Laser Tuning in Layered h-BN Crystals

Abstract

Integrated optics shows great potential in the current optical communication systems, sensor technology, optical computers, and other fields. Tunable laser technology within a certain range is the key to achieving on-chip optical integration; to realize which, Raman scattering is a competitive method that can effectively transfer incident laser energy to optical phonons due to the photon−phonon interaction. Here, we take hexagonal boron nitride as the energy conversion medium, and based on the angle-resolved polarized Raman spectroscopy, it is found that when laser polarization vector e i ⊥ c axis, the spectrum obtains maximal scattering across the cross section and a minimal depolarization ratio. At room temperature, h-BN obtains an output signal with a wavelength of 522.8 nm and a full-width at half-maximum of 0.24 nm under the excitation of 488 nm pump laser, and the depolarization ratio is 0.09 (theoretically, it is 0, and this difference is due to experimental errors). And then, within the temperature range of 80∼420 K, the scattered light wavelength shows a high-precision shift of 0.006 nm/25 K, indicating that continuous wavelength tuning has been successfully achieved in h-BN.

Isotope Effects on the Optical Phonons of Cubic Boron Phosphide

“…For c-BAs with the same structure as that of c-BP, the TO-LO splitting also cannot be observed in the Raman spectra. In addition, the two modes observed in the Raman spectra of c-nat BAs are absent in c- 10 BAs and c- 11 BAs, which is very similar to the phenomenon exhibited in c-BP. Hadjiev et al [17] and Rai et al [24] have investigated the Raman spectra of c-BAs with certain boron isotope ratios and identified the two signals as vibrational modes associated with 10 B and 11 B, respectively.…”

“…The purity of 10 B and 11 B raw materials is assumed as 90% in this research. Therefore, for the sample using the raw materials with a ratio of 10 B: 11 B as 7:3, corresponding component percentage of 10 B should be 66%. This hypothetical calculation is reasonable because the focus here is a qualitative discussion of the changes caused by isotope effects.…”

“…Isotope-induced changes in nuclear mass will affect the phonon properties directly, including frequencies, eigenvectors, and lifetime, [5] which further determines the thermal, elastic, and vibrational properties. [5][6][7] Raman spectroscopy is a good technique to characterize the optical phonons of materials at the center of the Brillouin zone (BZ), namely Γ point, [8][9][10] and thus it is taken here to analyze the isotopic effects.…”

“…The Raman spectrum of c- 11 BP has been studied recently but with little discussion. [1] The work conducted previously analyzed the Raman spectra of self-synthesized c-nat BP and isotope-purified c- 10 BP and c- 11 BP crystals, based on which a sharp peak with high intensity and small linewidth was identified as a mixed mode of transverse optical (TO) phonon and longitudinal optical (LO) phonon at Γ point through infrared reflectance spectra. [15,16] In c-nat BP, there is also a small Raman peak with low intensity and large linewidth at the low-frequency side of that TO-LO-mixed mode peak, which is hard to be observed in the spectra of isotopepurified crystals.…”

Raman tensor of graphite: Symmetry of G, D and D′ phonons

“…Its angleresolved polarized function can help with a uniform study on the symmetry of materials and Raman tensor. In our previous work, systematic studies have been conducted on the polarized characteristics and phonon symmetry of some typical optically anisotropic materials with aluminum nitride (AlN) [13][14][15][16] and transition metal dichalcogenides (TMDs) as the representatives [17][18][19][20][21][22][23][24][25][26][27], from which one method has been proved effective, that is, the information we need such as Raman tensor and differential polarizability can be obtained by fitting the experimental results with theoretical basis suitable for experimental system, so as to explore the vibrational symmetry of material phonon modes.…”