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Higher-Order Spectrum Coherent Receivers
Published in Le Nguyen Binh, Advanced Digital, 2017
One of the important applications of the χ(3) nonlinearity is parametric amplification. The optical parametric amplifiers (OPA) offer a wide gain bandwidth, high differential gain, and optional wavelength conversion and operation at any wavelength [7]. These important features of OPA are obtained because the parametric gain process do not rely on energy transitions between energy states, but it is based on highly efficient FWM in which two photons at one or two pump wavelengths interact with a signal photon. The fourth photon, the idler, is formed with a phase such that the phase difference between the pump photons and the signal and idler photons satisfies the phase-matching condition (Equation 16.21). The schematic of the fiber-based parametric amplifier is shown in Figure 16.12a. The parameters of the OPA are given in Table 16.1.
Ultrafast Electron–Phonon Coupling at Metal-Dielectric Interface
Published in Heat Transfer Engineering, 2019
Qiaomu Yao, Liang Guo, Vasudevan Iyer, Xianfan Xu
A Ti-Sapphire amplified femtosecond laser is used to generate laser pulses with 100 fs pulse width, central wavelength at 800 nm, and repetition rate of 5 kHz. A collinear pump and probe technique is used by dividing the laser beam into a relatively weak probe beam and higher power pump beam. The pump beam is focused to a 29.8 μm radius on the sample. The probe beam is sent to an optical parametric amplifier (OPA), which generates tunable wavelengths with nonlinear processes. The output from the OPA is fixed at the 490 nm wavelength in order to reduce the effect of non-thermalized electrons as discussed above. The probe spot radius is 13.8 μm, smaller than half of the pump spot radius. A computer-controlled mechanical delay stage is used to adjust the time delay between the pump and the probe beams in femtosecond time step.