THORLABS HRP350 User manual

HRP350, HRP350-EC
High Power HeNe Laser
Systems
Operating Manual

Red HeNe Laser System
12112-S01 Rev CB, August 31, 2010 Page 2 www.thorlabs.com
Table of Contents
Part 1.Safety ............................................................................................................................................4
CE Compliance ..........................................................................................................................................................5
Part 2.Description ...................................................................................................................................6
Laser Head .................................................................................................................................................................6
Laser Power Supply ...................................................................................................................................................7
HeNe Laser Overview................................................................................................................................................7
HeNe Applications.....................................................................................................................................................7
HeNe Linewidth.........................................................................................................................................................8
HeNe Polarization.................................................................................................................................................... 10
Part 3.Unpacking ..................................................................................................................................11
3.1.Unpacking...............................................................................................................................................11
Shipping Inventory ..................................................................................................................................................11
Part 4.Set-up..........................................................................................................................................12
4.1.Mounting the Laser Head......................................................................................................................12
4.2.Assembly .................................................................................................................................................12
Part 5.Operation....................................................................................................................................13
5.1.Alignment Procedure.............................................................................................................................14
Tools Required.........................................................................................................................................................14
Procedure ................................................................................................................................................................. 14
Part 6.Troubleshooting.........................................................................................................................15
6.1.Technical Failures..................................................................................................................................15
6.2.Application Trouble Shooting...............................................................................................................15
Noise, Oscillations, and Fluctuation Sources........................................................................................................... 16
Part 7.Specifications .............................................................................................................................17
7.1.Mechanical Drawing..............................................................................................................................17
Part 8.Regulatory ..................................................................................................................................18
Part 9.Thorlabs Worldwide Contacts ...................................................................................................19

Red HeNe Laser System
12112-S01 Rev CB, August 31, 2010 Page 3 www.thorlabs.com
Table of Figures
Figure 1Laser Head, Front................................................................................................................... 6
Figure 2Power Supply......................................................................................................................... 7
Figure 3Optical Resonator Cavity....................................................................................................... 8
Figure 4HeNe Gain Curve Showing Cavity Modes............................................................................ 9
Figure 5HeNe Energy Levels.............................................................................................................. 9
Figure 6HeNe Visible Laser Lines.................................................................................................... 10
Figure 7Laser System........................................................................................................................ 11
Figure 8Laser Rear Panel .................................................................................................................. 13
Figure 9Laser Shutter Control, Picture shows the Shutter CLOSED................................................ 13
Figure 10Dimensional Drawing .......................................................................................................... 17

Red HeNe Laser System
12112-S01 Rev CB, August 31, 2010 Page 4 www.thorlabs.com
Part 1. 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 back 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.

Red HeNe Laser System
12112-S01 Rev CB, August 31, 2010 Page 5 www.thorlabs.com
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.
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
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.

Red HeNe Laser System
12112-S01 Rev CB, August 31, 2010 Page 6 www.thorlabs.com
Part 2. Description
Thorlabs’ high-power red (632.8) Helium-Neon gas lasers have a maximum stable output power of
50.0 mW and a fundamental Gaussian beam. The laser comes in two versions, one for 115 VAC and
another for 220 VAC voltage source. The output beam is linearly polarized.
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 UNC holes to secure the optional accessory
mounting ring and other industry standard HeNe accessories. This laser also comes with a 3 ft long, high
voltage cable for connecting to the 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, Front
Manual Beam Shutter
Shutter slides side to side and is
marked ON and OFF
Laser Aperture
4 #4-40 UNC
Mounting Holes

Red HeNe Laser System
12112-S01 Rev CB, August 31, 2010 Page 7 www.thorlabs.com
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, a 3-port, high-voltage connector, a key safety switch, an interlock connector, and
a removable input power cable. The power supply comes pre-configured for either 120 VAC or
240 VAC use. This configuration cannot be changed by the user and can only be setby the factory.
Figure 2 Power Supply
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 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 at
one end of the laser tube, and an output coupler mirror with
approximately 1% transmission at the other end.
HeNe Applications
•Metrology
•Cleanroom Monitoring Equipment
•Food Sorting
•Flow Cytometry
•Confocal Microscopy
•Imaging and Medical Equipment
•Opacity Monitoring
•Alignment
•Maritime Visual Guidance
Systems

Red HeNe Laser System
12112-S01 Rev CB, August 31, 2010 Page 8 www.thorlabs.com
Figure 3 Optical Resonator Cavity
Typical HeNe Parameters
Beam Diameter (D) 1 mm
Cavity Length (L) 0.15 m (0.5 mW) to 1 m (50 mW)
Reflectivity at High Reflector (HR) >99.99%
Transmission at Output Coupler (OC) ~1%
HeNe lasers tend to be small, with cavity lengths of around 15 cm up to 0.5 m and optical output powers
ranging from 1 mW to 100 mW. Thorlabs offers output powers up to 50 mW.
HeNe Linewidth
A red HeNe laser wavelength is 632.816 nm in air, though it is often reported as either 632 nm or
633 nm. The wavelength gain curve is actually made of several longitudinal modes that fluctuate within
the range due to thermal expansion of the cavity and other external factors.
The linewidth of a HeNe laser is specific to the application. The axial mode structure of the HeNe laser
is characterized by the number of modes, the free spectral range (FSR), and the Doppler width (see
Figure 4 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 red HeNe laser, the coherence length is
approximately 30 cm.
D
L
Anode
High
Reflector
Output
Coupler
Helium-Neon Gas Mixture
Glass Tube
Laser Bore Tube
Cathode

Red HeNe Laser System
12112-S01 Rev CB, August 31, 2010 Page 9 www.thorlabs.com
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 632.82 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.
Neon Gain
Curve
FWHM ~1.5 GHz
Frequency
Gain/Output Power
Lasing
Cavity Modes
Lasing
Threshold
FSR ~1000 MHz
Short (0.2 m) Laser
FSR ~200 MHz
Long (1 m) Laser
Energy (Electron Volts)
Ground States
Metastable Collision
Metastable Collision
e Impact
3S2
1S
3S2S2
1S
2P4
3P4
(20.66 eV)
(20.30 eV)
(20.61 eV)
(19.78 eV) (19.78 eV)
(18.70 eV)
1
2
5
10
21
20
19
18
17
16
(16.70 eV)
(3391.2 nm Laser)
(632.8 nm Laser)
(1152.3 nm Laser)
Diffusion
Helium Neon

Red HeNe Laser System
12112-S01 Rev CB, August 31, 2010 Page 10 www.thorlabs.com
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.
Figure 6 HeNe Visible Laser Lines
HeNe Polarization
Unpolarized (Randomly Polarized) Beam
The output of an unpolarized HeNe laser consists of a rapidly fluctuating, linearly polarized beam whose
polarization orientation changes on a nanosecond time scale. Unpolarized lasers are ideal for
applications where there are no polarizing elements in the beam path. Depending on the time scale of an
application, large power fluctuations are possible.
Polarized Beam
The state of polarization in a polarized HeNe laser beam is linear, making these lasers ideal for
polarization-sensitive applications.
500 550 650
Wavelength (nm)
HeNe Visible Laser Lines
750600 700