Catalytic Mechanism of Fatty Acid Photodecarboxylase: On the Detection and Stability of the Initial Carbonyloxy Radical Intermediate.

In fatty acid photodecarboxylase (FAP), light-induced formation of the primary radical product RCOO⋅ from fatty acid RCOO occurs in 300 ps, upon which CO is released quasi-immediately. Based on the hypothesis that aliphatic RCOO⋅ (spectroscopically uncharacterized because unstable) absorbs in the red similarly to aromatic carbonyloxy radicals such as 2,6-dichlorobenzoyloxy radical (DCB⋅), much longer-lived linear RCOO⋅ has been suggested recently. We performed quantum chemical reaction pathway and spectral calculations.

Chirped pulse upconversion for femtosecond mid-infrared spectroscopy at 100 kHz.

We demonstrate that chirped pulse up-conversion (CPU), a method routinely used with systems based on 1-kHz Titanium:Sapphire lasers, can be extended to a repetition rate of 100 kHz with an Ytterbium diode-pumped femtosecond amplifier. Individual mid-infrared spectra can thus be measured directly in the near infrared using a fast CMOS linescan camera. After an appropriate Fourier processing, a spectral resolution of 1.

Intensity noise in difference frequency generation-based tunable femtosecond MIR sources.

We characterize the intensity noise of two mid-infrared (MIR) ultrafast tunable (3.5-11 μm) sources based on difference frequency generation (DFG). While both sources are pumped by a high repetition rate Yb-doped amplifier delivering 200 μJ 300 fs at a central wavelength of 1030 nm, the first is based on intrapulse DFG (intraDFG), and the second on DFG at the output of an optical parametric amplifier (OPA).

Inline amplification of mid-infrared intrapulse difference frequency generation.

We demonstrate an ultrafast mid-infrared source architecture that implements both intrapulse difference frequency generation (iDFG) and further optical parametric amplification (OPA), in an all-inline configuration. The source is driven by a nonlinearly compressed high-energy Yb-doped-fiber amplifier delivering 7.4 fs pulses at a central wavelength of 1030 nm, at a repetition rate of 250 kHz.

Enhanced intrapulse difference frequency generation in the mid-infrared by a spectrally dependent polarization state.

We present a technique to optimize the intrapulse difference frequency generation efficiency for mid-infrared generation. The approach employs a multi-order wave plate that is designed to selectively rotate the polarization state of the incoming spectral components on the relevant orthogonal axes for subsequent nonlinear interaction. We demonstrate a significant increase of the mid-infrared average power generated, of a factor ≥2.