Ti:sapphire-pumped deep-infrared femtosecond optical parametric oscillator based on CdSiP2.

We report on a femtosecond optical parametric oscillator (OPO) for the deep-infrared (deep-IR) based on the Kerr-lens-mode-locked Ti:sapphire laser as the pump source. By deploying a novel cascaded intracavity arrangement, comprising a femtosecond OPO based on the nonlinear crystal, CdSiP2, synchronously pumped internal to a MgO:PPLN femtosecond OPO, we have generated broadly tunable radiation across 5958-8117 nm using rapid static cavity delay tuning, with a maximum power of 64 µW at 6791 nm, limited by the absorption in mirror substrates as well as polarization-dependent intracavity losses. The deep-IR idler power exhibits excellent passive stability of better than 1.1% rms over 2 h, with a spectral bandwidth as large as ∼650 nm at ∼6800 nm. The demonstrated concept is generic and can be similarly deployed in other operating time scales and wavelength regions, also using different laser pump sources and nonlinear materials.

Two-crystal, synchronously pumped, femtosecond optical parametric oscillator.

We demonstrate a femtosecond optical parametric oscillator based on two nonlinear crystals synchronously pumped by a single ultrafast laser for efficient intracavity signal amplification and output power enhancement. By deploying two identical MgO:PPLN crystals in a single standing-wave cavity, and two pump pulse trains of similar average power from the same Kerr-lens-mode-locked Ti:sapphire laser, a minimum enhancement of 56% in the extracted signal power is achieved, with un-optimized output coupling, when temporal synchronization between the two intracavity signal pulse trains is established, resulting in a corresponding enhancement of 49% in pump depletion. Using intracavity dispersion control, near-transform-limited signal pulses with clean spectrum are obtained.

Fiber-laser-pumped, dual-wavelength, picosecond optical parametric oscillator.

We report a simple, compact, picosecond, dual-wavelength optical parametric oscillator (DW-OPO) at 160 MHz, based on two MgO:PPLN crystals sharing the same cavity and synchronously pumped by an Yb-fiber laser at 1064 nm. The two signal and idler wavelength pairs are independently tunable in the near- and mid-infrared across 1550-1615 nm and 3118-3393 nm, respectively, and can be arbitrarily tuned, even to degeneracy and beyond, without coherent coupling, irrespective of operating wavelength. The DW-OPO provides two signal and idler pulse trains and delivers as much as 1.5 W of average signal power at a degenerate wavelength of 1550 nm from each arm, at a total (signal plus idler) power extraction efficiency of as much as 44%. The two output signal pulse trains have durations of ∼18 ps and ∼15.2 ps, with Gaussian spatial quality, and exhibit passive power stability, better than 3.6% rms over >5 h. We also demonstrate the possibility of tailoring the pulse trains from the DW-OPO by controlling the delay between the pump pulses at the input to the two MgO:PPLN crystals.

Synchronized retroreflection-pumped femtosecond optical parametric oscillator.

We report a flexible technique for threshold reduction and output power enhancement in synchronously pumped optical parametric oscillators (SPOPOs) based on synchronized retroreflection of the undepleted pump using a collimating system and a delay line, which allows easy and independent adjustment of the spatial and temporal overlap of the retroreflected beam in the nonlinear crystal. The method permits initial synchronization of the forward and retroreflected pump by interferometry, providing threshold reduction before oscillation is initiated. We demonstrate the technique in a femtosecond SPOPO based on BiB3O6, where a threshold reduction of 22% and an output power enhancement of 70% are achieved compared with single-pass pumping, with no detrimental effect on the spectral and temporal characteristics of the output pulses.

Broadband, rapidly tunable Ti:sapphire-pumped BiB3O6 femtosecond optical parametric oscillator.

We report a femtosecond optical parametric oscillator (OPO) based on the nonlinear material BiB3O6 (BIBO) pumped directly by a Kerr lens mode-locked Ti:sapphire laser. Using a 1.5 mm long BIBO crystal cut at θ=11.4° for collinear type I (e→o+o) phase matching in the xz optical plane, femtosecond signal pulses across 1.4-1.6 µm, and idler pulses across 1.6-1.87 µm spectral range are generated, limited by the reflectivity bandwidth of the OPO mirrors. The high nonlinear gain and large spectral acceptance for type I interaction in the xz plane of BIBO permit rapid and continuous tuning across the entire range by simple fine adjustment of OPO cavity delay or through small changes in the pump wavelength, without varying any other parameters. Additionally, owing to the near-zero group velocity mismatch and dispersion, the OPO supports broad spectrum as wide as 33 nm, which results in self-compressed signal pulses. For 150 fs pump pulses, signal pulses with durations down to 106 fs with a time-bandwidth product of 0.48 are obtained without the need for intracavity dispersion compensation.