Pulse Picker / Cavity Dumper

Pulse Picker / Cavity Dumper

Keywords: Pulse Picker / Cavity Dumper, AOM, AO, acousto-optic
Jan 14, 2021 View: 2086 Data Sheet

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.

Pulse pickers and cavity dumpers are high speed acousto-optic modulators which separate and pert 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 inpidual 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, our 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:

ModelWavelengthRise/Fall TimeActive ApertureOperating FrequencyOptical Material
13389-BR AOCD/AOPP350-850 nm6 ns60 μm389 MHzFused silica
17389-.93-FOA AOPP700-1064 nm7 ns70 μm389 MHzTellurium dioxide
I-M041-2.5C10G-4-GH501030-1064nm113 ns/mm2.5mm40.68MHzCrystalline quartz
I-M080-2C10G-4-AM31030-1064 nm113 ns/mm2 mm80 MHzCrystalline quartz
I-M080-2.5C10G-4-AM31030-1064nm113ns/mm2.5mm80MHzCrystalline quartz
I-M080-4C10G-4-GH601030-1064 nm113 ns/mm4 mm80 MHzCrystalline quartz
I-M150-0.5C10G-8-GH481064 nm30 ns0.5 mm150 MHzCrystalline quartz
I-M110-1C10G-8-GH481064 nm60 ns1 mm110 MHzCrystalline quartz

1030-1064nm Acousto-Optic Modulator: I-M041-2.5C10G-4-GH50

An acousto-optic modulator for use in the 1030 –1064nm wavelength range, ideal for extra-cavity modulation, power control or stabilisation of high power picosecond or nanosecond solid state lasers. Manufactured in Crystal Quartz for improved thermal management and high damage threshold. This modulator combines high quality optical finishing with high grade anti-reflection coatings to maintain superior beam quality and high optical throughput. In addition to the specifications indicated, we also offer alternative wavelengths, RF frequencies, active apertures & a wide range of custom housing configurations. We also offer full custom design & manufacturing, enabling our customers to achieve the perfect solution. Our scientists and engineers are available to assist in selecting the most appropriate Acousto-Optic device and RF driver for your application. Please contact our sales team for further information.

The applications cover industrial (material processing), pulse picking and laser intensity control.

General Specifications

  • Interaction material: Crystal Quartz

  • Wavelength: 1030-1064nm

  • Damage threshold: > 1GW/cm2

  • AR coating reflectivity: < 0·3% per surface

  • Transmission: > 99·4%

  • Frequency: 40.68MHz

  • Optical polarisation: Linear, vertical to base

  • Active aperture: 2.5mm

  • Acoustic mode: Compressional

  • Separation angle: 7.6mrad

  • Rise-time (10-90%): 113ns/mm

  • Diffraction Efficiency: 85%

  • Maximum RF power: 20W

  • Cooling: Conduction

Ordering Code:

Explanation: I-M041-2.5C10G-4-GH50 (Modulator, 41MHz, 2.5mm active aperture, compressional mode, Crystal Quartz, 1030 - 1064nm, SMA female pigtail, GH50 housing).

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-BRFSPP-380-76-BR
SubstrateTeO2SiO2
Laser Wavelength (nm)700 - 1200700 - 1200
Active Aperture (mm)0.100.10
Center Frequency (MHz)200380
Digital Modulation Bandwidth (MHz)4080
Optical Transmission (%)> 99.8> 99.8
Diffraction Efficiency (%)~ 40-50> 25
Rise time (nsec)146
Acoustic Velocity (m/s)4.2E+35.96E+3
RF Power Level (W)2 (50% duty cycle max.)10 (10% duty cycle max.)
Bragg Angle (mrad)2925
Separation Angle (mrad)5950
Wave Front Distortionλ/10λ/10
Input Impedance50 ohms50 ohms
Optical PolarizationLinearLinear
VSWR2:12:1
RF connectorSMASMA

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-380-95-543TECD-380-50-780TECD-380-95-800FSCD-250-54-BR-400FSCD-380-92-BR-800
SubstrateTeO2TeO2TeO2SiO2SiO2
Wavelength543nm780 nm800 nm250-450 nm800nm
Active Aperture0.30 mm0.30 mm0.10 mm0.10 mm0.10mm
Center Frequency380 MHz380 MHz380 MHz250 MHz380MHz
3dB Modulation Bandwidth95 MHz50 MHz95 MHz54 MHz92MHz
Optical Transmission>95%>95 %>98 %>98 %>98%
Max Diffraction Efficiency70%@1W40%@1W60%@2W70%@5W30%@10W
Rise time10 nsec20 nsec5.8 nsec10 nsec6nsec
Beam spot size31 um62 um29 um72 um42um
Acoustic Velocity4.2E+3 m/s4.2E+3 m/s4.2E+3 m/s5.96E+3 m/s5.96E+3m/s
Wave Front Distortionλ/10
Bragg Angle1.4mrad2.0mrad36mrad9mrad@450nm25mrad
Input Impedance50 ohms
Optical PolarizationLinearLinearLinearLinear (vertical)Linear (vertical)
VSWR2.1:1

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.  For associated RF Drivers, please see “RF Drivers for STBR series”.

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