Solid state laser

Solid-state Lasers.—Fa(ii) colour centres in alkali halides were utilized to produce tunable-i.r. laser radiation in the ranges 1.7— 2 pm (KBr), 2.42—2.9 pm (KCl-Li), and 2.55—3.28 pm (RbCl-Li). A similar system, pumped using a Nd-YAG laser, produced 5 ns wide pulses with energies of 100 pJ. The laser was tunable over the range 3685—3697 cm with 0.3 bandwidth. 

A review of InGaAsP laser diodes, suitable for operation over the range l.O— 1.7 pm, has been published. 9mW of laser output were obtained from a CdS 

Curtois, C. Thiebeaux, A. Delanaigue, E. Merienne, and P. Jouve, Opt. Laser Technol., 1981,13, 155. 

Yoshida, J. Kuroda, and C. Yamanaka, Appl. Phys. Lett., 1981, 38, 72. 

Solid-state lasers Visible light (near UV - near IR) Y3Al50,2 Nd (YAG) IR 

The Nd-YAG laser uses a single crystal of Y3AI5O12 containing 1.4 x 10 Nd /cm. The active electronic states are the f levels of Nd .  

The properties of the ruby and Nd-YAG laser are summarized in Table 32.10. The Cr transition is a three-level 

The ruby laser uses a single CTystal of AI2O3 containing about 1.6 x 10 Cr Vcml The active electronic states are d levels of the Cr . 

TABLE 32.10 Characteristics of Typicai Soiid-State Laser Crystals  

We can already deduce that, due to the characteristics of the active medium, compact and miniaturized devices are attainable for semiconductor lasers. This fact, together with the possibility of custom-designed systems, constitutes a real advantage from the viewpoint of integrated opto-electronic devices. In the field of spectroscopy, they are commonly used as pumping sources for other types of solid state lasers, as will be seen later. 

Solid state lasers are those whose active medium consists of an insulating material activated by an optically active center. Three different types of active center have usually been used as active laser centers rare earth ions, transition metal ions, and color centers (see Chapter 6). 

When designing a new solid state laser system, an appropriate choice of the matrix - active center combination is needed. On the one hand, the active center should display optical transitions in the transparency region of the solid, which consequently requires the use of wide-gap materials. Additionally, the transitions involved in the laser action should show large cross sections in order to produce efficient laser systems. This aspect, which is directly related to the transition probability, is treated in depth in Chapters 5 and 6, where the physical basis of the behavior of an optically active center in a solid is studied. 

Some of the most commonly used solid state lasers by far are the Nd + based lasers, such as the Nd YAG laser (Nd + ions in yttrium aluminum garnet), Ndrglass materials, or more recently the Nd YLF or Nd YV04 lasers. Nd + lasers operate in a four-level scheme and they are optically pumped either by a flashlamp or, for a more 

The upward arrows in the figure indicate the pumping channels to various high energy levels by flashlamp (0.5 /tim) or semiconductor lasers (0.8 /rm), where Nd + ions display strong absorption transitions. The downward arrow indicates the widely used laser emission at 1.06 /xm, associated with the - ln/2 transition. In addition, laser action is also generally possible from the same F3/2 level to the 19/2 state at around 0.9 /xm and to the 113/2 state at around 1.3 /xm. 

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Seifert F, Petrov V and Woerner M 1994 Solid-state laser system for the generation of midinfrared femtosecond pulses tunable from 3.3-Mu-M to 10-Mu-M Opt. Lett. 19 2009-11... 

Table C2.15.1 Common laser sources (s denotes solid-state lasers and g denotes gaseous lasers).

Por IR-Raman experiments, a mid-IR pump pulse from an OPA and a visible Raman probe pulse are used. The Raman probe is generated either by frequency doubling a solid-state laser which pumps the OPA [16], or by a two-colour OPA [39]. Transient anti-Stokes emission is detected with a monocliromator and photomultiplier [39], or a spectrograph and optical multichannel analyser [40]. 

The reaction path shows how Xe and Clj react with electrons initially to form Xe cations. These react with Clj or Cl- to give electronically excited-state molecules XeCl, which emit light to return to ground-state XeCI. The latter are not stable and immediately dissociate to give xenon and chlorine. In such gas lasers, translational motion of the excited-state XeCl gives rise to some Doppler shifting in the laser light, so the emission line is not as sharp as it is in solid-state lasers. 

If the flash lamp is pulsed very rapidly, the emergent beam appears at a rate governed by the lifetime of the inverted population. The resulting laser beam becomes almost continuous because the pulses follow each other so rapidly. However, such a solid-state laser should not be pulsed too rapidly because, if it is, the rod heats to an unacceptable extent, causing distortion and even fracture. Generally, solid-state lasers are not used in continuous mode because of this heating aspect. Liquid or gas lasers do not suffer from this problem. 

Historically, the first type of laser to be tunable over an appreciable wavelength range was the dye laser, to be described in Section 9.2.10. The alexandrite laser (Section 9.2.1), a tunable solid state laser, was first demonstrated in 1978 and then, in 1982, the titanium-sapphire laser. This is also a solid state laser but tunable over a larger wavelength range, 670-1100 nm, than the alexandrite laser, which has a range of 720-800 nm. 

A diode, or semiconductor, laser operates in the near-infrared and into the visible region of the spectmm. Like the mby and Nd YAG lasers it is a solid state laser but the mechanism involved is quite different. 

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. 

Semiconducting polymers as materials for solid-state lasers. 

F. Hide, M.A. Dtaz-Gatcia, B.J. Schwarts, M.R. Andersson, P Qibing, A.J. Hecger, Semiconducting polymers a new class of solid-state laser materials. Science 1996, 273, 1833. 

M. Bcrggren, A. Dodabalapur, R. E. Slusher, Organic solid-state lasers with imprinted gratings on plastic substrates, Appl. Phys. Leu. 1998, 72, 410. 

Advances in laser technology now allow for solid-state lasers of high beam quality. These beams may be projected from a much smaller auxiliary telescope, which negates the need for optical switching and completely eliminates any main telescope fluorescence. Solid-state YAG lasers are the most common type of lasers commercially available. These lasers use a crystal as the lasing... 

One application of modem solid-state electronic devices is semiconductor materials that convert electrical energy into light. These light-emitting diodes (LEDs) are used for visual displays and solid-state lasers. Many indicator lights are LEDs, and diode lasers read compact discs in a CD player. The field of diode lasers is expanding particularly rapidly, driven by such applications as fiber optic telephone transmission. 

In this section, we describe a simple laser setup using a high-gain medium consisting of DCM-encapsulated dendrimers in a methanol solution. The results can be applied to a solid-state laser medium [42], described in the next section. In that case, we used RdB-dendrimer in the waveguide gain medium [43]. 

Lasers produce spatially narrow and very intense beams of radiation, and lately have become very important sources for use in the UV/VIS and IR regions of the spectrum. Dye lasers (with a fluorescent organic dye as the active substance) can be tuned over a wavelength range of, for instance, 20-50 nm. Typical solid-state lasers are the ruby laser (0.05% Cr/Al203 694.3 nm) and the Nd YAG laser (Nd3+ in an yttrium aluminium garnet host 1.06 pm). 

By the sol-gel-process, inorganic glassy and hybrid polymeric materials are accessible at comparatively low temperatures [1], Therefore, organic molecules or dyes can easily be incorporated into the oxide matrix. This combination is especially attractive for the development of the following devices optical filters, solid-state lasers, optical switches, nonlinear optical laser hosts, optical data storage media, and photoconductive devices and films [2]. 

Bis( 1,2-dithiolene) complexes are generally thermally and photochemically very stable, and their Vis-NIR absorption can be tuned in order to reach the wavelength ranges of interest for NIR lasers, such as Nd YAG, Nd YLF, and Er Glass solid-state lasers (emission wavelengths A.em = 1064, 1053, and 1540 nm, respectively). In this context, many groups of researchers have devoted their efforts to synthesising 1,2-dithiolene complexes for this type of application, and indeed some of them have been patented and are commercially... 

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