Low-cost, highly efficient, and tunable ultrafast laser technology based on directly diode-pumped Cr:Colquiriites

Abstract

This doctoral project aims to develop robust, ultra low-cost ($5,000-20,000), highly-efficient, and tunable femtosecond laser technology based on diode-pumped Cr:Colquiriite gain media (Cr:LiCAF, Cr3+:LiSAF and Cr:LiSGaF). By using inexpensive single-mode diodes ($150) as the pump source, we have obtained continuous-wave (cw) output powers >250-mW with slope efficiencies >50%. Record cw tuning ranges were demonstrated for Cr:LiSAF (775-1042 nm), Cr:LiSGaF (777-977 nm), and Cr:LiCAF (754-871 nm). For femtosecond pulse generation, semiconductor saturable absorber mirrors (SESAMs/SBRs) were developed, which were used to initiate and sustain mode-locking. Typical performance was ~25-100 fs pulses, with an optical spectrum in the 770-920 nm range, with ~1-2 nJ of pulse energies from ~100-MHz repetition rate cavities. Record electrical-to-optical conversion efficiencies of ~10% were demonstrated in the cw mode-locked regime. A mode-locked tuning range of 767-817 nm, with ~130-fs long pulses was obtained by using Cr:LiCAF as gain medium. With the Cr:LiSAF gain medium, using regular SESAMs/SBRs centered around 800 nm, 850 nm, and 910 nm, mode-locked tuning ranges of 803-831 nm, 828-873 nm, and 890-923 nm were demonstrated, respectively. By using a broadband oxidized SESAM/SBR, a record tuning range of 800-905 nm was demonstrated with ~150-fs long pulses. Using an extended cavity Cr:LiCAF laser, pulse energies >15-nJ with peak powers exceeding 100-kW were obtained. We performed the first cavity-dumping experiments with a Cr:Colquiriite laser and demonstrated pulse energies >100-nJ, and peak powers approaching MW level, at repetition rates up to 50-kHz. Cr:LiCAF gain media were also pumped by single-emitter multimode diodes, where we obtained >2-W output power in cw operation, and ~100-fs pulses with 390-mW of average power at a repetition rate of 140 MHz in cw mode-locked operation. As an example application area for this low cost technology, we performed multiphoton microcopy experiments with a single-mode diode-pumped Cr:LiCAF laser. We also performed attosecond-resolution timing jitter characterization experiments of the femtosecond Cr:LiSAF laser, and measured a record-low upper limit for the integrated timing jitter of the Cr:LiSAF laser (137-attoseconds in 10 kHz-10 MHz range).