Multi-component laser interferometry.
The Quartet 3D combines a Quartet platform and a Modulo-Quatro platform with a total of five collecting optical heads. This unlocks a new dimension in laser ultrasound testing by leveraging MCRQ technology and combining signals from multiple collecting heads. Using a single probe beam, it captures both out-of-plane and in-plane components of surface displacement, offering unparalleled insights into material behavior and wave dynamics. Optimized for scattering surfaces, this multi-component technology enables efficient detection of shear waves, especially when their propagation is normal to the inspection surface.
FEATURES
Robust & Versatile
Because the technology does not require control over the length of the optical path within the system, the Quartet 3D is not subject to stability issues common to most long cavity and path-stabilized interferometers. It does not require high accuracy optical components or positioning, making it exceptionally rugged.
3D Optical Head
Five simultaneous, independent measurements, resulting into the synchronized extraction of the out-of-plane and the two in-plane components (3D components). This is achieved by processing signals from multiple collection heads with different incidence and viewing angles. The five optical heads (one from the Quartet and four from the Modulo-Quatro) can be combined to form a super aperture for maximum light collection. This results in very high sensitivity (improved SNR) for detecting the component of ultrasonic displacement along the probe beam direction.
Analog & Digital Outputs
The Modulo produces both an analog and digital signal proportional to surface displacement.
High Sensitivity on all Surface Types and Materials
With the Quartet 3D, which combines a single laser probe beam at normal incidence with multiple collecting heads from different directions, the sensitivity to the out-of-plane component is never compromised — even in the case of highly specular surfaces where in-plane components cannot be effectively measured. The out-of-plane component will exhibit high SNR as long as the specular reflection is captured by at least one of the five collecting apertures.
Inspection on Rapidly Moving Objects
Streamlined electronic processing allows the Quartet to perform single shot measurements on fast-moving objects, at speeds up to meters per second.
Not Wavelength Dependent
The Quartet 3D can be fitted with a range of internal laser wavelengths ranging from visible to infrared.
Signal Indicators
Incorporated within the system are visual and audible signal indicators designed to help the user optimize their measurement setup. The Quartet also includes an internal calibration signal allowing for a calibrated output at 100mV per nanometer of displacement.
Upgrades and Add-ons
Beam Chopper
The beam chopper is an optional feature which allows the system to be used on materials with poor heat conductivity, such as plastics or carbon fiber materials without damaging the surface. A perforated disk synchronized with the generation laser “chops” the beam at a regular interval in order to prevent the sample from being exposed to continuous laser power. This feature does not affect the quality of the signal as it allows the laser to be used at full power, in contrast to alternative solutions such as using continuous but low laser power systems. Once installed, the chopper can be turned on and off to suit the application. This upgrade is compatible with new generation Quartets and is easily installed by replacing the top cover of the system.
Motorized Optical Head
The motorized optical head features a high-precision lead screw (TR82), facilitating a linear displacement of 2mm per revolution for fine focus control.
To ensure maximum operational flexibility, the optical head supports dual-mode functionality:
Remote Digital Control: Seamlessly interface with a computer for automated or long-distance adjustments.
Manual Override: Utilize the integrated external command for direct, tactile positioning.
TECHNICAL SPECIFICATIONS
TECHNOLOGY
Multi Channel Random Quadrature
DETECTION
In-plane & Out-of-plane
CONFIGURATION
Optical FIber
INTERNAL LASER POWER
Up to 3W
BEST NESD (out of plane motion)
2.10-6 nm/Hz1/2
DETECTION BANDWITH
Up to 60MHz
DIMENSIONS (L*W*H)
490*450*170 mm
WEIGHT
18Kg
ELECTRICAL REQUIEREMENTS
110V/50Hz – 220V/60Hz
TECHNOLOGY
The Quartet receiver combines the advantages of homodyne interferometry with the benefits of multi-detector technology. The beam reflected by the sample’s rough surface is comprised of many speckles. The multi-speckled signal beam is combined with the reference beam and focused on 50 photo-detectors. Each detector collects a few speckles and delivers a homodyne signal.
Each homodyne signal is processed in parallel using a patented signal processing architecture. The signal processing is based on a “random quadrature” demodulation scheme which takes advantage of the random phase distribution inherent to speckle light.
More about MCRQ (Multi Channel Random Quadrature)
Rational
The idea behind Multi-Channel Random Quadrature was to devise a laser-ultrasound technology with a robust, compact design and a large depth-of-field capable of functioning effectively in a wide range of environments without loses in sensitivity, including on rough surfaces. With support from the National Science Foundation and NASA, we developed the Quartet. By collecting and processing a multitude of speckles, the Quartet is fully functional in environments which would otherwise be unsuitable for most other receivers and can perform measurements on all surface types — from mirror-like to rough surfaces.
Multi Channel
Two detector arrays of 25 elements each allow the Quartet to collect more speckles than a standard receiver, which in turn translates to high sensitivity. To put it another way, employing MCQR technology is equivalent to using 50 Michelson interferometers in parallel.
The Quartet does not need to be stabilized as it relies on the random nature of speckles. Statistically, the speckle phase has a uniform distribution, meaning that it is 50% in-quadrature and 50% out-of-quadrature. The out-of-quadrature components don’t contribute to the signal, which is why we use 25 photodiodes on two detectors. Demodulation is required for both the in-phase and out-of-phase signals.
Optical Design
A laser beam generated by the internal laser passes through multiple optics within the receiver before being focused into a multimode fiber. At the end of the fiber, around 4-5% of the light is reflected back towards the receiver due to a natural optical phenomenon while the rest is focused onto the sample. The diffuse light reflected by the sample surface is collected by a large lens located at the front of the optical head, maximizing the quantity of speckles gathered for signal processing. The speckled beam then travels back through the optical fiber, interfering with the 4-5% partial reflection previously mentioned. It is important to note that the light polarization components are scrambled while traveling back through the multimode fiber. Once back in the system, the beam travels through a first Polarized Beam Splitter (PBS) which isolates the vertical polarization component and is in turn directed towards one of the two detector arrays. The rest of the beam travels through an Optical Isolator, which consists of a Faraday rotator and a PBS. This second PBS then sends the vertical (previously horizontal) component of the returning signal-beam back towards the second Multi-Channel Detector. Every signal from the photodiodes will be processed in parallel by an electronic demodulation.
Rectified Demodulation
Because of the random nature of the phase of each of the 50 signals detected, the quartet is designed to perform signal rectification without consideration of phase. The streamlined electronic processing allows the Quartet to perform single shot measurements on fast-moving objects. Rectified Demodulation is also effective at rejection of background noise vibration.
Rectified Demodulation alone has a few downsides: it has a high-frequency and small-displacement limitation, and the direction of displacement is unknown. Therefore, the Quartet also uses Linear Demodulation.
Linear Demodulation
Linear Demodulation is a similarly compact multi-channel architecture, but with a demodulation scheme that yields an output signal proportional to the wave-displacement. It is composed of a transimpedance followed by a logic control which detects the signal phase and switches between two summing amplifiers: one receives the in-phase and the other the out-of-phase signals. Lastly, both phases of the signal pass through a differential amplifier.
PATENTS.
Patent US7978341
Multi-channel laser interferometric method and apparatus for detection of ultrasonic motion from a surface.