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).
Highlights
The Ti:Sapphire gain medium (i) has an ultra-broad gain bandwidth supporting pulses as short as 5 fs as well as tunability from 680 to 1080 nm, and (ii) exhibits favorable thermal properties which enable power scaling to several watts [1,2]
This corresponds to a pulse energy of 5.4 nJ at the repetition rate of 77 MHz. These are the highest energies obtained from standard Cr:Colquiriite oscillators to date. These results show that Cr:Colquiriite lasers pumped with tapered diodes could become attractive alternatives to Ti:Sapphire for various applications in science and technology such as multiphoton microscopy [41], optical parametric oscillators (OPOs) pumping [42], amplifier seeding, etc
; even though there is some increase in Cr:LiCAF laser output power upon cooling, our results show that the improvements are of minor importance and the tapered diode pumped Cr:LiCAF laser can be operated efficiently at room temperature
Summary
The Ti:Sapphire gain medium (i) has an ultra-broad gain bandwidth supporting pulses as short as 5 fs as well as tunability from 680 to 1080 nm, and (ii) exhibits favorable thermal properties which enable power scaling to several watts [1,2]. In the laser experiments with a single TDL pumped Cr:Colquiriites, we have obtained up to 500 mW and 410 mW of output power and slope efficiencies of 47% and 41% from Cr:LiSAF and Cr:LiCAF lasers in cw operation at 1150 mW of absorbed pump power. Up to 850 mW and 650 mW of output power and slope efficiencies of 49% and 42% were demonstrated from Cr:LiSAF and Cr:LiCAF lasers in cw operation at 1750 mW of absorbed pump power, respectively Using this high power system for mode-locking of Cr:LiCAF, we have obtained ~220 fs long pulses centered around 810 nm, with 415 mW of average power. For TDL-2, we have measured the beam quality factor as 2.2 in the slow axis and as 1.1 in the fast axis (both at 1/e2 level)
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