Near-GHz scanned-wavelength-modulation spectroscopy for MHz thermometry and H$$_2$$O measurements in aluminized fireballs of energetic materials

Extended tuning of distributed-feedback lasers in a bias-tee circuit via waveform optimization for MHz-rate absorption spectroscopy

“…At very high scan rates, a sinusoidal waveform is commonly used for injection-current modulation, which gradually changes the heating applied to the laser between a maximum and minimum value. The harmonics of sinusoidal modulation may also be conveniently analyzed [9]. Here we rigorously examine the benefits and potential drawbacks of square-waveform modulation, which has previously shown some benefit to improving optical SNR for under-sampled spectra [34].…”

“…Microsecond time resolution of thermodynamic and thermochemical properties is critical for the assessment of transient physical processes occurring in many dynamic systems. Laser absorption spectroscopy (LAS) [1] at MHz rates has been demonstrated by various methods [2][3][4][5], and has proven useful in measuring gas properties in detonation environments [6,7], planetary-entry shock layers [3,8], and in the characterization of energetic materials [9]. The MHz scanned-wavelength techniques used in these works should be distinguished from fixedwavelength laser absorption [10][11][12][13][14], which is limited in measurement rate solely by detector bandwidth.…”

Optical measurements in multiphase combustion

“…The absorption coefficient is related to the ground state population, which may allow access to additional relevant species, but suffers from some of the same drawbacks present in heterogeneous combustion environments. Namely, both emission and absorption spectra are path-averaged and may be strongly biased towards high concentration or high-temperature regions [93].…”