Ultrafast Femtosecond Fiber Laser, 1550 nm

  • Erbium-Doped All-PM-Fiber Design
  • <40 fs Ultrafast Pulses
  • >500 mW Average Output Power
  • Peak Power: >60 kW


1550 nm Ultrafast Femtosecond Fiber Laser

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FSL1550 Spectrum
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Typical spectrum for the FSL1550 ultrafast fiber laser. A complete set of performance specifications is available on the Specs tab.

Reza Salem
BU Leader, Fiber Lasers
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The front-panel display shows the pump level, as well as the temperature, oscillator, shutter, and laser statuses.


  • Ultrashort Pulses: <40 fs (Typical)
  • 1560 nm ± 30 nm Center Wavelength
  • >500 mW Average Output Power, >5 nJ Pulse Energy, and 100 MHz Repetition Rate
  • Free-Space, Collimated Output Beam (2 mm Nominal Beam Diameter)
  • Air-Cooled Housing with Integrated Controller


  • Supercontinuum Generation
  • Terahertz Generation
  • Ultrafast Spectroscopy
  • Multiphoton Imaging

Thorlabs' FSL1550 High-Power Erbium-Doped Ultrafast Fiber Laser is a turnkey source that offers ultra-short pulses (<40 fs) in the 1550 nm wavelength band. This laser provides high peak power (estimated >60 kW) with >500 mW average power at the fundamental oscillator repetition rate of 100 MHz. The combination of a short pulse width and a high peak power make the FSL1550 ultrafast fiber laser an ideal source for nonlinear optics applications such as supercontinuum generation and terahertz generation, while the high repetition rate makes it compatible with Fourier-Transform Infrared (FTIR) spectrometers. This laser features an all-PM-fiber design with no free-space or moving parts to maximize environmental stability.

The ultra-short pulse width of the laser is achieved through nonlinear pulse compression and by managing the effects of dispersion and nonlinearity in the fiber. Due to this design, the output pulse width is a function of the output power level. This ultrafast fiber laser is designed for optimal pulse compression conditions (FWHM <40 fs) at a power level greater than 500 mW. All systems are shipped with a data sheet showing the measured pulse intensity profile at the optimal power level, as well as a few lower power set-points. A typical intensity profile of the output pulse as retrieved by frequency-resolved optical gating (FROG) measurement and a typical optical spectrum of the output pulses can be found on the Graphs tab.

The controller of the FSL1550 ultrafast fiber laser is fully integrated with the laser head inside a benchtop enclosure, making the source compact and easy to use. The laser platform includes standard Ø1" pedestal legs, which can be secured to the optical table using the four included CF175 clamping forks for added beam stability. The output of the laser is a collimated beam with a nominal diameter of 2 mm, which is accessible through a front panel aperture that sits 3.00" (76.2 mm) above the optical table. An electrically-controlled shutter is used to control access to the laser emission. The housing also features a vibration isolation mechanism to reduce the impact of the cooling fan vibration on the output beam stability, as well as on the optical table.

User control functions, such as laser enable, shutter control, and output power adjustment, are accessible through an intuitive front panel. Green indicator LEDs are included to show when the shutter is open and the laser emission turned on; note that the laser emission LED will blink rapidly for three seconds while the laser turns on. This ultrafast fiber laser also features a front-panel display (shown to the right) that shows the pump level and status indicators of the system, including the temperature and emission status. For additional safety, the user may connect an interlock circuit to the BNC connector on the rear panel. See the Front & Back Panels tab for more details.

This ultrafast fiber laser uses a universal power supply allowing operation over 100 - 240 VAC without the need to select the line voltage. A region-specific power cord is included.

Thorlabs also offers additional fiber lasers, including the FSL1950F 2 µm Femtosecond Fiber Laser and the SC4500 Mid-IR Supercontinuum Source. The 2 µm femtosecond laser produces ultrashort pulses (<80 fs) with a >500 mW average output power, while the supercontinuum source emits over a wavelength range from approximately 1.3 μm to 4.5 μm& with >300 mW of average output power in a collimated beam. See their respective web presentations for full performance details.

Please note: The FSL1550 laser will ship from the US within 4 weeks of placing an order if all component parts are available.
Item # FSL1550
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
Dimensions (L x W x H) 403.6 mm x 432.0 mm x 147.3 mm
(15.89" x 17.01" x 5.80")
  • The peak power is an estimate based on the retrieved intensity profile of the pulse and the pulse energy.
  • Maximum output average power is 1 W.
  • The maximum change in power for every 1 degree change in the environment temperature.
Electrical Requirements
Input Voltage 100 - 240 V
Frequency 50 - 60 Hz
Power Consumption 400 W (Max)
Environmental Requirements
Room Temperature Range 17 °C to 25 °C
Room Temperature Stability <3 °C over 24 Hours

Performance may vary from unit to unit; this data reflects the typical performance of our FSL1550 fiber laser and is presented for reference only. The guaranteed specifications are shown in the Specs tab.

FSL1550 Pulse Intensity
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A typical intensity profile of an output pulse from the FSL1550 fiber laser. This intensity profile is a single line trace extracted from a frequency-resolved optical gating (FROG) measurement. The output pulse has a power of 510 mW.
FSL1550 Spectrum
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A typical output spectrum for the FSL1550 fiber laser. The output pulse has a power of 510 mW.
FSL1550 Front Panel
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Front Panel
Front Panel
Callout Description
1 Push-Button Power Switch
2 Shutter Open/Close Switch
3 Emission Indicator
4 Laser Output Aperture
5 Shutter Indicator
6 Adjustment Knob (Push to Adjust)
7 Laser Enable Switch
Back Panel
Callout Description
1 Interlock Input (BNC)
2 Trigger Signal Output (BNC)
3 AC Power On/Off Switch
4 Fuse Tray
5 AC Power Cord Connector

The FSL1550 fiber laser contains the following components:

  • Benchtop Laser Unit
  • Interlock-Shorting BNC Connector (Installed)
  • IEC Power Cord
  • Four CF175 Clamping Forks

Laser Safety and Classification

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. Thorlabs offers a range of laser safety accessories that can be used to reduce the risk of accidents or injuries. 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. 

Laser Glasses Laser Curtains Blackout Materials
Enclosure Systems Laser Viewing Cards Alignment Tools
Shutter and Controllers Laser Safety Signs

Safe Practices and Light Safety Accessories

  • Laser safety eyewear must be worn whenever working with Class 3 or 4 lasers.
  • Regardless of laser class, Thorlabs recommends the use of laser safety eyewear whenever working with laser beams with non-negligible powers, since metallic tools such as screwdrivers can accidentally redirect a beam.
  • Laser goggles designed for specific wavelengths should be clearly available near laser setups to protect the wearer from unintentional laser reflections.
  • Goggles are marked with the wavelength range over which protection is afforded and the minimum optical density within that range.
  • Laser Safety Curtains and Laser Safety Fabric shield other parts of the lab from high energy lasers.
  • Blackout Materials can prevent direct or reflected light from leaving the experimental setup area.
  • Thorlabs' Enclosure Systems can be used to contain optical setups to isolate or minimize laser hazards.
  • A fiber-pigtailed laser should always be turned off before connecting it to or disconnecting it from another fiber, especially when the laser is at power levels above 10 mW.
  • All beams should be terminated at the edge of the table, and laboratory doors should be closed whenever a laser is in use.
  • Do not place laser beams at eye level.
  • Carry out experiments on an optical table such that all laser beams travel horizontally.
  • Remove unnecessary reflective items such as reflective jewelry (e.g., rings, watches, etc.) while working near the beam path.
  • Be aware that lenses and other optical devices may reflect a portion of the incident beam from the front or rear surface.
  • Operate a laser at the minimum power necessary for any operation.
  • If possible, reduce the output power of a laser during alignment procedures.
  • Use beam shutters and filters to reduce the beam power.
  • Post appropriate warning signs or labels near laser setups or rooms.
  • Use a laser sign with a lightbox if operating Class 3R or 4 lasers (i.e., lasers requiring the use of a safety interlock).
  • Do not use Laser Viewing Cards in place of a proper Beam Trap.


Laser Classification

Lasers are categorized into different classes according to their ability to cause eye and other damage. The International Electrotechnical Commission (IEC) is a global organization that prepares and publishes international standards for all electrical, electronic, and related technologies. The IEC document 60825-1 outlines the safety of laser products. A description of each class of laser is given below:

Class Description Warning Label
1 This class of laser is safe under all conditions of normal use, including use with optical instruments for intrabeam viewing. Lasers in this class do not emit radiation at levels that may cause injury during normal operation, and therefore the maximum permissible exposure (MPE) cannot be exceeded. Class 1 lasers can also include enclosed, high-power lasers where exposure to the radiation is not possible without opening or shutting down the laser.  Class 1
1M Class 1M lasers are safe except when used in conjunction with optical components such as telescopes and microscopes. Lasers belonging to this class emit large-diameter or divergent beams, and the MPE cannot normally be exceeded unless focusing or imaging optics are used to narrow the beam. However, if the beam is refocused, the hazard may be increased and the class may be changed accordingly.  Class 1M
2 Class 2 lasers, which are limited to 1 mW of visible continuous-wave radiation, are safe because the blink reflex will limit the exposure in the eye to 0.25 seconds. This category only applies to visible radiation (400 - 700 nm).  Class 2
2M Because of the blink reflex, this class of laser is classified as safe as long as the beam is not viewed through optical instruments. This laser class also applies to larger-diameter or diverging laser beams.  Class 2M
3R Class 3R lasers produce visible and invisible light that is hazardous under direct and specular-reflection viewing conditions. Eye injuries may occur if you directly view the beam, especially when using optical instruments. Lasers in this class are considered safe as long as they are handled with restricted beam viewing. The MPE can be exceeded with this class of laser; however, this presents a low risk level to injury. Visible, continuous-wave lasers in this class are limited to 5 mW of output power.  Class 3R
3B Class 3B lasers are hazardous to the eye if exposed directly. Diffuse reflections are usually not harmful, but may be when using higher-power Class 3B lasers. Safe handling of devices in this class includes wearing protective eyewear where direct viewing of the laser beam may occur. Lasers of this class must be equipped with a key switch and a safety interlock; moreover, laser safety signs should be used, such that the laser cannot be used without the safety light turning on. Laser products with power output near the upper range of Class 3B may also cause skin burns.  Class 3B
4 This class of laser 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. Class 4 lasers must be equipped with a key switch and a safety interlock.  Class 4
All class 2 lasers (and higher) must display, in addition to the corresponding sign above, this triangular warning sign.  Warning Symbol

Pulsed Laser Emission: Power and Energy Calculations

Determining whether emission from a pulsed laser is compatible with a device or application can require referencing parameters that are not supplied by the laser's manufacturer. When this is the case, the necessary parameters can typically be calculated from the available information. Calculating peak pulse power, average power, pulse energy, and related parameters can be necessary to achieve desired outcomes including:

  • Protecting biological samples from harm.
  • Measuring the pulsed laser emission without damaging photodetectors and other sensors.
  • Exciting fluorescence and non-linear effects in materials.

Pulsed laser radiation parameters are illustrated in Figure 1 and described in the table. For quick reference, a list of equations are provided below. The document available for download provides this information, as well as an introduction to pulsed laser emission, an overview of relationships among the different parameters, and guidance for applying the calculations. 



Period and repetition rate are reciprocal:    and 
Pulse energy calculated from average power:       
Average power calculated from pulse energy:        
Peak pulse power estimated from pulse energy:            

Peak power and average power calculated from each other:
Peak power calculated from average power and duty cycle*:
*Duty cycle () is the fraction of time during which there is laser pulse emission.
Pulsed Laser Emission Parameters
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Figure 1: Parameters used to describe pulsed laser emission are indicated in the plot (above) and described in the table (below). Pulse energy (E) is the shaded area under the pulse curve. Pulse energy is, equivalently, the area of the diagonally hashed region. 

Parameter Symbol Units Description
Pulse Energy E Joules [J] A measure of one pulse's total emission, which is the only light emitted by the laser over the entire period. The pulse energy equals the shaded area, which is equivalent to the area covered by diagonal hash marks.
Period Δt  Seconds [s]  The amount of time between the start of one pulse and the start of the next.
Average Power Pavg Watts [W] The height on the optical power axis, if the energy emitted by the pulse were uniformly spread over the entire period.
Instantaneous Power P Watts [W] The optical power at a single, specific point in time.
Peak Power Ppeak Watts [W] The maximum instantaneous optical power output by the laser.
Pulse Width Seconds [s] A measure of the time between the beginning and end of the pulse, typically based on the full width half maximum (FWHM) of the pulse shape. Also called pulse duration.
Repetition Rate frep Hertz [Hz] The frequency with which pulses are emitted. Equal to the reciprocal of the period.

Example Calculation:

Is it safe to use a detector with a specified maximum peak optical input power of 75 mW to measure the following pulsed laser emission?

  • Average Power: 1 mW
  • Repetition Rate: 85 MHz
  • Pulse Width: 10 fs

The energy per pulse:

seems low, but the peak pulse power is:

It is not safe to use the detector to measure this pulsed laser emission, since the peak power of the pulses is >5 orders of magnitude higher than the detector's maximum peak optical input power.

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1550 nm Femtosecond Fiber Laser

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FSL1550 Support Documentation
FSL15501550 nm Femtosecond Fiber Laser
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