Asynchronous Optical Sampling (ASOPS) Technique

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

ASOPS-TWIN

Asynchronous Optical Sampling System

RRE-SYNCRO

Repetition Rate Stabilization

Related Items

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Femtosecond Phase Stabilization

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Fiber-Coupled Photodetectors

SM1 Air Purge Connector

Avalanche Photodetector

Compact Frequency Comb

THz Antennas

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Overview
Specs
Pulse Calculations
Feedback

Jason Reeves Menlo Systems	Feedback? Questions? Need a Quote? 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 Email: ussales@menlosystems.com
Outside United States Phone: +49-89-189166-0 Email: sales@menlosystems.com

Applications

ASOPS-TWIN and ASOPS-DUAL-COLOR

Pump-Probe Spectroscopy
FTIR Spectroscopy
Time-Domain THz Spectroscopy
Material Characterization

RRE-SYNCRO

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

ASOPS-TWIN and ASOPS-DUAL-COLOR

Features

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.

RRE-SYNCRO

Features

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.

Item #	ASOPS-TWIN	ASOPS-DUAL-COLOR
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 Increment^b	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 fs^c	<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

Item #	RRE-SYNCRO
Relative Timing Jitter (RMS)	<200 fs (0.1 Hz - 500 kHz)^a
External Reference Input	10 MHz^b, 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

Click above to download the full report.

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 is 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.

Equations:
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:
	and
Peak power calculated from average power and duty cycle*:
	*Duty cycle () is the fraction of time during which there is laser pulse emission.

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
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	P_avg	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	P_peak	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	f_rep	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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