A method that detects the location of undesired levels of signal loss for DAS systems. In the method, raw data is received from a DAS system with dual photodetector. Statistics are obtained from the received raw data, then processed according to the dual photodetector. The obtained statistical data are reconstructed to remove noise and the reconstructed signal is used to form the power statistics of the DAS signal in each channel. The power statistics are expected to be linearly decreasing with the distance from the sensor. A change detection algorithm is developed to detect the possible undesired levels of signal loss and to find the location of the signal loss.

A laser system for acousto-optics imaging is disclosed. The system comprises: a continuous wave laser source; a first beam splitter configured to split a laser emitted by the continuous wave laser source into a lasing beam and a reference beam; a lasing optical fiber diffusing the lasing beam to a subject; a reference optical fiber providing the reference beam; a collecting optical fiber capable of receiving a scattered beam from the subject; a second beam splitter for merging the scattered and reference beams into a merged beam, and at least one photodetector assembly with a bandwidth higher than the ultrasound frequency to detect the merged beam.

A laser system for acousto-optics imaging is disclosed. The system comprises: a continuous wave laser source; a first beam splitter configured to split a laser emitted by the continuous wave laser source into a lasing beam and a reference beam; a lasing optical fiber diffusing the lasing beam to a subject; a reference optical fiber providing the reference beam; a collecting optical fiber capable of receiving a scattered beam from the subject; a second beam splitter for merging the scattered and reference beams into a merged beam, and at least one photodetector assembly with a bandwidth higher than the ultrasound frequency to detect the merged beam.

A method and a system for photoacoustic inspection of a part are provided herein. The method may include the following steps: photo-acoustically exciting a predetermined position in a predetermined region on a part by pulsed laser illumination, to yield ultrasonic excitation of the part; coherently illuminating a predetermined location in the predetermined region on the part; detecting an illumination scattered from the predetermined location; determining, based on the scattered illumination, a plurality of sequence of two or more temporally-sequential de-focused speckle pattern images, wherein each of the sequences corresponds to one of the predetermined illuminated locations; and determining a set of translations, each determined based on the sequences, wherein each translation in the set is determined based on two temporally-sequential speckle patterns images in the respective sequence.

A method and a system for photoacoustic inspection of a part are provided herein. The method may include the following steps: photo-acoustically exciting a predetermined position in a predetermined region on a part by pulsed laser illumination, to yield ultrasonic excitation of the part; coherently illuminating a predetermined location in the predetermined region on the part; detecting an illumination scattered from the predetermined location; determining, based on the scattered illumination, a plurality of sequence of two or more temporally-sequential de-focused speckle pattern images, wherein each of the sequences corresponds to one of the predetermined illuminated locations; and determining a set of translations, each determined based on the sequences, wherein each translation in the set is determined based on two temporally-sequential speckle patterns images in the respective sequence.

Systems and methods for Geiger-mode laser vibrometry are described. An example method for laser vibrometry includes receiving a first time-series of single photon arrivals corresponding to a laser beam reflected from or transmitted through a target, the single photon arrivals including information corresponding to vibrations of the target, each single photon arrival separated in time from another single photon arrival, determining, based on two or more of the single photon arrivals, a discrete time sequence having a binary value, and generating a second time-series by assigning a non-binary value to each of the discrete time points, wherein each of the assigned non-binary values is determined based on a number of discrete time points lacking a photon arrival prior to receiving a photon.

A vibrometer may measure acoustic responses in portions of a structure along a scan path to acoustic excitation of the structure. A ranging device may measure distances to the portions of the structure along the scan path. A three-dimensional point cloud may be generated based on the acoustic responses in the portions of the structure and the distances to the portions of the structure. The three-dimensional point cloud may include points representing geometry of the portions of the structure. The points may be associated with the acoustic responses in corresponding portions of the structure. One or more properties of the structure may be determined based on an analysis of the three-dimensional point cloud.

Systems and methods are provided for generating a model for detection of seismic events. In this regard, one or more processors may receive from one or more stations located along an underwater optical route, one or more time series of polarization states of a detected light signal during a time period. The one or more processors may transform the one or more time series of polarization states into one or more spectrums in a frequency domain. Seismic activity data for the time period may be received by the one or more processors, where the seismic activity data include one or more seismic events detected in a region at least partially overlapping the underwater optical route. The one or more processors then generate a model for detecting seismic events based on the one or more spectrums and the seismic activity data.

A sensor includes a first element part having a first member and a first element. The first member is a acoustic tubular waveguide and extends along a first direction. The acoustic tubular waveguide includes a first opening and a second opening. A direction from the second opening toward the first opening is along the first direction. The first element includes a vibratile first membrane, and a first supporter supporting the first membrane. The second opening is between the first opening and the first membrane in the first direction. The sensor may be a Piezoelectric Micro electro mechanical systems Ultrasonic Transducer and may be used for inspecting paper and/or resin including detecting thickness of a fed through banknote and/or the presence of foreign matter thereon such as tape. An optical element may alternatively measure the vibration of a membrane from acoustic through transmission instead of an acoustic receiver.

A sensor includes a first element part having a first member and a first element. The first member is a acoustic tubular waveguide and extends along a first direction. The acoustic tubular waveguide includes a first opening and a second opening. A direction from the second opening toward the first opening is along the first direction. The first element includes a vibratile first membrane, and a first supporter supporting the first membrane. The second opening is between the first opening and the first membrane in the first direction. The sensor may be a Piezoelectric Micro electro mechanical systems Ultrasonic Transducer and may be used for inspecting paper and/or resin including detecting thickness of a fed through banknote and/or the presence of foreign matter thereon such as tape. An optical element may alternatively measure the vibration of a membrane from acoustic through transmission instead of an acoustic receiver.