Spectroscopy and laser gain measurements of CaF2: Nd, X3+, Z3+ (X, Z = Gd, La, Ce, Y, Lu, Sc) crystals for broadband lasers applications

An efficient approach to avoid Nd3+ clustering in CaF2:Nd3+ is the co-doping with non-optically active buffer (Bu) ions creating Nd-Bu emitting clusters for laser applications around 1050 nm (4F3/2 → 4I11/2) taking advantage of their unique large absorption and emission bands. A detailed spectroscopic investigation of buffer codoping with Gd3+, La3+, Ce3+, Y3+, Lu3+ and Sc3+ ions is presented. The codoping with large buffer ions compared to Nd3+ like Gd3+, La3+, Ce3+ leads to one type of dominant Nd-Bu cluster, while the codoping with smaller ions like Y3+, Lu3+ and Sc3+ involves the formation of two types of Nd-Bu clusters, which can be discriminated in absorption/excitation/luminescence spectra and which further exhibit two different lifetimes. The laser gain performance of these codoped crystals with one or two buffer ions is investigated using a dedicated double modulation pump-probe setup allowing the tuning of both pump and probe wavelengths. As an example, a laser gain of 35% is measured in a 5 mm long CaF2: 0.5%Nd, 5%Lu crystal at 1054 nm for 400 mW of absorbed pump power at 797 nm. This direct measurement of the laser gain is particularly interesting for crystals codoped with small buffer ions where the presence of two Nd emitting centers complicates the calculation of the laser gain. For large buffer ions, a direct calculation of the laser gain is shown to be in good agreement with the experimental gain values. •Detailed spectroscopic analysis of CaF2:Nd codoped with one or two buffer ions.•Demonstration of one dominant Nd3+ center with large buffer ions and two dominant Nd3+ centers with small buffer ions.•Tuning of the emission spectral profile as well as the 4F3/2 lifetime by carefully choosing the right combination of buffer ions and excitation wavelength.•Laser gain in CaF2:Nd codoped using a dedicated double-modulation pump-probe setup with tunable pump and probe sources.