Pulse Picker / Cavity Dumper

  • Update:Jun 13, 2017
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Pulse pickers and cavity dumpers are high speed acousto-optic modulators which separate and divert a single laser pulse within a pulse train to a new optical path.

Product Introduction

Pulse pickers and cavity dumpers are high speed acousto-optic modulators which separate and divert a single laser pulse within a pulse train to a new optical path. A cavity dumper is used inside the cavity of a mode locked laser, while a pulse picker describes the same function when used externally. Both use high speed acousto-optic crystal and specialized design techniques to keep rise time to a minimum while operating at a low duty cycle to select individual laser pulses with speed and synchronization.

Tight focusing of the beam within the device is required to achieve the desired speed (typically <0.1 mm), resulting in very high input power density. Our rigorous manufacturing standards and high crystal quality minimize scatter and enable industry-leading optical power handling. Antireflection coatings minimize insertion loss.

By using a high RF carrier frequency and an optimized lens design, G&H pulse pickers and cavity dumpers provide large angular separation between the deflected and undeflected beams (up to 75 mrad). This makes it easy to separate the two beams in space and maintain a static contrast ratio of at least 500:1.

The choice of RF driver is particularly important to achieve accurate synchronization with the laser pulse train. Controls on the driver optimize the RF drive pulse shape and delay. The modulation signal is synchronized and optimized using a control loop to select the best time at which to pick off the pulse. Extinction ratio relative to adjacent and subsequent pulses can also be affected by the choice of driver, though >20 dB can be achieved.

Our standard models are below:

Model Wavelength Rise/Fall Time Active Aperture Operating Frequency Optical Material
13389-BR AOCD/AOPP 350-850 nm 6 ns 60 μm 389 MHz Fused silica
17389-.93-FOA AOPP 700-1064 nm 7 ns 70 μm 389 MHz Tellurium dioxide
I-M080-2C10G-4-AM3 1030-1064 nm 113 ns/mm 2 mm 80 MHz Crystalline quartz
I-M080-4C10G-4-GH60 1030-1064 nm 113 ns/mm 4 mm 80 MHz Crystalline quartz
I-M150-0.5C10G-8-GH48 1064 nm 30 ns 0.5 mm 150 MHz Crystalline quartz
I-M110-1C10G-8-GH48 1064 nm 60 ns 1 mm 110 MHz Crystalline quartz

STBR Series Free Space Pulse Picker / Cavity Dumper

The STBR series Free Space Cavity Dumper is typically used in a mode-locked laser cavity to separate a single optical pulse from the pulsed energy circulating. As a result, nearly all the laser energy is dumped out of the resonant cavity in the form of a single optical pulse. A cavity dumper offers high peak power and higher repetition frequencies. The STBR series high-speed Pulse Picker is used typically in high-speed optical pulse picking external to a laser cavity and is designed to extract single pulses from a fast train of laser pulses up to 100 MHz – few GHz pulse repetition rate, and re-direct the pulse into a different optical path. A cavity-dumped laser, a pulse picker is often called a cavity dumper, extracts the circulating pulse from the cavity in only every N-th round trip. The Pulse Picker is in most cases either an electro-optic modulator or an AO Modulator, combined with a suitable fast electronic driver.

Pulse Picker

Model # TEPP-200-40-BR FSPP-380-76-BR
Substrate TeO2 SiO2
Laser Wavelength (nm) 700 - 1200 700 - 1200
Active Aperture (mm) 0.10 0.10
Center Frequency (MHz) 200 380
Digital Modulation Bandwidth (MHz) 40 80
Optical Transmission (%) > 99.8 > 99.8
Diffraction Efficiency (%) ~ 40-50 > 25
Rise time (nsec) 14 6
Acoustic Velocity (m/s) 4.2E+3 5.96E+3
RF Power Level (W) 2 (50% duty cycle max.) 10 (10% duty cycle max.)
Bragg Angle (mrad) 29 25
Separation Angle (mrad) 59 50
Wave Front Distortion λ/10 λ/10
Input Impedance 50 ohms 50 ohms
Optical Polarization Linear Linear
VSWR 2:1 2:1
RF connector SMA SMA

Both case types allow for Brewster angle adjustment of the input optical beam. The device should operate only with pulsed RF power. The max CW RF power that can be used without damage is 1 Watt.

Cavity Dumper

Model # TECD-380-95-543 TECD-380-50-780 TECD-380-95-800 FSCD-250-54-BR-400 FSCD-380-92-BR-800
Substrate TeO2 TeO2 TeO2 SiO2 SiO2
Wavelength 543nm 780 nm 800 nm 250-450 nm 800nm
Active Aperture 0.30 mm 0.30 mm 0.10 mm 0.10 mm 0.10mm
Center Frequency 380 MHz 380 MHz 380 MHz 250 MHz 380MHz
3dB Modulation Bandwidth 95 MHz 50 MHz 95 MHz 54 MHz 92MHz
Optical Transmission >95% >95 % >98 % >98 % >98%
Max Diffraction Efficiency 70%@1W 40%@1W 60%@2W 70%@5W 30%@10W
Rise time 10 nsec 20 nsec 5.8 nsec 10 nsec 6nsec
Beam spot size 31 um 62 um 29 um 72 um 42um
Acoustic Velocity 4.2E+3 m/s 4.2E+3 m/s 4.2E+3 m/s 5.96E+3 m/s 5.96E+3m/s
Wave Front Distortion λ/10
Bragg Angle 1.4mrad 2.0mrad 36mrad 9mrad@450nm 25mrad
Input Impedance 50 ohms
Optical Polarization Linear Linear Linear Linear (vertical) Linear (vertical)
VSWR 2.1:1