous output.
The lamp and laser rod are located at the foci of a reflective
ellipse that concentrates the lamp light into the rod.
Higher power solid state lasers often use two lamps and a
double ellipse.
The optical cavity consists of a high reflector mirror at one
end of the rod and an output coupler at the other.
Solid State: Neodymium YAG Laser
The most common type of solid state laser is the Nd:YAG laser. The active medium of this laser is a crystalline rod
made of Yttrium Aluminum Garnett (YAG) with about 0.5% of the rare earth metal neodymium (Nd) included as an
impurity. The Nd atoms do the lasing. The transparent YAG crystal holds the Nd atoms in place at the necessary
density. Many other types of crystals can be used, but most solid state lasers use Nd:YAG.
Lamps for Nd:YAG lasers are made of fused silica and filled with krypton gas. Krypton produces red and IR light that is
most efficient for pumping YAGs and other IR lasers. Arc lamps produce constant pumping and continuous beams.
Flashlamps produce pulsed beams.
Cooling the laser rod is always important in Nd:YAG lasers. Lamp-pumped solid state lasers usually use cooling water
flowing across the rod and the lamps. Lower power, diode pumped solid state lasers can be cooled with air.
Nd:YAG lasers come in many designs. Welders often use pulsed Nd:YAG lasers with pulse durations of a few
milliseconds. Markers include a Q-switch to divide what would otherwise be a CW beam into thousands of pulses per
second. The Q-switch also compresses the pulse duration to around 100 ns in a marker. Some Nd:YAG lasers have
frequency doublers to change the laser wavelength from 1064 nm (near IR) to 532 nm (green light).
Neodymium YAG Laser

Rear Mirror
Adjustment Knobs
Safety Shutter Polarizer Assembly (optional)
Coolant
Beam
Tube
Adjustment
Knob
Output
Mirror
Beam
Q-switch
(optional)
Beam Tube
Nd:YAG
Laser Rod
Flashlamps
Pump
Cavity
Laser Cavity
Harmonic
Generator (optional)
Courtesy of Los Alamos National Laboratory
Diode Laser
Metallic Contact
10 - 20
mm
Current
Distribution
SiO2
+
P-N Junction
Elliptical
Beam
Cleaved
Facet
In diode lasers the laser light is produced in the junction between two semiconductor layers. Free
electrons in the N layer cross the boundary to occupy holes in the P layer. The excess energy
that made the electrons free is emitted as a photon. This laser is essentially a light emitting diode
with mirrors on the ends. The most common diode lasers are smaller than a grain of salt and
produce an output power of a few milliwatts. Larger diode lasers can produce powers of many
watts, and stacked arrays can produce thousands of watts. Diode lasers are available from the blue
into the far infrared.
The most important application of diode lasers is for fiber optic communication. They are also used
in CD players, laser pointers, measurement instruments, and many other applications. Diode lasers
are also important as the optical power for diode-pumped solid state (DPSS) lasers.
Light vs. LASER
Inverse-Square Law
Light point
source
2
Distance
Light vs. LASER

Laser light differs from a regular point source light:
Monochromatic: one wavelength (colour)

Directional: narrow beam in a specific direction
Coherent: wavelengths are in phase in space and time (polarized)
**Able to focus a lot of energy onto a small area**
Laser Basic
Laser Hazard
Laser Factoids
1 mW HeNe laser appears > 100x brighter than the sun
Can carry 10,000 times more information than microwaves,
1 billion times more than radiowaves
Focused to less than 1 micron, it can evaporate metal and
drill diamond
Can be focused to ~25 microns on the retina
Power density on the retina increases by a factor of 100,000!
A 1mW laser can produce ~400W/cm2 (surgical applications
use 500-15,000W/cm2)
The eye can focus both visible and invisible near infrared
radiation!
Types of Lasers
Lasing medium:
Gas
Liquid
Solid
Semiconductor
Dye
Duration of laser light emission:
Continuous wave (CW)
Pulsed
Q-switched
Lasers in the Workplace
Micro-welding
Micro-drilling
Scribing ceramics
Surface treating
High-speed marking
Precision wire stripping
Resistor trimming
Integrated circuitry
Holography
Printing
Science shows
Light shows
Point of sales terminals
Construction

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Risk Management Services

Laser Safety and Program Development

Module 1: Introduction and Basics

Components of a Laser Design

In 1917, Albert Einstein established the theoretic foundations for the

During emission the perturbing photon is not destroyed.

Feedback Mechanism: Optical Cavity

Helium-Neon Gas Laser

Courtesy of Metrologic, Inc.

Solid State Laser

Solid State Rod

Arc or Flash Lamp

Solid State Laser

Solid State: Neodymium YAG Laser

Neodymium YAG Laser

Courtesy of Los Alamos National Laboratory

Light vs. LASER

Light vs. LASER

Monochromatic: one wavelength (colour)

Lasers in the Workplace

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