We experimentally demonstrate and characterize an organic octagonal quasicrystal slab with a single-defect microcavity at low-index contrast. The gain medium is the conjugated-polymer, composed by two PPV derivatives, a BEHP-PPV and a MEH-PPV. By optical pumping, the lasing action is achieved at 607 nm with a FWHM of 1nm. The threshold of lasing is 9uJ/cm2. The intensity of the lasing peak depends linearly on the pump energy above the threshold.
A new method for precisely measuring the optical phase retardation of wave-plates in the
infrared spectral region is presented by using modulated-polarized visible light. An electro-optic
modulator is used to accurately determine the zero point by the frequency-doubled signal of the
Modulated-polarized light. A Babinet-Soleil compensator is employed to make the phase delay
compensation. Based on this method, an instrument is set up to measure the retardations of the
infrared wave-plates with visible region laser. Measurement results with high accuracy and sound
repetition are obtained by simple calculation. Its measurement precision is less than and repetitive
precision is within 0.3%.
A high stable wavelength-tunable fiber laser is experimentally demonstrated by using a digital-micromirror-device (DMD) processor and a polarization-maintaining erbium-doped fiber amplifier (EDFA).The electronic-addressed DMD processor is able to select and couple a waveband from of the polarization-maintaining EDFA back into the fiber ring to generate a narrow line-width laser output. The tunable fiber laser shows a line-width of 0.02nm, a tuning step of 0.08nm over the c-band and a side mode suppression ratio (SMSR) greater than 50 dB. The output power uniformity of 0.016dB is achieved by using the automatic power control (APC) system under room temperature. The center wavelength fluctuation during 1 hour is below 0.01 nm.
The use of laser diode in joint transform correlator (JTC) is discussed as an example of potential applications to optical signal processing. Effects of the coherence and astigmatism of laser diode beam are analyzed. Two methods for correcting laser diode beam using a cylindrical lens or a pair of cylindrical lenses are also reviewed. A corrected laser diode can be used in JTC to totally eliminate the effect of astigmatism.
We propose a new wavelet transform, which is the differential Haar-Gaussian wavelet transform. This new wavelet transform is applied to the edge detection, which can be processed in both spatial and the frequency domains. The bandwidth-matching algorithm and the telecentric optics are used to achieve fast calculation, and to produce high-precision edge detection results with large depth of focus.
A new method for fingerprint identification is proposed, using an ANFIS-based matching algorithm, which is suitable for large-scale identification systems. In this algorithm, the Gabor transform is used to extract features of fingerprints, while ANFIS is trained to identify the resultant Gabor features. Experimental verifications show that this proposed matching algorithm has high accuracy.
The use of a laser diode in a joint transform correlator (JTC) is proposed. Effects of temporal coherence, spatial coherence, astigmatism, and elliptical beams are analyzed. Laser diodes can be used in JTC, and also can be used for the correlation process in a Vander Lugt correlator and reading a hologram. Even a light-emitting diode (LED) may be used for the purposes mentioned, if its exit facet is sufficiently small. Two methods for correcting a laser diode beam using a cylindrical lens or a pair of cylindrical lenses are also reviewed. A corrected laser diode can be used in JTC to totally eliminate the effect of astigmatism.
The application of the wavelet transform to edge detection is discussed in general. In particular, two new wavelet transforms for edge detection as well as detecting the center of two edges are presented and discussed in detail. The proposed method is useful for lead inspection of surface mount devices in the electronic industry.
KEYWORDS: Near field scanning optical microscopy, Near field optics, Near field, Scanners, Nitrogen, Head, Signal detection, Cryogenics, Spectroscopy, Imaging spectroscopy
We have constructed a versatile low temperature scanning near-field optical microscope with the capability of near- field spectroscopy, operating at liquid nitrogen (LN) temperature. The compact low temperature scanning head was built on one piece of Marco with a unique linear nano-motor as the coarse approach. A tuning fork mechanism was adopted to detect and regulate the fiber tip-sample separation. The x-y scan can be performed either by the single tube scanner on triple tube scanner, depending on the application. A double shield dewar was used where the outer chamber was filled with LN. The core chamber was evacuated before cooling and then filled with cooled nitrogen gas, hence the working temperature can be controlled at around 80 K. A special designed coaxial double lens was used to introduce the illumination beam through a 200-micron fiber; the detected optical signal was transmitted via a fiber tip to a PMT or an APD. The performance test shows the stability of the new design. The resolution of shear force imaging and optical image of standard sample are shown.
KEYWORDS: Near field, Near field optics, Gallium nitride, Luminescence, Indium gallium phosphide, Indium gallium nitride, Semiconductors, Near field scanning optical microscopy, Optical microscopy, Optical microcavities
Microcavity shows the growing importance of the intensity enhancement, inhibition and spectral narrowing of spontaneous emission. The advantages of microcavity lasers are the very low threshold and small size. We have fabricated three types of semiconductor microdisks: InGaP, GaN, and InGaN multi-quantum-well microdisk with sun-like E- beam resist microstructure. The diameters are ranging from 5 - 20 micros. The photoluminescence of those microdisks in far-field and near-field observation are compared. Far-field fluorescence imaging shows bright emission of fluorescence around the circumference of the microdisks that can be interpreted as whispering-gallery mode in the disks. However, due to the different disk structures, near-field fluorescence images give several other different views of the light distribution of the microdisks corresponding to different optical modes in the disks. A theoretical calculation of the light distribution of InGaP microdisk based on the theory of optical modes in microdisk lasers is presented in this paper. The near-field mapping of the InGaN microdisks with sun-like E-beam resist structure demonstrates the possibility of using gratings made on the circumference to achieve directional emission without lowering output power.
KEYWORDS: Gallium nitride, Near field, Spectroscopy, Diodes, Near field scanning optical microscopy, Annealing, Near field optics, Luminescence, Optical microscopy, Optical spectroscopy
The light emitting properties of GaN blue light diode has been characterized by near-field optical microscopy, near- field spectroscopy and conventional spectroscopy. Since the mechanism of the light mission from this material with high defect density is not yet fully understand, it is necessary to study the optical properties in conjunction with the nano-scale structure. The conventional spectroscopic methods are limited by the diffraction barrier, hence the information of the correlation of light emission and defects is not sufficient. By using near-field spectroscopy and near-field optical microscopy, we have studied the electro- emission spectrum of GaN blue diode, which is fabricated on sapphire substrate using low-pressure MOCVD epitaxy technique in our lab. The results how that the near-field spectroscopy can provide spatially resolved local spectrum of the samples surfaces with sub-wavelength resolution and hence provide a new technique to study the mechanism of light emission at nanometer scale. The dependence of light emission intensities vs. injection currents in the near- field spectra reveals the donor levels of the energy bands in GaN blue diode.
KEYWORDS: Near field scanning optical microscopy, Near field optics, Near field, Imaging spectroscopy, Spectroscopy, Physics, Scanning tunneling microscopy, Optical microscopes, Spectroscopes, Ultrasonics
The progress of near-field optics research and its application in some Chinese universities and institutions is overviewed. The research activities on the instrumentation aspect of scanning near-field optical microscope, novel sample-tip regulation mechanism, fiber-tip preparations, high resolution imaging and near-field spectroscopy in confined mesoscopic systems, light emission new materials and devices, theoretical development of near-field light- matter interactions, new observations of physical phenomena in the near-field region, optical nanostructuring, are summarized. The current research projects and future prospective of the possible application of SNOM and near- field fluorescence imaging to biology, such as the in vitro cell nuclear assembly and apoptosis as well as gene recognition and DNA sequencing, and opto-electro devices are discussed.
KEYWORDS: Indium gallium phosphide, Near field scanning optical microscopy, Luminescence, Near field optics, Near field, Spectroscopy, Optical microscopy, Optical microcavities, Liquids, Nitrogen
Microcavity shows the growing importance of the intensity enhancement, inhibition nd spectral narrowing of spontaneous emission. The advantages of microcavity lasers are the very low threshold and small size. We have fabricated InGaP microdisks with radius of about 5 micrometers . The photoluminescence of our InGaP microdisks in far-field and near-field observation are compared. A strong enhancement of the photoluminescence intensity in the microdisks with respect to that of the un-patterned sample of the same epitaxial wafer is obtained. Far-field fluorescence imaging shows a bright red emission of fluorescence around the circumference of the microdisk. Simultaneous acquisition of near-field image and topography gives the correlation of the sample surface and light distribution. The optical disk mode pattern in our InGaP microdisks can be interpreted as whispering-gallery mode and the mixture of other modes.
A unique LDA system using a visible diode laser as the light source and an avalanche photodiode as the receiving detector is discussed in this paper. Experimental results with the system showed that under similar operational conditions, its signal to noise ratio is comparable to the results obtained using an Argon ion laser as the light source.
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