Focussed Ion Beam (FIB) machining has been demonstrated to be capable of fabricating nano and micro-structure elements. In this paper we demonstrate techniques to design and fabricate a 45° mirror on the end of both conventional single mode and multi-core fibres (MCF) using FIB processing. The mirror is finished by a two step process: first a scanning process is used to make a rough cut followed by a polishing process to create an optical surface finish. The machined 45° mirror can be accurately aligned with optical fibre core, which avoids issues associated with the alignment of external turning mirror components. Proof-of-concept tests demonstrate that the fabricated structure is capable of measuring two axis displacements interferometrically with a maximum displacement up to 1.0mm and an rms error of ~50nm.
We demonstrated coherent pulse synthesis between the carrier-envelope phase slip (CEPS) locked second-harmonic
(SH) pulses from an optical parametric oscillator (OPO) and those from its pump laser. By using a single nonlinear
crystal with cascaded gratings for parametric and SH generation, we maximized the common-mode rejection of
environmental noise, obtaining a temporal overlap between the pulses as low as 30 attoseconds in an observation time of
20 ms. The CEPS frequencies of the pump laser and the OPO SH signal were locked individually to the same subharmonic
of the repetition rate with a coherence time of at least 1.4 ms by using the pump supercontinuum as a common
reference. Auto-correlation traces of the combined pulses showed an 8:1 ratio between the peak and the background once
the CEPS frequencies were locked, in contrast with a much lower ratio when they were not locked, indicating successful
pulse synthesis. This research illustrates the viability of using OPOs for sub-femtosecond optical pulse synthesis. The
very low timing jitter and phase coherence between the pulses from this system, which spans from the ultraviolet (SH of
the pump) to mid-infrared (idler), also make the system a powerful tool for optical spectroscopy and optical metrology.