Laser ions neodymium

A comparison between the efficiency of excitation with lasers and mercury lamps has been undertaken by Evans etal. and Brandmuller etal. Since that time, lasers have improved considerably and a later comparison would be even more in favor of laser applications. Since several commercial laser Raman spectrometers are now available 190 ), with He-Ne lasers, Ar" or Kr -ion lasers and neodymium lasers, most current investigations employ lasers as light sources, j)... 

The neodymium laser is popular because it is a solid state laser. Trivalent neodymium ions are incorporated in a host crystal or glass, at about one atomic percent doping. In the solid state, high concentrations of ions are available as opposed to the gaseous state. Further the host crystal provides mechanical strength and chemical inertness. 

Neodymium and YAG Lasers. The principle of neodymium and YAG lasers is very similar to that of the ruby laser. Neodymium ions (Nd +) are used in place of Cr + and are often distributed in glass rather than in alumina. The light from the neodymium laser has a wavelength of 1060 nm (1.06 xm) it emits in the infrared region of the electromagnetic spectrum. Yttrium (Y) ions in alumina (A) compose a form of the naturally occurring garnet (G), hence the name, YAG laser. Like the ruby laser, the Nd and YAG lasers operate from three- and four-level excited-state processes. 

Solid-State Lasers. Sohd-state lasers (37) use glassy or crystalline host materials containing some active species. The term soHd-state as used in connection with lasers does not imply semiconductors rather it appHes to soHd materials containing impurity ions. The impurity ions are typically ions of the transition metals, such as chromium, or ions of the rare-earth series, such as neodymium (see Lanthanides). Most often, the soHd material is in the form of a cylindrical rod with the ends poHshed flat and parallel, but a variety of other forms have been used, including slabs and cylindrical rods with the ends cut at Brewster s angle. 

The term solid-state laser refers to lasers that use solids as their active medium. However, two kinds of materials are required a host crystal and an impurity dopant. The dopant is selected for its ability to form a population inversion. The Nd YAG laser, for example, uses a small number of neodymium ions as a dopant in the solid YAG (yttrium-aluminum-gar-net) crystal. Solid-state lasers are pumped with an outside source such as a flash lamp, arc lamp, or another laser. This energy is then absorbed by the dopant, raising the atoms to an excited state. Solid-state lasers are sought after because the active medium is relatively easy to handle and store. Also, because the wavelength they produce is within the transmission range of glass, they can be used with fiber optics. 

Solid-state lasers using substitutional neodymium (Nd3+ ions) as the active defects are widely available. Practical lasers contain about 1% Nd3+ dopant. The most common host materials are glass, yttrium aluminum garnet (YAG), Y3A15012, and calcium tungstate, CaW04. In the crystalline host structures, the defects responsible for amplification are NdY and Ndca-... 

It is convenient to divide the ions studied into four groupings, namely, terbium, europium, neodymium, and other trivalent ions. The reason for this grouping is that terbium, europium, and neodymium have been studied more extensively than the rest, and therefore the number of papers is larger. The greater attention paid to these trivalent ions is probably one of practical or potential practical applications to lasers. 

Hoskins and Soffer (117) measured the fluorescent lifetime of the neodymium 4Fy2 state in yttrium oxide. They found a value of approximately 260 /zsec both at room temperature and at liquid-nitrogen temperature. They also observed a weaker long-lived component in the decay. They were unable to say whether this was evidence for a low-transition-probability ion site, or an effect of trapping of the resonance radiation near 0.9 /x. They report laser action, with a threshold of 260joules. This is a fairly high value for most crystalline materials. 

Gandy and Ginther (132) studied simultaneous laser action of neodymium and ytterbium ions in glass. The base glass was LiMgAlSi03. When singly... 

To a very large extent, most of the recent data on fluorescent decay times of the other trivalent ions (those beside terbium, neodymium, and europium) stems in some way from laser experiments. In this section some representative data on these are considered. 

A neodymium-ytterbium-coupled rare-earth ion system was given extensive study by Peterson and Bridenbaugh (109, 166) Peterson et al. (167) and Pearson and Porto (168). The simultaneous doping of Nao.5Gdo.5-W04, or Calibo (168) glass with neodymium and ytterbium results in a resonance-coupled system in which energy pumped into the neodymium appears as fluorescence from the ytterbium. The fact that the energy absorbed by the neodymium is rather efficiently transferred to the ytterbium results in a substantial reduction in laser threshold for ytterbium. 

Similar up-conversion also takes place for fluoride complexes inserted in zeolites and luminescence from Ndm occurs for [La2NdxGd2-x(AlsSAl4024)(W04)2] or La4 xNdv (A18S AI4O24X W04)21 sodahtes upon pulsed diode laser excitation at 803 nm. The optimum content of neodymium maximizing the 1.06 pm emission in the second material is 0.2 NdnI ion per unit cell (Lezhnina et al., 2006 Lezhnina and Kynast, 2005). 

Neodymium-YAG (Nd YAG) are solid-state lasers. The YAG, or yttrium-aluminum-garnet (Y3AI5O12), in rod shape is host to Nd3+ ions, which actually do the lasing. The lasers are made in both CW and pulsed formats. 

The trivalent neodymium ion is a good example of a four-level laser system. The trivalent Nd3+ system is illustrated in Fig. 12.12 in a schematic fashion. 

---