Non-contact photoacoustic imaging using laser speckle contrast analysis

Non-contact detection of ultrasound with light - Review of recent progress

In this article, we present an overview of recent progress in non-contact remote optical detection of ultrasound in application to nondestructive testing and evaluation of materials. The focus of the review is on the latest advances in optical detection that offer mature and robust field-applicable solutions for diagnostics and imaging of engineered structures. We provide a detailed description of these solutions, including their operation principles, their evolution from the previously known designs to commercial devices, and their contribution to solving the most important problems associated with non-contact optical detection of ultrasound. Several application examples are presented to demonstrate the capabilities of optical detection and provide ideas to a reader on how it can be used in practice. We also discuss the main challenges of modern non-contact detectors which have not yet been addressed, as well as the directions and prospects for their development.

Spectral interference contrast based non-contact photoacoustic microscopy realized by SDOCT

We introduce a method to extract the photoacoustic (PA) signal from a contrast reduction of the interference spectrum acquired by spectral domain optical coherence tomography (SDOCT). This all-optical detection is achieved in a noncontact manner directly on the water surface covered on the sample by using its specular reflection. During SDOCT exposure, the phase of the interference spectrum keeps shaking according to the water surface vibration induced by PA excitation. This results in an interference contrast reduction which is quantified by a fast Fourier transform (FFT) for PA imaging. A tungsten filament, asparagus fern leaf, and mouse auricle are imaged to demonstrate the method.

All Optical Speckle Contrast-Based Vibration Sensor for Photoacoustic Signal Detection

Remote detection of photoacoustic signals is a well desired ability, enabling to perform advanced imaging in scenarios where contact is not possible. Various unique solutions have been suggested, including a camera-based speckle contrast photoacoustic detection. In this manuscript, a significant upgrade to the camera-based speckle contrast approach is presented and experimentally demonstrated. This solution is based on all-optical vibration sensing setup. The technique is based on spectral estimation of speckle pattern contrast and relies on several pre-developed works. First, it relies on the suggested application of speckle contrast to vibration sensing, and then on the realization of intensity pattern spectral manipulation, using a shearing interferometer. The method is evaluated and compared to traditional contrast estimation, and demonstrated in several applications in various vibration frequency band such as photoacoustic signal analysis and phonocardiographic heart sounds. The method is also applicable to measuring contrast changes due to a general speckle changing behavior, rather than surface vibration alone.

Photoacoustic measurement of localized optical dichroism in chiral crystals

In this communication, we present a novel method to measure local optical dichroism (OD) in opaque crystal powder suspensions using photoacoustic (PA) effect. Our method is based upon the novel laser speckle contrast technique, in combination with a simple statistical approach, we were able to measure the OD of chiral crystals suspensions under completely random orientation.

Towards non-contact photoacoustic imaging [review]

Photoacoustic imaging (PAI) takes advantage of both optical and ultrasound imaging properties to visualize optical absorption with high resolution and contrast. Photoacoustic microscopy (PAM) is usually categorized with all-optical microscopy techniques such as optical coherence tomography or confocal microscopes. Despite offering high sensitivity, novel imaging contrast, and high resolution, PAM is not generally an all-optical imaging method unlike the other microscopy techniques. One of the significant limitations of photoacoustic microscopes arises from their need to be in physical contact with the sample through a coupling media. This physical contact, coupling, or immersion of the sample is undesirable or impractical for many clinical and pre-clinical applications. This also limits the flexibility of photoacoustic techniques to be integrated with other all-optical imaging microscopes for providing complementary imaging contrast. To overcome these limitations, several non-contact photoacoustic signal detection approaches have been proposed. This paper presents a brief overview of current non-contact photoacoustic detection techniques with an emphasis on all-optical detection methods and their associated physical mechanisms.