Abstract
Comparative investigation of stimulated Raman scattering (SRS) characteristics in the YVO4, GdVO4, and Ca3(VO4)2 orthovanadate crystals at both low and high frequency anionic group vibrations is presented. It was found that GdVO4 is the most perspective for SRS generation on both the ν1 stretching and ν2 bending modes of internal anionic group vibrations with the strongest SRS pulse shortening under synchronous picosecond pumping. It is as a result of GdVO4‘s widest linewidth (17cm−1) of the homogeneously broadened scheelite-type component of the bending ν2 Raman line that led to the strongest SRS pulse shortening down to the dephasing time of the widest (scheelite-type) Raman mode at the secondary intracavity short-shifted SRS conversion. It allowed us to achieve SRS pulses with sub-picosecond duration under tens-of-picoseconds pumping due to the strongest 42-fold pulse shortening. Using the Ca3(VO4)2 crystal with essentially wider Raman lines (~50cm−1) did not allow us to generate SRS pulses shorter than 1 ps. It can be explained by inhomogeneous broadening of the Raman lines in Ca3(VO4)2 because of its structural disordering. Using the measured SRS pulse duration, the homogeneous broadening of the inhomogeneously broadened bending Raman line of Ca3(VO4)2 was estimated to be ~9cm−1. Among the orthovanadate crystals, the YVO4 crystal with the highest Raman gain and with homogeneously broadened Raman lines allowed us to realize the most efficient SRS lasing and SRS pulse shortening truly down to inverse half-width of the bending Raman line.
Highlights
Gadolinium, and calcium orthovanadate crystals are well-known as the laser host materials [1,2]
One more interesting property of the orthovanadate crystals is the presence of two intense vibrational lines in one of the polarized spontaneous Raman scattering configurations: the most intense one corresponds to the above mentioned high-frequency (ν1 ) stretching mode, but the second line with a low frequency of ν2 ~354–382 cm−1 corresponds to O-V-O bending internal vibration of the crystal anionic group [11,12]
This is similar to polarized Raman spectra of scheelite-type crystals [13], but the crystalline structure is different leading to wider Raman lines in the orthovanadate crystals
Summary
Gadolinium, and calcium orthovanadate crystals are well-known as the laser host materials [1,2]. This method comprises a cascade process of primary extracavity Raman conversion from pump radiation into a ν1 -shifted Stokes component and secondary intracavity Raman conversion from the ν1 -shifted Stokes component into the (ν1 + ν2 )-shifted Stokes component with significant pulse shortening down to the inverse width of the widest ν2 line It was realized in a set of alkali-earth molybdate and tungstate crystals having a scheelite-type structure [14,15,16,17] where the ν2 line is the widest because of an overlap of two symmetric bending (scissoring and twisting) modes (Ag + Bg ) of internal vibrations of the crystal anionic group [13]. Comparative investigation of SRS in YVO4 , GdVO4 , and Ca3 (VO4 ) crystals with a single and combined frequency shift on both Raman modes (stretching and bending) under synchronous picosecond pumping was carried out taking into account the crystalline and vibrational structure to answer the question how the nature of the bending Raman mode line widening affects the SRS pulse shortening
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