Keywords: Mode Locker, AOM, AO, acousto-optical
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.
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. Our 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||Operating Frequency||Active Aperture||Window Type||Optical Material|
|I-ML041-3C4G-3-GH101||1064 nm||41 MHz||3 mm||AR coated||Fused silica|
|I-ML080-3C4G-3-GH101||1064 nm||80 MHz||3 mm||AR coated||Fused silica|
|I-ML041-4.5C4R4-3-GH102||700-1100 nm||41 MHz||4.5 mm||Brewster||Fused silica|
|I-ML080-4.5C4R4-3-GH102||700-1100 nm||80 MHz||4.5 mm||Brewster||Fused silica|
|12080-3-TE||1064nm||80MHz||3mm||AR coated||Fused silica|
|12083-3-TE||1064nm||38MHz||3mm||AR coated||Fused silica|
|12041-3-TE||1064nm||41MHz||3mm||AR coated||Fused silica|
|12050-3-TE||1064nm||50MHz||3mm||AR coated||Fused silica|
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|
|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|
|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