Pulse Picker / Cavity Dumper

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:

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

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

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”.