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We demonstrate a monolithic continuous wave (CW) fiber laser source at 1080 nm, producing 2.5 kW average laser power with near diffraction-limited beam quality (M~2 < 1.3). The laser consists of a CW fiber laser oscillator and one double cladding (DC) fiber amplifier in the master oscillator-power amplifier (MOPA) configuration. The optical-to-optical conversion efficiency of the entire laser system with respect to the launched pump power is ～77.9%....
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We demonstrate a monolithic continuous wave (CW) fiber laser source at 1080 nm, producing 2.5 kW average laser power with near diffraction-limited beam quality (M~2 < 1.3). The laser consists of a CW fiber laser oscillator and one double cladding (DC) fiber amplifier in the master oscillator-power amplifier (MOPA) configuration. The optical-to-optical conversion efficiency of the entire laser system with respect to the launched pump power is ～77.9%.
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We study the impact of standard active double-clad (DC) fiber characteristics and laser architectures on the generation of long-wavelength Yb-doped high-power fiber lasers around 1154 nm. Both theoretical and experimental works ha...
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We study the impact of standard active double-clad (DC) fiber characteristics and laser architectures on the generation of long-wavelength Yb-doped high-power fiber lasers around 1154 nm. Both theoretical and experimental works have been performed highlighting that Yb-doped fiber lasers can emit efficiently in multiwatts operation at wavelengths higher than 1150 nm. This study has been focused on the use of standard all-fiber active and passive components as well as on the use of standard DC Yb-doped fibers without any spectral filtering except cavity mirrors.
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The disordered crystal LiGd0.936Yb0.064(MoO4)(2) was grown with high optical quality by the flux method using Li2MoO4 as a solvent. The crystal possesses tetragonal symmetry belonging to the space group I (4) over bar, with two no...
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The disordered crystal LiGd0.936Yb0.064(MoO4)(2) was grown with high optical quality by the flux method using Li2MoO4 as a solvent. The crystal possesses tetragonal symmetry belonging to the space group I (4) over bar, with two nonequivalent sites occupied by the dopant. Spectroscopic studies at 5 and 300 K provided information on the Stark energy-level splitting and the absorption and emission cross sections of the Yb3+ ion. Laser operation of Yb3+ was obtained for the first time in such a Li-containing double tungstate or molybdate. The tuning range with a Ti:sapphire laser pumping extended over similar to 32 nm for the sigma polarization and 23 nm for the pi polarization. Without a tuning element the laser performance was similar for the two polarizations. By using a 10% transmission output coupler, a maximum output power of approximate to 470 mW was obtained with a slope efficiency eta = 64.5% and the absorbed pump power at threshold was 520 mW. Laser operation was also achieved by pumping with a tapered diode laser and a fiber-coupled diode laser module, with a Yb laser output power of 0.66 W in the latter case. (c) 2006 Optical Society of America.
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Reliable operation of 650-nm laser bars with GaInP quantum wells embedded in AlGaInP waveguide layers and n-AlInP and p-AlGaAs cladding layers is reported. The 5-mm-wide bars consisting of ten emitters with 100-$muhbox m$-wide str...
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Reliable operation of 650-nm laser bars with GaInP quantum wells embedded in AlGaInP waveguide layers and n-AlInP and p-AlGaAs cladding layers is reported. The 5-mm-wide bars consisting of ten emitters with 100-$muhbox m$-wide stripe width showed reliable operation over 2000 h at 5 W.
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We present a novel method for ground moving target imaging using a synthetic aperture radar system transmitting ultranarrowband continuous waveforms (CW). Our method exploits the high Doppler resolution provided by ultranarrowband...
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We present a novel method for ground moving target imaging using a synthetic aperture radar system transmitting ultranarrowband continuous waveforms (CW). Our method exploits the high Doppler resolution provided by ultranarrowband CW signals to image both the scene reflectivity and to determine the velocity of multiple moving targets. We develop a new forward model based on the temporal Doppler induced by the movement of antennas and moving targets. The forward model relates reflectivity and velocity information at each location to a correlated received signal. We form the reflectivity images of the moving targets and estimate their motion parameters using a filtered-backprojection (FBP) technique combined with the contrast or gradient optimization method. The method results in focused reflectivity images of moving targets and their velocity estimates, regardless of the target location, speed, and velocity direction. We show that the amplitude and visible edges of the targets can be correctly reconstructed when the correct target velocity estimate is used in the FBP imaging. We present the resolution analysis of the reflectivity images. Extensive numerical simulations demonstrate the performance of our method and validate the theoretical results.
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We consider synthetic aperture radar (SAR) imaging using ultranarrowband continuous waveforms (CWs). Because of the high Doppler resolution of CW signals, we refer to this imaging modality as Doppler synthetic aperture radar (DSAR...
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We consider synthetic aperture radar (SAR) imaging using ultranarrowband continuous waveforms (CWs). Because of the high Doppler resolution of CW signals, we refer to this imaging modality as Doppler synthetic aperture radar (DSAR). We present a novel model and an image formation method for the bistatic DSAR for arbitrary imaging geometries. Our bistatic DSAR model is formed by correlating the translated version of the received signal with a scaled or frequency-shifted version of the transmitted CW signal over a finite time window. High-frequency analysis of the resulting model shows that the correlated signal is the projections of the scene reflectivity onto the bistatic iso-Doppler curves. We next use microlocal techniques to develop a filtered-backprojection (FBP) type image reconstruction method. The FBP inversion results in the backprojection of the correlated signal onto the bistatic iso-Doppler curves as opposed to the bistatic iso-range curves used in the traditional wideband SAR imaging. We show that our method takes advantage of the velocity, as well as the acceleration of the antennas in certain directions, to form a high-resolution SAR image. Our bistatic DSAR imaging method is applicable for arbitrary flight trajectories and nonflat topography, and can accommodate system-related parameters. We present resolution analysis and extensive numerical experiments to demonstrate the performance of our imaging method.
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The study presents a simultaneous variation of equatorial electrojet (EEJ) current and the ionospheric F2-layer maximum electron density (NmF2) during geomagnetic quiet days and moderate solar conditions (solar radio flux, 饾惞10....
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The study presents a simultaneous variation of equatorial electrojet (EEJ) current and the ionospheric F2-layer maximum electron density (NmF2) during geomagnetic quiet days and moderate solar conditions (solar radio flux, 饾惞10.7 魛祹 120 sfu). The geomagnetic measurements at Kotatobang (KTB) and Langkawi (LKW) stations have been used to estimate the magnetic daily variation in H-component and in deriving EEJ. The NmF2 data set is from Frequency Modulation Continuous Wave (FM-CW), an analogue ionosonde located at the KTB station. The study examines both the diurnal and seasonal variation in EEJ and the corresponding effect on the measured NmF2. The results obtained show that the derived EEJ at LKW shows a daytime peak which coincides with the period NmF2 measurement at KTB station depleted to a daytime low value. The role of EEJ at the LKW station correlates poorly with the NmF2 at KTB in which their correlation coefficient (r) is in the range of 0.02 to 0.04 for equinox, summer and winter, respectively. However, an r-value of 0.33 was observed when the whole data set for the year 2012 was considered. The poor correlation coefficient between derived EEJ and NmF2 measured at KTB during the moderate solar condition suggest that EEJ has little or no influence on the prevailing ionospheric condition at a low latitude station located outside the EEJ strip.
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We propose a theory and experimentally verify ultraflat comb generation by dual-sine-wave phase-only modulation. This novel approach requires a single optical element and is very practical and efficient in terms of both power budg...
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We propose a theory and experimentally verify ultraflat comb generation by dual-sine-wave phase-only modulation. This novel approach requires a single optical element and is very practical and efficient in terms of both power budget and bandwidth. Using this approach, we have generated two optical spectra, one with 11 comb lines and 1.9-dB flatness and the other with 9 comb lines and 0.8-dB flatness.
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In this paper, a concurrent dual-band hybrid down conversion architecture based on continuous-wave (CW) Doppler radar is demonstrated. The proposed system operates at 2.05-/1.64-GHz simultaneously. The dual-band can solve the null...
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In this paper, a concurrent dual-band hybrid down conversion architecture based on continuous-wave (CW) Doppler radar is demonstrated. The proposed system operates at 2.05-/1.64-GHz simultaneously. The dual-band can solve the null detection point problem generated at quarter-wavelength distance between the target and antenna. The detection results from different channels can be mutually verified to improve the system accuracy. The vital sign can be detected by the radar through the wooden board at higher transmit power. For satisfying the requirements of dual-band RF transmitters, and a two-stage dual-band power amplifier is designed. Experimental results have demonstrated the feasibility of the system.
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