Tion, with this architecture, it can be easier to achieve mode matching and proper thermal management, since the two cavities are separated. The experimental setup in the Raman laser and its basic pump supply is shown in Figure 1. The pump laser was an EO actively Q-switched Tm:YAP laser. The EOM operated using the polarization modulation process that was described in detail in a prior study [22]. The cavity incorporated a 10 mm length a-cut Tm:YAP (3 at.) crystal having a three 3 mm2 cross-section, as a get medium, end-pumped by a 30 W, 793 nm laser-diode. The pump beam was focused to a beam diameter of 330 inside the Tm:YAP crystal. Each the diode and Tm:YAP crystal were water-cooled to 18 . A plano-concave mirror having a 200 mm radius of curvature (ROC) was utilised as an input mirror, having an AR coating in the pump wavelength, and a higher reflectance (HR) coating at 1850000 nm. A plano-concave mirror using a 100 mm ROC was made use of as an output coupler (OC) with a partially reflecting (PR) coating of 55 reflectance for the 1850000 nm. The cavity length was 150 mm. The EOM was based on a KLTN electro-optic crystal. The crystal had a trapezoidal shape to minimize acoustic waves inside the crystal. The KLTN crystal was 2 mm extended, and the clear aperture was three three mm2 . The KLTN crystal was installed inside a temperature-controlled holder that maintained its temperature at six degrees above the phase transition temperature. A quarter wave plate (QWP) was inserted involving the Tm:YAP and also the KLTN. When the QWP axes was tilted 45with respect for the crystals axes the modulator was in “off” state. an uncoated yttrium aluminum garnet (YAG) etalon plate, with 100 thickness, was inserted in to the laser cavity to narrow the laser spectral line. The lasing wavelength was PHA-543613 Cancer measured to be 1935 nm. The pulse duration was measured to possess a 19 ns BMS-8 custom synthesis complete width at half-maximum (FWHM). The laser beam was linearly p-polarized. The output beam in the Tm:YAP was imaged by a pair of antireflective (AR) coated, plano-convex lenses, to a spot diameter of 220 in the center on the KGW crystal. Resulting from the divergence of your beam, the beam size improved to 300 at the facets in the Raman crystal. A half-wave-plate (HWP) was added among the lenses to manage the polarization orientation and allow switching involving the two different Raman vibration shifts from the KGW crystal, thereby enabling selective lasing at 2273 and 2344 nm. Such an external cavity configuration is advantageous for any two-wavelength Raman laser, since it allows for straightforward switching among the two Raman-shifted modes.Photonics 2021, 8,4 ofFigure 1. Experimental setup with the external KGW Raman laser and its actively Q-switched Tm:YAP seed laser.A plano-plano mirror, AR coated for 1860960 nm and HR coated for 2170700 nm, was used as an input mirror for the Raman laser cavity, in addition to a plano-concave mirror having a 100 mm ROC was employed as an OC. This mirror had a PR-coating of 93 reflectance amongst 2170 and 2450 nm and HR coating for 1850960 nm, enabling double-pass pumping from the 30 mm lengthy KGW crystal, which was utilised because the active Raman medium. The crystal was AR coated for the fundamental and Raman wavelengths, and its cross-section was 7 7 mm2 . This crystal was oriented for propagation along the b-axis, getting 901 cm-1 shift and 768 cm-1 shift, for E (electric field) perpendicular for the c-axis and a-axis, respectively, [16]. As described just before, the handle of your electric field polarization was facilitated usin.