Fast Laser Power Modulators for Two-Photon Microscopy


  • Region of Interest Selection, Edge Blanking, and Frame Blanking
  • Pockels Cell and Acousto-Optic Modulator Alternative
  • Photoactivation Control up to 500 nJ
  • Near-Zero Dispersion Reduces Need for Pre-Compensation

OM6N

Fast Laser Power Modulator

Two-channel 2P image of mouse kidney cells acquired with Thorlabs' Bergamo® II microscope and Tiberius® fast-tuning Ti:Sapphire laser, using the OM6N fast laser power modulator to define a region of interest.

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OM6N(/M) Typical Transmission
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Typical transmissions for the OM6N (solid) and OM6NH (dashed) modulators at 700 nm (blue traces) and 1100 nm (red traces). For each unit, the full transmission (at 0 V) differs with wavelength due to the reflective nature of the gold-coated mirrors. Additional performance graphs are available on the Graphs tab.

Applications

  • Fast Power Modulation of NIR Femtosecond Lasers
  • Two-Photon Fluorescence Microscopy
  • Photoactivation
  • Galvo-Galvo or Galvo-Resonant Scanning
  • Edge and Frame Blanking
  • Region of Interest Selection
OM6N(/M) shown without photodector
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Our Fast Laser Power Optical Modulator shown with the PDA100A2 Photodetector removed, providing access to four 4-40 taps for 30 mm cage system compatibility.

Features

  • Offers DC Power Attenuation and High-Speed Modulation
  • Pockels Cell Alternative with Polarization-Independent Performance
  • 700 nm to 1100 nm Operating Range
  • <2 µs On/Off Time
  • Contrast Ratios up to 2500:1
  • DC and AC Modulation up to 20 kHz
  • Compatible with ThorImage®LS and ScanImage Software
  • External Photodetector for Monitoring/Calibrating Output Power
    (PDA100A2 Si Detector Included)
  • Near-Zero (<100 fs2) Dispersion
  • Passively Cooled to Eliminate Vibrations

Thorlabs' Fast Laser Power Modulators use deformable mirror technology to provide high-speed intensity modulation and beam attenuation. The all-reflective design incorporates gold-coated MEMS mirrors that are polarization independent and introduce minimal (<100 fs2) dispersion. This unidirectional device is designed for a collimated, 1 to 2 mm (1/e2) diameter input beam with up to 10 W of optical power and up to 500 nJ of pulse energy, enabling use with popular 1 µm high-pulse-energy photoactivation lasers. These modulators are available with either standard (>250:1) or high (>2500:1) contrast ratios.

Transmission, which is a function of both input voltage and wavelength as shown in the graph to the right, is controlled by a 0 to 1 V analog input voltage; this voltage can be easily generated by off-the-shelf data acquisition (DAQ) hardware or other electronics. The device supports continuous DC operation as well as modulation frequencies up to 20 kHz, making it ideal for imaging applications such as fly-back blanking or region of interest (ROI) selection.

The higher contrast achieved with the OM6NH(/M) modulator is made possible by incorporating two MEMS mirrors, the deformation of which behaves like a grating, into the design; one diffracts horizontally and the other vertically to provide enhanced contrast performance.

Ideal for Photoactivation and Two-Photon Fluorescence Applications
This modulator is suitable for many applications including two-photon fluorescence microscopy and photoactivation. Both of these techniques require fast laser power modulation of ultrafast NIR laser pulses, such as those generated by the tunable Ti:sapphire Tiberius® laser, to limit sample exposure during imaging and reduce thermally induced damage. High-speed modulation is traditionally accomplished with bulk crystal modulators, such as Pockels cells and acousto-optic modulators (AOMs). As they rely on bulk materials, they introduce significant dispersion, degrading image quality.

Replaceable Photodetector
An internal beam sampler directs a small portion (<1%) of the modulated beam to a separate output port where a photodetector can be used to monitor the transmission. If desired, the included, pre-installed Thorlabs PDA100A2 Si Switchable Gain Detector can be easily removed and replaced with a user-supplied detector; to do so, loosen the 8-32 mounting screw located on the underside of the modulator.

Housing and Mounting Features
The input and output ports of the laser power modulator feature internal SM05 (0.535"-40) threading, which can be used to install external SM05-threaded alignment targets or irises (not included). All three ports also have 4-40 threaded holes for compatibility with our 30 mm cage systems. To aid in initial alignment, we recommend using an SM05 slotted lens tube or a 30 mm cage system assembly on the modulator input.

Three slots in the enclosure allow the modulator to be mounted directly to an optical table with table clamps, such as our CL6 clamps (not included), resulting in a minimum beam height of 1.25". The base also includes three 8-32 (M4) mounting holes for attaching pedestal posts, which can be used to elevate the modulator to the desired beam height.

The unit is shipped with a 24 V power supply with an KPJX-4S-S connector for the modulator, as well as a ±12 V supply for the photodetector. For more information, please see the Pin Diagrams tab.

Laser Power Modulator Housing Dimensions
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Laser Power Modulator Housing Dimensions
Item # OM6N(/M) OM6NH(/M)
Contrast Ratio >250:1 >2500:1
Operating Rangea 700 - 1100 nm
Input Polarization Any
Rise Timeb 1.5 - 5 µs
Fall Time <2 µs
Modulation Frequency 0 - 20 kHz 
Modulation Voltagec 0 - 1 V
Input Impedancec 10 kΩ
Transmission (at 800 nm) >80%
Input Pulse Energy 500 nJ (Max)
Input Optical Power 10 W (Max)
Internal Apertured Ø3.8 mm
Internal Optical Path Length 100 cm
Dispersion <100 fs2
Transmitted Wavefront Errore <λ/4 (at 633 nm)
Power Supply 24 V, 1 A
Power Connector R7B Female Connector
Operating Temperature 15 - 35 °C
Operating Humidity 20 - 60%
Storage Temperature -25 - 70 °C
Housing Dimensions (L x W x H) 11.45" x 6.83" x 2.80"
(290.8 mm x 173.4 mm x 71.1 mm)
  • The laser power modulator can be used outside the wavelength range. However, the damage threshold for wavelengths outside this range is unspecified and may be lower, especially for shorter wavelengths. The modulator may not be able to achieve full extinction for wavelengths above 1100 nm.
  • The time required for the transmission to rise from 10% to 90%. Response depends on DC attenuation level.
  • A 10 kΩ internal pull-down resistor holds the input voltage at 0 V if no input is provided.
  • The recommended collimated input beam diameter (1/e2) is 1 to 2 mm.
  • Independent of modulation level.

Performance Graphs

This data reflects the typical performance of our high-speed optical modulators and is presented for reference only. The guaranteed specifications are shown in the Specs tab.

OM6N(/M) Transmission at 700 nm
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Typical transmission for the OM6N and OM6NH at 700 nm. The transmission will vary from device to device. Please note that the maximum contrast ratio, defined as maximum transmission to minimum transmission, can only be achieved when the extinction voltage is carefully calibrated.
OM6N(/M) Transmission at 1100 nm
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Typical transmission for the OM6N and OM6NH at 1100 nm. The transmission will vary from device to device. Please note that the maximum contrast ratio, defined as maximum transmission to minimum transmission, can only be achieved when the extinction voltage is carefully calibrated.
OM6N(/M) Extinction Voltage
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Typical extinction voltages as a function of input wavelength. For each unit, the extinction voltage is the input voltage resulting in minimum transmission. The exact voltage for maximum extinction varies from device to device.
OM6N(/M) Extinction Voltage
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Plot showing the high-frequency temporal response of the OM6N(/M) and OM6NH(/M) Optical Modulators.
Fast Laser Power Modulator Side Panel
Callout Description
1 0 to 1 V Modulation Voltage (BNC)
2 DC Power Switch 
3 LED Power Indicator
4 DC Power Cord Connector for Modulator (R7B)
5 0 to 10 V Photodetector Output (BNC)
6 DC Power Cord Connector for Photodetector
Laser Power Modulator Electrical Connections
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High-Speed Optical Modulator Electrical Connections

OM6N(/M) and OM6NH(/M) Fast Laser Power Modulator Connections

BNC Female, Modulation Signal Input

BNC Female

Modulation Signal Input is 0 - 1 V

KPJX-4S-S Connector, Female Power IN

Pinout for KPJX-4S-S Connector


PDA100A2 Detector Connections

BNC Female Output (Photodetector)

BNC Female

PDA100A2 has a 0 - 10 V Output

Male (Power Cable)*

Pinout for PDA Power Cable

*For the Included LDS12B Power Supply

Female Power IN (Photodetector)

Pinout for PDA Power Connector


Posted Comments:
Yaqing Zhang  (posted 2021-07-03 03:41:25.42)
Hi, Could you please provide the optical path length from the input aperture to output aperture of the fast modulator (OM6NH)? The specs says the internal optical path length is 100mm, but the housing length is already 290.83 mm, so I believe the optical path from the two apertures must be larger than 290.83mm. Thanks!
YLohia  (posted 2021-07-12 10:36:04.0)
Hello, thank you for bringing this typo to our attention. The path length is approximately 100 cm, not 100 mm. This will be corrected on our web documentation shortly.

Fast Laser Power Modulators

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