Analysis of Embedded Optical Interferometry in Transparent Elastic Grating for Optical Detection of Ultrasonic Waves

In this paper, we propose a theoretical framework to explain how the transparent elastic grating structure can be employed to enhance the mechanical and optical properties for ultrasonic detection. Incident ultrasonic waves can compress the flexible material, where the change in thickness of the elastic film can be measured through an optical interferometer. Herein, the polydimethylsiloxane (PDMS) was employed in the design of a thin film grating pattern. The PDMS grating with the grating period shorter than the ultrasound wavelength allowed the ultrasound to be coupled into surface acoustic wave (SAW) mode. The grating gaps provided spaces for the PDMS grating to be compressed when the ultrasound illuminated on it. This grating pattern can provide an embedded thin film based optical interferometer through Fabry–Perot resonant modes. Several optical thin film-based technologies for ultrasonic detection were compared. The proposed elastic grating gave rise to higher sensitivity to ultrasonic detection than a surface plasmon resonance-based sensor, a uniform PDMS thin film, a PDMS sensor with shearing interference, and a conventional Fabry–Perot-based sensor. The PDMS grating achieved the enhancement of sensitivity up to 1.3 × 10−5 Pa−1 and figure of merit of 1.4 × 10−5 Pa−1 which were higher than those of conventional Fabry–Perot structure by 7 times and 4 times, respectively.

Laser Ranging Interferometer on GRACE Follow-On: Current Status

<p>The GRACE Follow-On satellites were launched <span>on</span> <span>22</span>nd May <span>2018</span> <span>to</span> <span>continue</span> the measurement of Earth’s gravity field from the GRACE satellites (<span>2002</span>-<span>2017</span>). A few weeks <span>later</span>, <span>an</span> inter-satellite laser link was established with the novel Laser Ranging Interferometer (LRI), which offers <span>an</span> additional measurement of the inter-satellite <span>range</span> <span>next</span> <span>to</span> the one provided by the conventional microwave ranging instrument. The LRI <span>is</span> the <span>first</span> optical interferometer in space between orbiters, which <span>has</span> demonstrated <span>to</span> measure distance variations with <span>a</span> noise below <span>1</span> <span>nm</span>/√Hz at Fourier frequencies around <span>1</span> Hz, well below the requirement of <span>80</span> <span>nm</span>/√Hz. In this talk, we provide <span>an</span> overview <span>on</span> the LRI, present the current status of the instrument <span>and</span> show results regarding the characterization of the instrument. We will address impulse events that are apparent in the accelerometer <span>and</span> LRI <span>range</span> acceleration data, most of which are expected <span>to</span> <span>be</span> micro-meteorites. Other short-term disturbances in the ranging data will <span>be</span> addressed <span>as</span> well. We conclude with some learned lessons <span>and</span> potential modifications of the interferometry <span>for</span> future geodetic missions.</p>

All-optical attosecond time domain interferometry

Interferometry, a key technique in modern precision measurements, has been used for length measurement in engineering metrology and astronomy. An analogous time-domain interferometric technique would represent a significant complement to spatial domain applications and require the manipulation of interference on extreme time and energy scales. Here, we report an all-optical interferometer using laser-driven high order harmonics as attosecond temporal slits. By controlling the phase of the temporal slits with an external field, a time domain interferometer that preserves attosecond temporal and hundreds of meV energy resolution is implemented. We apply this exceptional temporal resolution to reconstruct the waveform of an arbitrarily polarized optical pulse, and utilize the provided energy resolution to interrogate the abnormal character of the transition dipole near the Cooper minimum in argon. This novel attosecond interferometry paves the way for high precision measurements in the time energy domain using all-optical approaches.