Use of the Gerchberg–Saxton algorithm in optimal coherent anti-Stokes Raman spectroscopy

Pseudo-arbitrary sideband generation by phase modulation calculated with iterative phase retrieval

A method for arbitrarily tailoring amplitude and phase of sidebands generated with a phase shifting electro-optic modulator (EOM) is presented. The technique is extremely simple experimentally, requiring only a single EOM driven by an arbitrary waveform generator. The required time domain phase modulation is calculated using an iterative phase retrieval algorithm, which takes into account the desired spectrum (both amplitude and phase), and other physical constraints. The algorithm works consistently and finds solutions which accurately recreate the desired spectrum. Since EOMs only modulate phase, the solutions will usually match the desired spectrum over the specified range by redistributing optical power to regions of the spectrum that are unspecified. This basic Fourier limitation is the only in-principle limit to the arbitrariness of the spectrum tailoring. An experimental demonstration of the technique is performed, which shows complex spectra can be generated with high accuracy.

Advances in explosives analysis--part II: photon and neutron methods

The number and capability of explosives detection and analysis methods have increased dramatically since publication of the Analytical and Bioanalytical Chemistry special issue devoted to Explosives Analysis [Moore DS, Goodpaster JV, Anal Bioanal Chem 395:245-246, 2009]. Here we review and critically evaluate the latest (the past five years) important advances in explosives detection, with details of the improvements over previous methods, and suggest possible avenues towards further advances in, e.g., stand-off distance, detection limit, selectivity, and penetration through camouflage or packaging. The review consists of two parts. Part I discussed methods based on animals, chemicals (including colorimetry, molecularly imprinted polymers, electrochemistry, and immunochemistry), ions (both ion-mobility spectrometry and mass spectrometry), and mechanical devices. This part, Part II, will review methods based on photons, from very energetic photons including X-rays and gamma rays down to the terahertz range, and neutrons.