Recently, bioassay has been getting much attention as it can comprehensively evaluate water toxicity without identifying the individual chemical component. In this technique, a microscope observation is required to know the critical features of the targeted microorganisms. However, as the size of the microorganism becomes smaller, observation becomes more difficult due to the narrower focal depth of the imaging system. Here, to overcome these difficulties, a novel biospeckle technique is used for the microbioassay utilizing the biospeckle in the diffraction field generated from the microorganisms. Paramecium caudatum (200-300µm) and Euglena gracilis(50-60µm) were used as a microorganism. Dynamic biospeckle patterns were captured using a CCD camera to evaluate the swimming activity of microorganisms under varying water toxicity levels induced by heavy metal pollutants (Zn(NO₃)₂·6H₂O and FeSO₄·7H₂O). To quantitatively evaluate the swimming activity of microorganisms, the crosscorrelation function between the initial frame as a reference frame and the subsequent frames was measured, and the correlation time was evaluated as a measure of their swimming ability. Results show a concentration dependent effect of Zn on both species, leading to decreased swimming ability. Conversely, Fe exhibited varying effects on Paramecia and Euglena, with the latter displaying tolerance at lower concentrations but a notable response at higher concentrations. The advantage of the method is that owing to the non-imaging system, an enormous number of planktons can be processed. This allows for an immediate and statistically significant estimation of their swimming ability in response to environmental pollution.
Elasticity of blood vessels makes them contract or dilate in regulating the body temperature to changes in external temperature changes such as air-conditioning. However, ageing makes them gradually lose elasticity, making it difficult for blood vessels to make adjustments. In this study, we propose the use of biospeckle Optical Coherence Tomography (b-OCT) to visualize the dynamic changes within the skin. A total of 20 subjects with equal number of male and female particpants with ten in their 20’s and the other ten subjects in their 30’s or older were subjected to heating of the palmar forearm of their dominant hand by a USB hot pad (40°C) for five minutes. A swept source OCT (SS-OCT) operating with a central wavelength of 1310nm, a bandwidth of 125 nm and a sweep frequency of 20kHz was used to obtain OCT structural images at 12fps. From the OCT structural images obtained before and after heating, biospeckle contrast was calculated from the temporal variation in the images and compared. Biospeckle contrast results were compared for the depth, gender, and age differences. With heating, a clear difference of increased contrast was observed at shallower depths in comparison to deeper regions for both genders, while, as a whole, a larger contrast difference was observed for male in comparison to female participants. Furthermore, in the age group larger than 30, the contrast change with change in environment was smaller, suggesting the loss of elasticity to adjust to the environmental changes.
Nanoparticles (NPs) have become more prevalent in the agricultural, industrial, and medicinal fields. There is rising interest in how nanomaterials interact with plants since they influence plants and seeds differently depending on their size, shape, and dose. The techniques to monitor the response of plants to NPs are crucial since the effects of nanomaterials on seed germination and plant growth are uncertain. In this study, a highly sensitive, real-time, non-invasive novel technique called Biospeckle optical coherence tomography (bOCT) is used to examine the size-dependent impact of metal oxides NPs and microparticles (MPs) like Zinc Oxide (ZnO) with a size less than 50 nm, and 45μm and Titanium dioxide (TiO2) with a size 21 nm and <5μm at concentrations of 25mg/L and 100mg/L on the internal activity of lentil seeds before germination. The results showed that ZnO NPs had an adverse effect at both higher and lower concentrations on the internal activity of lentil seeds, while MPs of 45μm had significantly positive effects even with higher concentrations. However, TiO2 MPs and NPs showed a significant positive effect on Lentil seed’s internal activity at both concentrations in comparison to control. The proposed method was able to detect the response of Lentil seed’s internal activities to different concentrations and sizes of metal oxides NPs and MPs at an early stage just after 5 hours of exposure before the germination. On the other hand, the conventional physiological methods required a week for the effects to be detected, and the results from bOCT after 5 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. Furthermore, the technique is capable of monitoring internal biological activities while the conventional OCT monitors just structural images. It has not only the potential to screen but could also constantly monitor long-term changes, thus contributing to the study of the effects of nanomaterials on plants.
Microplastic pollution has become prevalent due to industrialization and the wide use of plastic. In this study, the individual and combined effects of polyethylene microplastic with Zn on lentil seed germination were monitored using Biospeckle Optical Coherence Tomography (bOCT), a technique established by authors to visualize the internal activity of biological objects. The results imply that both 100 mg L-1 heavy metal Zn or polyethylene microplastics (PEMPs) alone had a strong inhibitory effect on lentils. However, in combination with PEMPs, the Zn toxicity on lentils was reduced due to the reduction of Zn uptake by the seedlings through the interaction of Zn and MPs. These findings suggest that PEMPs could be able to mitigate the effect on the bioavailability and toxicity of Zn on lentils.
Recently, the pollution caused by various hazardous chemicals has become a very serious problem. Currently, 200 million kinds of chemical substances are registered, and it is technically and costly very difficult or even impossible to analyse, identify each chemical individually and then evaluate their toxicity on the environment. On the other hand, bioassay has been getting a lot of attention where the toxicity of environmental toxicity is assessed based on the reaction of micro-organisms such as plankton without identifying each chemical individually. For this technique, a microscope observation is required to obtain critical features such as alive/dead status and swimming ability. With smaller microorganisms, microscope observation becomes more difficult due to the narrower focal depth of the imaging system. In our study, to overcome these difficulties, we proposed a novel technique for the micro-bioassay utilizing laser biospeckle in the diffraction field generated from plankton. Paramecium chilomonas of size 30-40 µm was exposed to different pH conditions from control 7.2 to gradually decreasing by 0.5 till 3.7. Results reveal the sensitivity of laser biospeckles in detecting the subtle changes in the swimming behavior, the health of the microbe with change in pH suggesting the potential for fast assessment the toxicity of an environment.
Heavy metals are one of the important components of water pollution. Heavy metals such as copper, zinc and cobalt are essential for the growth of living organisms as micronutrients. However, copper above critical levels can pose serious problems for the environment and human health. The biospeckle observed in OCT have the potential to map dynamic activities inside the plants. We propose biospeckle optical coherence tomography (bOCT) and demonstrate that the technique can monitor biological activity in plants. In bOCT, the temporal speckle contrast variation of the OCT reflection signal is used as a parameter to characterize the internal activities of the aquatic plant (Myriophyllum). Plant stems were observed using the bOCT technique after 7 days of exposure to copper solutions of three different copper concentrations to 0, 30, 100 mg/l. In addition, statistical Interferometry Technique (SIT) system that is also a very sensitive optical measurement technique developed in our lab. SIT enables the direct observation of short-term displacement or extension / shrinkage of plant surface with precision of nanometer scale and on a time scale of seconds. Compared with the bOCT technique, it takes short time. It does not require 7 days of exposure time. In just 3 hours of experiment time, we observed that the plants were receiving heavy metal stress in the copper solution. Under the same heavy metal exposure conditions (7 days), enzyme activities in plants were also measured and analyzed to demonstrate the reliability of our two laser measurement techniques. It can be seen that the increase of copper solution has a significant effect on the activity of plants. It was not possible to observe the effects of 7 days of heavy metal exposure on plants by measuring their length or the color of their leaves. Compared with traditional bioassay methods, SIT technology is the fastest, followed by bOCT technology. Both technologies are advanced and can be used as a new method for the determination of plant bioactivity.
Statistical Interferometry Technique (SIT) developed in our laboratory is a unique optical interferometry method using the statistical property of a complete randomness of fully developed speckle field. SIT enables non-invasive and real-time measurement of short-time sub-nanometric growth behaviors of plants. Applying SIT to the measurement of plant leaf elongation, we found that plants grow with very small fluctuations at nanometric scale, named as Nanometric Intrinsic Fluctuation (NIF) that formed the basis of our research. Our previous studies have demonstrated that NIF seems to reflect the healthiness of plants sensitively. In other words, SIT could assess an environmental condition through a plant NIF. However, the origin of NIF is still unknown. In this study, we focus on the effect of far-red light (FR) of wavelength 700-800 nm and evaluate how it affects NIF to infer the origin of NIF from the mechanism of FR-induced growth. LED (wavelength of 730 nm) was employed as a FR source, and fresh rice seedlings (2-4 weeks age) were used in the experiment. FR illumination at 50 µmol/m2 /s increased the standard deviation of NIF of rice seedlings approximately 50% within 30 minutes. According to the literatures, FR increase endogenous auxin level via phytochrome signaling, and auxin-induced growth may occur within a few tens of minutes. In addition, it was found in our previous study that low concentration of exogenous auxin increases the magnitude of NIF. Hence, these results implies that not only FR has a positive effect on plant growth but also the increase may be caused by auxin-induced growth.
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.
Acid mine drainage (AMD) is generated during the mineral extraction process. AMD contaminates farmland and rivers, so it makes sense to study the effects of AMD on crops. Since the conventional methods for studying plant responses to environmental stress are damaging and time-consuming, we propose the Biospeckle OCT (bOCT) method to evaluate the response of plants to AMD in a rapid and non-invasive way. In this study, we selected rice plant and soybean as experimental subjects. The seeds were exposed to 40 and 80 ml/L of simulated AMD solution, and the seed condition was monitored by bOCT. OCT images of the seeds were obtained at a speed of 10 frames per second for a few tens of seconds. For each pixel of the OCT structural images, the contrast across the temporal axis was calculated to give bOCT images. Meanwhile, we measured the root shoot length of rice and soybean after growing in AMD as a comparison. It was found that bOCT images clearly distinguished the changes in biological activities of seeds due to 40 and 80 ml/L of AMD treatments from those of control within much shorter time, 48 hours and 72 hours for soybean and rice, respectively, compared to the conventional method that failed to show any changes within the same time. And The seedling growing status of soybean and rice after 7 and 10 days showed the same trend as the bOCT results, respectively. This suggests that the proposed bOCT method can reveal the different responses of soybean and rice to different concentrations of AMD at a very early stage. This technique may be able to provide a reference indicator for studying plant response to environmental stress, and it is efficient and non-invasive.
Seed germination rate and seedling growth differ based on environmental factors requiring non-invasive and non-contact seed screening techniques in agriculture. Moreover, the widespread usage and mismanagement of plastics have led to significant environmental problems affecting seed germination and seedling growth. Recently the attention of seed scientists and other biologists has been paid to optical sensing technologies-based measurements to observe the quality of seeds owing to the non-destructive and non-invasive detection capabilities. Moreover, the vigor of seeds is directly affected the crop yield. Therefore, here we propose to employ Biospeckle Optical Coherence Tomography (bOCT) in investigating the effect of polyethylene microplastics (PEMPs) on lentil seed germination. bOCT is a non-contact, nondestructive in vivo monitoring technique to visualize the change of internal activity of a biological object. Lentil seeds were exposed to PEMPs for 24 h bioassay with 10, 50, and 100 mg/L concentrations. The average speckle contrast was calculated after 0, 6, 12, and 24 h of exposure and statistically significant differences in bOCT contrast for all the treatments were observed just after 6 h of exposure. Thus, the results of the present study revealed that the presence of PEMPs significantly reduced the internal activity at the initial stages that could be visualized only because of the use of bOCT, in the early stage prior to the germination. Furthermore, this might be utilized as a trustworthy seed screening tool in the seed industry, which could save the screening time significantly compared to traditional approaches while assessing environmental pollution.
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.
Gemination tests and vigor tests are destructive sampling tests used to ensure the quality of seeds. However, the yields may depend on the conditions of the fields even the quality of seeds were tested. A non-destructive method to inspect the properties of seeds in the fields can improve the yields of crops. A biospeckle OCT was developed to measure the biological activities of germinating seeds. Twenty-nine radish seeds were measured by the OCT under 3 conditions. Nine seeds were treated with hot water to terminate the biological activities before the measurement of OCT and imbibed in room temperatures. Ten seeds were germinated for each condition at room and low temperatures. Low temperatures were to slow down the biological activities. The speckle contrast, defined as the ratio of the standard deviation to the mean of OCT intensities, was used to quantify the biological activities. The modal values of speckle contrast largely increased in 1.8 days when the seeds were germinated at room temperatures. When the seeds were germinated at low temperatures the modal values of speckle contrast took 14 days to increase to the same level of that of the seeds germinated at room temperatures. The modal values of speckle contrast remained low for 14 days of OCT measurements when the seeds were heated. As a conclusion, the results showed that the speckle contrast of OCT intensities quantified the biological activities of seeds during the process of germination and it may be used to evaluate the ability of seed germination.
Statistical interferometer technique (SIT) is a highly sensitive optical interferometer developed by us capable of measuring sub-nanometer displacements and when applied to plant growth studies revealed nanometric intrinsic fluctuations (NIF). NIF observed in minimum time scale of several tens of seconds is strongly influenced by the environmental conditions. Our earlier experiments with rice under ozone or heavy metal stress, such as cadmium even for a short duration of one hour decreased NIF. In contrast, having a micronutrient, such as zinc increased NIF. Therefore, presence of NIF is found to be a novel phenomenon characterizing plant condition that could appear only under sub-nanometric measurement. In this study, we report the effects of adding a plant growth hormone called auxin. Roots of rice seedlings were exposed to auxin solutions of different concentrations of 0, 1, and 4 μM for 24 hours. Significant increment was seen in NIF for a concentration of 1 μM while a significant reduction was seen in NIF for 4 μM within an hour after immersion of the roots. Application of an inhibitor to auxin called TIBA also resulted in almost immediate reduction of NIF. Current results suggest for NIF affected by the enodgenous hormones to be related to growth, as the action of a growth-related endogenous hormone auxin is chemically inactivated. Thus, NIF not only could be applied to investigate and speedily assess the effects of environmental agents on plant elongation or shrinkage but also could be implicated as one of the possible mechanisms for the origin of NIF itself.
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.
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.
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 CdCl2 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.
Recently, a demand for the precise observation of a multilayered paint system have been increasing such as in car industry. However, conventional methods can observe only the surface condition of the paint. In this study, we propose a new method to observe a three dimensional drying process of the multilayered paint using functional Optical Coherence Tomography (fOCT). In this method, the dynamic speckles that appear in OCT signal were utilized. The temporal properties of the dynamic speckle is related to the Brownian motion of the scattering particles in the paint, and thus depends on the drying condition. Autocorrelation function of the speckle signal was calculated and its width, i.e., correlation length (CL), was used as a measure. In the experiment, two layer system consisting of different paints on the thin glass plate, and the drying process was observed for two hours. In the second layer exposed to the air, CL showed a monotonic increment indicating a steady progress of the drying process while in the first layer (deeper layer), CL decreased slightly for the first 50min. and then started to increase. This implies that drying process has been reversed due to the transport of the solvent from the second layer in the early stage. Such a complicated drying process of the multilayer system could also be confirmed from OCT signal image of the interface between the layers. This analysis was performed using the phase term obtained in the OCT interference signal with an accuracy of 0.1μm.
KEYWORDS: Ozone, Optical coherence tomography, Coherence imaging, Ions, Mirrors, Imaging systems, Data acquisition, Humidity, In vivo imaging, Signal detection
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.
We have measured the growth of vegetable leaves in real-time by means of digital speckle correlation to detect speckle
displacement caused by the growth. We employed two optical configurations, the first for detecting strain component
by a pair of CCDs and the second for detecting in-plane translation by a single CCD. We could clearly observe the
influence of white light irradiation on the growth rate.
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.
In this study, behavior of ball grid arrays (BGA) under external cycling loading was studied. A loading system for
inducing cycling stress to BGA was successfully built. Dynamic electronic speckle pattern interferometry (DESPI)
with in-plane sensitivity and Hilbert transform for phase analysis was applied. The cycling deformation of one solder
ball was measured continuously. Temporal, whole-field deformation on one solder ball was demonstrated.
In this study, a novel optical interferometric technique called 'statistical interferometry'1-3 has been developed. 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 to monitor biological activity or growth rate of plant, aiming to investigate the influence of the environmental pollutions. In the experiments, the plants were exposed to Ozone that is the main substance of photochemical smog, and the growth rates were measured before and after the exposure. It was clearly observed that the fluctuation of growth rate as well as its mean rate was dramatically affected by the exposure of ozone. By the observation of growth rate of plant with the accuracy of sub-nanometer scale and a time scale of second, it was newly revealed that the fluctuation of the growth rate reflects the biological activity of the plant.
A new phase contrast imaging system that permits a quantitative observation of phase distribution of a general object is proposed and experimentally demonstrated. This is realized by implementing the phase shifting technique in the phase contrast imaging system. A dye-doped nematic liquid-crystal (NLC) is newly employed for this purpose as a variable phase filter in contrast to the constant phase plate employed in the conventional phase contrast microscope (PCM). The dye-doped NLC provides a practical advantage to the system that realizes an alignment-free optical system for the phase plate. The self-alignment property of the phase filter is realized by utilizing the local phase transition from the liquid-crystal to liquid, which is induced by the relatively strong incident light of the specular component of the object. In the experiment, the fundamental phase modulation property and the response of phase modulation ability were measured as a function of incident power of light. Next, the phase measurements were performed with several phase gratings and composite objects having different phase amplitudes and absorption. As an experimental result, the usefulness of the proposed method was confirmed, and the accuracy of the phase measurement was estimated to be λ/40. In addition, it was also demonstrated that the phase information could be obtained independently from the absorption component of the object.
In relation to the monitoring the influence of the environmental pollution on the plant, we proposed a difference-image method and performed some preliminary experiments to observe the biological activities of the botanical objects based on the dynamic properties of laser speckles. Two successive speckle images of the plant obtained with a certain delay time are subtracted to show the difference in the two patterns due to the biological activity. In the experiments, validity of the proposed method was examined for the plants under the influence of the artificial acid rain and the ozone exposure. As experimental results, some characteristic changes were observed in the speckle difference images due to the damages, while it was very hard to recognize those changes by the human eye.
Optical intrinsic signal imaging (OISI) provides the surface activation map of brain and has provided many insights. In this study, we show that the optical coherence tomography (OCT) can indeed provide depth resolved functional map of cat visual cortex. Activation profile obtained by integrating OCT signal across depth correlates well with that determined by the OISI. Functional OCT (fOCT) promises to be a valid technique for revealing unexplored organization inside the brain at a micro system level.
In this paper we proposed a Hilbert Transform to calculate the phase map. The data processing is performed in temporal domain, considering the temporal history of the interference signal at every single pixel. This results in a relatively high spatial resolution of the phase map. In addition, the phase method enables a fully automatic and does not require human interaction. The final results give a temporal development of two-dimensional deformation field. To reduce the influence of the fluctuations of bias intensity on the calculated phase, it was removed prior to performing the Hilbert Transform. The proposed method for analysis of the phase of dynamic ESPI was examined in two different experiments, i.e., plastic deformation studies, and thermal expansion studies. The dynamic range of measurements is increased from several tens of nanometers to several micrometers, which makes the method very attractive for dynamic measurement.
In this study, we are developing optical methods to monitor the condition of plant, i.e., biological activity or growth, aiming to investigate the influence of the environmental conditions. The statistical interferometry developed by the authors has been applied to measure the growth of the plant. This method utilizes the statistical properties of a fully developed speckle field and has the advantage of simple optical system to achieve measurements with an extremely high accuracy. In the experiments to demonstrate the validity of the method, the growth speeds of the plants were measured under various environmental conditions of watering and light illumination. It has been clearly demonstrated that the statistical interferometry has a high sensitivity for monitoring the growth of the plant at a nanometer scale with a high temporal resolution of second scale.
We report the application of Optical coherence tomography (OCT) for visualizing a one dimensional depth resolved functional structure of cat brain in vivo. The OCT system is based on the known fact that neural activation induces structural changes such as capillary dilation and cellular swelling. Detecting these changes as an amplitude change of the scattered light, an OCT signal reflecting neural activity i.e., fOCT (functional OCT) could be obtained. Experiments have been done to obtain a depth resolved stimulus-specific profile of activation in cat visual cortex. Our results in one dimension indicate that indeed an orientation dependent functional signal could be obtained. Further, we show that this depth resolved fOCT signal is well correlated with the stimulus dependent column determined by OISI. Based on the results, the smallest functional unit in depth, resolved by the proposed system is around 40 micrometers . We are extending our system to perform two dimensional functional imaging.
We propose a optical coherence tomographic (OCT) system for imaging functional organization of brain. To enhance the reflectivity of OCT signal, simulation studies have been done with iron particles as the tracer elements. It has been found that by proper choice of the size of the particles, the OCT signal can be greatly enhanced.
Statistical interferometry is applied to the measurement of thermal strain of object having an interface of two different materials. The technique is based on the statistics of the fully developed speckle field. 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 the conventional interferometry. In this study, the optical system is optimized to measure the thermal strain in a very small region around the interface of joint specimen. Experimental results show that the present method permits the measurement of strain with the accuracy approximately 10-6 with a spatial resolution > 50 micrometers .
In this study, we have examined the possibility of using an anti-ferroelectric liquid-crystal (AFLC) as a high speed phase modulator. The AFLC has the major advantage that it has three stable states in contrast to the ferroelectric liquid-crystal which has only two states. This feature permits the application of AFLC as a fast phase modulator in the phase shifting interferometer. However, AFLC also modulates the intensity of transmitted light as well as its phase. Based on theoretical analysis, it was found that doping a dichroic dye to AFLC cell can suppress the intensity modulation. Moreover, such a dye-doped AFLC phase modulator can perform as a self- align phase modulator. Such a self-align phase modulator permits a practically advantageous alignment-free optical system, for instance, in phase contrast microscope, point diffraction interferometer etc. Preliminary experiments were performed to demonstrate the validity of the dye-doped AFLC cell. Finally, we also examine the application of the dye- doped AFLC phase modulator to phase shifting interferometer.
In this study, an optical system to generate contrast- enhanced speckles from ordinary rough surface object is proposed. Its statistical properties are studied as a function of the surface roughness and the defocusing distance in detail with special attention to its application to the determination of the roughness. It is revealed that the contrast of contrast-enhanced speckles depends only on the rms roughness of the rough surface object. Usefulness of the contrast-enhanced speckles on the measurement of surface roughness of the object is experimentally confirmed.
Fundamental properties of phase modulation ability of a nematic liquid-crystal (NLC) cell is first studied. Based on the phase modulation property of the liquid-crystal (LC) cell, a new type of speckle shearing interferometer is proposed. In the method, a LC cell is employed as a phase shifter to implement the phase shifting method for the conventional speckle shearing interferometer. Next, a phase unwrapping method that particularly has the advantage of unwrapping of phase distribution with severe noise such as those obtained in speckle interferometry is proposed. Computer simulations were carried out to examine the performance of the proposed method. Finally, experiments were made to demonstrate the usefulness of the proposed phase shifting speckle interferometer together with the improved phase unwrapping method.
Generally, in conventional optical interferometry, generation of speckles has been regarded as a noise and an error source degrading the reliability of the measurement because the phase is determined in a completely deterministic way. Recently, we have proposed and developed a new interferometric technique called statistical interferometry and demonstrated its validity1,2). In the method, completely random wave fronts, i.e. speckle fields, play a role of the standard of phase in a statistical sense. In the present study, we have applied the statistical interferometry to the measurement of thermal expansion of an object.
Fundamental properties of phase modulation ability of a nematic liquid crystal cell is first studied. Based on the phase modulation property of the liquid crystal cell, a new type of speckle shearing interferometer is proposed and studied experimentally. In the method, a liquid crystal cell is employed as a phase shifter to implement the phase shifting method for the conventional speckle shearing interferometer. From the experiments to measure the deformation of an object, usefulness of the method is confirmed.
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 a 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.
A new type of speckle shearing interferometer is proposed and studied experimentally. In the method a liquid-crystal is employed as a phase shifter to apply the phase shifting method for the conventional speckle shearing interferometer. The phase of the transmitted light is changed due to its birefringent property for the applied electric field. It is shown from the measurements of the fundamental properties of the liquid-crystal that the additional phase introduced between the sheared two images can be precisely controlled up to about 2ir by changing the applying voltage. From the experiments to measure the deformation of an object having a rough surface usefulness of the method is confirmed. 1.
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