Measuring optical signals in the femtowatt (10-15) to nanowatt (10-9) range can be a daunting task. In order to achieve significant improvements in noise rejection we need to turn to a lock-in amplifier, which can improve noise rejection by 3 orders of magnitude or more.
Professor Tobias Schaetz from the Amo Research Group at the University of Freiburg, Germany describes the group's experimental work with trapped ion systems. Coulomb crystals consisting of isotopically pure Magnesium ions are built employing a new tunable continuous-wave (cw) laser light source: Mg atoms are isotope-selective ionized by resonant two-photon excitation at a wavelength of 285.3 nm.
Fluorescence spectroscopy has been used to characterise natural organic matter (NOM) in water. Excitation-Emission maps reveal the nature and concentration of NOM in river water and can be used as a routine analysis technique in water treatment facilities.
The fluorescence excitation spectra of single organic molecules in a solid state crystal are measured at cryogenic temperatures using a single frequency tunable laser light source based on optical parametric oscillator technology. This laser exhibits promising features as a light source for spectroscopy applications, including a broad tuning range from 450 to 650 nm, narrow linewidth < 1 MHz and mode-hop-free tuning over > 25 GHz. This application note presents the experimental setup, measured spectra and discusses the applicability of this kind of laser for high-resolution spectroscopy.
Excitation-emission spectroscopy becomes increasingly useful in the study of photo-luminescent materials. The spectral selectivity of the technique enables the quantification of multiple emitting sites in rare-earth doped crystals as well as the rapid acquisition of polycyclic aromatic hydrocarbons (PAH) in contaminated water. In order to obtain a complete spectral fingerprint via excitation-emission spectroscopy, scans at multiple excitation wavelengths over the emission spectra are required. Especially in the case of rare-earth materials with narrow emission linewidths, this is extremely demanding in terms of resolution. The acquisition time of such excitation-emission maps (EEM) can be significantly reduced by using Charge Coupled Device (CCD) detectors.