Midinfrared frequency comb by difference frequency of erbium and thulium fiber lasers in orientation-patterned gallium phosphide

Abstract

We generate over 60 mW of pulses with wavelengths from 6 to 11 micrometers by difference frequency mixing between erbium and thulium fiber amplifiers in orientation-patterned GaP with a photon conversion efficiency of 0.2. By stabilizing the repetition rate of the shared oscillator and adding a frequency shifter to one arm, the output becomes a frequency comb with tunable carrier envelope offset.

Multi-octave spanning, Watt-level ultrafast mid-infrared source

“…Parametric frequency downconversion of light from the near-infrared to the MIR and terahertz domain is capable of generating extremely broadband ultrashort pulses [55]. While devices such as optical parametric oscillators and amplifiers can provide high conversion efficiency, practical implementations of such a system often require synchronizing multiple pump and signal beams, while locking their spatial and temporal overlap to ensure a stable nonlinear mixing process [38]. Intra-pulse DFG relies on a single broadband driving pulse, providing both pump and signal photons simultaneously, eliminating the need for tight temporal and spatial overlap control.…”

“…In order to access the longer wavelength fingerprint region, more traditional nonlinear parametric processes can be employed. Light sources in this region have been realized using optical parametric oscillation [36,37], and DFG [15,38]. One particular type of DFG process known as intra-pulse DFG (IDFG) has shown promise as a relatively simple method for waveform-stable MIR generation.…”

Phase-stabilized 100 mW frequency comb near 10 μm

“…More recently, a higher power (~ 240 mW) DFG comb has been reported at 2.7–4.2 μm based on Raman-induced soliton self-frequency shift in a nonlinear fiber [18]. Longer MIR wavelengths which are comparable to those in the present work have been achieved with a GaSe crystal at 7.5–12.5 μm (~ 15 μW) [19] and 8–14 μm (~ 4 mW) [20], with a AgGaS 2 crystal at 7.5–11.6 μm (~ 1.55 mW) [21], and with an orientation-patterned (OP) GaP at 6–11 μm (~ 60 mW) [22]. …”

Long-wave infrared generation from femtosecond and picosecond optical parametric oscillators based on orientation-patterned gallium phosphide

“…OPGaP OPOs pumped by 1.5-µm pump lasers and generating mid-IR light have been demonstrated, including femtosecond frequency comb spanning 2.3-4.8 µm [24] and 3.5-5.0 µm [25]. Utilising the transparency of OPGaP, Lee et al used an erbium fiber laser which was spectrally broadened and amplified with a thulium amplifier to mix 1.5 and 2 µm for difference frequency generation (DFG) producing tunable and spectrally broad 6-11 µm output with up to 70 mW of average power [26]. Recent work uses DFG of the different spectral components from a 1.5-µm erbium fiber laser broadened in nonlinear fiber to produce a frequency comb spanning 4-12 µm, and demonstrates dual-comb spectroscopy (DCS) over this broad spectrum [27].…”