A source of tunable coherent radiation based on the use of Ti(3+):Al(2)O(3) crystals pumped by Cu-vapor laser radiation is studied experimentally. This source is promising for applications to atmospheric sensing as well as for use in applied optics and spectroscopy studies. Energy, kinetic, spectral, and spatial characteristics of lasing in nonselective and selective cavities and in the master oscillator power amplifier system are measured. Based on the latter scheme an experimental model of the source is developed. It permits continuously tunable radiation to be obtained in two spectral regions, i.e., within the fundamental band from 680 to 980 nm with a maximum average output power of ~2.6 W and in its second harmonic range from 340 to 490 nm with a maximum average output power of 450 mW. The linewidth of the emission is ~2 pm everywhere in the operating wavelength ranges, and the beam divergence is close to that of the diffraction. The pulse repetition rate is 5 kHz. A further increase in the output power is possible.
Nuclear magnetic resonance imaging (MRI) provides excellent images of organs and is an essential diagnostic tool in the medical field. Electron paramagnetic resonance imaging (EPRI) is being increasingly used in the biomedical field because of recent hardware advances. We present the first images obtained with a low-field (35.7 mT) multimodal apparatus that combines MRI and pulsed EPRI. For this purpose,the sample is composed of two sections, one sensitive to MRI and the other sensitive to EPRI. The MRI section of the sample is composed of three tubes containing 7 ml of a 10 mM CuSO 4 water solution. The EPR section of the sample is composed of two tubes containing 350 mg of lithium phthalocyanine. The EPR image represents the two-dimensional projection of the whole sample and is reconstructed from 32 one-dimensional projections by using the Fourier reconstruction method. The MRI image is obtained by selecting a sample slice, 10 mm in thickness, by using a spin-echo sequence and the two-dimensional fast Fourier transform. The experimental results obtained with this apparatus show that the spatial resolution is better than 1 mm for the MRI section and better than 7 mm for the EPRI section. The measured SNR of the MRI and EPRI images were about 60 and 160, respectively. A detailed description of the hardware, pulse sequences and image reconstruction techniques is reported.
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