Hyperspectral imagery typically possesses high spectral resolution but low spatial resolution. One way to enhance the spatial resolution of a hyperspectral image is to fuse its spectral information and the spatial information of another high resolution image. In this paper, we propose a novel image fusion strategy for hyperspectral image and high spatial resolution panchromatic image, which is based on the curvelet transform. Firstly, determine a synthesized image with the specified RGB bands of the original hyperspectral images according to the optimal index factor (OIF) model. Then use the IHS transform to extract the intensity component of the synthesized image. After that, the histogram matching is performed between the intensity component and the panchromatic image. Thirdly, the curvelet transform is applied to decompose the two source images (the intensity component and the panchromatic image) in different scales and directions. Different fusion strategies are applied to coefficients in various scales and directions. Finally, the fused image is achieved by the inverse IHS transform. The experimental result shows that the proposed method has a superior performance. Comparing with the traditional methods such as the PCA transform, wavelet-based or pyramid-based methods and the multi-resolution fusion methods (shearlet or contourlet decomposition), the fused image achieves the highest entropy index and average gradient value. While providing a better human visual quality, a good correlation coefficient index indicates that the fused image keeps good spectral information. Both visual quality and objective evaluation criteria demonstrate that this method can well preserve the spatial quality and the spectral characteristics.
Sha Wang, Stefan Meister, Shaimaa Mahdi, Bülent Franke, Aws Al-Saadi, Lars Zimmermann, Harald Richter, David Stolarek, Viktor Lisinetskii, Viachaslau Ksianzou, Sigurd Schrader, H. Eichler
Raman scattering in planar silicon on insulator (SOI) waveguides with 2 μm width, 220 nm height and
2 cm length is investigated. A cw Nd:YAP laser at 1340.6 nm with 7 GHz FWHM spectral width is
used as the pump source. A lensed fiber of 2.5 μm focus diameter is used to couple the pump laser into
the waveguide. The coupling efficiency is estimated to be around 10%. Spontaneous Raman scattering
is observed with as low as 2.5 mW pump power inside the waveguide. The spontaneous Raman
spectrum is measured by an optical spectrum analyzer. The first order Raman peak is measured at
around 1441.4 nm corresponding to a Raman shift of 15.6 THz, while the FWHM of Raman spectrum
is measured as around 100 GHz. Maximum Raman output of around 90 pW is obtained by around 22
mW pump. The stimulated Raman gain coefficient is estimated as around 56 cm/GW from the
relationship between spontaneous Raman output power and pump power. A temperature dependence of
Raman frequency shift of about 0.6 GHz/K is measured. The spontaneous anti-Stokes Raman scattering
output peak at 1253 nm is also observed with around 35 mW pump. Stimulated Raman amplification
measurement is carried out with a SLED white light source as probe signal. With 35 mW pump power,
around 0.6 dB gain has been determined with both pump and probe being TE polarized.
Long range water vapor DIAL-systems require efficient and rugged laser sources. The quasi-three-level transition
from R1 to Z5 in Nd:GSAG with 943nm wavelength is a promising candidate. An actively Q-switched Nd:GSAG
laser was established. Up to 31mJ output pulse energy and up to 26Hz repetition rate was achieved. Injection
seeding was used to obtain single frequency operation. The seed laser is a distributed feedback laser diode. Laser
frequency was stabilized by ramp-hold-fire method. By tuning the wavelength of the seed laser a 0.83nm tuning
range of the pulsed Nd:GSAG laser was obtained. Measured by Fabry-Perot interferometer the spectral line width
was approximately 50MHz.
Wavelength around 940 nm lasing can be obtained by quasi-three-level operation of Nd doped laser crystal.
Diode end pumping provides the necessary high pump intensity in the laser crystal. In order to get high efficiency of the
end pumped laser system, the overlap coefficient between pump beam and laser beam should be optimized. Thermal lens
coefficient is one of the most important parameters to design the laser cavity structure. The time dependent heat
conduction equation is solved numerically in order to study the thermal lens effect in pulsed pumping laser crystal.
Calculated results showed that the thermal lens coefficients change with different pump frequencies. Experiments are
done with Nd:YAG and Nd:GSAG laser rod. The thermal lens coefficient of Nd:YAG at pump frequency 50 Hz with
pump beam diameter 1.5 mm is 10.2 Wm, while the thermal lens coefficient of Nd:GSAG at pump frequency 50 Hz with
pump beam diameter 1.75 mm is 5.9 Wm.
An actively Q-switched Nd:GSAG laser with 942nm wavelength was frequency doubled in a critically type-I
phase-matched LBO. Maximum pulse energy of 8mJ with 300ns pulse duration at 471 nm was obtained with 19mJ
incident radiation at 10Hz. The corresponding conversion efficiency was 42%. The frequency doubling of a focused
Gaussian beam involves spatially dependent phase mismatching due to beam divergence. It decreases the conversion
efficiency and deteriorates the beam quality. According to the theoretical calculation, elliptical focusing was used to
improve the second harmonic beam quality and slightly increase the conversion efficiency.
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