KEYWORDS: Light emitting diodes, Signal to noise ratio, Photoacoustic spectroscopy, Photoacoustic imaging, Pulse signals, Signal processing, Laser systems engineering, Autocorrelation
Photoacoustic imaging is a new imaging technique that can measure optical absorbers with high resolution. Lasers are commonly used as light sources for photoacoustic imaging, but there are many safety restrictions. Therefore, devices in which the light source is replaced by LEDs, which have fewer safety restrictions, are attracting attention. However, LED light sources have very low energy, and the photoacoustic signal generated is correspondingly small. Therefore, the photoacoustic signal is buried in noise, resulting in a low signal-to-noise ratio (SNR). Averaging can also improve SNR, but it is difficult to maintain a high frame rate. M-sequence signal processing can improve SNR while maintaining a high repetition rate, and its effectiveness has been demonstrated in photoacoustic measurements of laser light sources. However, LED power supplies have time delays in emission and circuit jitter, which affect decoding. Therefore, we propose a new decoding algorithm that compensates for LED jitter. We then experimentally verified the SNR improvement using this signal processing in practice.
While artificial cultivation is gaining prominence due to rapid climate change, lighting costs remain a challenge. Therefore, research is needed to cultivate plants more efficiently. At the same time, it has been found that a mixture of far-red light (FR) and red light (R) also promotes growth through the action of phytochrome, a photoreceptor in the plant body. However, these studies require time and damaging of the plant to measure the dry mass and area of leaves, and immediate effects have not been investigated so far. Therefore, in this study, we propose laser biospeckle to evaluate the relationship between plant growth duration and FR response. Laser biospeckles are formed by light scattered from organelles in plant tissues by laser irradiation. The intensity of these speckles changes with time, and by examining these changes, the activity inside the plant can be evaluated. Biospeckles of arugula leaves were obtained by irradiating the leaves with laser light of wavelength 852 nm and simultaneously with LED light of wavelength 735 nm (FR) and 630 nm (R). Biospeckle movies under FR and non-irradiation were recorded by a CMOS camera at 15 frames/sec for 20 seconds. From the movie, correlation between the first frame and the subsequent frames were calculated. Experimental results showed that arugula at 1-month after seed planting showed an immediate FR response, while those at 3-month showed a sustained response. The relationship between biospeckle movement and plant growth behaviour is under investigation.
Sound has been established to play an essential role in plant growth. Sound of a particular frequency has been proven to increase yield and immunity. In this study, we have considered the possibility of functional Optical Coherence Tomography (fOCT) in investigating the changes in the internal structures in response to sounds of different frequencies, 100 Hz and 10kHz. Results showed a clear dependence of the fOCT signal on the sound frequency, with 100 Hz showing an increase while 10kHz showing a decrease. Our results extend the possibility of the application of OCT to the field of plant photonics.
Existing method of surveying supermicroplastics (fragments ≤ 350 µm) in sea remains a challenge. To this end, we propose a new method based on laser speckles and two submersible spheres. In simulation experiments, a 630 nm laser illuminated a cuvette containing polystyrene particles and zooplanktons producing speckles recorded by a CMOS camera. Speckles were analyzed to discriminate different sized polystyrene spheres (2 μm, 20 μm and 200 μm) and zooplanktons. As discrimination algorithms, difference of subsequent frames of the speckle movie and deep learning were investigated. Deep learning was found to be capable of distinguishing speckles from different particle sizes.
In recent years, it has been found that sound also has effect on plant growth and its yield with certain sound directing the seedling of corn toward the sound source and its ability in distinguishing stuttering of larvae from other sounds. However, methods investigating the effects of sound either take a long time or destructive. Here, we have used laser biospeckle, a non-destructive and non-contact technique to investigate the activities of an arugula plant (2-4 weeks old) under sounds of different frequencies of 0 Hz or control, 100 Hz, 1 kHz, 10 kHz. Laser biospeckle has been proved to be valid for investigating the aging of fruits, believed to be due to the movement of water, organelles etc.. Biospeckle activities were recorded for 20 sec at 15 fps following exposure to sounds for 1min. The correlation parameter (r) of biospeckle activity was used to characterize the activity of the plant with r being 1 for highly active and 0 for reduced plant activity. Sound level of 100 dB was the same for all frequencies. There was a clear difference in r between the control and other frequencies and r was lower than that of control indicating a reduction in the activity. Moreover, r for 100 Hz was found to be closer to control while at higher frequencies, r was much lower indicating a dependence of the activity on the frequency.
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