Mode Locker

  • Update:Jun 13, 2017
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An acousto-optic mode locker (AOML) modulates the loss within a laser cavity at its resonant frequency effectively locking the phase of the longitudinal modes to generate very narrow laser pulses of high intensity.

Product Introduction

An acousto-optic mode locker (AOML) modulates the loss within a laser cavity at its resonant frequency, effectively “locking” the phase of the longitudinal modes to generate very narrow laser pulses of high intensity. G&H standing wave mode lockers yield near-theoretical mode locked laser pulse widths, with industry-leading transmission performance. Available in antireflection (AR) coated and Brewster angle options, they can also be customized for demanding one-off scientific and OEM applications. We combine extensive AO device design experience with strict manufacturing controls to deliver high-Q (very low loss) mode lockers with minimal extraneous modes, achieving picosecond and femtosecond length pulses at repetition rates of up to 200 MHz. To ensure high quality and reliability lockers use high quality fused silica, polished and fabricated in-house. Greater than 99% transmission at 1064 nm is achieved with a durable in-house antireflection V-coat. Transmission over a broader range of wavelengths (700-1100 nm) can be achieved using windows cut to the Brewster angle. Low scatter and tight quality controls ensure that every mode locker is capable of handling high peak laser power over the long term without damage.

RF driver selection impacts mode locking system performance, as active temperature control of the acoustic resonator can assist in controlling resonant frequency such that resonance at the precise frequency of the driver’s oscillator can be maintained. G&H can assist in choosing the right driver for your application, advising on how performance of each RF driver will influence mode locking efficiency and pulse width.

Our standard models are below:

Model Wavelength Window Type Active Aperture Operating Frequency Optical Material
I-ML041-3C4G-3-GH101   1064 nm AR coated 3 mm 41 MHz Fused silica
I-ML080-3C4G-3-GH101 1064 nm AR coated 3 mm 80 MHz Fused silica
I-ML041-4.5C4R4-3-GH102 700-1100 nm Brewster 4.5 mm 41 MHz Fused silica
I-ML080-4.5C4R4-3-GH102 700-1100 nm Brewster 4.5 mm 80 MHz  Fused silica

STBR free space Mode Lockers

The STBR Free Space Acousto-Optic (AO) Standing Wave Mode Lockers, with corresponding RF Variable Frequency drivers, are designed so the frequency matches the customer's laser resonant cavity longitudinal mode frequencies. It is necessary to adjust the resonant laser cavity mode spacing frequency to be equal to twice the original acoustic wave frequency to achieve mode locking. The mode-locking technique is actually a phaselocking process, connecting the various longitudinal modes by fixing the relative phase differences among them.
Our STBR serie Mode Lockers are below:

Model # FSML-40-20-BR- 800  FSML-80-20- BR1064 FSML-125-30- BR800 FSML-125-30- BR1064
Substrate Fused Silica Fused Silica Fused Silica (uncoated) Fused Silica (uncoated)
Brewster cut Brewster cut optimizes for horizontal polarization at:
Laser Wavelength (nm) 800 1064 800 1064
Active Aperture (mm) Up to 5 x 5 mm Up to 5 x 5 mm Up to 5 x 5 mm Up to 5 x 5 mm
Carrrier Frequency (MHz) 40 80 125 125
Modulation Rate (MHz) 80 160 250 250
3dB Bandwidth +-50 +-10 +-15 +-15
Optical Transmission 99.7% 99.7% 99.7% 99.7%
Resonant Modulation Depth 70% 60% 50% 30%
Acoustic Velocity (m/s) 5.96E+3 5.96E+3 5.96E+3 5.96E+3
Wave Front Distortion λ/10 λ/10 λ/10 λ/10
Input Impedance 50 ohms 50 ohms 50 ohms 50 ohms
Maximum Electric Input Power 5-7 Watts 5-7 Watts 5-7 Watts 5-7 Watts
VSWR N/A N/A N/A N/A
Case Type Water cooled Water cooled Water cooled Water cooled

For the associated RF drivers, please refer to “RF Drivers for STBR series”. For Q-switches, you can consider RF Driver model STBR-VFE-XX-YY-DSP1kHz-B2-F7-X. The VFE-XX-YY-DSP1KHz-B2-F7-X is a variable frequency driver operating from 40 MHz to 60 MHz. The frequency adjustment is done via front panel switches with a 1 KHz step size. The output RF power is ~7 Watts optimized for maximum performance of the AO device. A TTL-compatible modulation input is provided to turn “off” the mode-locking function. Also, using the “return voltage read-out” output can identify the resonant or non-resonant frequencies. At resonant frequency, most of the RF energy entering the crystal is absorbed and the minimal back reflection is monitored using this port

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