Pulsed laser interferometry with sub-picometer resolution using quadrature detection.

Lei Shao,Jason J Gorman

doi:10.1364/oe.24.017459

Abstract

Femtosecond pulsed laser interferometry has important applications in measuring picometer-level displacements on sub-nanosecond time scales. In this paper, we experimentally examine its achievable displacement resolution, as well as the relationship between the laser's optical spectrum and the interferometer's effective wavelength. The resulting broadband displacement noise and noise floor of the pulsed laser Michelson interferometer are equivalent to that achieved with a stabilized continuous wave HeNe laser, where values of 1.01 nm RMS and 27.75 fm/√Hz have been demonstrated. It is also shown that a single effective wavelength can accurately describe the fringes of the pulsed laser interferometer but the effective wavelength value can only be determined from the optical spectrum under certain conditions. These results will be used for time-resolved displacement metrology with picosecond temporal resolution in the future.

Highlights

Femtosecond pulsed laser interferometry is capable of measuring periodic picometer-level displacements occurring at nano- to picosecond time scales using a stroboscopic measurement
It is shown that a single effective wavelength can accurately describe the fringes of the pulsed laser interferometer but the effective wavelength value can only be determined from the optical spectrum under certain conditions
It’s unclear if the performance of pulsed laser interferometry can match that achieved with a frequency-stabilized continuous wave (CW) helium neon (HeNe) laser, which is the predominant choice for displacement metrology due to its accurate and stable wavelength. We examine these performance metrics using a two-quadrature Michelson interferometer with a pulsed laser and compare the results with that obtained with a CW HeNe laser

Summary

Introduction

Femtosecond pulsed laser interferometry is capable of measuring periodic picometer-level displacements occurring at nano- to picosecond time scales using a stroboscopic measurement. Within the research described above, the resolution and noise limits of pulsed laser interferometry have not been investigated in detail. We examine these performance metrics using a two-quadrature Michelson interferometer with a pulsed laser and compare the results with that obtained with a CW HeNe laser. The presented results will support future studies on measuring highfrequency surface acoustic waves and micromechanical resonators with improved accuracy and bandwidth using pulsed laser interferometry. These results are used to determine the effective wavelength of the pulsed laser interferometer and compare these results to the primary peak found in the optical spectrum of the laser for different spectral filtering conditions. The interferometer’s broadband displacement noise and displacement noise floor are compared with the CW HeNe laser in Section 4, followed by conclusions

Pulsed laser interferometer

Quasi-static displacement measurements

Displacement noise measurements

Findings

Conclusion