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Autocorrelator for Femtosecond Lasers

  • Ultrafast Interferometric Autocorrelations for 650 - 1100 nm
  • User-Adjustable Scan Range from 50 fs to 10 ps
  • Integrated Iris and Alignment Target for Easy Setup

Front View

Back View


Interferometric Autocorrelator

Related Items

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Autocorrelator Alignment
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View Imperial Product List
Item #QtyDescription
FSAC1Autocorrelator for Femtosecond Lasers
RS1.5P3Ø1" Pedestal Pillar Post, 1/4"-20 Taps, L = 1.5"
RS0283Ø1" Post, 1/4"-20 Tap, L = 0.28"
VRC21VIS/IR Detector Card, 400 - 640 nm, 800 - 1700 nm
CF038-P51Clamping Fork, 0.38" Counterbored Slot, Universal, 5 Pack
View Metric Product List
Item #QtyDescription
FSAC1Autocorrelator for Femtosecond Lasers
RS1.5P/M3Ø25.0 mm Pedestal Pillar Post, M6 Taps, L = 38 mm
RS7/M3Ø25 mm Post, M6 Tap, L = 7 mm
VRC21VIS/IR Detector Card, 400 - 640 nm, 800 - 1700 nm
CF038-P51Clamping Fork, 0.38" Counterbored Slot, Universal, 5 Pack
The iris and VRC2SM1 Alignment Target provide two reference points for alignment. Our VRC2 Viewing Card (sold separately) may be used to visualize the beam; it uses the same fluorescent material as the VRC2SM1 target.
Interferometric Autocorrelation
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This interferometric autocorrelation was obtained using our Octavius® laser. UMC10-15FS Precompensating Mirrors were used to chirp the beam prior to entering the autocorrelator.


  • Ultrafast Pulse Width Characterization for 650 - 1100 nm
  • For Pulses from 40 fs to 1 ps, or Pulses Down to 15 fs with Precompensation
  • Selectable Gain up to 70 dB to Accommodate Large Range of Input Powers
  • Interferogram Signal Output through BNC
  • Scan Rate of 5 Hz
  • Compact Footprint: 6.90" x 5.53" x 4.82"

Thorlabs' FSAC Interferometric Autocorrelator provides approximate pulse width measurements in the 650 - 1100 nm wavelength range. Well suited for diagnostics of femtosecond Ti:Sapphire lasers, it consists primarily of a modified Michelson interferometer with a nonlinear detector at the output.

A BNC connector outputs the autocorrelation signal, which can be viewed on any oscilloscope with >1.5 MHz bandwidth. An example of the direct output from the FSAC is shown in the graph to the right. A photodiode amplifier with selectable gain from 0 dB to 70 dB provides compatibility with a large range of optical input powers, up to a maximum average power of 150 mW.

Intuitive, easy-to-reach controls on the outside of the enclosure allow the user to optimize the resolution and fringe contrast. The controls for the delay arm enable a full scan range of 50 fs to 10 ps (i.e., ±25 fs to ±5 ps), and a micrometer tunes the detector's position for maximum signal. Detailed usage recommendations and examples are available in the manual.

Setup Details
The FSAC autocorrelator is compatible with horizontally polarized input beams up to Ø4 mm (1/e2) and has a beam height of 3" (76.2 mm). A permanently installed SM1D12D Ring-Actuated Iris and an internally SM1-threaded side port provide two reference points for optical alignment. We include a VRC2SM1 Alignment Target and an SM1CP2 End Cap for this side port. To align, simply insert the FSAC into the beam path and rotate until the beam is centered on the target. A flip mount may be used to pick off the beam for regular diagnostics.

Two slots in the enclosure allow the autocorrelator to be locked down with the two included CL5 Table Clamps. In addition, three 1/4"-20 and three M6 x 1.0 tapped holes are located in the base, allowing the unit to be elevated to a desired height. Alternatively, the beam height and polarization may be adjusted by a suitable periscope, such as Thorlabs' RS99(/M) Periscope Assembly. In the image to the right, Thorlabs' Ø1" (Ø25.0 mm) Pedestal Posts have been used to set the FSAC at an optical height of 4.75". Recommended posts are given in the Specs tab.

It is important to note that the pulse width measured by the unit is obtained immediately before the photodiode. Thorlabs' Chirped Mirrors may be used to compensate for dispersion in the optical path. The group delay dispersion caused by the FSAC's internal optics is nominally 230 fs2 at 800 nm. Pulses as short as 40 fs FWHM can typically be measured without precompensation, but sub-40 fs FWHM pulses will require it.

Front View
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Front View
The front is labeled with the design input beam parameters.
Side View
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Side View
Each side has a centered slot that accepts
one of the included CL5 Table Clamps.

Back View
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Back View
The back has controls for the scan range, photodiode
gain, and photodiode position, as well as the three
BNC outputs (see the Pin Diagrams tab).

Item # FSAC
Input Wavelength Range 650 - 1100 nm
Input Pulse Duration Without Precompensation 40 fs to 1 ps (FWHM)
With Precompensationa 15 fs to 1 ps (FWHM)
Full Scan Range 50 fs to 10 ps
(±25 fs to ±5 ps)
Scan Rate 5 Hz
Noise-Equivalent Sensitivityb 0.1 W2 at 800 nm for Ø1 mm Beam (1/e2)
Input Polarization Horizontal
Input Beam Diameter <Ø4 mm (1/e2)
Input Repetition Ratec >300 kHz
Required Sampling Rate >1.5 MHz for 10 ps Scan Range at 650 nm
>150 kHz for 1 ps Scan Range at 650 nm
Internal Dispersion
GDD 230 fs2 at 800 nm (Nominal)
TOD 345 fs3 at 800 nm (Nominal)
Maximum Average Input Power 150 mW
Dimensions 6.90" x 5.53" x 4.82"
(175.3 mm x 140.4 mm x 122.4 mm)
Room Temperature Range 17 to 25 °C
  • Pulses as short as 15 fs may be measured by using dispersion-compensating optics such as Thorlabs' Chirped Mirrors.
  • Peak Power × Average Power of Input Laser
  • Once the interferogram is obtained, lower input repetition rates may be used by triggering the oscilloscope directly from the autocorrelation signal.


Recommended Posts for Common Beam Heightsa
4.27" Beam Height
Imperial Ø1" Posts Three RS1P Pedestal Posts with
Three RS028 Posts
Metric Ø25.0 mm Posts
Three RS1P/M Pedestal Posts with
Three RS7/M Posts
4.75" Beam Height
Imperial Ø1" Posts Three RS1.5P Pedestal Posts with
Three RS028 Posts
Metric Ø25.0 mm Posts Three RS1.5P/M Pedestal Posts
Three RS7/M Posts
  • The base of the FSAC has three 1/4"-20 tapped holes and three M6 x 1.0 tapped holes.

Trigger Output

BNC Female

BNC Female

Outputs TTL Signal Synchronized with the 5 Hz Scan Rate

Delay Output

BNC Female

BNC Female

Outputs Signal Proportional to Position of Delay Arm
-5 V to +5 V; ≥100 kΩ

Photodiode Output

BNC Female

BNC Female

Outputs Autocorrelation Signal
0 V to +10 V; ≥100 kΩ

Cable on Included Power Supply

LUMBERG RSMV3-657/2M Male Connector


Sample MATLAB and Python Scripts

The download button below links to sample scripts that convert the interferometric autocorrelation from the FSAC into an intensity autocorrelation. Details are in Section 5.3 of the manual.

Software Download
Items Included with FSAC
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Items Included with FSAC (Region-Specific Power Cord Not Shown)

Each FSAC ships with the following:

  • FSAC Interferometric Autocorrelator
  • CL5 Mounting Clamps (Qty. 2)
  • 5/32" Stubby Hex Key
  • VRC2SM1 Fluorescent Alignment Disk
  • SM1CP2 End Cap
  • R1DS3N Alignment Reticle
  • Power Supply with Region-Specific Power Cord

Posted Comments:
ruben.criado  (posted 2017-10-26 11:21:53.173)
Can you offer the autocorrelator at 1550 nm? Thanks
tfrisch  (posted 2017-10-31 04:23:43.0)
Hello, thank you for contacting Thorlabs. I will reach out to you directly about the details of your source and our custom capabilities.

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available / Ships
FSAC Support Documentation
FSACAutocorrelator for Femtosecond Lasers
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