Manifestations of nonlinear optical effects in a novel SRS-active crystal—natural topaz, Al₂(F_1−x(OH)_x)₂SiO₄: many-phonon χ⁽³⁾-lasing, more than sesqui-octave Stokes and anti-Stokes multi-wavelength comb lasing, cascaded and cross-cascaded χ⁽³⁾↔χ⁽³⁾Raman-induced interactions under single- and dual-wavelength picosecond collinear coherent pumping, THG and combined SRS-promoting phonon modes

Abstract

Natural crystals of topaz, Al 2 (F 1−x (OH) x ) 2 SiO 4 were found to be an attractive Raman gain material and a subject for the investigation of different χ (3) -nonlinear optical effects. We present several manifestations of photon-phonon interactions related to SRS and RFWM processes initiated by picosecond excitations at room and cryogenic (≈9 K) temperature. Among them are octave-spanning Stokes and anti-Stokes generation in the visible and near-IR spectral * On the 50th anniversary of the discovery of stimulated Raman scattering.

Tetragonal LiLuF4 - A novel crystal simultaneously active for SRS- and Ln3+ -lasing

“…As a consequence of the nonlinear coupling of these vibrational modes, a coherent combined SRS‐promoting mode emerges with energy ω SRS4C (≈820 cm −1 ) = ω SRS3 (≈385 cm −1 ) + ω SRS2 (≈435 cm −1 ). The appearance of “combined” SRS‐promoting phonon modes has already been observed in similar experiments performed with the following crystals: YPO 4 , LaBO 2 MoO 4 , Na 3 Li(MoO 4 ) 2 · 6H 2 O , Ca 2 ZnSiO 2 O 7 , (NH 2 ) 2 CNHCO(NH 2 ) · H 2 PO 3 , topaz (Al 2 (F 1− x (OH) x ) 2 SiO 4 ) , and GdVO 4 . Remarkably, the spontaneous Raman scattering spectra of all of these crystals do not show any line at frequencies of the respective “combined” phonon modes.…”

Low‐temperature stimulated Raman scattering spectroscopy of tetragonal GdVO4 single crystals

“…Unfortunately, oriented samples with high optical quality and the required sizes are temporarily unavailable for these experiments owing to the difficulties of growing the majority of these crystals. It is important to note here that combined SRS‐promoting phonon modes have also been detected in the following crystals: in tetragonal YPO 4 , in monoclinic LaBO 2 MoO 4 , in tetragonal Ca 2 ZnSi 2 O 7 , in orthorhombic Al 2 (F 1− x (OH) x )SiO 4 and others. Figure shows the SRS spectrum of GdVO 4 under pumping at λ f1 = 1.06415 µm wavelength in the excitation geometry c (≈ ab , ≈ ab ) c .…”

“…In particular, the most active modes are assigned as follows: ω SRS1 is related to the totally symmetric (stretching) A 1g (ν 1 ) vibration, ω SRS2 to B 1g (ν 3 ), ω SRS3 to E g (ν 3 ), and ω SRS7 to A 1g (ν 2 ). Regarding the vibrational nature of combined modes ω SRS5 and ω SRS6 current results and the analysis of such modes in four other SRS‐active crystals suggest that the occurrence of χ (3) ‐promoting vibrational modes is the effect of an interaction of coherent vibrational modes ω SRS1 and ω SRS2 , which are manifested only in the SRS‐lasing regime. This experimental finding in the studied vanadate as well as in the four other crystals mentioned above, however, still lacks a theoretical corroboration.…”

Beryllium Silicate, Be2SiO4 (phenakite) – a Novel Trigonal SRS‐Active Crystal

“…, and also, more recently, for the generation of broadband Stokes and anti‐Stokes lasing combs by cascaded processes, which could serve as a prerequisite for Fourier synthesis of ultrashort lasing pulses. Among others, particularly silicate crystals turned out to be promising material candidates for the generation of lasing frequency combs with bandwidths of up to two octaves , a compilation of known SRS‐active crystals with structures containing [SiO 4 ] groups is given in Table . Among them the most attractive crystals are the tecto ‐silicate α‐quartz (SiO 2 ) with a framework structure of [SiO 4 ] tetrahedral groups, and Al 2 [F 1– x (OH) x ] 2 SiO 4 (topaz) .…”

“…Among others, particularly silicate crystals turned out to be promising material candidates for the generation of lasing frequency combs with bandwidths of up to two octaves , a compilation of known SRS‐active crystals with structures containing [SiO 4 ] groups is given in Table . Among them the most attractive crystals are the tecto ‐silicate α‐quartz (SiO 2 ) with a framework structure of [SiO 4 ] tetrahedral groups, and Al 2 [F 1– x (OH) x ] 2 SiO 4 (topaz) . In the neso ‐subsilicate Al 2 [F 1– x (OH) x ] 2 SiO 4 the [SiO 4 ] structural units can be regarded, in reasonable approximation, as being isolated.…”