The FSL1950F's high peak power of >100 kW enables a range of nonlinear phenomena. In this example, the laser was used to pump a dispersion-engineered InF3 fiber manufactured by Thorlabs. The InF3 fiber broadens the pump light toward the NIR and MIR regions of the spectrum. The MIR portion consists of a supercontinuum extending past 4.0 µm. An MIR Supercontinuum Source using this technique is available here.
Ultrashort <80 fs Pulses at 1950 nm ± 30 nm Center Wavelength
>500 mW Average Output Power, >10 nJ Pulse Energy, and 50 MHz Repetition Rate
All Polarization-Maintaining Fiber Design
Reliable Passive Mode-Locking Using a Saturable Absorber
Pigtailed, FC/APC-Terminated Delivery Fiber Simplifies Coupling into Free Space
SMA Connector Provides Fast Photodiode Output for External Synchronization
MIR Supercontinuum Generation
MIR Frequency Combs
Thulium- or Holmium-Doped Amplifier Seeding
Thorlabs is pleased to offer a femtosecond fiber laser with emission at 2 µm. With <80 fs pulse widths, >500 mW average output power, and a repetition rate of 50 MHz, the FSL1950F enables a wide range of applications, including seeding of thulium-doped amplifier systems, nonlinear optics, and MIR supercontinuum generation (see the Application Example to the right).
This ultrafast laser is based upon an oscillator-amplifier combination that uses only polarization-maintaining fiber, yielding reliable turnkey operation and exceptional long-term reliability. The pulses are delivered through a pigtailed FC/APC-terminated fiber with a nominal length of 12" (30 cm). The laser is controlled using our included Windows®-based GUI (computer not included), which is shown in the screenshot above.
The FSL1950F's delivery fiber is intended for use with free-space coupling optics, such as Thorlabs' Reflective Collimators with Protected Silver Coatings, FiberPorts, and Triplet Collimators. Its output pulses are polarized parallel to the fiber alignment key. This delivery fiber should not be connected to another patch cable, since even short lengths of fiber (>5 cm) will significantly alter the pulse characteristics. Because of the high power emitted at the fiber tip, it is important to keep the fiber tip clean using, for example, the FCC-7020 Fiber Connector Cleaner; otherwise dust may burn onto the facet.
1950 nm ± 30 nm
<80 fs (FWHM)
>500 mW (Average)
50 MHz (Nominal)
Polarization Extinction Ratioa
External Sync Output
2.0 mm Narrow Key FC/APC
Numerical Aperture (NA)
Mode Field Diameter
12" (30 cm) [Nominal]
Minimum Bend Radius
Ø3 mm Stainless Steel
Laser Head Dimensions
17.46" x 15.80" x 5.60" (443.5 mm x 401.3 mm x 142.2 mm)
15.68" x 19.00" x 5.24" (398.3 mm x 482.6 mm x 133.1 mm)
100 - 240 V, 50 - 60 Hz
Input Power Consumption
700 W (Max)
Room Temperature Range
17 °C to 25 °C
Room Temperature Stability
<3 °C over 24 Hours
The output polarization is parallel to the fiber alignment key.
Click to Enlarge Click for Raw Data This intensity autocorrelation, taken at the FSL1950F's full output power of 500 mW, demonstrates pulse widths shorter than 100 fs. It is provided as a reference and is not guaranteed.
These plots compare spectra obtained at the full output power of 500 mW and an attenuated output power of 200 mW. The output power was attenuated by reducing the pump current. Because of the intrinsic nonlinearities in the fiber cavity, which are necessary for obtaining high-power femtosecond pulses, the pulse width and spectral shape depend heavily on the desired output power. If your application would benefit from pulses with different temporal or spectral structure, please contact us with your application requirements.
An installer for the Windows®-based GUI of the FSL1950F Femtosecond Fiber Laser.
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.
Safe Practices and Light Safety Accessories
Thorlabs recommends the use of safety eyewear whenever working with laser beams with non-negligible powers (i.e., > Class 1) 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.
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.
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:
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 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 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).
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.
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 are limited to 5 mW of output power in this class.
Class 3B lasers are hazardous to the eye if exposed directly. However, diffuse reflections are not harmful. Safe handling of devices in this class includes wearing protective eyewear where direct viewing of the laser beam may occur. In addition, laser safety signs lightboxes should be used with lasers that require a safety interlock so that the laser cannot be used without the safety light turning on. Class-3B lasers must be equipped with a key switch and a safety interlock.
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.
All class 2 lasers (and higher) must display, in addition to the corresponding sign above, this triangular warning sign
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:
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.
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.
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.
The amount of time between the start of one pulse and the start of the next.
The height on the optical power axis, if the energy emitted by the pulse were uniformly spread over the entire period.
The optical power at a single, specific point in time.
The maximum instantaneous optical power output by the laser.
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.
The frequency with which pulses are emitted. Equal to the reciprocal of the period.
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.