Jingmin Dai

Double-image encryption based on the affine transform and the gyrator transform

We propose a kind of double-image-encryption algorithm by using the affine transform in the gyrator transform domain. Two original images are converted into the real part and the imaginary part of a complex function by employing the affine transform. And then the complex function is encoded and transformed into the gyrator domain. The affine transform, the encoding and the gyrator transform are performed twice in this encryption method. The parameters in the affine transform and the gyrator transform are regarded as the key for the encryption algorithm. Some numerical simulations have validated the feasibility of the proposed image encryption scheme.

Image encryption by using gyrator transform and Arnold transform

We propose an optical image encryption algorithm based on Arnold transform and gyrator transform. The amplitude and phase, which are the outputs of gyrator transform, are separated into several sub-images. Arnold transform is introduced for scrambling the data of the sub-images. The random spectrum composed of the scrambled sub-images is transformed by gyrator transform. An iterative structure of the algorithm is designed for enhancing the security of the encryption algorithm. The parameters of gyrator transforms and separating scheme serve as the key of the encryption method. The encryption process can be implemented by an electro-optical setup. Some numerical simulations have been given to demonstrate the security and validity of this algorithm.

Generation of hollow Gaussian beam by phase-only filtering.

We propose a novel phase retrieval algorithm in Hankel (or called Fourier-Bessel) transform domains by using Monte-Carlo method. Based on the proposed algorithm, we investigate the generation of Gaussian-like beams, such as hollow Gaussian beam, Bessel-Gaussian beam and Laguerre-Gaussian beam, with double phase filtering operations. The phase distributions of filters are determined by employing the proposed phase retrieval algorithm. The advantage of the method is that the total energy of the beam is conservative. Numerical simulations are shown to demonstrate the validity of the scheme.

Retrieval of particle size distribution in the dependent model using the moment method

The problem of determining particle size distribution using the moment method in the spectral extinction technique is studied. The feasibility and reliability of the retrieval of spherical particle size distribution using the moment method are investigated. The single spherical particle extinction efficiency, which is derived theoretically using the Mies solution to Maxwells equation, is approximated with a higher order polynomial in order to apply the moment method. Simulation and experimental results indicate that a fairly reasonable representation of the particle size distribution can be obtained using the moment method in the dependent model algorithm. The method has advantages of simplicity, rapidity, and suitability for in-line particle size measurement.

Image encryption based on random scrambling of the amplitude and phase in the frequency domain

We propose an image encryption algorithm by using random position scrambling of the amplitude and phase functions in the frequency domain of optical transform. The positions of amplitude and phase data are scrambled randomly in the horizontal or vertical direction. The random position orders can be regarded as the key of the algorithm. Moreover, random phase encoding is not used in the proposed algorithm. A feasible optical implementation of the encryption algorithm is given. Some numerical simulations have demonstrated the capability of the algorithm.

REALIZATION OF HOLOGRAPHIC STORAGE ON METAL FILM BY FEMTOSECOND LASER PULSES MICROMACHINING

Optical information has been stored on the metal film by femtosecond laser pulses with the aid of the computer-generated hologram (CGH). The Fourier transform of an object is performed by a computer, and then the resulted complex amplitude distribution is encoded by the detour phase method. The resulted cell-oriented CGH is directly written on the metal film deposited on the glass substrate using femtosecond laser by selective ablation. The object wave has also been reconstructed with high fidelity by using a collimated He-Ne laser beam.

Spectral emissivity and transmissivity measurement for zinc sulphide infrared window based on integrating-sphere reflectometry

Abstract. The spectral emissivity and transmissivity of zinc sulphide (ZnS) infrared windows in the spectral region from 2 to 12 μm and temperature range from 20 to 700°C is measured by a facility built at the Harbin Institute of Technology (HIT). The facility is based on the integrating-sphere reflectometry. Measurements have been performed on two samples made of ZnS. The results measured at 20°C are in good agreement with those obtained by the method of radiant energy comparison using a Fourier transform infrared spectrometer. Emissivity measurements performed with this facility present an uncertainty of 5.5% (cover factor=2).

Multi-wavelength emissivity measurement of stainless steel substrate

The emissivity is a key parameter to measure the surface temperature of materials in the radiation thermometry. In this paper, the surface emissivity of metallic substrates is measured by the multi-wavelength emissivity measurement apparatus developed by the Harbin Institute of Technology (HIT). The measuring principle of this apparatus is based on the energy comparison. Several radiation thermometers, whose emissivity coefficients corrected by the measured emissivity from this apparatus, are used to measure the surface temperature of stainless steel substrates. The temperature values measured by means of radiation thermometry are compared to those measured by means of contact thermometry. The relative error between the two means is less than 2% at temperatures from 700K to 1300K, it suggests that the emissivity of stainless steel substrate measured by the multi-wavelength emissivity measurement apparatus are accurate and reliable. Emissivity measurements performed with this apparatus present an uncertainty of 5.9% (cover factor=2).

Near infrared tunable diode laser absorption spectroscopy for ethylene concentration analysis

The absorption spectra of ethylene (C2H4) located at v5+v9 band near 1626nm involve some strong peaks that are suitable for trace gas concentration detection. They are interference free from other abundant molecules that are normally present in the atmosphere. An ethylene analysis system has been developed based on the tunable diode laser absorption spectroscopy. The high resolution transmission of ethylene near 1626nm has been measured by this system under different concentration. The severe overlapping between neighboring spectral lines of ethylene is observed and they cannot be separated with each other easily under atmospheric pressure and room temperature, so a multi-peaks spectrum recognition method is proposed to separate the ethylene spectrum from other interference gas while the ethylene concentration is ultra low. A mixture of high concentration methane, low concentration ethylene with air is used to evaluate the recognition efficiency. The result shows that the ethylene line can be abstract from strong background interference using multi-peaks spectrum recognition method and the accuracy of concentration measurement can reach about 5% comparing with a mass flow meter.

A method to identify material based on spectrum analyses

According to radiation temperature measurement theory, the key of temperature measurement is to choose the appropriate temperature model, which depends on the type of measured material. So how to identify the material type is significant to measure its surface temperature. Different materials have different spectral characters at the same temperature. In this paper, a method based on spectrum analysis is proposed to identify material. The spectrum of four kinds of materials is measured using Fourier transform infrared spectrometer (FTIR) at the same temperature 873K. The peak values extracted from each spectrum are used to train the identification algorithm. Then one material is chosen from the measured materials to verify the identification algorithm if the type of material can be identified. The experimental results suggest that the new method based on spectrum analyses can accurately identify the type of material.