Asynchronous Optical Sampling (ASOPS) Technique

  • Solutions for Pump-Probe and Two-Color Pump-Probe Spectroscopy
  • High-Speed Scanning
  • No Mechanical
    Adjustment Necessary


Asynchronous Optical Sampling System


Repetition Rate Stabilization

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Simon Kocur
Simon Kocur
Menlo Systems
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Please note that these ASOPS and Repetition Rate Stabilization Systems are available directly from Menlo Systems, Inc. within the United States and from Menlo Systems GmbH outside the United States.
United States
Phone: +1-973-300-4490
Outside United States
Phone: +49-89-189166-0


  • Pump-Probe Spectroscopy
  • FTIR Spectroscopy
  • Time-Domain THz Spectroscopy
  • Material Characterization
  • Repetition Rate Synchronization
  • Precision Timing

Optional Packages

VARIO User-Defined Repetition Rate
Factory-Set Value Selectable in the 50 - 250 MHz Range

MULTIBRANCH Additional Seed Ports
Seeding of Multiple Amplifiers with Optional Subsequent Frequency Conversion to Cover Multiple Wavelengths



  • Measurements in a 4 ns or 10 ns Time Window
  • Sub-150 fs Pulses
  • Fiber-Coupled or Free-Space Design
  • ASOPS Control Software
  • See Specs Tab for Details

In time-resolved measurements, an ultrafast pulse triggers a reaction, and a second pulse takes a snapshot of the induced change. By shifting the arrival time of the probe pulse with respect to the pump pulse, the stimulated process can be followed in time.

The Asynchronous Optical Sampling (ASOPS) technique allows for high-speed scanning over a few nanoseconds of time delay without a mechanical delay line. The ultrafast lasers delivering the pump and probe pulses are locked together at a tunable repetition rate difference. The lasers can also be locked to the same repetition rate value, and by shifting the relative phase between the laser pulses, the system will allow measurements in a reduced time window of several hundred picoseconds. Switching between the two modes can be done at the touch of a button.



  • Synchronization to Fixed or Tunable Repetition Rate
  • Relative Timing Jitter <200 fs (RMS) (0.1 Hz - 500 kHz)
  • Plug-and-Play Use
  • Modular Design
  • Fully Customizable
  • Two-Stage Locking Scheme Possible (Fundamental/Harmonic)

The RRE-SYNCRO, included with the ASOPS-TWIN and ASOPS-DUAL-COLOR, provides state-of-the-art phase lock electronics used to synchronize pulsed laser sources with high accuracy. The main application is the synchronization of a pulsed laser to a radio frequency reference, derived from a radio frequency clock or an optical reference clock. An embedded microcontroller for the stepper motor and piezo control in the laser cavity ensures long-term stability. The complete, user-friendly system allows for plug-and-play use.

Repetition Rate 250 MHz 100 MHz
Repetition Rate Offset Tuning Range (Δf) ±10 kHz, in Steps of 10-5 Hz
Time Measurement Window 4 ns 10 ns
Scan Duration (1/Δf)a 0.1 ms @ 10 kHz Offset,
1 s @ 1 Hz Offset
Data Point Incrementb 160 fs @ 10 kHz,
0.016 fs @ 1 Hz
1 ps @ 10 kHz,
0.1 fs @ 1 Hz
Relative Timing Jitter (RMS) (0.1 Hz - 500 kHz) <150 fs
Laser Head Specifications
Wavelength 1560 nm 1560 nm 780 nm
Average Output Power >75 mW (From Each Laser) >100 mW
Output Port Fiber Coupled, FC/APC Free Space
Pulse Length <150 fsc <90 fs <120 fs
Piezo Tuning Range >625 Hz >100 Hz
Piezo Bandwidth >30 kHz >30 kHz
Stepper Motor Tuning Range >2 MHz >330 kHz
Trigger Signal TTL Level at Offset Frequency,
<10 ns Rise Time
Environmental Specifications
Operating Voltage 110/115/230 VAC
Frequency 50 to 60 Hz
Cooling Requirements No Water Cooling Required
Operating Temperature 22 ± 5 °C
Optical Unit Dimensions / Weight 415 mm x 400 mm x 110 mm3 / 35 kg
(16.3" x 15.7" x 4.3" / 77 lbs)
500 mm x 535 mm x 110 mm3 / 35 kg
(19.7" x 21.1" x 4.3" / 77 lbs)
Control Electronics Dimensions / Weight Mounted in 19" Rack Cabinet
800 mm x 600 mm x 1800 mm / 75 kg
(31.5" x 23.6" x 70.9" / 165 lbs)
  • Scales Inversely with Repetition Rate Offset
  • Scales with Ratio of Repetition Rate Offset and Repetition Rate Squared
  • After 6 m of PM Fiber
Relative Timing Jitter (RMS) <200 fs (0.1 Hz - 500 kHz)a
External Reference Input 10 MHzb,
Signal Level +5 dBm to +10 dBm
Stepper Motor Signal Output Stepper Motor Control, Sub-D, 9 Pin
Piezo Signal Output Piezo Control 0 - 150 V, BNO
Error Signal Output Error Signal for Monitoring, BNC
Environmental Specifications
Operating Voltage 110/220 V
Storage Temperature 0 to 40 °C
Dimensions / Weight 449 mm x 148 mm x 317 mm / 7 kg
(17.7" x 5.8" x 12.5" / 15.4 lbs)
Remote Control PC Connection via USB or RS232 Interface
  • Or Same as Reference, Whichever Applies First. Values are specified for models of Menlo Systems' C-Fiber femtosecond fiber laser series. Please contact Menlo Systems when stabilizing lasers from other manufacturers to optimize the performance of the RRE locking electronics.
  • Provided by User. Please contact Menlo Systems for custom reference frequencies.

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
Click to Enlarge

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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Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
ASOPS-TWIN Support Documentation
ASOPS-TWINAsynchronous Optical Sampling System for 1560 nm, 250 MHz
Menlo Lead Time
ASOPS-DUAL-COLOR Support Documentation
ASOPS-DUAL-COLORAsynchronous Optical Sampling System for 1560 nm & 780 nm, 100 MHz
Menlo Lead Time
RRE-SYNCRO Support Documentation
RRE-SYNCRORepetition Rate Stabilization, Complete Phase Lock Loop
Menlo Lead Time