Non-contact and non-invasive target detection in scattering media is a crucial task for advancements in biomedical imaging and environmental measurements. A novel sensing approach which combination of Michelson interferometer and ghost imaging (MIGI) is designed and developed for reconstructing the real image of target sample in scattering media. The limitations of optical interferometry, such as the need of scanning time for two-dimension measurements, and the inability of ghost imaging to capture cross-sectional images, can be effectively mitigated through their combination. However, this technique necessitates numerous illuminations of random structured light in ghost imaging to reconstruct the image of the target with high quality, thereby extending the measurement time. To address this issue and facilitate real-time measurement in MIGI, we reconstructed the real image close to the target sample being measured by passing degraded images obtained through short-term measurement through deep learning. This approach significantly reduces the number of measurements required to obtain a clear image in the simulation by 90%. In practical experiments, the number of measurements needed to achieve an equivalent structural similarity index method (SSIM) value is reduced. This paper discusses analysis of measurement time and SSIM based on the values of the dataset used for model construction.
Light detection and ranging (lidar) have been valuable tools in remote sensing of aerosols near the ground. For the operation of a lidar system, the laser, as a transmitter, plays a vital role in the whole system. Laser Diodes (LD) and Diode-Pumped Solid State (DPSS) laser technology have evolved, making the lidar system more compact compared to Nd:YAG laser sources. However, the lidar system’s long time and continual operation need maintenance to keep the laser source output stable. Also, the laser source is vulnerable to static electricity and needs to stabilize electric power. In this work, a multiwavelength lidar system with a Light Emitting Diode (LED)-based light source is designed and developed to monitor aerosol distribution in the near-ground atmosphere during continuous observation. The LED light source does not require any heat dissipation system and can emit light for long periods with constant output. The LED lamp light sources with wavelengths of 365, 450, 525, and 630 nm (peak power of up to 2W) are used as lidar transmitters. This lidar system visualizes rapid activities of aerosols in the near-range measurement due to its repetition frequency of over 250 kHz. Analysis of the backscattering light intensity with four wavelengths from this LED lidar system produces real time extinction coefficient and size distribution in the near-ground atmosphere. This report discusses the design and practical test of the multi-wavelength LED Lidar.
Laser beam propagation in highly scattering media has attracted much attention for optical sensing fields because the propagation of the light is often limited to the near-surface regions of the media. To increase the sensing capability in such scattering conditions, we focus on the propagation property of an annular beam in a highly scattering media. In our previous work, the non-diffractive beam was generated by propagating an annular beam in a scattering medium of colloidal suspension (diluted milk) up to the concentration of 22%, which is near the human tissue. In this study, the propagation property of a partially blocked annular beam using a fan-like obstacle with different apex angles is investigated to realize object detection in highly scattering media such as human tissue, fog, or cloud. Simulation results show that non-diffractive beams can be generated when partially blocked annular beam with blocking angle from 0° to 30o is propagated in free space. The propagation experiment of partially blocked annular beam in scattering media shows that the center peak intensity in scattered light is detected when the apex angle is set up to 30° . By measuring scattered light at different receiving distances, the experiment results show that the center peak is kept at a certain distance away from the optical cell. This result verifies that the central peak intensity of this scattered light is a non-diffractive beam.
We focused on the propagation property of an annular beam in strong scattering random media such as nimbostratus or dense fog. An annular beam as a lidar transmitted beam can propagate a longer distance even through atmospheric fluctuation. The reason is that an annular beam can self-transform to a non-diffracting beam, which is called non-diffractive effect. In this work, the center peak intensity as result of non-diffractive effect was generated after the propagation of an annular beam in random media with different concentrations and propagation distances. The linear relationship between the propagation distance and the transport mean free path calculated from the media concentration that caused the maximum center peak intensity was obtained. The generation condition of the non-diffractive beam was discussed under arbitrary parameters of beam diameter, propagation distance and media concentration.
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