Femtosecond Cr:LiSAF and Cr:LiCAF lasers pumped by tapered diode lasers

Abstract

We report compact, low-cost and efficient Cr:Colquiriite lasers that are pumped by high brightness tapered laser diodes. The tapered laser diodes provided 1 to 1.2 W of output power around 675 nm, at an electrical-to-optical conversion efficiency of about 30%. Using a single tapered diode laser as the pump source, we have demonstrated output powers of 500 mW and 410 mW together with slope efficiencies of 47% and 41% from continuous wave (cw) Cr:LiSAF and Cr:LiCAF lasers, respectively. In cw mode-locked operation, sub-100-fs pulse trains with average power between 200 mW and 250 mW were obtained at repetition rates around 100 MHz. Upon pumping the Cr:Colquiriite lasers with two tapered laser diodes (one from each side of the crystal), we have observed scaling of cw powers to 850 mW in Cr:LiSAF and to 650 mW in Cr:LiCAF. From the double side pumped Cr:LiCAF laser, we have also obtained ~220 fs long pulses with 5.4 nJ of pulse energy at 77 MHz repetition rate. These are the highest energy levels reported from Cr:Colquiriite so far at these repetition rates. Our findings indicate that tapered diodes in the red spectral region are likely to become the standard pump source for Cr:Colquiriite lasers in the near future. Moreover, the simplified pumping scheme might facilitate efficient commercialization of Cr:Colquiriite systems, bearing the potential to significantly boost applications of cw and femtosecond lasers in this spectral region (750-1000 nm).

Tapered diode-pumped continuous-wave alexandrite laser

“…This value is higher than Ti:sapphire (131 μs × 10 −20 cm 2 [34]), which is also known for its high lasing thresholds, but lower than Cr:LiCAF (228 μs × 10 −20 cm 2 [34]) and Cr:LiSAF (322 μs × 10 −20 cm 2 [34]). We also note here that the beam quality of the TD in this study (M 2 slow ∼ 5) was worse than what has been used earlier in pumping Cr:LiCAF/LiSAF lasers (M 2 slow ∼ 2.5 [54]). Due to the multimode nature of the pump beam in the slow axis, the alexandrite laser output was also multimode in the corresponding axis.…”

“…Using the above-mentioned parameters, the brightness of the laser device is estimated as B 500 mW∕μm 2 , which is about 2 times higher than the commercial single-mode diodes and single-emitter devices on the market. However, it is possible to grow TDs with brightness approaching 1000 mW∕μm 2 [54,55]. Hence, the results presented in this study are likely to be improved in the near future by using even higher quality TDs.…”

“…We have been using similar TDs to pump Cr:LiCAF and Cr:LiSAF gain media to minimize the complexity in pumping geometry [54]. Similarly, we believe that the TDs that provide the highest brightness output at these wavelengths will considerably simplify the complexity and lower the cost of cw alexandrite lasers.…”

“…The TDL provided up to 1 W of output power with a tunable optical spectrum centered around 678.5 or 680.4 nm, which is suitable for in-line pumping of alexandrite by populating the R-lines. The diodes possess M 2 (1∕e 2 ) values of 1.1 in the fast axis and 5 in the slow axis, and a brightness of about 500 mW∕μm 2 , which represents a twofold improvement compared to the state-of-the-art singlemode and broad-stripe single-emitter diodes in the same wavelength range [54]. While pumping at the 678.5 nm line, using a 0.5% output coupler, we have obtained output powers as high as 168 mW, slope efficiency as high as 38%, and a cw tuning range from 724 to 816 nm.…”

Effect of co-doping on luminescence of LiCaAlF6:Eu phosphor

“…LiCaAlF 6 :Pr 3 þ exhibits photon cascade emission which can be useful for obtaining phosphors with quantum efficiency exceeding 100% [4]. LiCaAlF 6 :Ce [5,6], LiCaAlF 6 :Er [7,8], LiCaAlF 6 :Cr [9][10][11], and LiCaAlF 6 doped with other 3d transition elements [12] are wellknown laser materials. LiCaAlF 6 :Tm 3 þ [13] and LiCaAlF 6 :Pr 3 þ [14], Ce 3 þ , Gd 3 þ [15] have been studied for their vacuum ultraviolet (VUV) excited luminescence.…”