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.
|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|
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.
|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|
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.
|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|
|Input Impedance||50 ohms|
|Optical Polarization||Linear||Linear||Linear||Linear (vertical)||Linear (vertical)|