Picosecond supercontinuum light source for stroboscopic white-light interferometry with freely adjustable pulse repetition rate.

Steffen Novotny,Matti Kaivola,Igor Shavrin,Lauri Lipiäinen,Vasuki Durairaj,Kimmo Kokkonen,Hanne Ludvigsen

doi:10.1364/oe.22.013625

Abstract

We present a picosecond supercontinuum light source designed for stroboscopic white-light interferometry. This source offers a potential for high-resolution characterization of vibrational fields in electromechanical components with frequencies up to the GHz range. The light source concept combines a gain-switched laser diode, the output of which is amplified in a two-stage fiber amplifier, with supercontinuum generation in a microstructured optical fiber. Implemented in our white-light interferometer setup, optical pulses with optimized spectral properties and below 310 ps duration are used for stroboscopic illumination at freely adjustable repetition rates. The performance of the source is demonstrated by characterizing the surface vibration field of a square-plate silicon MEMS resonator at 3.37 MHz. A minimum detectable vibration amplitude of less than 100 pm is reached.

Highlights

White-light interferometry (WLI) is a well established and widely used optical method for noncontact 3D profiling of static surface features with a height range extending from the nanometer up to the millimeter scale [1,2,3]
We present a picosecond supercontinuum light source designed for stroboscopic white-light interferometry
The measured pulse width of 310 ps (FWHM) is significantly influenced by the detector performance and can be considered as the upper limit. This is in agreement with an estimated temporal pulse width of less than 200 ps, which was obtained by solving the generalized nonlinear Schrodinger equation for the pulse propagating through the microstructured optical fiber (MOF) and by calculating the temporal broadening caused by modal-dispersion in an idealized multi-mode optical fiber

Summary

Introduction

White-light interferometry (WLI) is a well established and widely used optical method for noncontact 3D profiling of static surface features with a height range extending from the nanometer up to the millimeter scale [1,2,3]. The resolution of the surface profiling can, be further improved by combining the fringe envelope location measurement with the phase information of the interferometric signal [4] Through this approach surface height features even down to the sub-nanometer scale can be identified by WLI [4,5,6,7]. We have recently achieved a detection limit below 100 pm [8] using LED-based stroboscopic WLI with 8 ns optical pulses This detection limit is comparable to that of full-field laser interferometry [14] currently employed for vibration measurements at high frequencies. The source is based on supercontinuum generation (SCG) and it emits broadband picosecond light pulses at a freely adjustable repetition rate up to 50 MHz. The all-fiber pump source consists of a gain-switched laser diode whose output pulses are amplified in a two-stage Ytterbium-doped polarization maintaining fiber (YDPMF) amplifier. Together with illumination times shorter than 310 ps, the performance opens up a possibility for characterization of vibration fields even up to the GHz range when illuminating the surface motion at the nth subharmonic of the vibrational frequency, with n being an integer number [13]

Supercontinuum source setup and characterization

Conclusions