Dynamic dispersive spectrometer using a fiber Bragg grating for high pressure measurements

Abstract

A new high resolution dispersive spectrometer has been developed to measure high pressure shock profiles every 10 ns using long Fiber Bragg Gratings. The performances are compared with a dynamic AWG-based spectrometer. Two small diameter fibers allow inserting in parallel two 50-mm long gratings into the target. The use of slightly chirped gratings provides the localization of the shock-wave along them. Placed along the target axis, a gratings reflected spectrum is "blue shifted". The FBG's central wavelength are 1605 nm to cover a pressure range of 0-8 GPa. The new spectrometer is based on a femtosecond laser source, a long dispersive fiber and a fast acquisition system with an electrical bandwidth above 30 GHz. The experimental setup was a symmetric impact with 6061T6 aluminum, performed with a 110-mm in diameter single-stage gas gun. An impact velocity of 314 m/s is obtained and generated a sustained level of 2.1 GPa during few microseconds. A resulted Bragg shift of (16 ± 1) nm is measured. The dispersive spectrometer offers much greater resolution than the AWG one which is favorable to retrieve more easily a pressure profile.

Development of a Shock and Detonation Velocity Measurement System Using Chirped Fiber Bragg Gratings

“…Their integration needs to be improved and better understood to increase the sensitivity. Therefore, new experiments were recently carried out using a dynamic dispersive spectrometer [36,37] in order to dynamically measure the entire reflected spectrum of the CFBG. Such a system was developed to measure pressure levels in inert and HE materials using monochromatic FBGs, but it can also detect any defect or delay in the shortening process of a CFBG during an SDT, for instance.…”

Dynamic Strain Measurements by Fiber Bragg Gratings and a 100 MHz Dispersive Spectrometer

“…The BraggPulse system is described in Fig. 1 and details can be found in [6][7][8]. The concept is based on a modelocked laser source with a wide optical spectrum; the repetition sets the interrogation rate (100 MHz).…”

“…The LANL initiated this approach in 2015 [5] for shock sensing. Since, CEA regularly published results [6][7][8] for detonation speed measurements (5-8 km/s) and shock pressure measurements (1-6 GPa). This high speed spectrometer is internally called BraggPulse.…”

Ultrafast Fiber Bragg Grating Interrogation for Sensing in Detonation and Shock Wave Experiments

“…Even when shock pressures are sufficiently low that an elastic strain response is present, the strains are still very high, exceeding 10${}^4$ $\mathrm{sans-serif\mu }ϵ$, and it may be possible that the coating may be contributing. However, shock studies of FBG elastic response under conditions of high strain and high strain rate as in a shock wave are the subject of on going work [8,9,10]. Table 1 lists the various CFBGs used in this work.…”