Laser basics

Laser sources - Analysis and characterization

Figure 1 - Interaction of photons with two electronic energy levels of an atom

Figure 2 - The Einstein coefficients for absorption b  12, stimulated emission b21 &#61; b 12 and spontaneous emission a 21 which is negligible in the laser kinetic scheme

Figure 3 - Chromium ion energy levels in the ruby crystal, Maiman&#039;s first laser (1960), still of interest today

Figure 4 - Four-energy-level medium with kinetic pattern of transitions

Figure 5 - Schematic of the first ruby laser, whose principle can be found in all lasers.

Figure 6 - The longitudinal (m) modes of the amplified laser cavity (in bold) are necessarily of wavelength in the emitter spectrum.

Figure 7 - Examples of transverse TEM modes of a laser cavity

Figure 8 - Mode locking (phase synchronization) generates short-duration pulses. Here, three modes produce pulses of width

Figure 9 - Principle of the titanium : sapphire femtosecond laser (after Manuel Joffre ). The oscillator part generates femtosecond pulses.

Figure 10 - Non-linear optics applied to laser beam frequency conversion

Figure 12 - Optical particle trapping used for immobilization in Raman spectroscopy

Figure 13 - Example of surface laser ablation: crater obtained in polyimide with the excimer laser at 193 nm, a hundred pulses at a fluence of 200 mJ/cm 2.

Figure 14 - KrF laser ablation in micro-drilling mode of poly(ethylene terephthalate) illustrating the limit where the profile becomes stationary , hole diameter 25 m

Figure 15 - Principle of multiphoton absorption and ionization. The simultaneous absorption of two photons can excite the fluorescence of the medium.

Figure 16 - Principle of nanoscopic absorption at the femtosecond laser focal point by multiphoton excitation

Figure 17 - Microchannels made in glass by fs laser ablation at 527 nm, using the multiphoton absorption principle (Reproduced with permission from the authors )

Figure 18 - Principle of fluorescence-Rayleigh-Raman scattering transitions

Figure 19 - Principle of confocal microscopy applied to Raman microanalysis of liquid and solid samples

Figure 20 - Principle of the transitions involved in the CARS phenomenon (coherent anti-Stokes Raman scattering)

Figure 21 - Typical probe molecule used in laser-induced fluorescence detection: fluorescein isothiocyanate (FITC), laser used Ar &#43; at 488 nm (vertical dotted line).

Figure 24 - Principle of the MALDI technique, which enables the desorption and ionization of very large molecules (e.g. proteins in blue) while minimizing the risk of fragmentation.

Figure 25 - Principle of photoacoustic and photothermal spectroscopy taking advantage of photothermal relaxation in photon-absorbing molecules

Figure 26 - Principle of an experimental photoacoustic spectroscopy setup, with wavelength scanning provided by an OPO laser, (from reference )

Figure 27 - Schematic diagram of saturation spectroscopy enhanced by OPO tunable lasers

Figure 28 - Balmer line saturation spectrum  of atomic deuterium (solid line) compared with the emission line spectrum (dotted line).

Figure 29 - Principle of four-wave mixing detection

Figure 30 - Measurement of tungsten isotopes by LA-ICP-MS (blue peaks). Femtosecond laser ablation provides far superior resolution to high-voltage evaporation technique

Figure 31 - Photon time-of-flight principle used in optical coherence tomography analysis