HNLS008R(L) Red HeNe Laser System
Chapter 5: Troubleshooting
Rev C, March 23, 2015
Page 14
Chapter 5
Troubleshooting
5.1. Technical Failures
Problem
Fix
No light is being emanating from
the laser.
Make sure that the aperture is open.
Check to make sure that
the power supply is plugged into a working outlet, and
the connector is fully seated into the back of the laser
housing.
The laser does not work and
there is something rattling
around inside the laser head.
The glass gas tube may have broken during shipping. Please contact
your local tech support office for help.
The laser has low output power.
The laser requires 10 minutes to meet published specifications. Make
sure to let it warm up.
5.2. Application Trouble Shooting
Some sources of trouble of a HeNe laser do not come from the laser failing or being out of spec. In some cases,
these laser are not suited to the application. One common mis-application comes from a HeNe laser, especially a
low power laser (~0.5 mW), being used in a metrology application.
Environment is an important consideration as well. Dirty environments can cause the optics to become
contaminated and the power output to drop below expected levels. Unstable output beams can be caused by
noisy environments with large sources of vibrations. Proper mounting on an optical table can reduce the effects of
ambient vibrations. Temperature is also a factor. If the environment where the laser is being used fluctuates in
temperature, the output power can experience a large amplitude change. Even blowing on the laser tube can
cause the output power to fluctuate significantly.
Randomly polarized lasers are actually rapidly changing, single polarization lasers. When averaged over time, the
light emitted from these lasers appears randomly polarized. However, any polarization optics in the path
(intentional or unintentional) can cause large variations in the output power. Only polarized lasers should be used
in applications that involve polarization optics.
While HeNe lasers are less sensitive to variations caused by back reflections, they are not immune to them. Large
retro-reflections back into the laser can cause unpredictable power changes. A free-space isolator can be used to
reduce or eliminate these effects. If possible, only a small angular deviation is needed to eliminate the back
reflections.
These HeNe lasers are ill suited to any application or experiment where a single frequency or long coherence
length is required.
5.2.1. Noise, Oscillations, and Fluctuation Sources
There are many sources of noise, oscillations and fluctuations of the output of a HeNe laser. One of the most
common is from longitudinal modes drifting into and out of the gain curve. The frequency of these fluctuations
vary from less than a Hz to as high as several kHz, depending on the stability of the environment.
Other, more constant sources of fluctuations are from the following (with corresponding frequencies):
Line Noise from AC High-Voltage Power Supplies (50/60 Hz, 100/120 Hz, etc.)
Switching Noise from DC High-Voltage Power Supplies (40 kHz)
Plasma Oscillation (Tens of MHz)
Transverse Mode Beat Notes (Hundreds of MHz)
Axial Mode Beats (at FSR, Hundreds of MHz)
