Basic Elements of a Laser

1) The active medium which amplifies an incident E.M. wave. 

2) The energy pump which selectively pumps energy into the active medium to populate selected levels and to achieve population inversion. 

3) The optical resonator, composed of two opposite mirrors, which stores part of the induced emission, concentrated within a few resonator modes. 

The energy pump (e.g., flash lamps, gas discharges, or other lasers) generates a population distribution N(E) in the laser medium which strongly deviates from the Boltzmann distribution (2.18) that exists for thermal equilibrium. At sufficiently large pump powers the population density N(Ej ) of a specific level E may exceed that of a lower level E. (Fig.5.2). 

For such a population inversion, the induced emission rate N B. p(v) on a transition E E. exceeds the absorption rate N. B. j p(v). An E.M. wave. 

Demtroder, Laser Spectroscopy 1, DOI 10.1007/978-3-642-53859-9 5, Springer-Verlag Berlin Heidelberg 2014 

The function of the optical resonator is the selective feedback of radiation emitted from the excited molecules of the active medium. Above a certain pump threshold this feedback converts the laser amplifier into a laser oscillator. When the resonator is able to store the EM energy of induced emission within a few resonator modes, the spectral energy density p v) may become very large. This enhances the induced emission into these modes since, according to (2.22), the induced emission rate already exceeds the spontaneous rate for p v) hv. In Sect. 5.1.3 we shall see that this concentration of induced emission into a small number of modes can be achieved with open resonators, which act as spatially selective and frequency-selective optical filters. 

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Figure C3.1.1. The basic elements of a time-resolved spectral measurement. A pump source perturbs tlie sample and initiates changes to be studied. Lasers, capacitive-discharge Joule heaters and rapid reagent mixers are some examples of pump sources. The probe and detector monitor spectroscopic changes associated with absorjDtion, fluorescence, Raman scattering or any otlier spectral approach tliat can distinguish the initial, intennediate and final...

The basic elements of a LIF-CPT system consist of a laser source, silica-clad silica optical fibers to conduct laser light to the sample and fluorescence to the detector, a sapphire optical window inserted into a brazed or welded channel in the push rod wall, and a detector. 

The basic element of a large number of solid-state optical devices of technological interest is an imperfect crystal that incorporates a lanthanide ion as a substitutional impurity. Lanthanide-activated solid-state lasers, scintillators, and lamps reflect the ability of the lanthanide ions to absorb, transfer, exchange, and emit light under the influence of the host crystal, which deforms and multiplies the lanthanide s atomic electronic states in various ways and extents, until local electronic states arise in the imperfect crystal, which are rooted in the lanthanide and capable of administering a variety of energy-related processes. 

C. The Basic Elements of the Experimental Setup. The basic elements of TRRR experiments are a photolysis source a laser probe source (whose scattered radiation by the photolabile sample contains the vibrational spectra of the photodecomposed sample and its transients) a dispersing instrument (e.g., a spectrometer) and an optical multichannel analyzer (OMA) system used as a detector. 

Fig. 2 Schematic representation of the basic detection elements of the scanning force microscope and of the piezoelectric transducers generating the displacement modulations for purposes of dynamic mechanical measurements. The dynamic components of the tip-sample forces resulting from the normal/lateral displacement modulations are detected via the torsion/bending of the microscopic cantilever and the deflection of the laser beam reflected off the rear side of the cantilever. The positional shift of the latter is registered by means of a segmented photo-diode...

Atomic Force Microscopy Atomic force microscopy is a direct descendant of STM and was first described in 1986 [254], The basic principle behind AFM is straightforward. An atomically sharp tip extending down from the end of a cantilever is scanned over the sample surface using a piezoelectric scanner. Built-in feedback mechanisms enable the tip to be maintained above the sample surface either at constant force (which allows height information to be obtained) or at constant height (to enable force information to be obtained). The detection system is usually optical whereby the upper surface of the cantilever is reflective, upon which a laser is focused which then reflects off into a dual-element photodiode, according to the motion of the cantilever as the tip is scanned across the sample surface. The tip is usually constructed from silicon or silicon nitride, and more recently carbon nanotubes have been used as very effective and highly sensitive tips. 

According to Venky Venkatesan, Bellcore s research manager for the project, the new process can work with any yet-to-be-developed superconducting materials. It s a very basic process, he said. You name the bulk material, we can shoot at it and make a thin film out of it. And more important, it will have the same ratio of elements that it did in bulk form. Using a laser preserves this ratio, while other processes don t. ... 

Lasers are very powerful instruments to separate elements. Since the separation of isobars from different elements is the most difficult task in AMS, the use of lasers in connection with AMS could provide a very effective clean-up of background. The basic idea in a recent proof-of-principle experiment at the Rehovot AMS facility was to clean a negative ion beam from unwanted isobaric background ions by selective electrons detachment. S ions which have an electron affinity of 2.08 eV were effectively neutralized by interaction with 2.33 eV photons from a pulsed Nd YAg laser. The same photons did not affect Cl ions whose electron affinity is 3.62 eV. This clearly demonstrated that a laser depletion of S background in C1 measurements is feasible, opening up the possibility for sensitive C1 measurement at small AMS facilities where the ion energy is too low to perform isobar separation. However, for actual applications in AMS measurements, a substantial improvement in overall efficiency of the laser depletion process is necessary. 

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