Abstract
Precise delay control is of paramount importance in optical pump-probe measurements. Here, we report on a high-precision delay tracking technique for mechanical scanning measurements in a Mach-Zehnder interferometer configuration. The setup employs a 1.55-µm continuous-wave laser beam propagating along the interferometer arms. Sinusoidal phase modulation at 30 MHz, and demodulation of the interference signal at the fundamental frequency and its second harmonic, enables delay tracking with sampling rates of up to 10 MHz. At an interferometer arm length of 1 m, root-mean-square error values of the relative delay tracking below 10 attoseconds for both stationary and mechanically scanned (0.2 mm/s) operation are demonstrated. By averaging several scans, a precision of the delay determination better than 1 as is reached. We demonstrate this performance with a mechanical chopper periodically interrupting one of the interferometer arms, which opens the door to the combination of high-sensitivity lock-in detection with (sub-)attosecond-precision relative delay determination.
Highlights
Ultrafast pump-probe measurements such as attosecond streaking [1,2] or THz-TDS [3,4] require precise time-delay measurements, sometimes with a precision down to a few attoseconds [5]
Low frequency intensity noise has been addressed in several pump-probe measurements like in THz-TDS and can be suppressed by a lock-in amplifier (LIA), where the THz beam is modulated
We propose and characterize an interferometric delay tracking (IDT) method for accurate and real-time delay corrections in pump-probe setups using conventional delay stages and heterodyne measurements with LIA
Summary
Ultrafast pump-probe measurements such as attosecond streaking [1,2] or THz-TDS [3,4] require precise time-delay measurements, sometimes with a precision down to a few attoseconds [5]. A long scan range is necessary to follow the reactions in the case of attosecond streaking or for the study of molecular rovibrational signals with high spectral resolution and accuracy, gaseous samples in time-domain spectroscopy. Low frequency intensity noise has been addressed in several pump-probe measurements like in THz-TDS and can be suppressed by a lock-in amplifier (LIA), where the THz beam is modulated (most commonly amplitude modulation by mechanical chopping) and the local oscillator (probe signal) is measured after a nonlinear optical interaction. The intensity noise of the local oscillator can be suppressed by 100 dB after the demodulation and proper filtering [7]
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