Coherent pulse interrogation system for fiber Bragg grating sensing of strain and pressure in dynamic extremes of materials

Abstract

A 100 MHz fiber Bragg grating (FBG) interrogation system is described and applied to strain and pressure sensing. The approach relies on coherent pulse illumination of the FBG sensor with a broadband short pulse from a femtosecond modelocked erbium fiber laser. After interrogation of the FBG sensor, a long multi-kilometer run of single mode fiber is used for chromatic dispersion to temporally stretch the spectral components of the reflected pulse from the FBG sensor. Dynamic strain or pressure induced spectral shifts in the FBG sensor are detected as a pulsed time domain waveform shift after encoding by the chromatic dispersive line. Signals are recorded using a single 35 GHz photodetector and a 50 G Samples per second, 25 GHz bandwidth, digitizing oscilloscope. Application of this approach to high-speed strain sensing in magnetic materials in pulsed magnetic fields to ~150 T is demonstrated. The FBG wavelength shifts are used to study magnetic field driven magnetostriction effects in LaCoO₃. A sub-microsecond temporal shift in the FBG sensor wavelength attached to the sample under first order phase change appears as a fractional length change (strain: ΔL/L<10^-4) in the material. A second application used FBG sensing of pressure dynamics to nearly 2 GPa in the thermal ignition of the high explosive PBX-9501 is also demonstrated. Both applications demonstrate the use of this FBG interrogation system in dynamical extreme conditions that would otherwise not be possible using traditional FBG interrogation approaches that are deemed too slow to resolve such events.

Fiber Bragg Grating Dilatometry in Extreme Magnetic Field and Cryogenic Conditions

“…We studied the insulating perovskite cobaltite LaCoO 3 , whose octahedrally-coordinated Co 3+ (3d 6 ) ions are natural candidates to explore field-induced transitions of the electronic configuration [10,14,16,17]. A small gap ≈ 12 meV separates the s = 0 spin singlet ground state (6 electrons in the t 2g orbitals) from the lowest excited magnetic configuration.…”

“…Each pulse arrival constitutes an independent measurement, and therefore, an FBG interrogation rate of 100 MHz is achieved. A more detailed description of the ultrafast setup is published elsewhere [16,17]. This system has also been used to measure other fast processes such as explosive detonations and shock wave propagation [43].…”

“…Coherent pulse FBG interrogation system working at 100 MHz [16,17]. ( a ) Pulsed laser light source, ( b ) circulator, ( c ) controlled sample environment in a 250 T single turn coil magnet, ( d ) 1 × 2 99:1 splitter sends 1% of the light to spectrometer, ( e ) 50–100 km spool of chromatic dispersive fiber, ( f ) Erbium-doped fiber amplifier, ( g ) ultrafast 25 GHz oscilloscope, ( h ) line array camera used for monitoring of the FBG reflection.…”

“…Sensing of magnetostriction with single mode SiO 2 FBGs in pulsed magnetic fields is successfully utilized at the National High Magnetic Field Laboratory (NHMFL) with a resolution as good as a few parts per hundred million ( ΔL/L ≈ 10 −8 ) in the best cases. This capability allows for the study of a variety of insulating and metallic condensed matter systems including geometrically frustrated magnets, quantum magnets, multiferroics, and uranium- and cerium-based antiferromagnets [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30]. Figure 1 shows an example of magnetoelastic effects in pulsed magnetic fields to 60 T at cryogenic temperatures on a sample of uranium dioxide (UO 2 ), which is the most commonly used nuclear fuel.…”

Ultrafast and High Resolution Crack Detection Using Fully Distributed Chirped Fiber Bragg Grating Sensors

“…This is made possible by using chromatic dispersion to largely stretch an ultrashort broadband optical pulse such that the FBG wavelength change can be mapped to a temporal waveform shift, which can be detected in real-time with a speed identical to the repetition rate of the optical pulse train [3]. With this greatly improved temporal resolution, PTS-based FBG sensors have now found new applications in studying dynamic phenomena and monitoring dynamic extremes of materials [4]. Most recently, research efforts have been made to improve the wavelength resolution and signal-to-noise ratio based on pulse compression [5] and to overcome the fundamental trade-off between interrogation speed and resolution using interferometric real-time spectroscopy [6].…”