Stimulated Raman scattering in natural crystals of fluorapatite, Ca 5 (PO 4 ) 3 F

Hexagonal Ca 5 (PO 4 ) 3 F, known as natural crystal fluorapatite and oldest host‐crystal for Ln 3+ ‐lasant ions, is presented as a Raman‐active material. High‐order Raman‐induced χ (3) ‐nonlinear processes are discovered in natural crystals of fluorapatite under picosecond pumping at 1.064 μm and 0.532 μm wavelength. A multitude of Stokes and anti‐Stokes components is generated in the ultraviolet, visible and near‐infrared spectral region by stimulated Raman scattering (SRS) and Raman four‐wave mixing (FWHM), resulting in a frequency comb with a width of 520 THz. The spectral lines are identified and attributed to the ν 1 (A g ) vibration mode of the tetrahedral [PO 4 ] units which is related to a Raman shift of ω SRS ≈ 965 cm −1 . The first Stokes steady‐state Raman gain coefficient in the near‐infrared spectral range is estimated to be >0.38 cm·GW −1 . Finally, a short review of SRS‐promoting vibration modes and observed χ (3) ‐ nonlinear interactions in all known SRS‐active natural crystals (minerals) is given.