RESUMEN
Laser Doppler anemometry (LDA), sometimes also referred to as cw Doppler lidar, is a promising optical technique for the measurement of primary flight data such as true air speed, angle of attack, and angle of sideslip. Multiple flight campaigns have shown the potential of this technique for future air data systems. However, LDA remains challenging in low aerosol environments at cruise altitude, and the high raw-data bandwidth of LDA sensors impedes real-time operation. In this work, we present a real-time preprocessing scheme, which is optimized to handle the signal structure of single-particle scattering events. We discuss how this scheme is implemented on system-on-chip field-programmable-gate-array hardware and how it is used with a four channel laser Doppler anemometer.
RESUMEN
A low-cost scheme of high-speed asynchronous optical sampling based on Yb:KYW oscillators is reported. Two GHz diode-pumped oscillators with a slight pulse repetition rate offset serve as pump and probe source, respectively. The temporal resolution of this system is limited to 500 fs mainly by the pulse duration of the oscillators and also by relative timing jitter between the oscillators. A near-shot-noise noise floor around 10-6 (∆R/R) is obtained within a data acquisition time of a few seconds. The performance of the system is demonstrated by measurements of coherent acoustic phonons in a semiconductor sample that resembles a semiconductor saturable absorber mirror or an optically pumped semiconductor chip.
RESUMEN
We present a high-speed asynchronous optical sampling system, based on two different Kerr-lens mode-locked lasers with a GHz repetition rate: An Yb:KYW oscillator and a Ti:sapphire oscillator are synchronized in a master-slave configuration at a repetition rate offset of a few kHz. This system enables two-colour pump-probe measurements with resulting noise floors below 10â»6 at a data aquisition time of 5 seconds. The measured temporal resolution within the 1 ns time window is below 350 fs, including a timing jitter of less than 50 fs. The system is applied to investigate zone-folded coherent acoustic phonons in two different semiconductor superlattices in transmission geometry at a probe wavelength far below the bandgap of the superlattice constituents. The lifetime of the phonon modes with a zero wave vector and frequencies in the range from 100 GHz to 500 GHz are measured at room temperature and compared with previous work.