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A wavelet transformation method is introduced to remove the large fluorescence background from polarized Raman spectra of stained tooth enamel. This method exploits the wavelet multiresolution decomposition where the experimental Raman spectrum is decomposed into signals with different frequency components, and where the lowest frequency background and highest frequency noise are removed. This method is optimized using a simulated collection of parallel-polarized and cross-polarized Raman spectra of the enamel and then applied to a set of experimental data. The results show that the wavelet transform technique can extract the pure spectra from background and noise, with the depolarization ratio used to discriminate between early dental caries and sound enamel preserved. Copyright © 2010 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.

We report on a sub-cellular resolution photoacoustic microscopy (PAM) system that employs microcavity synchronous parallel acquisition technique for detecting the weak photoacoustic (PA) signal excited by a modulated continuous wave (CW) laser source. The gas microcavity transducer is developed based on the fact that the bulk modulus of the gas is far less than the solid and the change of the air-gas pressure is inversely proportional to the gas volume, making it extremely sensitive to the tiny PA pressure wave. Besides, considering PA wave expends in various directions, detecting PA signals from different position and adding them together can increase the detecting sensitivity and the signal to noise ratio(SNR), then we employs two microphone to acquire PA wave synchronously and parallelly. We show that the developed PAM system is capable of label-free imaging and differentiating of the hemoglobin distribution within single red blood cells under normal and anemia conditions.

We present a high-speed polarization-coding method, which makes use of phase modulation, for use in a quantum key distribution (QKD) system. This technique has been introduced into a QKD system for the first time. A completely quantum mechanical method is employed to describe quantum information processing here. Experiments on a balanced element for polarization coding by phase modulation are described in detail. The experimental results demonstrate that this technique can encode or decode polarization at high speed (with feasibility in the GHz range) and low voltage (a few volts) successfully.

The transportation and focusing in turbid media by means of Monte Carlo method is presented; by changing the numerical aperture (NA) of lens, the distributions of the intensity of focal spots were obtained. It shows: the NA is larger, the radius of focal spot is larger; all that answers the result of the experiments. Whereas in theory of scalar diffraction: the focal spot is getting smaller when the NA of lens increases. In the process of Monte Carlo simulation, every steps of photons motion are pursued and the scattering and absorption are taken into account; but we have no way to consider the scalar diffraction in it with the limit of the method itself. In fact, the scalar diffraction plays a role in light propagation otherwise it couldn't focus in turbid media. The figure of the NA versus focal spot is plotted using two methods with Monte Carlo simulation and with the scalar diffraction theory. With two methods, we suppose there is a balance position, which we can choose the lens of appropriate NA and get the optimal focal spot.

In this article, the focal properties of cylindrically polarized beams through a high numerical aperture parabolic mirror are numerically investigated. The vector field distributions within the focal region for cylindrically polarized beams are calculated by using the Richards-Wolf vectorial diffraction theory. It shows that the three-dimensional intensity distributions in the vicinity of the focus is dependent on the polarization rotation angle, topological charge and numerical aperture value. Additionally, some interesting focal volume structures, such as adjustably confined flat-topped focus, doughnut focal hole can be obtained by controlling polarization rotator angle. The tightly focused cylindrically polarized beams by a high numerical aperture parabolic mirror have possible applications in particle acceleration, optical trapping and manipulating, single molecule imaging and high resolution imaging microscopy, et al.

The theory of photoacoustic tomography (PAT) imaging using a 4f acoustic lens imaging system has been investigated, and the theoretical results show that a 4f acoustic lens has the ability of imaging and guarantees axial and lateral unit magnification of image. A system, a 4f acoustic lens imaging system combining with time-resolved technique, is developed to acquire PAT images. The 4f acoustic lens is able to image initial photoacoustic (PA) pressure distribution, which exactly resembles the absorption distribution, onto an imaging plane. Combining with time-resolved technique, the linear transducer array is adopted to acquire the PA pressure distribution to reconstruct the PAT images. Experimental results demonstrate that the system is able to obtain PAT images and the images contrast sharply with their backgrounds.

This study aims to develop a simultaneous photoacoustic tomography imaging technique in multilayer media. With an acoustic lens which has the ability of parallel imaging instead of other PA image reconstruction methods on the basis of complex algorithms, obtaining a two-dimensional (2D) PA image in real-time is available. Combining the advantages of the acoustic lens which has long focal depth and the fast data acquisition system, the new system is particularly excellent that it can acquire the complete PA signals from all the object planes. With the time-resolved technique, the PA signals from different object planes can be distinguished. As a result, the multilayer PAT images can be reconstructed simultaneously without any complicated reconstruction algorithms. According to the experimental results, the reconstructed multilayer images agree well with the original samples.

We present implementation of phase modulated polarization coding by polarizing sagnac interferometers. At four different low input voltages of the phase modulator, coder encodes pulse into four different polarization states, 45°, 135° linearly polarized or right, left circle polarized, while the decoder serves as the complementary polarizers. The mean visibility of the system is tested at 94.31%.

A new method of photoacoustic (PA) imaging based on an acoustic lens and the peak-hold technology is presented in this article. A fast PA imaging system, which consists of an acoustic lens, a 64-element linear transducer array, and a peak detection-and-hold circuit, is developed to obtain the two dimensional (2D) PA images of the experimental samples. By utilizing an acoustic lens, the PA signals generated from the sample are directly imaged on the imaging plane and collected by the 64-element linear transducer array which changes the PA signals into the corresponding electronic signals. Then the electronic signals are converted into a one dimensional image using the peak detection-and-hold circuit. After vertical scanning with a step motor on the imaging plane, the 2D PA image of the sample is achieved successfully. The results show that the images reconstructed in this experiment agree well with the original samples. Compared to other methods, this PA imaging system can acquire the PA images more rapidly without any complex algorithms, and it may provide a more convenient method for future in vivo noninvasive imaging of tissues and clinic diagnosis.

Optoacoustic tomography can be applied into medical imaging, which can detect the light absorption distribution of target hidden inside scattering media. When a short laser pulse illuminates the optical turbid media, such as biological tissue, the media will generate ultrasound pulses, which is linearly proportional to the optical absorption of the media. The acoustic pressure distribution can be imaged with an acoustic lens. Similar to an optically imaging system, the optoacoustic signals from a plane in tissue require the same delay time to reach a detecting plane. While the optoacoustic signals from different planes in media require different delay time to reach an image plane. A BOXCAR was used to go on with the same delay-time, and a 64-element linear transducer array was one-dimensional scanned on an imaging plane, and thus the acoustic pressure distribution was acquired. The signals were recorded and reconstructed by a computer. By scanning the sampling gate of BOXCAR, the optoacoustic images of different planes in media could be obtained. The experimental result indicates that the system is able to obtain optoacoustic tomography images of targets hidden optical turbid media, and the reconstructed images agree well with the original samples. The results show that the lateral resolution is about 5mm and the axial resolution is about 1.5mm.

We describe a new method for evaluating the viscoelastical characterization of biological tissue by photoacoustic technique in this paper. The amplitude attenuation curse of the tissue photoacoustic signals (the stress waves) induced by Q-YAG laser provides necessary data for us to work out the decay time of the stress waves. According to the theory of viscoelasticity, the decay time is equal to the tissue viscosity-elasticity ratio. The result we get from measuring gelatin shows the viscosity-elasticity ratio of Kelvin-Voigt model tissue obtained by photoacoustic measurement almostly equals that by conventional rheometer. The agreement is almost 97%. Furthermore, we firstly apply the method to measure the tissue viscosity-elasiicity ratio of Maxwell model. From the theorical analysis and the experimental result, we can conclude that the method can be applied to any model tissue, because it is only related with its acoustic impedance, having nothing to do with tissue state. In short, photoacoustic measurement is real-time, noninvasive and highly sensitive and repetitive. Based on the virtues mentioned above, it can be widely applied to biology and medicine.

Total suspended particles (TSP) are one of the main atmospheric pollutants. The ingredients are very complex, mainly including black carbon (C),organic compound, inorganic compound and biologic component, which will do great harm to human's health. During environmental monitoring, the airborne suspended particle always is an index for evaluating the quality of atmosphere. In this article, possible mixture of TSP is proposed to determine its ingredients and content by photoacoustic spectroscopy. The normalized photoacoustic (PA) signal of the sulfur powder, mixtures of sulfur and black carbon in different proportions are obtained respectively. Simulation with linear equation says that the PA signal has a certain relationship with the content of sample. The normalized PA spectroscopy of various materials is acquired via examining the sample of the powder of cupric sulfate mixed with nitro compound (2, 5 -methoxybenzoic-4nitro-dehyde), Portland cement, residual particles of automobile exhaust pipe, ash of power plant's stocks. The experimental results have important reference value to the practical analysis of TSP, it also provides new possible methodology to the environmental monitoring.

The tight focusing of femtosecond radially polarized vortex laser pulse by a high numerical aperture objective is investigated in this paper. Based on Richards-Wolf vectorial diffraction theory, the electric field and the group velocity of the radially polarized vortex femtosecond laser pulse are studied in great detail. It finds that the femtosecond radially polarized vortex laser pulse can travel at various group velocities near the focus, that is, slower or faster than light velocity in vacuum, depending on the numerical aperture of the focusing objective system. Moreover, the effect of spherical aberration of objective, topological charge and time duration of the radially polarized vortex laser pulse on the group velocity distribution near the focus is discussed.

Photoacoustic microscopy (PAM), whose image quality largely depends on the optical absorption of samples, provides endogenous information for structural and functional imaging. However, PAM technology in general can not provide edge enhancement imaging for absorbing objects. Therefore, PAM and differential microscopy are integrated for the first time in a single technique to obtain an edge enhancement image. The resolution test target RTA-07 and red blood cells are used as samples to achieve the desired spatial differential photoacoustic imaging. The feasible biomedical application of edge enhancement from the improved differential PAM was demonstrated.

Acoustic lens is applied in the research of photoacoustic imaging. The aberration is always inevitable due to the existence of the acoustic lens, and it influences the resolution of the imaging system severely. However, the imaging system based on an acoustic lens also provides a new method for observing the aberration of a system and testing the quality of the acoustic lens. In this paper, a method of observing the aberration of photoacoustic imaging system is reported, and the causes of aberrations are discussed based on the theory of lens aberration. All these would be helpful to correct the aberration and improve the resolving power of acoustic lens.

Photoacoustic microscopy (PAM) is dominantly sensitive to the endogenous optical absorption compared with the confocal microscopy which images with scattering photons. PAM has similar structure such as optical transportation system, the optical scanning, and light source with the laser scanning confocal microscopy (LSCM). In order to match the PAM with LSCM, a special design microcavity photoacoustic (PA) transducer with high sensitivity is developed to detect the photoacoustic signals induced by modulated continuous wave (CW) laser. By employing a microcavity PA transducer, a PAM can be integrated with LSCM. Thus a simultaneous multimodal imaging can be obtained with the same laser source and optical system. The lateral resolutions of the PAM and the LSCM are both tested to be better than 1.25 μm. Then subcellular multimodal imaging can be achieved. Images from the two modes are corresponding with each other but functionally complementary. Combining PAM and LSCM provides more comprehensive information for the cytological test. This technique is demonstrated for imaging red-blood cells and meristematic cells.

Photoacoustic tomography has the potential to image the configuration or function of animal or human organs with simultaneous high contrast and high spatial resolution. This article provides an overview of photoacoustic tomography with an acoustic lens. And a new fast photoacoustic tomography technique is introduced. An acoustic lens is able to map the initial photoacoustic pressure distribution in an object in real time without the need of complicated computational reconstruction. Further more, this method produces no artifacts in reconstructed images. Finally, a new fast photoacoustic tomography system based on acoustic is discussed in detail in this paper.

The propagation of radially polarized partially coherent beams in uniaxial crystals orthogonal to the optical axis is investigated. The analytical formulae for the elements of the cross-spectral density matrix of radially polarized partially coherent beams propagating through uniaxial crystals orthogonal to the optical axis are derived. The effect of initial coherence and ratio of extraordinary and ordinary refractive indices on the intensity and effective beam widths is illustrated analytically and numerically. The results show that the propagation properties of radially polarized partially coherent beams in uniaxial crystals orthogonal to the optical axis are closely related to the initial coherence and the ratio of extraordinary and ordinary refractive indices.

In this paper, we propose a simultaneous multiple-slice photoacoustic (PA) imaging technique by utilizing an acoustic lens with parallel imaging ability. Our method can directly image multiple slices of the three-dimensional (3D) PA images in real-time without utilizing special reconstruction algorithms. Combining the advantages of an acoustic lens with long focal depth and a fast data acquisition system with high sampling rate, the new system can acquire all slices of a 3D object simultaneously. This is achieved by utilizing the time-resolved technique that allows to distinguish PA signals from different object planes. According to the experiment results, the reconstructed sectional images match the original samples well. The proposed technique provides a fast and reliable approach to multiple-section PA imaging. Our study can be applied to noninvasive imaging and medical diagnosis.

Tight focusing properties of partially coherent radially polarized vortex beams are studied based on vectorial Debye theory. We focus on the focal properties including the intensity and the partially coherent and polarized properties of such partially coherent vortex beams through a high numerical aperture objective. It is found that the source coherence length and the maximal numerical aperture angle have direct influence on the focal intensity, as well as coherence and polarization properties. This research is important in optical micromanipulation and beam shaping.

A simultaneous photoacoustic (PA) tomography imaging technique in multilayer samples was developed. Instead of using the PA image reconstruction methods on the basis of complex algorithms, obtaining a two-dimensional PA image in real time is available by using an acoustic lens that has the ability of parallel imaging. The imaging system can acquire the complete PA signals of high signal-to-noise ratio from all the object planes by utilizing the advantages of the acoustic lens with long focal depth and a fast data acquisition system with a high sampling rate. With the time-resolved technique, the PA signals from different object planes can be distinguished and then the high optical contrast multilayer PA images can be reconstructed simultaneously without any algorithms. The experimental results show that the reconstructed sections agree well with the original samples.

Photoacoustic (PA) measurement is noninvasive. We used the PA technique to measure the viscoelasticity of red blood cells (RBCs) to determine whether it could elucidate mechanical characteristics at a cellular level. A single-pulse laser beam was used as the light source to generate a PA signal. A “thin” glass was used as an acoustical impedance medium to form the attenuation signal. From the amplitude attenuation curves of the signals of a control RBC group and some glutaraldehyde-treated RBC groups, we obtained the decay times. As decay time is equal to the viscosity-elasticity ratio, we could obtain the viscoelasticity characteristics of the RBC. The PA technique is a simple, real-time, and noninvasive way to acquire the viscoelastic properties at a cellular level.

This report presents a practical analytical method of photoacoustic (PA) spectroscopy that is based on wavelet transform (WT) and the first-derivative PA spectrum. An experimental setup is specially designed to obtain the first-derivative spectrum, which aims to identify some unnoticeable absorption peaks in the normal PA spectrum. To enhance the detectability of overlapping spectral bands, the WT is used to decompose the PA spectrum signals into a series of localized contributions (details and approximation) on the basis of the frequency. For the decomposed contributions do not change the absorption peak position of PA spectrum, one can retrieve the weak absorption signals by the decomposed result of WT. Because of the use of derivative spectroscopy and WT, three unnoticeable absorption peaks that are hidden in the PA spectrum of carbon absorption are precisely retrieved, the wavelengths of which are 699.7, 752.7, and 775.5nm, respectively. This analytical method, which has the virtue of using a physical...

In this paper we present a new high-contrast photoacoustic tomography (PAT) imaging system using a 4f acoustic lens, a 64-element linear transducer array and peak-hold technology. This PAT imaging system has been developed to obtain three-dimensional (3D) PAT images of experimental samples. By utilizing a 4f acoustic lens, the photoacoustic (PA) signals generated from the sample are directly imaged on the imaging plane and collected by the 64-element linear transducer array, which changes them into the corresponding electronic signals. Then we can get one-dimensional (1D) images from the electronic signals using a peak detection-and-hold circuit. After vertical scanning with a stepping motor on the imaging plane, a 2D PA image of the sample is successfully obtained. Combined with the time-resolved technique, we can then get 3D PAT images. The results show that the reconstructed images agree well with the original samples.

The theory of photoacoustic tomography imaging using an acoustic lens imaging system has been investigated, and the photoacoustic (PA) Fourier imaging property of an acoustic lens is presented. The theoretical results show that an acoustic lens is able to realize two-dimensional PA Fourier imaging and the focal depth of the acoustic lens is 20mm. The PA signals with the advantage of time resolution can be resolved in time domain by time-resolved technique. Therefore, this long focal depth characteristic of the acoustic lens can be combined with time-resolved technique to realize PA tomography imaging. It is demonstrated by experiments that this method is able to provide PA tomography images of biological tissue. The images are clear and contrast sharply with their backgrounds. The depth resolution is 1.54mm.

A design of derivative photoacoustic spectrometer is presented in this article. It mainly includes a wavelength-intensity splitter and a complementary chopper. In our design, a dual wavelength derivative method is introduced to implement a derivative operation. Through the wavelength-intensity splitter, two beams are obtained and then complementarily modulated by the complementary chopper to satisfy the first derivative requirements as well as to achieve the differential of photoacoustic signals. As examples, the first derivative photoacoustic spectra of He-Ne laser and xenon lamp are also presented in this article. The results show that the first derivative photoacoustic spectrum can provide a superior fine spectral structure and spectral resolution compared to the photoacoustic absorption spectrum.

A new highly sensitive spectroscopy technique- differential photoacoustic spectroscopy (PAS) is presented in this paper. The blood samples from 3 healthy persons, patients with leukemia, patients with pregnancy-induced hypertension (PIH), and 40 patients with nasopharyngeal carcinoma were measured by the PAS technique. The normalized, the first order, and the second order differential photoacoustic spectroscopy of the blood were gained. The results show that (i) weak absorption peaks or shoulder peaks, which could not be found using conventional photoacoustic spectroscopy, were determined by the first order and the second order differential photoacoustic spectroscopy which significantly improve the sensitivity of detection; and (ii) that two characteristic absorption peaks were found at the wavelength of 637 and 664 nm in all persons’ blood samples by the differential photoacoustic spectroscopy technique. This experiment concludes that the differential photoacoustic spectroscopy technique is superior to the conventional photoacoustic spectroscopy technique in detecting photoacoustic spectroscopy of biological samples.