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We demonstrate a Nd : YLF-YVO4 intracavity Raman laser in the 1.5 μm eye-safe region. The fundamental wave at 1314 nm from the end-pumped Nd :YLF is down-converted to 1488 nm, utilizing the 890 cm−1 Raman shift of an YVO4 laser crystal. We use two etalons in the fundamental cavity and Stokes cavity, respectively, to suppress their spectral line width. Under a diode pump power of 43 W at 806 nm, we obtain an average Stokes output power of 3.75 W at an acousto-optic Q-switched pulse repetition frequency of 20 kHz, corresponding to an optical efficiency of 8.7%. With the etalons used, the spectral line width of the Stokes laser is narrowed from over 0.2 to 0.04 nm. The beam quality factor of the eye-safe Stokes output is measured to be 1.12 and 1.19 in the x and y directions, respectively. [ABSTRACT FROM AUTHOR]

In this manuscript, a reconfigurable leaky wave antenna is proposed with linearly polarized and circularly polarized properties, which is composed of two layers with feeding waveguide and radiation elements. The bottom layer is a half-mode substrate integrated waveguide etched with a spoof surface plasmon polaritons structure as a high-dispersion feeding waveguide to excite 8 circular patches as radiation elements in the top layer. In a unit element, the horizontal linear polarization (HLP) and right-hand circular polarization (RHCP) radiation are switched using a p-i-n diode crossing a slot of a circular metal patch. HLP performance is achieved as the p-i-n diode is switched off, and RHCP is achieved as the p-i-n diode is switched on. The measured results verify the design theory and the simulated results. Over the working band of 10.4~12.8 GHz, the proposed antenna can radiate scanning beams covering about a 73° region, including the broadside direction with HLP and RHCP. [ABSTRACT FROM AUTHOR]

To measure the concentration of trace CO2 with high performance, tunable diode laser absorption spectroscopy technology was adopted in this paper. Kalman‐wavelet algorithm was used to depress the detector noise and optical interference fringe noise. Experimental results show that the second harmonic signal‐to‐noise ratio of the measuring system at 50ppmv CO2 gas was improved by 2.06 times compared with no filtering. Under different CO2 concentrations, the measuring errors are from 2.57% to 2.66%. According to Allan variance analysis, the minimum detection limit was reduced to 5.2 ppmv with the optimal integration time of 61 s. And, the standard deviation value was decreased from 33 to 19 ppmv during long‐term measurement, which can guarantee the high‐performance measurement of CO2 gas. [ABSTRACT FROM AUTHOR]

A dual‐band leaky wave antenna (LWA) based on substrate integrated waveguide (SIW) is presented in this paper. The radiation elements are composed of a set of periodical transverse slots and a long longitudinal slot that can radiate scanning beams at two different bands under TE10‐mode and TE20‐mode excitation, respectively. The scanning beams in the two bands both cover the forward region, and polarizations are perpendicular. Under TE10 excitation, the proposed antenna radiates scanning beams in the low band (8.2 GHz ~ 9.1 GHz) with gain varying from 10.6 to 15.9 dBi. Under TE20 excitation, the beams of the proposed antenna scan in the high band of 18.8 GHz ~ 22 GHz with gain varying in 11.7 dBi ~ 16 dBi. The measured results of the fabricated prototype confirm the design theory and simulated results. [ABSTRACT FROM AUTHOR]

We demonstrate a narrow-linewidth passively Q-switched Raman laser at a sodium line of 589.16 nm. Fundamental laser at 1066 nm is generated by c-cut Nd:YVO4 laser crystal and shifted to 1178 nm by intracavity stimulated Raman scattering (SRS) conversion using a-cut YVO4 crystal. Two etalons are used to narrow the fundamental laser linewidth and the resultant Stokes linewidth, as well as to tune the fundamental wavelength for obtaining the yellow output at the sodium line. The frequency-doubled Raman laser produced the 330 mW average output power at 589.16 nm, with a narrow linewidth of ∼0.01 nm. [ABSTRACT FROM AUTHOR]