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Rapidly Swept Tunable Laser

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Rapidly Swept Tunable Laser

Item #Center Wavelength*3 dB Tuning Range*Optical Power*
SL1325-P161325 nm125 nm15 mW

*Typical values, full specifications available on Specs tab.


  • Ideal for Optical Coherence Tomography
  • Center Wavelength: 1325 nm
  • 3 dB Tuning Range: 125 nm
  • Real-Time 2D Imaging at 16,000 Lines per Second in OCT Applications

Thorlabs' SL1325-P16 OCT-proven frequency swept tunable laser is specifically designed for Swept Source Optical Coherence Tomography (SS-OCT) and Optical Frequency Domain Reflectometry (OFDR) applications. This laser utilizes Thorlabs' patented Cat-Eye external cavity laser design to continuously sweep across a broad wavelength range. Each laser includes an integrated Mach-Zehnder Interferometer, which can be used for easy wavenumber triggering. A BNC connection is located on the rear panel of the laser to access the interferometer's signal.

The SL1325-P16 has a typical center wavelength of 1325 nm, which is able to penetrate multi-layer biological tissues. The laser can continuously scan at a rate of 16 kHz over its tuning range to provide real-time 2D and 3D imaging capabilities when used in an OCT system. The image at the top right corner of this page shows an example screenshot of 2D imaging that is possible when building a SS-OCT system with these lasers. Please see the OCT Integration tab for details on how the lasers are used in our SS-OCT imaging systems. The broad wavelength tuning range of this laser is important for SS-OCT because the broader the spectral range, the higher axial resolution. Please see the Specs tab and the Graphs tab above for detailed specifications and spectrums.

Thorlabs' swept source laser is ideal for OEM integration. Please contact tech support for more information on our custom swept source laser capabilities.

Front Panel Controls
The front overlay of this laser features a power switch, a Laser Enable button, a Tuning Enable button, an FC/APC fiber connection, and indicator lights. When the power switch is flipped on, a "Power On" light will illuminate. The Laser Enable button will turn the laser on, but the laser's output will not be swept across its wavelength range until the Tuning Enable button is pressed. Indicator lights alert the user if the laser has not yet reached its set temperature (during startup) or if the laser has overheated. If the laser has overheated, the unit will automatically turn off the laser, scanner, and TEC to protect them from damage. Once the unit has cooled, the TEC will turn back on, but the laser and tuning must be re-enabled by the user.

Center Wavelength1310 nm1325 nm1340 nm
Tuning Range (-3 dB Cutoff Point)110 nm125 nm-
Tuning Range (-10 dB Cutoff Point)120 nm140 nm-
Repetition Rate15.7 kHz15.9 kHz16.1 kHz
Average Optical Output Power*10 mW15 mW-
Optical Power Stability**-±0.5 dB-
Optical Isolation50 dB
Linear Polarization>80:1
Coherence Length5 mm6 mm7 mm
Operating Temperature10 °C25 °C40 °C
Storage Temperature10 °C25 °C40 °C
Humidity>85%, Non-condensing Environment
Laser Classification (per IEC 60825-1)Class 1M
Physical Size (w x d x h) 315 mm x 295 mm x 146 mm

*Averaged over 1 s
**Forward to forward scan or backward to backward scan during 1 hr usage

Mach-Zehnder Interferometer Output

BNC Connection

Sinusoidal Trigger Pulse Interference Signal from MZI

Trigger Output

BNC Connection

8 kHz TTL Trigger Output Signal for Tuning Scan

D-type Female

DB9 Female

Used Primarily for Internal Diagnostics

The graphs below are an example of the performance of one SL1325-P16 laser. The spectrum varies from unit to unit.

Swept Source OCT System

Figure 1, below, shows a Thorlabs swept source OCT system. This system utilizes the SL1325-P16 swept source laser, coupling the laser's output to a Michelson interferometer. The reference and sample arms are split using a broadband 50/50 coupler. Light from the reference arm is reflected back into the fiber with a mirror; a variable optical attenuator controls the amount of light incident on this mirror. The sample arm is connected to an imaging probe, which first collimates the laser beam that is then incident on scanning galvo mirrors. The mirrors scan the beam across an LSM03 scan lens. The scan lens then focuses the laser onto the sample, which is placed on a rotation stage with XY translation. The scanning galvo mirrors allow the OCT system to image in 1D, 2D, or 3D. If you are an OEM customer interested in using our swept source laser, please contact Tech Support to learn about our extensive capabilities.

OCT-SS Schematic

Figure 1. Schematic of Swept Source OCT Microscope: swept laser source (SS), fiber coupler (FC), polarization controller (PC), circulator (CIR), collimator (C), variable attenuator (VA), mirror (M), balanced detector (BD), data acquisition board (DAQ), XY scanner driver (SD), CCD camera (CCD), objective (OBJ), microscope (MS), analog output (AO), aiming laser (AL). The Mach-Zehnder interferometer (MZI), which is built in the swept light source, provides the frequency clock signal for the laser.

Signal Processing
In Thorlabs' OCS1300SS OCT system, the interference signal is detected using a high-transimpedance gain balanced photodetector (PDB145C), which suppresses the DC and autocorrelation noise in the interference signals. A 14-bit high-speed digitizer is used to sample the OCT interference fringe signals, which are first converted from time to frequency space using a fast Fourier transform (FFT) and then recalibrated. The FFT of the interference signal yields the depth dependent reflectivity profile for the OCT image.

Electrical Connections

The rear panel of the SL1325-P16 has two BNC connections and one RS-232 connection. The first BNC connector is the Mach-Zehnder Interferometer output, which serves as the laser's clock. These lasers use our OCT-proven interferometers, which have a DC to 200 MHz 3 dB bandwidth. The other BNC connector is for an 8 kHz TTL trigger output signal. An RS-232 connection is primarily used for diagnostic purposes. A 100-240 VAC power input is also on the rear panel. Each laser includes a line cord for use in North America.

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. 

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

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.
  • Laser Barriers and 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 laser sign lightboxes 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 Laser Barrier or 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:

ClassDescriptionWarning Label
1This 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
1MClass 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
2Class 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
2MBecause 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
3RLasers 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 3R
3BClass 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. Class 3B
4This 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
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Posted Comments:
Poster: jlow
Posted Date: 2012-11-06 15:34:00.0
Response from Jeremy at Thorlabs: We would not be able to supply the replacement SOA to you but we could possibly replace these in house. I will get in contact with you regarding the details of your system.
Poster: avle
Posted Date: 2012-10-24 02:04:43.093
SL1325-P16 What is the cost to replace the SOA in this laser? We have one of the 16khz lasers, as well as 4 of the older 8khz scan rate ones that all need the SOA's replaced. Could you email and quote a cost?
Poster: jlow
Posted Date: 2012-07-31 17:08:00.0
A response from Jeremy at Thorlabs: The SL850-P16 was offered in our V19 catalog. We do not offer this exact one any longer. However, we will get in contact with you directly to discuss your application in more detail.
Poster: reavesm
Posted Date: 2012-07-25 12:54:17.0
Hello, I am interested in Item # SL850-P16 (a frequency-swept laser around 850nm) for use in an OFDR system. Can you provide information on the mode-hop free tuning range of this laser. The catalog states a tuning range of 60-80nm with center wavelengths of 835nm-855nm, but does not specify whether this tuning range is mode-hop free. Please email or call 540-953-4261 with more information. Regards, Matt Reaves
Poster: tcohen
Posted Date: 2012-05-23 10:31:00.0
Response from Tim at Thorlabs: Thank you for contacting us! Our swept laser source continuously sweeps the full bandwidth forward and backwards 16,000 times a second. We do not have a frequency scan step measurement because the sweep is continuous.
Poster: nickle.gong
Posted Date: 2012-05-20 23:22:37.0
hello. Would you tell me what is the swept frequency, the 16kHz in your system? Is it means scan all the source band(100 or 200nm) 16k times per second or only the frequency scan step 16k times per second? And how much is the scan frequency step? I can not find these information in your manual. Thank you!
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