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Reliable seed screening that can speedily detect qualities such as dormancy and seed germination can be of great significance in improving plant growth, crop yield, and quality. On the other hand, Optical Coherent Tomography (OCT) has been extensively used as a potential tool in visualizing structures of biological objects, especially the retina. However, its role in visualizing temporal changes that accompany these structures as speckle noise remains relatively underexplored. The present study of biospeckle OCT or bOCT demonstrates the potential of speckles in plant physiological studies. In this paper, the potential of bOCT in speedily investigating the positive and negative phenotyping of increasing Zn concentrations on lentil seed (Lens culinaris) germination and seedling growth were demonstrated. Lentil seeds were exposed to three different Zn concentrations of 0 (control), 5, 10, and 100 mg/L for 24 h, and the structural OCT images were acquired to calculate the temporal fluctuations in the image as a quantity called the average speckle contrast (γ). The average speckle contrast was calculated after 6 h, 12 h, and 24 h of exposure to different concentrations. Statistically significant differences were observed even within 12 h of exposure under all the Zn treatments compared to control. In comparison, the conventional measurements of germination rate, root and shoot lengths, and fresh and dry weights of seedlings took nearly 48 h to observe significant changes. Furthermore, the Zn uptake measurements were significant for all the tested concentrations after seven days of exposure. Further, bOCT results showed a clear concentration dependent effect with 5, 10 mg/L producing positive effects, while a high concentration of 100 mg/L showing a detrimental effect on seed germination and seedling growth. Thus, the current study results imply that bOCT can be used to investigate the positive and negative effects of increasing Zn concentrations on seed germination and seedling growth at an early stage before germination.

In recent years, it is becoming clearer that plant growth and its yield are affected by sound with certain sounds, such as seedling of corn directing itself toward the sound source and its ability to distinguish stuttering of larvae from other sounds. However, methods investigating the effects of sound on plants either take a long time or are destructive. Here, we propose using laser biospeckle, a non-destructive and non-contact technique, to investigate the activities of an arugula plant for sounds of different frequencies, namely, 0 Hz or control, 100 Hz, 1 kHz, 10 kHz, including rock and classical music. Laser biospeckles are generated when scattered light from biological tissues interfere, and the intensities of such speckles change in time, and these changes reflect changes in the scattering structures within the biological tissue. A leaf was illuminated by light from a laser light of wavelength 635 nm, and the biospeckles were recorded as a movie by a CMOS camera for 20 sec at 15 frames per second (fps). The temporal correlation between the frames was characterized by a parameter called biospeckle activity (BA)under the exposure to different sound stimuli of classical and rock music and single-frequency sound stimuli for 1min. There was a clear difference in BA between the control and other frequencies with BA for 100 Hz being closer to control, while at higher frequencies, BA was much lower, indicating a dependence of the activity on the frequency. As BA is related to changes from both the surface as well as from the internal structures of the leaf, LSM (laser scanning microscope) observations conducted to confirm the change in the internal structure revealed more than 5% transient change in stomatal size following exposure to one minute to high frequency sound of 10kHz that reverted within ten minutes. Our results demonstrate the potential of laser biospeckle to speedily monitor in vivo response of plants to sound stimuli and thus could be a possible screening tool for selecting appropriate frequency sounds to enhance or delay the activity of plants. (337 words)

In this study, fractal geometry was applied to characterize the complexity of the root system morphology of wheat plants under the exposure of heavy metals, namely cadmium (Cd), copper (Cu) and zinc (Zn). We proposed a measure called, relative complexity index (RCI), a ratio based on fractal dimension (FD) before and after exposure to heavy metals. FDs were calculated by box-counting method with digitized and skeletonized images of roots of wheat plants cultivated in hydroculture system. RCI, and relative weight were mesuared under different concentrations of Cd (0.001, 0.01 and 0.05 mM), Cu (0.016, 0.4 and 1.2 mM) and Zn (0.3 and 0.75 mM). Results showed significant reduction of RCI for Cd stress with 0.01 and 0.05, all Cu concentrations and promotion at all zinc concentrations. In comparison, no statistically significant changes were found in conventional relative weight measurement at low concentrations of Cu, Cd and Zn. RCI were more sensitive and were reliable in reflecting the influence of heavy metals than the conventional measure. These results imply that RCI can be an effective measure of the negative and positive effects of heavy metals on the development of complexity of root system under heavy metal exposures.

In the study, we have combined speckle metrology and deep learning tools in discriminating supermicroplastics (SMPs) sizes and concentrations. Polystyrene spheres used as SMPs were introduced in the container filled with salt water. The particles were illuminated with the 635 nm laser, and the scattered light was recorded with the CMOS camera. For the simulation studies, different sized particles (2 µm, 20 µm, and 200 µm) and concentrations were used. Speckles were analyzed using a deep learning algorithm to distinguish particles sizes and concentrations. It was demonstrated that the convolutional neural networks (CNNs) trained with speckles could distinguish feeble differences in speckle patterns depending on particle sizes and concentrations. Deep learning was found to be capable of distinguishing different particle sizes and concentrations from the speckle patterns. We suggest our combined technique could be effectively used in investigating MPs in the ocean where it remains challenging to conduct in situ surveys and obtain the SMP distribution in deeper regions of the ocean.

Acid mine drainage is a serious environmental problem faced by the mining industry globally, causing the contamination of numerous agricultural lands and crops. Against this background, this study aims to investigate the effects of AMD on soybean, one of the major crops. To monitor the effects of AMD on soybean quickly and non-destructively, we have proposed a technique called biospeckle optical coherence tomography (bOCT). Soaked soybean seeds were monitored by bOCT, once after 6 h and again after germination, i.e., 48 h, and the results were compared with conventional parameters such as enzyme activity, iron uptake, and seedling length. It was found that bOCT could detect the effects due to the AMD after just 6 h with a decrease in a parameter called bisopeckle contrast that reflects the internal activity of the seeds. On the other hand, the conventional parameters required a week for the effects to appear, and the results from bOCT after six hours were consistent with those obtained by conventional measures. Because of the non-invasive nature of bOCT, requiring only tens of seconds of measurement with an intact, it has not only the potential to screen but could also constantly monitor long-term changes, thus possibly contributing to the study of the effects of AMD on crops.

Widespread use of plastics and mishandling has resulted in severe environmental issues affecting seed germination and seedling growth. This study investigates the effect of polyethylene microplastics (740-4990 nm PEMPs) on lentil (Lens culinaris) seed germination and seedling growth using Biospeckle Optical Coherence Tomography (bOCT), a technique that we successfully demonstrated earlier in visualizing the internal activity of plants. Lentil seeds were exposed to PEMPs bioassay for seven days with 10, 50, and 100 mg L

Statistical interferometric technique (SIT) is a highly sensitive, high speed non-contact, and non-destructive optical technique developed by our group capable of measuring instantaeoues sub-nanometer displacements. SIT applied to plant leaf elongation revealed nanometric intrinsic fluctuaitons (NIF) that are robust and sensitive to variations in the environment making NIF as a measure of healthiness of the plants. In this study, exogenous plant hormones, auxin (2,4-dichlorophenoxyacetic acid-2,4-D), and gibberellic acid (GA(3)), along with an auxin transport inhibitor 2,3,5-triiodobenzoic acid-TIBA, that affect plant growth were used to investigate their effects on NIF. Rice (Oriza sativa) seedlings were used, and their roots were exposed to 1, 2, and 4 µM 2,4-D, and the auxin transport inhibitor, TIBA, of 10, and 20 µM for 22 h and GA(3) solution of different concentrations of 10, 40, and 100 µM for 5 h. Results showed significant increment in NIF for 1 µM and reduction for 4 µM 2,4-D while applicaiton of both 10, and 20 µM TIBA led to reduction in NIF. On the other hand, significant increment in NIF for 40 µM, and a significant reduction at a higher concentration of 100 µM for 5 hours of GA(3) were also observed in comparison to those of control. Our results indicate that NIF as revealed by SIT could show both the positive and negative effects depending on the concentration of exogenous hormones, and transport inhibitors. Results suggest that SIT could be a valuable tool being sensitive enough to speedily assess the effects of plant growth hormones.

Plant growth apart from being a complex and highly dynamic is dependent on its immediate environment. Leaf expansion measurements using Statistical Interferometry Technique, a sensitive interferometric technique at nanometric accuracy and at sub-second levels revealed the presence of characteristic nanometric intrinsic fluctuations [Plant Biotechnology 31, 195 (2014)]. In this paper, we demonstrate that the nanometric intrinsic fluctuations are sensitive enough that they change under exposure of heavy metals, essential micronutrient zinc and non-essential element cadmium, at relatively low concentrations in the leaves of Chinese chive (Allium tuberosum). The nanometric intrinsic fluctuations of leaves were observed for 4h under three cadmium concentrations or two zinc concentrations. Results showed significant reduction of nanometric intrinsic fluctuations for all cadmium concentrations, and in contrast significant increase of nanometric intrinsic fluctuations for all zinc concentrations. There was significant reduction of nanometric intrinsic fluctuations for cadmium exposure of concentrations of 0.001mM for even an hour, and significant increment of nanometric intrinsic fluctuations under 0.75mM zinc from 1hr exposure. For comparison, antioxidative enzymes and metal uptake were also measured under 4hr exposure of cadmium or zinc. However, no significant changes could be seen in antioxidative enzymes within 4h under the smaller concentration of 0.001mM cadmium as seen for nanometric intrinsic fluctuations. The results imply that nanometric intrinsic fluctuations can be not only used as a measure for heavy metal stress but also it can be more sensitive to detect the toxic as well as positive effects of smaller amounts of heavy metal on plants at an early stage.

Crop yields are frequently affected by the vigor of seeds. Although germination tests and vigor tests are performed on sampled seeds to ensure the quality of seeds, selection of crops is based on the appearance or physical properties of roots and shoots of seedlings. Monitoring of the biological activities of seed by biospeckle Optical Coherence Tomography (OCT) was proposed for the selection of seeds. Biospeckle OCT used speckle contrast, which is defined by the ratio of standard deviation to mean value, of the temporal fluctuation of OCT intensities to indicate the biological activities of seeds. Seeds of pea were germinated for the experiment. As a comparison of the level of biological activities, some seeds were boiled to terminate the biological activities. Multiple OCT scans at the same positions on the seeds were obtained for the analysis of biospeckle. The speckle contrast was calculated for each pixel of OCT intensities at each measurement. Increased speckle contrast was observed in the seeds even before the radicle emerged. Low speckle contrast was observed in the boiled seeds. As a conclusion, the speckle contrast of OCT intensities indicated biological activities of seeds in the process of germination. It has the potential to indicate if a seed is dead or alive in an early stage of germination for the purpose of seed selection.Crop yields are frequently affected by the vigor of seeds. Although germination tests and vigor tests are performed on sampled seeds to ensure the quality of seeds, selection of crops is based on the appearance or physical properties of roots and shoots of seedlings. Monitoring of the biological activities of seed by biospeckle Optical Coherence Tomography (OCT) was proposed for the selection of seeds. Biospeckle OCT used speckle contrast, which is defined by the ratio of standard deviation to mean value, of the temporal fluctuation of OCT intensities to indicate the biological activities of seeds. Seeds of pea were germinated for the experiment. As a comparison of the level of biological activities, some seeds were boiled to terminate the biological activities. Multiple OCT scans at the same positions on the seeds were obtained for the analysis of biospeckle. The speckle contrast was calculated for each pixel of OCT intensities at each measurement. Increased speckle contrast was observed in the seeds even before the radicle emerged. Low speckle contrast was observed in the boiled seeds. As a conclusion, the speckle contrast of OCT intensities indicated biological activities of seeds in the process of germination. It has the potential to indicate if a seed is dead or alive in an early stage of germination for the purpose of seed selection.

As a critical factor for the resources acquisition of water and nutrient, the root system responding the in-situ environment includes root length, root weight, root branching density, root hair density etc. Fractal geometry has been used to describe the complexity of many objects in nature such as leaves, trees, sea shores and so on. The aim of this study is to use fractal geometry in examining the developmental responses of the root system under a heavy metal stress, namely, Cd stress. Based on fractal geometry, fractal dimension (FD) was evaluated and comparison with conventional measurements was done. Wheat plants that were grown in hydroculture system for three weeks under different concentrations, 0, 0.001, 0.01, and 0.05mM of Cd were used as samples. Photographs of the entire root systems of the plants were taken weekly with a digital camera for three consecutive weeks, and then, they were used for analysis. The analysis of the images involved segmentation and skeletonization followed by application of box-counting method to calculate the FD. The changes of FD in response to different Cd stresses were examined. The results indicate that FDs under Cd stress were lower than those for the control condition. The results demonstrate that FD can be an effective measure to describe the changes in the structural development of the root system under heavy metal stress. It was also found that FD was more sensitive to changes under the influence of the heavy metals than those of the conventional measurements.

Instantaneous growth related changes of leaves of Radish, Soybean and rice plants were investigated with a highspeed and ultra-high accuracy optical interferometer. The interferometer, called statistical interferometer, SIT (Statistical Interferometric Technique) is a real-time, non-contact, and robust one and has a subnanometric accuracy and can measure leaf elongation changes every 500 ms. SIT revealed the existence of nanometric fluctuations in the elongation of leaves. Control experiments with dead and mature leaves did indeed establish the existence of null or smaller standard deviations in the fluctuations in contrast to the large deviations obtained for young and healthier leaves. Moreover, the standard deviations of the fluctuations were found to be sensitive to environment of ozone(O3), a secondary atmospheric pollutant. Long term O3 exposure with Radish and Soybean leaves led to a decrease in the standard deviations of nanometric fluctuations with increase in O3 concentrations which correlated with a decrease of gas exchange measures. Under short term O3 exposures for 3 h with two Japanese rice cultivars, cv. Koshihikari and cv. Fusaotome that are known to have varying O3 tolerance made the nanometric fluctuations to decrease in comparison to gas exchange measures which showed no variation. The fluctuations could also differentiate the cultivar’s sensitivity to O3 with cv. Koshihikari showing a drastic reduction in comparison to cv. Fusaotome. The results suggest that the nanometric fluctuations may possibly relate to the life maintaining physiological state of the plant and thus may act as an indicator of the vitality of the plant.

This study presents a new technique to measure root elongation of Japanese red pine ( Pinus densiflora Seibold & Zucc.) seedlings with very high sensitivity in the order of sub-nanometer by using a novel optical interference method called statistical interferometry. The principle of the statistical interferometry is based on the statistics of a speckle field, which is generated when a rough surface is illuminated by a laser light. The technique facilitates to obtain minute root elongation measurements in the order of sub-seconds. The root elongation behavior of Pinus densiflora seedlings infected with ectomycorrhizal fungi, Pisolithus sp. ( Ps ) and Cenococcum geophilum Fr. ( Cg ), was investigated in comparison with that of an uninfected control. In the experiments, two points on a root with the separation of 3 mm were illuminated by laser beams and the elongation was measured continuously by analyzing speckle patterns successively taken by a CCD camera. The root elongation rate (RER), measured as the length of root elongation per second per millimeter (mean ± S.D.) for Ps -infected, Cg -infected and uninfected seedlings were 10.85 ± 2.41, 5.54 ± 1.43, and 2.41 ± 1.01 nm s −1 mm −1 , respectively. We found that the RERs of seedlings infected with ectomycorrhizal fungi were significantly higher than that of the uninfected seedlings, and the seedlings infected with Ps fungi showed the highest RER. We conducted another experiment to observe two-dimensional root growth, in which the growth measurements were obtained for 4 months. From this experiment, we observed that root growth of ectomycorrhizal fungi infected seedlings were higher than that of the uninfected seedlings. The evaluation of results from these two techniques proves that the proposed statistical interferometry is much faster and very sensitive technique, where the time required for growth monitoring is 10 7 times less than the other. We can conclude that, at the scale of either very short time or relatively long time, the symbiotic relationship between root and ectomycorrhiza has a positive effect steadily on the root elongation.

This study presents the effects of short-term ozone exposure on the nano-scale growth behavior of the fine roots of Pinus densiflora (Japanese red pine) seedlings. Root elongation measurements were obtained in nanometers for very short (sub-second) time intervals by using the optical interference method called statistical interferometry, developed by the authors. Three categories of P. densiflora seedlings were investigated; two categories were infected with ectomycorrhiza of Pisolithus sp. (Ps) and Cenococcum geophilum (Cg), while the third was without any fungal infection. In experiments, two points on a root with a separation of 3 mm were illuminated by laser beams and the elongation was measured continuously by analyzing speckle patterns successively taken by a CCD camera. The ectomycorrhizal fungi-infected and uninfected seedlings were exposed to ozone at concentrations of 120 and 240 ppb for periods of 1, 3, or 5 h in separate treatments. The root elongations of P. densiflora seedlings were measured before and immediately after the each ozone treatment and then the root elongation rates (RER) were determined for growth-measurement periods of 5.5 s and 9.5 min. From the measurements obtained for 9.5 min, we found that the RERs of uninfected and Cg-infected seedlings were reduced by 42 and 18%, respectively, after 5 h of exposure to 120 ppb ozone compared with that before exposure, while the reduction in RER of Ps-infected seedlings was not significant. When the concentration of ozone was increased to 240 ppb, the RERs of Ps-infected and Cg-infected seedlings were reduced by 32 and 44%, respectively, after exposure for 5 h, while the reduction in RER of uninfected seedlings was 59%. These observations prove that the non-mycorrhizal seedling roots are more sensitive to ozone stress. From this study, we found that the RERs of both mycorrhizal and non-mycorrhizal seedlings apparently fluctuated throughout the measurements, even within a few minutes.

Dynamic processes of deformation in tensile experiments of plates of SUS304 stainless steels at low strain rates less than 10-4 s-1 were investigated by dynamic ESPI (DESPI). Full-field deformation behaviors could be observed continuously and totally as moving speckle correlation patterns from the start of a tensile test to fracture of a specimen. In later stage of plastic deformation, anomalous stress fluctuations or projections in a stress-strain curve were found. Correspondingly, characteristic X-shaped strain localizations which swept over the specimen repeatedly were found. Dependence of anomalous deformation behavior on strain rate was precisely examined. Changes in magnetic properties before and after passing the X-shaped strain localization were also investigated by the ferritescope. Propagating strain localization can be considered as the front of strain induced martensitic transformation.

Cadmium(Cd) is an environmental contaminant heavy metal having high toxicity. The aim of this study is to investigate the effect of Cd on growth dynamics of plants in the order of sub-nanometers, using a novel optical interference technique, named as Statistical Interferometry Technique(SIT). In this study, a special attention is paid to the short-term growth fluctuation in measurements of the in-plane displacement of the leaf. In the experiments, Chinese chives( Allium Tuberosum ) were used as samples, and the growth and its nanometric growth fluctuations were measured for Cd exposure. This nanometric fluctuation that was found in our previous study, is an intrinsic property of the plant and is referred to as nanometric intrinsic fluctuations(NIF). The effect of Cd on plant growth fluctuation, i.e., NIF of growth rate was observed for three days continuously by exposing their roots to four CdCl 2 concentrations 0, 0.001, 0.01, and 0.1mM. The standard deviation(SD) of NIF of healthy leaf was 4.0nm/mm sec, and it reduced to 3.1nm/mm sec and 1.8nm/mm sec after 6 hours and 54 hours after exposing to 0.1mM Cd, respectively. For smaller concentration of 0.01mM, less reduction in SD of NIF was confirmed compared to those for 0.1mM. In addition, under 0.001mM, a significant recovery could be observed after a rapid reduction in the first 6 hours. The results imply that NIF can be a measure for heavy metal stress and is sensitive enough to detect the influence of smaller amount of Cd(from 0.001mM to 0.1mM) on plants in a very early stage.

Dynamic electronic speckle pattern interferometry (DESPI) was developed for in situ observations. The quantitative evaluation of the deformation field was performed through 2-D subtraction–addition method (SAM) for phase analysis. This method does not require additional phase modulation, which makes it applicable to studying dynamic events. The method utilizes the ratio of the subtraction and addition correlation fringe patterns. The bias intensity that has to be removed from the addition images was determined by temporal averaging of a sequence of speckle patterns. To reduce the error, Gaussian filter was applied to the correlation fringe patterns. The deformation field was evaluated with accuracy of λ /10.

Resently a demand to monitor the biological condition of plant has been increased due to the improvement of environmental pollution. Processes such as cytoplasmic streaming, organelle movement, cell growth and division, and biochemical reactions are the functional activities occurring inside of plant leaf. These activities are changed under the influence of environmental stresses. In this study, we proposed to utilize a biospeckle signal to achieve a functional optical coherence tomography (fOCT) to monitor the biological activities of plant. The dynamic speckle pattern obtained when a laser light illuminates leaf is characteristic for living objects and these functional activities and has been called a biospeckle.

In this study, Optical Coherence Tomography (OCT) was used to investigate the effect of short term ozone exposure on both front and back surfaces of the leaves of Allium tuberosum plant. Plant leaves were subjected to treat with 240ppb level of ozone, and imaging data were acquired from back and front surfaces of the leaves. Variations of the biological activations were monitored based on the biospeckles. Standard deviations (SD) of OCT temporal signal at each point were calculated and used to visualize the effect of ozone exposure. Leaf back surface showed higher SDs in biospeckle OCT signal in comparison to these of the front surface. These observations prove that the short term ozone stress on plant can be investigated successively with biospeckle OCT imaging technique.

Using statistical interferometry technique (SIT), a highly sensitive interferometry technique developed in our laboratory, we reported about the existence of nanometric intrinsic fluctuations (NIF) in a variety of plants. SIT permits noncontact, noninvasive, and fast detection of plant growth fluctuations in subnanometer scale. We propose the application of NIF to investigate the effect of heavy metal, cadmium, on growth dynamics of Chinese chive (Allium tuberosum). NIFs of leaves were observed for 3 days under four different concentrations of CdCl2: 0, 0.001, 0.01, and 0.1 mM. Results showed significant reduction of NIFs within 4 h for all Cd concentrations, and there was a further decrease with the exposure time of Cd under 0.1 and 0.01 mM. In addition, under 0.001 mM, a significant recovery could be observed after a rapid reduction in the first 4 h. As a comparison, measured antioxidative enzymes increased with increasing Cd concentration. However, no significant increase could be seen within the initial 4 h under a smaller concentration of 0.001 mM as seen for NIFs. The results imply that NIF can be used as an indicator for heavy metal stress on plants as well as it can be more sensitive to detect the influence of smaller Cd amounts on plants at an early stage.

A common path phase shifting interferometer is proposed using a liquid-crystal cell as a phase modulator. In the proposed common path interferometer, the specular component of the object light, separated in the Fourier transform plane, plays the role of a reference wave for the diffracted component of the object. A homogeneous-type nematic liquid-crystal cell is used as a phase only modulator, to introduce an arbitrary phase modulation between the specular and the diffracted components to achieve phase shifting interferometry. This makes quantitative measurements possible as well as qualitative observations for phase objects like in a Zernike's phase contrast microscope. Finally, experiments were carried out to show the validity of the proposed method. Experimental results show that the present method is quite stable against mechanical shocks and air fluctuation owing to its common path arrangement. The accuracy of the present method was experimentally verified to be better than 1 30 of wavelength by comparing the results with those obtained by the heterodyne interferometer.

Multiple channel vibration signals have been obtained simultaneously by measuring correlation signals between a multiple speckle pattern displayed on a LCTV panel and each independent live speckle pattern. The influence of multiplication was investigated by a numerical calculation of the correlation of the speckle patterns. Two-channel experiments were carried out, and the free vibration of two points on a cantilever excited by impulsive force was measured.

In Digital holography (DH), an in-line optical setup is commonly employed due to relatively low spatial resolution of CCD camera. In DH, a phase shifting method is commonly employed to determine the complex amplitude on the recording plane. In this study, we propose a phase shift error compensation method based on the statistics of the diffraction field of object. In most cases of the measurement using the digital holography, the object has an optically rough surface, and a fully developed speckle field is produced in the diffraction field, i.e., the recording plane. It is well known that the speckle phase takes a uniform probability density function (PDF). This statistical property is very stable and can be used as a constrain in the determination of actual phase shifts. The experiments were performed, and it was demonstrated that the phase shift error is well compensated over a fairly large amount of phase shift error. This method has a great advantage that any modification on ordinary digital holographic system with the phase shifting method is not required since the method utilizes information that was discarded in the conventional method.

This paper describes a nonintrusive measurement method of lateral and tilt vibration for a light weight structure with dynamic speckle correlation. A speckle pattern under an initial state of an object is recorded on a liquid crystal TV (LCTV) panel. Optical correlation between the speckle pattern on the LCTV panel and a live speckle pattern is taken by a photo-detector in real-time. Demonstrative free vibration experiments with a cantilever were carried out. Eigen-frequencies of more than 11.1 kHz were measured.

Color classification by a statistical pattern recognition method, the subspace method, was implemented by a simple optical system including a liquid crystal spatial light modulator. Area coding filters corresponding to eigenvectors were drawn on the liquid crystal panel. The vector inner products between the filter functions of each class and the input spectral distributions were calculated instantaneously. To construct low-dimensional subspaces for each class, the recognition system for arbitrary spectral distributions was used and efficient classification filters were constructed after several iterative learning cycles. Samples with small hue differences were correctly classified.

A new technique of optical interferometry based on the statistics of the fully developed speckle field is proposed. It is revealed that the complete randomness of the speckle phase can play the role of a standard phase in a statistical sense, and the phase of the object under testing can be derived in a statistical way, in contrast to conventional interferometry. The technique is first described in relation to the phase-shifting interferometry and the compensation problem for the phase-shift error. Next the method is generalized as an independent interferometric technique.

In this study, a highly accurate optical interferometric technique called ‘statistical interferometry’[1–3] has been developed and improved to expand its dynamic range. In contrast to the conventional interferometry where the phase is determined in a completely deterministic way, we consider the interference of completely random wave fronts, i.e., speckle fields, and it has been proved that the complete randomness of the speckle field can play the role of a standard phase in a statistical sense. The advantage of the method is that since the phase of the object under testing can be derived in a statistical way, the accuracy of the measurement depends only on the number of data taken to calculate a probability density distribution of speckle phase. This feature permits a simple optical system to achieve measurements with an extremely high accuracy. According to a computer simulation, the accuracy of λ/1000 can be achieved using 40,000 data of the speckle intensity. Statistical interferometry was applied as a strain sensor to monitor growth behavior of plant in ultra-short term, aiming to investigate the influence of the environmental conditions. In the experiments, the plants were exposed to ozone that is the main substance of photochemical oxidants. It was demonstrated that growth behavior of the plant could be measured with the accuracy of sub-nanometer and a time scale of second achieving a dynamic range of several hundred microns.

In this study, response of leaves of Chinese chives (Allium tuberosum) to ozone stress was investigated using functional optical coherence tomography (fOCT) based on biospeckle. The biospeckles arising out of dynamic motion of organelles can reflect the biological activities of plant. The fOCT biospeckle image was obtained by calculating the standard deviation (SD) of the fOCT temporal signal (biospeckle signal) at each and every point from the successively acquired OCT images. Plant leaves were subjected to treatment under different concentrations of O3, and imaging data were acquired from back and front surfaces of the leaves. The internal cell structure within the Chinese chives leaves could be clearly visualized in the functional OCT biospeckle image, which was not clearly visible in conventional OCT cross-sectional image. The SDs were found to be increasing significantly, especially in the surface layers of both front and back sides of the leaf with ozone exposure. Thus, the fOCT based on biospeckle is found to be suitable for fast, non-destructive monitoring environmental stresses on plants, which can potentially lead to significant time saving, for which conventional techniques require a few days to a few weeks time.