THORLABS FSL1550 User manual

FSL1550
1.55 µm Femtosecond
Fiber Laser
User Guide

1.55 µm Femtosecond Fiber Laser
Table of Contents
Chapter 1 Warning Symbol Definitions.............................................................................................1
Chapter 2 Safety...................................................................................................................................2
Chapter 3 Description .........................................................................................................................5
3.1. Introduction................................................................................................................... 5
3.2. Shipping List................................................................................................................. 5
Chapter 4 Setup and Operation .........................................................................................................6
4.1. Environmental Requirements...................................................................................... 6
4.1.1. Temperature Range..............................................................................................................6
4.1.2. Humidity Range.....................................................................................................................6
4.2. Electrical Requirements............................................................................................... 6
4.3. Setting the AC Line Voltage......................................................................................... 6
4.4. Changing the Fuse ....................................................................................................... 6
4.5. Setup ............................................................................................................................. 6
4.6. Operating the Laser...................................................................................................... 9
4.6.1. Starting the Laser..................................................................................................................9
4.6.2. Controlling the Laser Output Power....................................................................................11
4.6.3. Turning Off the Laser..........................................................................................................11
Chapter 5 Maintenance .....................................................................................................................12
Chapter 6 Warranty............................................................................................................................13
Chapter 7 Specifications...................................................................................................................14
7.1. Optical Specifications ................................................................................................ 14
7.2. Electrical Requirements............................................................................................. 14
7.3. Environmental Requirements.................................................................................... 14
Chapter 8 Regulatory ........................................................................................................................17
Chapter 9 Thorlabs Worldwide Contacts........................................................................................19

1.55 µm Femtosecond Fiber Laser Chapter 1: Warning Symbol Definitions
Page 1 TTN231462-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

1.55 µm Femtosecond Fiber Laser Chapter 2: Safety
Rev A, January 20, 2021 Page 2
Chapter 2 Safety
All statements regarding safety of operation and technical data in this instruction manual will only apply when the
unit is operated correctly in accordance to this user manual.
SHOCK WARNING
High voltage inside. To avoid electrical shock, before powering the unit on, make sure that the
protective conductor of the 3-conductor power cord is correctly connected to the protective earth
contact of the socket outlet. Improper grounding can cause electric shock resulting in severe injury or
even death. Do not operate without cover installed.
EXPLOSION WARNING
This instrument must not be operated in an explosion endangered environment.
LASER WARNING
The FSL1550 is a Class IV laser. Avoid Eye or Skin Exposure to Direct or Scattered Radiation.
LASER WARNING
Always wear appropriate laser safety eyewear during laser setup and operation.
CAUTION
Note: This equipment has been tested and found to comply with the limits for a Class B digital device,
pursuant to part 15 of the FCC Rules. These limits are designed to provide reasonable protection
against harmful interference in a residential installation. This equipment generates, uses and can
radiate radio frequency energy and, if not installed and used in accordance with the instructions, may
cause harmful interference to radio communications. However, there is no guarantee that interference
will not occur in a particular installation. If this equipment does cause harmful interference to radio or
television reception, which can be determined by turning the equipment off and on, the user is
encouraged to try to correct the interference by one or more of the following measures: Reorient or
relocate the receiving antenna.—Increase the separation between the equipment and receiver.—
Connect the equipment into an outlet on a circuit different from that to which the receiver is
connected.—Consult the dealer or an experienced radio/TV technician for help.
CAUTION
This instrument should be kept clear of environments where liquid spills or condensing moisture are
likely. It is not water resistant. To avoid damage to the instrument, do not expose it to spray, liquids,
or solvents.

1.55 µm Femtosecond Fiber Laser Chapter 2: Safety
Page 3 TTN231462-D02
Class IV lasers such as the FSL1550 may cause damage to the skin, and also to the eye, even from the viewing of
diffuse reflections. These hazards may also apply to indirect or non-specular reflections of the beam, even from
apparently matte surfaces. Great care must be taken when handling these lasers. They also represent a fire risk,
because they may ignite combustible material.
Safe practices and proper usage of safety equipment should be taken into consideration when operating lasers.
The eye is susceptible to injury, even from very low levels of laser light. Laser emission in the visible and near
infrared spectral ranges has the greatest potential for retinal injury, as the cornea and lens are transparent to those
wavelengths, and the lens can focus the laser energy onto the retina.
1. Follow all safety precautions in the operator’s manual.
2. Never aim the laser at a person’s eye, skin, or clothes.
3. Always use proper laser safety eyewear.
4. Avoid wearing watches, jewelry, or other objects that may reflect or scatter the laser beam.
5. Keep the laser beam paths above or below eye level for both sitting and standing positions.
6. Ensure that individuals do not look directly into a laser beam.
7. Eliminate all unnecessary reflective surfaces from the vicinity of the laser beam path.
8. Ensure that all individuals who operate Class 4 lasers are trained in laser safety and authorized to
operate a laser. Do not leave a running laser unattended if there is a chance that an unauthorized user
may attempt to operate the laser. A key switch should be used if untrained persons may gain access to
the laser. A warning light or buzzer should be used to indicate when the laser is operating.
9. Use low power settings, beam shutters, and laser output filters to reduce the beam power to less
hazardous levels when the full output power is not required.
10. Make sure that spectators are not exposed to hazardous conditions.
11. Operate the laser only in a well-controlled area (for example, within a closed room with covered or
filtered windows and controlled access).
12. Label the laser and the room with appropriate Class 4 laser warning signs.
13. Mount the laser on a firm support to ensure that the beam travels along the intended path.
The unit is supplied with a region-specific power cord. If using your own power cord, make sure it is IEC 320
compatible.
Make sure that the line voltage rating marked on the rear panel agrees with your local supply and that the
appropriate fuses are installed. Changing of the mains fuse can be done by the user (see Section 4.4, Changing
the Fuse). With the exception of the mains fuses, there are no user serviceable parts in this product.
Do not operate in wet or damp conditions. Do not obstruct the air ventilation slots in the housing!
This device can only be returned when packed into the complete original packaging, including all foam packing
inserts. If necessary, ask for a replacement package.
LASER RADIATION
AVOID EYE OR SKIN
EXPOSURE TO DIRECT
OR SCATTERED RADIATION
CLASS 4 LASER PRODUCT

1.55 µm Femtosecond Fiber Laser Chapter 2: Safety
Rev A, January 20, 2021 Page 4
Mobile telephones, cellular phones, or other radio transmitters should not to be used within the range of three
meters of this unit since the electromagnetic field intensity may exceed the maximum allowed disturbance values
according to EN50082-1.
All statements regarding operational safety and technical data in this manual will only apply when the unit is
operated correctly.

1.55 µm Femtosecond Fiber Laser Chapter 3: Description
Page 5 TTN231462-D02
Chapter 3 Description
3.1. Introduction
Thorlabs’ FSL1550 Femtosecond Fiber Laser emits <50 fs pulses with a center wavelength of 1.55 µm at a 100 MHz
repetition rate. This fiber laser is based upon an oscillator-amplifier combination that uses only polarization-
maintaining fiber, yielding reliable turn-key operation and exceptional long-term reliability. The FSL1550 has a
collimated free-space output with a 2.2 mm beam diameter. The laser is used in applications where high peak power
is required, such as supercontinuum and terahertz generation. The product is intended to be used in indoor
laboratory environment.
The pump current of the amplifier stage in the FSL1550 is adjustable through the instrument's front panel, allowing
the user to vary the output power of the laser. The display screen shows the pump level, as well as the temperature
and emission status. An enable key-lock switch must be set to turn on the laser emission, and a green LED indicator
displays the current state of the unit. There is a 3 second delay before the fiber amplifier turns on, and the user is
warned by the rapidly blinking LED. An aperture shutter allows blocking the output beam even when the laser
emission is on. The shutter can be opened and closed using a push button switch on the front panel. The shutter
status is displayed on the front panel display and through an LED indicator next to the output aperture.
For added safety, there is an interlock connector located on the rear panel that must be shorted in order for the
output to be enabled. This can easily be configured to be triggered by doors or an emergency push button to disable
the fiber amplifier in unsafe conditions.
The amplifier includes a universal power supply allowing operation over 100 to 240 VAC without the need for
selecting the line voltage. The fuse access is conveniently located on the rear panel
3.2. Shipping List
The FSL1550 consists of the following components:
•Benchtop Laser Unit
•IEC Power Cord
•Four CF175 Clamping Forks
•Interlock-Shorting BNC Connector (Installed)

1.55 µm Femtosecond Fiber Laser Chapter 4: Setup and Operation
Rev A, January 20, 2021 Page 6
Chapter 4 Setup and Operation
4.1. Environmental Requirements
The FSL1550 should be operated under controlled conditions to achieve stable performance.
4.1.1. Temperature Range
For any laser, the ambient temperature must be well controlled. The ambient temperature of the lab environment
should be in the 17 °C - 25 °C range, and should not change by more than 3 °C over any 24 hour period.
4.1.2. Humidity Range
Humidity control (<50%) is required to prevent condensation from forming on optical surfaces. Keep the system
away from air conditioning vents, which can cause sudden humidity and temperature changes.
4.2. Electrical Requirements
The following table lists the electrical requirements of the FSL1550.
Electrical Requirements
Input Voltage
100 - 240 V
Frequency
50 - 60 Hz
Power Consumption
400 W (Max)
A region-specific power cord is included with the laser, which is compatible with a standard wall outlet.
4.3. Setting the AC Line Voltage
The fiber laser has been shipped configured for 100 to 240 VAC operation. There is no end user adjustment of the
line voltage for 110 or 220 VAC. The user needs to select the correct AC cord for their location.
4.4. Changing the Fuse
To change the power fuse, follow the following steps.
1. Remove the AC power cord if it is connected to the unit.
2. Locate the fuse tray directly adjacent to the AC power cord connection on the rear panel of the unit.
3. Carefully use a flat blade screwdriver to open the fuse tray.
4. Remove the existing fuses and install two fuses with the appropriate specifications. The replacement fuses
must be ceramic 5 mm x 20 mm, 10 A, 250 VAC, slow-blow type.
5. Push the fuse tray back into place making sure that it snaps and sits correctly.
6. Connect the appropriate power cord into the AC receptacle and plug the unit in.
4.5. Setup
The laser system requires roughly 19" x 15" of optical table space. In addition, the laser has air intakes and outlets
on both sides of the enclosure, which are perforated to permit airflow. Allow at least an additional 3" on each side
for proper circulation. After choosing the location, secure the laser head’s pedestal posts to the optical table using
the supplied CF175 clamps.

1.55 µm Femtosecond Fiber Laser Chapter 4: Setup and Operation
Page 7 TTN231462-D02
4.5.1 Powering the laser
Use this procedure to connect the laser to AC line power, and power the unit on and off. Always connect the laser
to the AC power mains using the power cord that shipped with the laser. Always leave enough distance between
the back panel and any walls or barriers such that the power cord can be disconnected when needed.
1. Connect the supplied power cord to the power connector on the rear panel.
2. Confirm that the rear panel AC power switch is in the “0” off position.
3. Connect the supplied power cord to an appropriate AC mains source.
4. Toggle the rear panel AC power switch to the “1” on position. Power is supplied to the internal power
supply whenever the AC power cord is connected to a live mains circuit and the AC power switch is in the
“1” on position. The laser will now be in the standby state.
5. Push the front panel power button to power the instrument on and off. The power button will illuminate
Green to indicate that the unit is powered on.
6. To completely remove power from the unit, toggle the rear panel AC power switch to the “0” off position
and disconnect the power cord.
4.5.2 Checking Status Indicators
When the system is powered on, the temperature stability indicator on the front panel display shows a “Temp
stabilizing” status while the system reaches a thermally stable condition, as shown in the screen shot below. The
temperature stability indicator should show “Temp OK” status within 5-20 minutes from turning the system on, as
shown in the screen shot on the following page (Figure 2). The amount of time to reach stable condition will depend
on the environment temperature where the system is being operated. If the temperature status indicator does not
show a stable condition for more than 20 minutes, or if a temperature error is displayed, please contact Technical
Support ([e-mail]) for assistance. Please note that the oscillator status should always show
“OSC OK” status. If an oscillator error status is displayed, please contact Technical Support. The interlock circuit in
the system should be closed by shorting the BNC connector on the back panel either through a BNC short plug-in
connector or a remote interlock circuit. If the circuit is open, an interlock error status will be shown as seen in the
screen shot on the following page (Figure 3).
Figure 1 Screen shot of the laser display during the initial system warm-up.

1.55 µm Femtosecond Fiber Laser Chapter 4: Setup and Operation
Rev A, January 20, 2021 Page 8
Figure 2 Screen shot of the laser display after temperature stabilization has been reached.
Figure 3 Screen shot of the laser display when interlock circuit is open.

1.55 µm Femtosecond Fiber Laser Chapter 4: Setup and Operation
Page 9 TTN231462-D02
4.6. Operating the Laser
WARNING
Only qualified professionals should service the laser or perform optical alignment.
WARNING
While operating the laser, it is mandatory that the temperature status indicator is showing stable
temperature. Failure to follow this instruction can cause severe damage to the laser.
4.6.1. Front and Back Panel Overview
Figure 4 Front Panel of the FSL1550
Callout
Description
A
Push-Button Power Switch
B
Laser Enable Switch
C
Adjustment Knob (Push to Adjust)
D
Shutter Open/Close Switch
E
Emission Indicator
F
Laser Output Aperture
G
Shutter Indicator
A
B
C
D
E
F
G

1.55 µm Femtosecond Fiber Laser Chapter 4: Setup and Operation
Rev A, January 20, 2021 Page 10
Figure 5 Back Panel of the FSL1550
Callout
Description
A
Trigger Signal Output (BNC)
B
Remove Interlock Input (BNC)
C
AC Power On/Off Switch
D
Fuse Tray (See Section 4.4 for Replacement Details)
E
AC Power Cord Connector
4.6.2. Starting the Laser
Before starting the laser, ensure that the interlock circuit is closed using a short-circuited connection on the interlock
BNC connector on the laser’s back panel. A BNC short connector is shipped with the laser to be used when a
remote interlock circuit is not needed.
Before turning on the laser, ensure that the temperature is stable and no errors are displayed on the front panel
display.
The output from the laser aperture is a collimated beam as specified in the specifications table in this manual. The
output should be guided into the user’s setup or measurement devices while observing all application laser safety
precautions based on the classification of the laser system. Use the Laser On/Off key-lock switch on the front panel
to enable laser emission. The Laser Emission indicator on the display and the LED indicator next to the laser
aperture will blink for 3 seconds before the output is enabled.
A shutter blocks access to laser emission from the output aperture. The shutter status is by default “closed” when
the laser is powered on. The shutter can be closed and opened using the push button on the front panel. An indicator
on the display as well as an LED indicator next to the output aperture show the shutter status.
Please note the following when operating the laser:
a. The laser has been tested, optimized, and specified for a particular output power level. To achieve the
specified pulse width, the laser should be operated at the optimal pump current value in the test report
included with the laser.
b. In the event that the red interlock indicator is turned on, the laser emission cannot be enabled. Please
ensure that the BNC interlock connector on the back panel of the laser has been shorted.
c. Please note that the BNC connector labeled as “TRIGGER” and the USB connector labeled as
“DIAGNOSTIC PORT” are intended for factory use during initial build, calibration, or service of the laser.
A
B
C
D
E

1.55 µm Femtosecond Fiber Laser Chapter 4: Setup and Operation
Page 11 TTN231462-D02
4.6.3. Controlling the Laser Output Power
The pump current of the amplifier stage in the FSL1550 can be adjusted using the rotary knob on the front panel.
There are two adjustment modes available: Coarse and Fine. Pushing the knob once will activate the coarse
adjustment mode. Pressing the knob a second time will activate the fine adjustment mode. Pressing the knob a
third time exits the adjustment mode. It is important to note that the pulse shape and duration are strongly dependent
on the output power of the laser. The laser is shipped with a test report that shows the measured autocorrelation
and spectrum at a few power levels, which can be used as a guideline for adjusting the output power. The laser
performance specifications are only guaranteed at the factory-specified operating pump current set-point in the test
report.
The laser system can be left on continuously for extended periods of time, as long as there are no error indicators
displayed. It is recommended to turn off the laser emission whenever the system is not in use. While not required,
it is also recommended to turn the power off when the system is not in use for long intervals, e.g. a few days. The
system can be turned on immediately after being powered on, and emission can be switched on when the
temperature indicator shows stable operation.
4.6.4. Turning Off the Laser
Use the Laser On/Off key-lock switch to disable the laser emission. This disables the laser emission, but will leave
the temperature control loops engaged. The oscillator also remains on when the laser emission has been turned
off. Do not terminate the main power unless the laser will be disabled for more than a day before its next use.

1.55 µm Femtosecond Fiber Laser Chapter 5: Maintenance
Rev A, January 20, 2021 Page 12
Chapter 5 Maintenance
WARNING
Always wear appropriate laser safety eyewear during laser setup and operation.
Aside from the AC input fuse, the FSL1550 does not require regular maintenance. Please keep the shutter closed
when laser is not being used in order to keep the optics inside the laser enclosure clean. If you suspect something
has failed in the unit, please contact Thorlabs for advice on returning the unit for evaluation.

1.55 µm Femtosecond Fiber Laser Chapter 6: Warranty
Page 13 TTN231462-D02
Chapter 6 Warranty
Thorlabs warrants to the buyer of the laser system described in this manual that it conforms to the published
specifications and is free from defects in materials and workmanship for a period of 12 months or 5,000 hours of
operation, whichever occurs first. The warranty period begins at the date of shipment.
The buyer must provide the appropriate utilities and operating environment as outlined in Chapter 4 of this manual.
Damage to the laser system caused by failure of the buyer’s utilities is solely the responsibility of the buyer and is
specifically excluded from any warranty.
The obligations of Thorlabs are limited to repairing or replacing, without charge, equipment which proves to be
defective during the warranty period. Repaired or replaced parts are warranted for the duration of the original
warranty period only. This warranty does not cover damage due to misuse, negligence, or damage due to
installations, repairs or adjustments not specifically authorized by Thorlabs. All repairs for this product are performed
at the factory.
The warranty terms are in accordance with and subject to the terms and conditions set forth in Thorlabs’ General
Terms and Conditions of Sale which can be found at:
https://www.thorlabs.com/Images/PDF/LG-PO-001_Thorlabs_terms_and_%20agreements.pdf

1.55 µm Femtosecond Fiber Laser Chapter 7: Specifications
Rev A, January 20, 2021 Page 14
Chapter 7 Specifications
7.1. Optical Specifications
Optical Specifications
Center Wavelength
1560 nm ± 30 nm
Pulse Width (FWHM)
<40 fs (Typical)
<50 fs (Max)
Peak Powera
>60 kW
Output Powerb
>500 mW (Average)
Repetition Rate
100 MHz (Nominal)
Pulse Energy
>5 nJ
Polarization Extinction Ratio
>15 dB
Beam Size
Ø2 mm (Nominal)
Output Power Stabilityc
<0.4% / °C
a. The peak power is an estimate based on the retrieved intensity profile of the
pulse and the pulse energy.
b. Maximum output average power is 1 W.
c. The maximum change in power for every 1 degree change in the environment temperature.
7.2. Electrical Requirements
Electrical Requirements
Input Voltage
100 - 240 V
Frequency
50 - 60 Hz
Power Consumption
400 W (Max)
7.3. Environmental Requirements
Environmental Requirements
Room Temperature Range
17 °C to 25 °C
Room Temperature Stability
<3 °C over 24 Hours

1.55 µm Femtosecond Fiber Laser Chapter 7: Specifications
Page 15 TTN231462-D02
7.4. Typical Pulse Performance Plots
1300 1400 1500 1600 1700 1800
-30
-25
-20
-15
-10
-5
0FSL1550 Spectrum
Normalized Amplitude (dB)
Wavelength (nm)

1.55 µm Femtosecond Fiber Laser Chapter 8: Mechanical Drawings
Rev A, January 20, 2021 Page 16
Chapter 8 Mechanical Drawings
Figure 6 FSL1550 Mechanical Drawing

1.55 µm Femtosecond Fiber Laser Chapter 9: Regulatory
Page 17 TTN231462-D02
Chapter 9 Regulatory
As required by the WEEE (Waste Electrical and Electronic Equipment Directive) of the European Community and
the corresponding national laws, Thorlabs offers all end users in the EC the possibility to return “end of life” units
without incurring disposal charges.
This offer is valid for Thorlabs electrical and electronic equipment:
•Sold after August 13, 2005
•Marked correspondingly with the crossed out “wheelie bin” logo (see right)
•Sold to a company or institute within the EC
•Currently owned by a company or institute within the EC
•Still complete, not disassembled and not contaminated
As the WEEE directive applies to self-contained operational electrical and electronic products, this end of life take
back service does not refer to other Thorlabs products, such as:
•Pure OEM products, that means assemblies to be built into a unit by the user (e. g. OEM laser driver cards)
•Components
•Mechanics and optics
•Left over parts of units disassembled by the user (PCB’s, housings etc.).
If you wish to return a Thorlabs unit for waste recovery, please contact Thorlabs or your nearest dealer for further
information.
Waste Treatment is Your Own Responsibility
If you do not return an “end of life” unit to Thorlabs, you must hand it to a company specialized in waste recovery.
Do not dispose of the unit in a litter bin or at a public waste disposal site.
Ecological Background
It is well known that WEEE pollutes the environment by releasing toxic products during decomposition. The aim of
the European RoHS directive is to reduce the content of toxic substances in electronic products in the future.
The intent of the WEEE directive is to enforce the recycling of WEEE. A controlled recycling of end of life products
will thereby avoid negative impacts on the environment.
Wheelie Bin Logo