7  Tunable infrared laser spectroscopy

Second harmonic generation in AlGaAs photonic wires using low power continuous wave light

“…Frequency conversion relying on quadratic electronic nonlinearities has sparked a vast amount of research focused on diverse applications including the generation of coherent sources in otherwise unattainable spectral regions [1], gas sensing [2], bio-photonics [3], time resolved spectroscopy [4], the realization of correlated photon pair sources [5], as well as all-optical signal processing for wavelength division multiplexing, routing and for solutions to wavelength contention [6]. In particular, nonlinear frequency mixing in waveguide devices offers several key breakthroughs, including compact on-chip integration and an important increase of the energetic efficiency when compared to traditional bulk crystals [6,7].…”

“…Due to the inherent material dispersion, momentum conservation is difficult to achieve, requiring the effective index at the fundamental wavelength to be equal to the effective index at the second harmonic for a type I interaction [n eff (ω) = n eff (2ω)]. This interaction has been nonetheless observed and exploited in numerous configurations using bulk media, and has been typically achieved through the use of birefringent crystals such as BBO and KTP [9], as well as in waveguide geometries [10][11][12][13][14][15][16][17][18][19][20][21][22][23] A surge of scientific activity has recently been devoted to developing novel phase matching techniques and to increasing the overall conversion efficiency in waveguiding structures [10][11][12][13][14][15][16][17][18][19][20][21][22][23], in an effort to develop a practical low power integrated frequency converter for all-optical signal processing systems and sensing/spectroscopy applications [1][2][3][4][5][6][7]. In particular, SHG was reported in AlGaAs/Al x O y with a record theoretical conversion efficiency of 20,000%/W/cm 2 (practical efficiency ~1400%/W/cm 2 ) [19], whereby phase matching and tight modal confinement were achieved through the introduction of thin Al x O y layers in the core of the waveguide, creating an artificial birefringence and thus removing the inherent isotropic nature of AlGaAs.…”

Quantifying nanoscale biochemical heterogeneity in human epithelial cancer cells using combined AFM and PTIR absorption nanoimaging

“…For single wavelength applications, high quality lasers are essential for artefact free imaging [23]. Specifically, for IR nanospectroscopy the laser must have a suitably narrow linewidth, a low signal-to-noise ratio (SNR), and ideally be compact [24] with wide spectral tuneability [25].…”

Nitrogen dioxide detection using an optoelectronic sensor

“…There are others methods using a high-finesse optical cavity consisting of two highly reflective mirrors (R > 0.9999) such as cavity enhanced absorption spectroscopy (CEAS) with off-axis laser and cavity adjustment, integrated cavity output spectroscopy (ICOS) with piezoelement or ring-down spectral photography (RSP) [5][6][7][8].…”