228‐nm quadrupled quasi‐three‐level Nd:GdVO₄ laser for ultraviolet resonance Raman spectroscopy of explosives and biological molecules

Abstract

We describe a new compact diode-pumped solid-state frequency quadrupled quasi-three-level neodymium-doped gadolinium vanadate (Nd:GdVO 4) laser that generates $50 mW of 228-nm quasi-continuous wave light as ns pulses at a tunable kilohertz repetition rate. We developed two generations of this laser. The first generation has a high duty cycle and a tunable repetition rate. The second generation is optimized for maximum output power. We utilize these new lasers to measure ultraviolet resonance Raman (UVRR) spectra of many important chromophores that absorb in deep ultraviolet (UV). We demonstrate the utility of this excitation by measuring the 228-nm absolute differential Raman cross sections of explosives, peptides, aromatic amino acids, and DNA/RNA nucleotides. Deep UV excitation at 228 nm occurs within the π ! π* electronic transitions of these molecules. The 228-nm resonance excitation enhances the Raman intensities of vibrations of NO x groups, peptide bonds, aromatic amino acid side chains, and DNA/RNA nucleotides. The measured 228-nm UVRR cross sections of these molecules are 10 3-10 4 fold greater than those excited in the visible spectral region. These new lasers should be of great interest for UVRR spectroscopy and for other applications that benefit from compact, high average power deep UV laser light sources with low peak powers.

Standoff Deep Ultraviolet Raman Spectrometer for Trace Detection

“…We described this new laser elsewhere. 18 The 228 nm Raman excitation overlaps with the π→π* electronic transitions associated with conjugated double bonds, aromatic rings, amides, NO x compounds, and other DUV chromophores.…”

All-Solid-State DUV Light Source by Quadrupling of an Acousto-Optically Q-Switched Nd:YVO4 Laser

“…One way of achieving ~228 nm lasers is the quadruple-frequency conversion of either the 914 nm output of Nd:YVO4 crystal, or 912 nm output of Nd:GdVO4 crystal. Sergei V. Bykov et al [17] reported acousto-optically Q-Switched, frequency quadrupled 912 nm Nd:GdVO4 laser with the average output power of 30 mW. Nd:YVO4 and Nd:GdVO4 have some advantages in common, including high absorption cross section, broad absorption bandwidth and polarization output.…”