Laser & Photonics Reviews

Scattering SNOM: Vibrational microspectroscopy techniques are promising tools for obtaining chemical “fingerprints” with nanometer scale spatial resolution or a few to single molecules. (Picture: illustrated by I. Kopf. See D. A. Schmidt, I. Kopf, E. Bründermann, pp. 296–332, in this issue

Noble metal nanoparticles can support localized surface plasmon resonances (LSPR), acting as nanoscale classical oscillator systems. The large field enhancements and confinement effects which they bring about have motivated a vast range of studies and applications. For instance, LSPR can enhance signals in diagnostic characterization methods (SERS, SEIRA). Moreover, they are highly sensitive to their nanoscale environment and can therefore be used in sensing applications.

Vibrational spectroscopy is a powerful analytical tool which provides chemical information about a sample without a priori knowledge. By combining vibrational spectroscopy with different microscopic techniques, scientists can visualize and characterize the chemical composition of a sample on length scales which cover many orders of magnitude; from far-field radiation used in microwave astronomy and Fourier transform infrared microscopy, to near-field scattering used in tip-enhanced Raman spectroscopy and scanning near-field optical or infrared microscopy. Here, various modern chemical mapping techniques are reviewed and their advantages and disadvantages are discussed. Also, a basic theoretical background is provided for each technique along with several illustrative examples.

This paper reviews recent efforts to realize a high efficiency memory for optical pulses using slow and stored light based on electromagnetically induced transparency (EIT) in ensembles of warm atoms in vapor cells. After a brief summary of basic continuous-wave and dynamic EIT properties, studies using weak classical signal pulses in optically dense coherent media are discussed, including optimization strategies for stored light efficiency and pulse-shape control, and modification of EIT and slow/stored light spectral properties due to atomic motion.

Diffraction is a natural phenomenon, which occurs when waves propagate or encounter an obstacle. It is also a fundamental aspect of modern optics: all imaging systems are diffraction systems. However, like a coin has two sides, diffraction also leads to some unfavorable effects, such as an increase in the size of a beam during propagation, and a limited minimal beam size after focusing. To overcome these disadvantages, many techniques have been developed by various groups, including apodization techniques to reduce the divergence of a laser beam and increase the resolution.

In this work self-mixing interferometry (SMI), a new configuration of interferometry, is discussed. SMI has practical advantages compared to standard interferometry, for example SMI does not require any optical part external to the laser chip and can be employed in a variety of measurements. Applications range from the traditional measurements related to optical pathlength to sensing of weak optical echoes and also measurements of physical parameters, like the laser linewidth, coherence length, and the alfa factor.