Section 1: 10 Key Parameters
of a Laser System
6 +44 (0) 1904 788600 | Edmund Optics®
Laser
Mirror
Focusing Lens
Air Assist
Material
Beam Expander
635nm, 10W
1, 2, 3, 4, 5, 7, 8
9 10
7
7
5, 6, 8
Figure 1.1: Schematic of a common laser materials processing system
in which each of the 10 key parameters of a laser system are indicated
by their corresponding numbers
1000
100
10
1
0.1
0.1 1 10
Pulse Energy (J)
10 kW
1 kW
100 W
10 W
Repetition
Rate (MHz)
1 W
Figure 1.2: Visual representation of the relationship between pulse energy,
repetition rate, and average power for pulsed lasers
There is a vast range of common laser systems from applications as
diverse as materials processing, laser surgery, and remote sensing, but
many laser systems share common key parameters. Establishing common
terminology for these parameters prevents miscommunication,
and understanding them allows for properly specifying laser systems
and components to meet your application needs.
Section 1.1: Fundamental Parameters
The following fundamental parameters are the most basic concepts of
laser systems and are critical for understanding more advanced topics.
1: Wavelength (Typical Units: nm to μm)
A laser’s wavelength describes the spatial frequency of the emitted light
wave. The optimal wavelength for a given use case is highly applicationdependent.
Different materials will have unique wavelength-dependent
absorption properties in materials processing, leading to different interactions
with the material. Similarly, atmospheric absorption and interference
will affect certain wavelengths differently in remote sensing,
and various complexions will absorb certain wavelengths differently in
medical laser applications. Shorter wavelength lasers and laser optics
are advantageous for creating small and precise features with minimal
peripheral heating, but they typically are more expensive and prone to
damage than those at longer wavelengths.
2: Power and Energy (Typical Units: W or J)
The power of a laser is measured in Watts (W) and is used to describe
either the optical power output of a continuous wave (CW) laser or the
average power of a pulsed laser. Pulsed lasers are also characterized by
their pulse energy, which is directly proportional to average power and
inversely proportional to the laser’s repetition rate (Figure 1,2):
Higher power and energy lasers are typically more expensive, and they
generate more waste heat. As powers and energy increase, it also becomes
increasingly more difficult to maintain high beam quality. More
information on pulsed and CW lasers can be found in the Section 12:
Laser Induced Damage Threshold from pages 43-50.
3: Pulse Duration (Typical Units: fs to ms)
The laser pulse duration, or pulse width, is commonly defined as the full
width at half-maximum (FWHM) of the laser’s optical power vs. time
(Figure 1,3). Ultrafast lasers, which have numerous benefits for a range of
applications including precise materials processing and medical lasers,
are characterized by short pulse durations on the order of picoseconds
(10-12 s) to attoseconds (10-18 s). More information can be found in Section
10: Ultrafast Dispersion from pages 38-40 and Section 11: Highly Dispersive
Mirrors from pages 41-42.
4: Repetition Rate (Typical Units: Hz to MHz)
A pulsed laser’s repetition rate, or pulse repetition frequency, describes
the number of pulses emitted every second, or the inverse temporal
pulse spacing (Figure 1,3). As mentioned earlier, repetition rate is inversely
proportional to pulse energy and directly proportional to average
power. While repetition rate is often dependent on the laser gain
medium, in many cases it can be varied. Higher repetition rates result in
less thermal relaxation time at the surfaces of the laser optics and at the
final focused spot, which leads to more rapid material heating.
P (W)
Ppeak
τ 1/Repetition Rate
Pavg
Time (s)
Figure 1.3: The pulses of a pulsed laser are temporally separated by the
inverse of the repetition rate
1,1