THORLABS HRS015B User manual

HRS015B
Stabilized Red HeNe
Laser
User Guide

Stabilized HeNe Laser Chapter 1: Warning Symbol Definitions
Rev F, July 15, 2022 Page 1
Table of Contents
Chapter 1 Warning Symbol Definitions................................................................................2
Chapter 2 Safety.....................................................................................................................3
2.1. CE Compliance ............................................................................................................. 4
Chapter 3 Description............................................................................................................5
3.1. Laser Head.................................................................................................................... 5
3.2. Modes of Operation...................................................................................................... 5
3.2.1. Frequency Stabilization Mode...............................................................................................6
3.2.2. Intensity Stabilization Mode ..................................................................................................6
3.3. Laser Power Supply ..................................................................................................... 6
3.4. HeNe Laser Overview................................................................................................... 7
3.5. HeNe Linewidth............................................................................................................. 7
3.6. HeNe Polarization......................................................................................................... 9
3.6.1. Random Polarized Beam......................................................................................................9
3.6.2. Polarized Beam.....................................................................................................................9
3.6.3. Stabilized HeNe Polarization.................................................................................................9
Chapter 4 Unpacking...........................................................................................................10
4.1. Unpacking................................................................................................................... 10
4.2. Shipping Inventory..................................................................................................... 10
Chapter 5 Setup ...................................................................................................................11
5.1. Mounting the Laser Head........................................................................................... 11
5.2. Alignment.................................................................................................................... 11
5.3. Assembly .................................................................................................................... 11
Chapter 6 Operation ............................................................................................................12
6.1. HeNe Power Supply.................................................................................................... 12
6.1.1. Introduction..........................................................................................................................12
6.1.2. Fuse Replacement..............................................................................................................13
6.1.3. Remote Interlock Operation................................................................................................13
Chapter 7 General Maintenance .........................................................................................15
7.1. Cleaning...................................................................................................................... 15
Chapter 8 Troubleshooting.................................................................................................16
8.1. Technical Failures ...................................................................................................... 16
8.2. Application Troubleshooting..................................................................................... 17
8.2.1. Noise, Oscillations, and Fluctuation Sources......................................................................17
Chapter 9 Specifications.....................................................................................................18
Chapter 10 Mechanical Drawing...........................................................................................19
Chapter 11 Regulatory...........................................................................................................20
Chapter 12 Thorlabs Worldwide Contacts...........................................................................21

Stabilized HeNe Laser Chapter 1: Warning Symbol Definitions
Page 2 TTN091077-D02
Chapter 1 Warning Symbol Definitions
Below is a list of warning symbols you may encounter in this manual or on your device.
Symbol
Description
Direct Current
Alternating Current
Both Direct and Alternating Current
Earth Ground Terminal
Protective Conductor Terminal
Frame or chassis Terminal
Equipotentiality
On (Supply)
Off (Supply)
In Position of a Bi-Stable Push Control
Out Position of a Bi-Stable Push Control
Caution, Risk of Electric Shock
Caution, Hot Surface
Caution, Risk of Danger
Warning, Laser Radiation
Caution, Spinning Blades May Cause Harm

Stabilized HeNe Laser Chapter 2: Safety
Rev F, July 15, 2022 Page 3
Chapter 2 Safety
WARNING
Laser Radiation –Avoid Exposure to Beam –Class 3R Laser Product
The laser described in this operating manual emits visible light. This laser is safe to operate provided that the user
complies with all safety warnings. It is recommended that all personnel who will operate or be in the vicinity of the
laser during operation read and be familiar with this manual as well as be made aware of the following safety
warnings.
•Never look directly into the laser light source or at scattering laser light from reflective surfaces. Laser light
is hazardous to the eyes. Never stare down the beam into the source.
•Install the laser so that the laser beam is not at eye level.
•Whenever the laser is operating and the beam is not in use, block the beam with the shutter on the output
aperture. Avoid direct exposure to the laser beam.
•As a precaution against accidental exposure to either the laser beam or its reflection, operators should wear
laser safety glasses designed for this type of laser.
•High voltage is present at all times when the key switch on the control box is in the “ON” position.
•Ensure that the laser head is securely connected to the power supply. To prevent faulty operation, be sure
that the male connector is fully seated in the of the power supply.
•The power cord and plug are provided with a ground line. To avoid possible shock, ensure that the plug is
properly connected to a ground point at the electrical connection.
•Do not attempt to open the sealed laser housing or the power supply. The power supply and laser are not
user accessible and service operations inside the enclosure must only be performed by authorized and
trained personnel. Opening the laser or power supply will result in loss of warranty.
•Do not perform any operating or maintenance procedure not described in the user’s manual.
•Do not operate this product if the cover has been removed.
•This product is for indoor use only. To prevent potential fire or shock hazard, do not expose the unit to any
source of excessive moisture.
•Operating this product in the presence of flammable gases or fumes is extremely hazardous.
•Disconnect the power cord before replacing fuses.
•Clean the laser head and power supply with a dry, soft cloth. Do not use liquids.
WARNING
Use of controls or adjustments or performance of procedures other than those specified herein may
result in hazardous radiation exposure. Avoid unnecessary exposure to laser or collateral radiation
that exceeds the accessible emission limits listed in the safety regulation guidelines 21 CFR
Subchapter J 1040.10 and 1040.11. This federal regulation is administered by the National Center for
Devices and Radiological Health under the Food and Drug Administration.
WARNING
Safety glasses with an optical density (OD) of 2.4 or greater are required while operating this
product. Safety glasses can be purchased from Thorlabs at www.thorlabs.com. For assistance in
choosing the proper safety glasses, please contact Thorlabs Technical Support.

Stabilized HeNe Laser Chapter 2: Safety
Page 4 TTN091077-D02
Each Visible Helium-Neon Laser System that is certified to be in compliance with the CDRH regulations is equipped
with a key-switch, remote interlock connector, laser radiation emission indicator, time delay relay (built into the
power supply), a beam attenuator (a manual shutter located in the front bezel of the laser housing), and all
appropriate warning labels. To ensure continued compliance, verify on an annual basis or, if the product has been
subjected to adverse environmental conditions, such as fire, flood, mechanical mishandling, or solvent spillage that
your system’s safety features listed above are available and operational.
For further information and assistance on laser safety, contact the following agencies:
Laser Institute of America
13501 Ingenuity Drive, Suite 128
Orlando, FL 32826
** Safety Guides **
American National Standards Institute, Inc.
25 West 43rd Street
New York, NY 10036
** Safety Guides**
Food and Drug Administration
Center for Devices and Radiological Health
2098 Gaiter Road
Rockville, MD 20850
2.1. CE Compliance
For European customers who require a CE-approved laser system, Thorlabs certifies that our laser heads and lab
power supplies meet the appropriate CE requirements. In order for the CE regulations to be met, all Thorlabs power
supplies must be used with an input line cord with a length of less than three meters. The factory-included line cord
has a length of approximately two meters. Other cords may be used, but they must have a length of no longer than
three meters in order for the laser system to remain CE compliant.

Stabilized HeNe Laser Chapter 3: Description
Rev F, July 15, 2022 Page 5
Chapter 3 Description
Thorlabs offers an extensive selection of CE compliant 632.992 nm (red) Helium Neon (HeNe) Lasers with powers
from 0.5 mW to 35 mW. HeNe lasers are widely chosen for use in educational applications and as alignment tools
due to their excellent beam quality and gas discharge laser characteristics. In addition to these standard lasers,
Thorlabs now offers a stabilized HeNe where you can choose between frequency and intensity stabilization. In
frequency stabilization mode the HeNe will keep its lasing frequency, or wavelength, constant, while in intensity
stabilization mode the laser will keep its output power constant.
3.1. Laser Head
This laser head comes equipped with a manual shutter installed in the front bezel of the laser housing (see Figure
1 below). The front bezel has four 4-40 tapped holes to secure the optional accessory mounting ring and other
industry-standard HeNe accessories. There are also four 2-56 tapped holes to secure Thorlabs FiberPorts.
However, properly aligned FiberPorts can cause light to reflect back into the laser which would destabilize it. To
overcome this issue, the FiberPort would have to be purposely misaligned, reducing the coupling efficiency.
Additonally there is also a SM1 thread to allow mounting of accessories with external SM1 threads like lens tubes,
etc. This laser also comes with a 3.5 ft. long high-voltage cable to connect with the included power supply. This
particular laser head is designed to operate at an optimum performance level when used with the required Thorlabs
power supply.
Figure 1 Laser Head and Mounting Hole Pattern
3.2. Modes of Operation
The user has the ability to change between two modes of operation, frequency and intensity stabilization. Each
mode is being selected by the switch on the laser head. Allow the laser up to 2 minutes to stabilize on the different
mode.
Laser Aperture
4, 4-40 Mounting Holes
4, 2-56 Mounting Holes
for FiberPorts
Polarization Alignment Line
Intensity (I) and
Frequency (f) Stabilization
Mode
Selection Switch
Manual Beam Shutter
Status LED
If the LED is off, the laser MAY NOT be on. If the LED is
blinking, the laser is warming up, and if the LED is solid,
the laser is stabilized.
SM1-Threaded Port

Stabilized HeNe Laser Chapter 3: Description
Page 6 TTN091077-D02
3.2.1. Frequency Stabilization Mode
The frequency stabilization mode will balance the intensity of the two modes under the gain curve in order to keep
the frequency of the laser stable. The tube length is specifically chosen to allow only two cavity modes to oscillate
under these conditions. The polarization states of the modes are orthogonal (i.e., one will be S-polarized and the
other will be P-polarized). Using a polarizing beam splitter, one of the modes is directed to a photodetector, while
the remaining mode passes through a second beamsplitter where 5% of the output is reflected to a second
photodetector. An error signal generated by the two photodetectors is used to control a heater wrapped around the
laser tube. The heater causes the tube to expand and contract as necessary to stabilize the frequency. The
frequency stabilization mode also delivers some intensity stability, which is still far superior compared to an ordinary
HeNe laser.
3.2.2. Intensity Stabilization Mode
Intensity stabilization mode will stabilize the intensity of the output beam. This mode operates on the same principle
as frequency stabilization. However, only one of the photodetectors is used to generate the feedback error signal
to control the heater. The intensity stabilization mode also delivers some frequency stability, which is still superior
compared to an ordinary HeNe laser. The intensity stabilization mode is very useful if transmittances or efficiencies
of optical components are being measured and a highly stable light source is being needed.
Either mode can be quickly selected by adjusting the toggle switch into the desired position. See Figure 1.
3.3. Laser Power Supply
The laser includes a power supply that is specially designed to be used with the HeNe laser and is CE-certified.
The power supply is enclosed in a protective housing and is CDRH compliant with a built-in 3 to 5 second time
delay, an Alden high-voltage connector (see Figure 4 below), a key lock switch with two removable keys, a power
on indicator
1
, a fuse access point, a remote interlock connector, and a removable input power cable.
WARNING
Always be careful when handling HeNe tubes and their connectors. HeNe tubes require high voltage
operation (1500 V in this case and up to 10,000 V at startup) and they hold a charge. There is a
shock hazard. Keep body parts away from the metal contacts on the Alden connectors and be
careful when handling the connector. It is best to short the tube contacts to an earth-grounded
point, such as a properly grounded breadboard.
NEVER plug or unplug the Alden plug from the power supply unit while the power supply is on. This
may result in damage to the power supply and/or laser head and is not covered under warrenty.
Figure 2 High-Voltage Alden Plug
1
The “Laser On”indicator will come on when the key is turned on. It does not indicate the laser is on, lasing, or the power supply is working. It
only indicates that there may be power going to the laser head.

Stabilized HeNe Laser Chapter 3: Description
Rev F, July 15, 2022 Page 7
3.4. HeNe Laser Overview
A helium-neon laser, typically called a HeNe laser, is a small gas
laser with many industrial and scientific uses. The primary
wavelength they are used at is 632.8 nm, in the red portion of the
visible spectrum.
The gain medium of the laser is a mixture of helium and neon gases
in a 5:1 to 20:1 ratio that is contained at low pressure in a sealed
glass tube. The excitation source for these lasers is a high voltage
DC electrical discharge through an anode and cathode at each end
of the glass tube. The optical cavity of the laser consists of a flat,
high-reflecting mirror (HR) at one end of the laser tube, and an
output coupler mirror (OC) with approximately 1% transmission at
the other end.
HeNe lasers tend to be small, with cavity lengths of around 10 cm
up to 1 m and optical output powers ranging from 0.5 mW to 50 mW.
Thorlabs offers output powers up to 35 mW.
Typical HeNe Parameters
Beam Diameter (D)
1 mm
Cavity Length (L)
0.10 m (0.5 mW) to 1 m (50 mW)
Reflectivity at High Reflector (HR)
>99.99%
Transmission at Output Coupler (OC)
~1%
Figure 3 Optical Resonator Cavity
3.5. HeNe Linewidth
The red HeNe laser wavelength is 632.8168 nm in air, though it is often reported as either 632 nm or 633 nm.
However, it is not a pure wavelength but is actually made of several lasing lines called axial or longitudinal modes
that fluctuate within the gain bandwidth of neon due to thermal expansion of the cavity and other external factors.
The axial mode structure of the HeNe laser is characterized by the number of modes, the free spectral range (FSR,
distance between the modes), and the Doppler-broadened width of the neon gain curve (see Figure 6 below). The
linewidth of individual axial modes is usually small (~kHz) and is primarily determined by external factors and
measurement timescales rather than fundamental laser parameters. In most interferometric applications, the most
relevant parameter is the coherence length, which is determined by the axial modes that are furthest apart. For a
typical unstabilized (non-single frequency) red HeNe laser, the coherence length is approximately 30 cm.
HeNe Applications
•Metrology
•Cleanroom Monitoring Equipment
•Food Sorting
•Flow Cytometry
•Confocal Microscopy
•Imaging and Medical Equipment
•Opacity Monitoring
•Alignment
•Maritime Visual Guidance
Systems
•Spectroscopy

Stabilized HeNe Laser Chapter 3: Description
Page 8 TTN091077-D02
Figure 4 HeNe Gain Curve Showing Cavity Modes
The laser process in a HeNe laser starts with the collision of electrons from the electrical discharge with the helium
atoms in the gas. This excites helium from the ground state to a long-lived, metastable excited state. Collision of
excited helium atoms with ground-state neon atoms results in excited neon electrons.
Figure 5 HeNe Energy Levels
The number of neon atoms entering the excited states builds up until population inversion is achieved. Spontaneous
and stimulated emission between the states results in emission of 632.8168 nm light along with other emission
wavelengths. From these states, the electrons quickly decay to the ground state. The HeNe laser’s power output is
limited because the neon upper level saturates with higher current, while the lower level varies linearly with current.
The laser cavity can be designed with the correct mirrors and length to promote other wavelengths of laser emission.
There are infrared transitions at 3.39 μm and 1.15 μm wavelengths, and a variety of visible transitions, including a
green (543.365 nm, sometimes called GreeNe laser), a yellow (593.932 nm), a yellow-orange (604.613 nm), and
an orange (611.802 nm) transition. The typical red, 633 nm wavelength output of a HeNe laser actually has a much
lower gain compared to other wavelengths, such as the 1.15 μm and 3.39 μm lines.

Stabilized HeNe Laser Chapter 3: Description
Rev F, July 15, 2022 Page 9
Figure 6 HeNe Visible Laser Lines
3.6. HeNe Polarization
3.6.1. Random Polarized Beam
Most common HeNe laser tubes are randomly polarized since for many applications the polarization of the beam
does not matter. The term "random" here really does not mean that the polarization is changing to totally arbitrary
orientations or at high frequency. In fact, such behavior would be rather unusual. It just means that nothing special
is done to control the polarization. The typical random polarized HeNe laser will lase on several longitudinal modes
(how many will depend on tube length of the resonator) with adjacent modes having polarizations orthogonal to
each-other, with the two polarization axes fixed for the life of the tube. Each of the modes will change their relative
intensities periodically over time, most notably during warmup as the cavity length changes due to thermal
expansion.
Random polarized lasers are acceptable for applications where there are no polarizing elements in the beam path.
Depending on the time scale of an application, polarizing elements could result in large power fluctuations.
Reorienting the laser head (about its axis) may help to minimze these, but the use of a linearly polarized laser is
the best solution.
3.6.2. Polarized Beam
The state of polarization in a polarized HeNe laser beam is linear, making these lasers ideal for polarization-
sensitive applications.
3.6.3. Stabilized HeNe Polarization
The output of the stabilized HeNe laser will be linearly polarized and aligned with the engraving on the front of the
unit.

Stabilized HeNe Laser Chapter 4: Unpacking
Page 10 TTN091077-D02
Chapter 4 Unpacking
4.1. Unpacking
Inspect the packing container for any damage that may have occurred during shipment. Contact your local Thorlabs
customer service office for assistance. Packing materials are specifically designed to protect against shipping
damage. Please keep this container and reuse if your system needs to be returned to Thorlabs for service or
evaluation.
Carefully remove the laser system from the packing container. Inspect for damage, including dents and scratches.
There should not be anything rattling around inside the laser head. Rarely during shipping the glass tube may break
Figure 7 Laser System
4.2. Shipping Inventory
The equipment included in this shipment should match the packing slip attached to the box. Verify that the correct
product was shipped to you by matching the item number on the box. If the shipment is incomplete, or if an incorrect
item was shipped to you, please notify Thorlabs immediately.
This package should contain:
•Cylindrical Laser Head
•Power Supply
•2 Keys for Power Supply
•Remote Interlock for Power Supply
•Pre-Installed 1.25 A, 250 V, 5 mm x 20 mm Time Lag Fuse
Power
Supply
Keys
Power Supply Module
Laser Head
Laser head with manual shutter and
power cord with Alden connector
AC Power Cord
Make sure the plug is
the correct version
for your region

Stabilized HeNe Laser Chapter 5: Setup
Rev F, July 15, 2022 Page 11
Chapter 5 Setup
5.1. Mounting the Laser Head
The cylindrical construction of the laser head allows for
easy mounting in ring clamps, V-blocks, or similar
mounting hardware without affecting the laser’s
alignment. Use caution when clamping onto the laser,
as too much pressure can damage the aluminum
housing or cause misalignment. The front bezel has
four 4-40 and four 2-56 tapped holes to secure optional
HeNe accessories. The laser head should always be
secured in place and not allowed to move freely. Not
only can the laser roll off the work surface and break,
but the laser emission can be a health hazard.
The recommended mount is Thorlabs’ line of V-clamp
mounts. Thorlabs offers fixed (Item # C1502) and
kinematic (Item # C1503, shown in Figure 8) V-clamp
mounts.
Figure 8 Laser Mounted in a V-Clamp Mount
(Item # C1503)
5.2. Alignment
Alignment of the laser beam is critical to the operation of the system. Back reflections into the laser aperture will
impair the ability of the control loop to stabilize the frequency or intensity of the laser. Back reflected light will add
with the laser light striking the photodiode, directly impacting the error feedback system. More fundamentally, back
reflections may actually affect the lasing process itself, resulting in sudden and random changes in polarization of
the lasing modes. Stabilization cannot occur under these conditions. Align the laser such that back reflection cannot
enter the output aperture. Even low amplitude reflections from an uncoated (or even coated) optical surface may
cause problems. For applications where this cannot be avoided, Thorlabs recommends using an optical isolator
(Item # IO-2D-633-VLP) at the output of the laser.
5.3. Assembly
It is suggested that the HeNe Laser Quick Start Guide be used to assemble the laser system. The steps to assemble
the laser system are listed here.
1) This laser system includes a universal 120/240 VAC power supply. The proper main voltage cord must be
used. The unit should have been set up at the factory with the correct fuse setting; however, it is
highly recommended that the user double check that the fuse is properly set before use.
2) Plug the high-voltage cable from the laser into the front of the power supply. Confirm that the Alden plug is
well-seated. The first few times the plug is inserted, it may require more force than expected. Failure to plug
the connector all the way in can result in the laser failing to lase or arcing and damage to the power supply
or laser head.
3) Plug the low voltage supply and control cable into the front of the power supply. The HeNe laser will operate
without this connection but the stabilization circuitry will not operate.
4) Insert the interlock plug into the connector marked “INTERLOCK” on the back of the power supply. Note
that the LED light on the front of the power supply will light even if the interlock is not inserted.
5) Insert the key into the front panel of the power supply. Each stabilized HeNe unit comes with 2 keys.
Replacement keys may be purchased by calling Thorlabs and using Item # HRS015-KEY.

Stabilized HeNe Laser Chapter 6: Operation
Page 12 TTN091077-D02
Chapter 6 Operation
To operate the laser system, follow the following procedures.
1) Make sure the laser is pointing safely away from people and is securely mounted.
2) Turn the key switch on the power supply to “ON.” The “Laser On” LED indicator will light. NOTE: There is
a 3 to 5 second CDRH safety delay before the voltage turns on. The “Status” indicator on the laser and the
power supply will blink until the laser is warmed up and switches into stabilized mode. At this time the
blinking turns into a solid light.
3) Open the aperture by turning the screw 90° in either direction using a flat head screwdriver.
Figure 9 Laser Shutter Control, Picture shows the Shutter Open.
4) Some models may take up to 30 seconds to begin to lase. If the laser has not started lasing 20 sec after
turning the power key on, you can turn the power supply off and then back on again. This will not damage
the laser or power supply. Be sure to give enough time to allow the CDRH safety delay to elapse before
turning the system off and on.
5) Allow the laser to warm up for approximately 30 minutes. This is necessary for the laser to fully stabilize.
The feedback control circuitry will monitor the warm-up and will use the heater to accelerate the warm-up
process. When the circuit determines the tube is at an appropriate temperature, it will switch to a
stabilization mode. If the unit has been stored in a cold environment, the warm-up time will be longer. A
status LED is provided on both the power supply and laser tube. It will blink during warm-up and will be
solidly lit once the laser is stabilized.
6) Verify that there are no back reflections. See Section 5.2 for details.
6.1. HeNe Power Supply
6.1.1. Introduction
The HeNe Control Unit (HCU) is a turn-key power supply for HeNe laser tubes that incorporates all of the appropriate
safety features required by US federal regulations. This unit is RoHS compliant.
Shutter Control Screw
The shutter is closed when screw is
perpendicular to tube.
The shutter is opened when screw is
turned 90° so the slot is parallel with
tube as shown in the figure.

Stabilized HeNe Laser Chapter 6: Operation
Rev F, July 15, 2022 Page 13
6.1.2. Fuse Replacement
Your HRS015 Stabilized HeNe has been shipped from Thorlabs configured for 100 –240 VAC, 50 –60 Hz
operation. There is no line switch adjustment to be made. However, it may be necessary to replace an open fuse.
To do this you must perform the following procedure:
1) Remove the AC power cord if it is connected to the unit.
2) Locate the fuse tray directly below the AC power cord connection on the rear panel of the HCU.
3) Carefully use a flat-bladed screwdriver to open the fuse tray.
4) Remove the existing fuse and install the appropriate 1.25 A fuse. The replacement fuse must be a 5 mm x
20 mm, 250 VAC, Type T fuse (IEC 60127-2/III, low breaking capacity, slow blow).
5) Push the fuse tray back into place making sure that it snaps and seats correctly.
6) Connect the supplied UL rated, female to NEMA 5-15P power cord into the AC receptacle and plug the unit
in.
WARNING
Use only 250 V, 1.25 A, Type T, slow-blow fuses with this product.
6.1.3. Remote Interlock Operation
To use the remote interlock connector, remove the shorting conductor from the connector provided. The connector
may then be wired into the user’s interlock system. The circuit is designed to activate the laser output when the two
contacts of the connector are shorted together. This can be achieved via a simple switch or with relay contacts.
Internally, this connection is referenced to the safety ground.
The voltage on this connector is 12 VDC and is generated internally within the HCU. The connector voltage is
completely isolated from the AC line voltage. Do not apply a voltage across the interlock connector! Failure of
the remote interlock feature due to improper application of external voltages is not covered by warranty.
WARNING
Use of controls, adjustments, or performance of procedures other than those specified herein may
result in hazardous radiation exposure.

Stabilized HeNe Laser Chapter 6: Operation
Page 14 TTN091077-D02
Figure 10 Front of the Power Supply Module
Figure 11 Back of the Power Supply Module
Power Cord Connector and
Fuse Assembly
2 Position
Key Switch
Laser On LED
LED only indicates the power
supply is on and that the laser
MAY be emitting light.
High Voltage Alden
Connector
Status LED
If the LED is off, the laser MAY NOT be on. If
the LED is blinking, the laser is warming up,
and if the LED is solid, the laser is stabilized.
Low-Voltage Supply Connector
for Stabilization Circuits
Remote Interlock Connector
Fuse Tray

Stabilized HeNe Laser Chapter 7: General Maintenance
Rev F, July 15, 2022 Page 15
Chapter 7 General Maintenance
Aside from the AC input fuse, there are no user-serviceable parts in this product. If you suspect something has
failed on the unit and the steps in Chapter 8 do not solve the problem, please contact Thorlabs for advice on
returning the unit for evaluation. Always follow safe operating procedures as described in Chapter 6. When not
operating the laser, the output aperture should be closed to prevent accidental exposure to laser beams and also
to keep the internal optical elements from collecting dirt and dust.
7.1. Cleaning
The power supply and HeNe tube can be cleaned using a soft, slightly damp cloth. Avoid using any solvents on or
near the unit. Allowing dust and dirt into the aperture will degrade the performance of this laser.

Stabilized HeNe Laser Chapter 8: Troubleshooting
Page 16 TTN091077-D02
Chapter 8 Troubleshooting
8.1. Technical Failures
Case
Fix
No Light Emanating from the
Laser
Make sure that the aperture is open.
Check to make sure:
•the laser is plugged into a working outlet,
•the power cord is fully seated into the power supply,
•the Alden plug is firmly seated into the power supply (it may
take more force to push the plug in all the way the first few
times),
•the interlock connector is plugged in and fully seated, and
•the aperture is open.
The laser can take up to 30 seconds to lase. Turning the power off
then on again can speed up the start time without damaging the laser.
Note: there is a built in CDRH safety delay of 4 - 5 seconds. Be
sure to wait longer than 5 seconds to turn the laser off then on.
The Laser Does not Work and
There Is Something Rattling
Around in the Laser Head Tube
The glass gas tube may have broken during shipping. Please contact
your local tech support office for help.
The Power Supply Laser On
Indicator Does Not Light
Make sure the power supply is plugged in. Check the fuse as
described in Section 5.3
The Power Supply Does Not Turn
On
Make sure the power supply is plugged in. Check the fuse as
described in Section 5.3.
There Is a Clicking Noise In either
the Power Supply or Laser
Arcing in the laser head or the power supply can result in a flickering
laser or the laser not igniting at all. Turn off the power and contact
your local tech support office immediately.
The Laser Has Low Output Power
The laser can requires 30 –40 minutes to meet published
specifications. Make sure to let it warm up.
Make sure the laser is mounted correctly. See Section 5.1 for proper
mounting techniques.
The Laser Does Not Stabilize
According to the Status
Indicators
Allow the laser ~25 minutes to warm up and stabilize. This may take
longer if the laser tube was stored in a cold environment.
Make sure that no light is being reflected back into the laser. This will
destabilize the laser immediately. See Section 5.2 for alignment
details.
Check the room temperature. It may be outside the specified range for
the laser.
Turning the laser on and off multiple times in a short time period may
lead to a slight overheating of the laser due to the warm up period the
laser needs to stabilize. Turn off the laser and let it cool down for 15
minutes. Turn it back on and ensure proper operation.
The Status Indicators Are Off
Make sure the power supply is plugged in and turned on.
Check if light is being emitted by the laser. The indicator is telling you
that no light is being detected by the internal photodiode.
Verify the low-voltage power cable is installed.
If light is being emitted by the laser and the Indicator is not working
you most likely have a problem with the electronics. Turn off the
power and contact your local tech support office.

Stabilized HeNe Laser Chapter 8: Troubleshooting
Rev F, July 15, 2022 Page 17
8.2. Application Troubleshooting
Some sources of trouble for a HeNe laser do not come from the laser failing or not meeting its specifications.
Instead, these lasers may not be suited for the 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 or become unstable. Even blowing on the laser tube
can cause the output power to fluctuate significantly.
Randomly polarized HeNe lasers actually produce a pair of polarizations with orthogonal axes that are generally
fixed for the life of the laser. The optical power in these axes varies over time as the tube's cavity length changes.
However, any polarization optics in the path (intentional or unintentional) can cause large variations in the output
power. Re-orienting the laser head may help. But the use of a polarized laser is the best solution.
While HeNe lasers cannot be damaged by back reflections, they are not immune to them. Reflections back into the
laser can cause unpredictable power changes, excessive optical noise in the laser beam, or destabilization in case
of the stabilized HeNe. A free-space isolator can be used to reduce or eliminate these effects. Only a small angular
deviation is needed to eliminate the back reflections.
8.2.1. 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 varies
from very slow (much less than 1 Hz) to as much as several kHz depending on the stability of the environment. The
stabilized HeNe will compensate for these fluctuations by adjusting the length of the laser tube on a scale of
nanometers.
Other, more constant sources of fluctuations include the following (with typical corresponding frequencies):
•Line Noise from AC High Voltage Power Supplies (50/60 Hz, 100/120 Hz, etc.)
•Switching Noise from AC and DC High Voltage Power Supplies (20 - 100 kHz and Harmonics)
•Plasma Oscillation (Hundreds of kHz to Tens of MHz)
•Transverse (Spatial) Mode Beat Notes (Hundreds of MHz)
•Axial (longitudinal) Mode Beats (at the FSR, Hundreds of MHz)

Stabilized HeNe Laser Chapter 9: Specifications
Page 18 TTN091077-D02
Chapter 9 Specifications
Item #
HRS015B
Wavelength
632.992 nm
Series Resistors in Housing
66 kΩ
Operating Current
5.0 mA
Weight
600 g
CDRH/CE Classification
IIIa/3R (HRR005 is IIa/2)
Un-stabilized Power
1.2 mW min, 2.7 mW max
Stabilized Power
>1.2 mW
Polarization
Linear > 1000:1
Mode Structure
TEM00 > 99%
Beam Diameter
0.65 ± 0.05 mm
Beam Divergence
1.4 ± 0.2 mrad
Beam Drift (during warm-up)
<0.2 mrad
Long-Term Beam Drift
<0.02 mrad
Noise (30 Hz –10 MHz)
< 1% rms max.
Starting Voltage
< 7 kV (DC)
Operating Voltage (DC)
1400 V
Length (L)
11.66" (296.1 mm)
Diameter
Ø1.77" (Ø45 ± 0.5 mm)
Operating Temperature2
15 –30 °C
Time to Lock3
< 15 minutes, Typical
Power Input
100 - 240 VAC, 50 - 60 Hz
Power Consumption
< 40 VA
Lifetime (Typ.)4
25,000 h
Frequency Stabilized Mode
1 min
±1 MHz
1 hour
±2 MHz
8 hours
±3 MHz
Intensity Stabilized Mode
1 min
±0.1 %
1 hour
±0.2 %
8 hours
±0.3 %
2
The ambient temperature must be within the operating temp range to ensure frequency or intensity lock.
3
For a typical HeNe at an ambient temperature of 25 °C
4Laser lifetime is defined as the usage time required before the laser output power drops to 50% of the specified output power.