Lasers alexandrite

A further advantage is the higher efficiency of the alexandrite laser because of its being a four-level laser. In the illustration in Figure 9.2(c), level 4 is a vibronic level and level 3 the zero-point level of the T2 state. Level 2 is a vibronic level of the 2 state and level 1 the zero-point level. Because of the excited nature of level 2 it is almost depopulated at room... 

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 further advantage, compared with the alexandrite laser, apart from a wider tuning range, is that it can operate in the CW as well as in the pulsed mode. In the CW mode the Ti -sapphire laser may be pumped by a CW argon ion laser (see Section 9.2.6) and is capable of producing an output power of 5 W. In the pulsed mode pumping is usually achieved by a pulsed Nd YAG laser (see Section 9.2.3) and a pulse energy of 100 mJ may be achieved. 

CH3I (methyl iodide) principal axes, 103 If rotation, 113 CH2NH (methanimine) interstellar, 120 Cr203 (chromium trioxide) in alexandrite laser, 347ff in ruby laser, 346ff HC3N (cyanoacetylene) interstellar, 120 HCOOH (formic acid) interstellar, 120 NH2CN (cyanamide) interstellar, 120... 

The optical features of a center depend on the type of dopant, as well as on the lattice in which it is incorporated. For instance, Cr + ions in AI2O3 crystals (the ruby laser) lead to sharp emission lines at 694.3 nm and 692.8 nm. However, the incorporation of the same ions into BeAl204 (the alexandrite laser) produces a broad emission band centered around 700 nm, which is used to generate tunable laser radiation in a broad red-infrared spectral range. 

Lasing has been demonstrated at 1.06 /tm in Nd3+-doped ZBLAN and BIG fluoride glass rods pumped by an alexandrite laser and xenon flashlamps, respectively [71,72], Fig. 6 shows the 1.06 //m laser output energy out of Nd3+-doped and Cr3+ Nd3+-codoped fluoroindate glass rods of 40 mm length. In presence of Cr3+ ions, which are efficient absorbers of excitation light from flashlamps,... 

For certain special purposes, e.g., the excitation of resonance Raman spectra, tunable dye lasers and solid state lasers are used, e.g., the chromium doped Alexandrite laser and the titanium doped sapphire laser (Demtroder, 1991). 

Figure 1. Raman spectra in the radial breathing mode region for a) a Nd YAG-produced sample with a H2 adsorption capacity of 7 wt%, and b) a sample produced with the Alexandrite laser operating with a 200 ns pulse width at a peak power of 10.5 MW/cm. The red curves (highest curve on each figure) are for Raman excitation at 632.8 nm and show the SWNT size distribution for excited metallic and semiconducting tubes. The blue curves (lowest curve on each figure) were obtained at 488 nm and show predominantly semiconducting tubes.

Fitzpatrick R.E. 1993. Comparison of the Q-switched Ruby, Nd YAG, and alexandrite lasers in tattoo removal. Lasers Surg. Med. (Suppl.) 6 52. 

McGillis S.T., Bailin P.L., Fitzpatrick R.E. et al. 1994. Successful treatments of blue, green, brown and reddish-brown tattoos with the Q-switched alexandrite laser. Laser Surg. Med. (Suppl.) 6 52. Meijering L.J.T., VanGermert M.J.C., Gijsbers G.H.M. et al. 1993. Limits of radial time constants to approximate thermal response of tissue. Lasers Surg. Med. 13 685. 

Walling JC, Jenssen HP, Morris RC, Odell EW, Peterson OG (1979) Broad-band tuning of solid-state Alexandrite laser. J Opt Soc Am 69 373... 

Comparing the QS laser with the long-pulsed 532-nm Nd YAG laser in the treatment of melasma, the latter produced less PIH because it lacks the photomechanical effects of the QS laser [126]. QS alexandrite laser or PLDL combined with 15-25% TCA peel and/or Jessner s solution was shown to be effective, safe, and relatively inexpensive treatment modalities in the recalcitrant pigmentary disorders [92]. Combination of QS alexandrite and ultrapulse CO lasers yielded statistically significant result in improving refractory melasma compared to QS alexandrite laser alone [5]. Erbium YAG used on patients with skin phototypes II-V may have demonstrated improvement but transient PIH developed 3-6 weeks after laser treatment [100]. 

Angsuwarangsee S, Polnikorn N (2003) Combined ultrapulse COj laser and Q-switched alexandrite laser compared with Q-switched alexandrite laser alone for refractory melasma split-faced design. Dermatol Surg 29 59-64... 

Nanni CA, Alster TS (1999) Laser-assisted hair removal side effects of Q-switched Nd Yag, long-pulsed ruby, and alexandrite lasers. J Am Acad Dermatol 41(2 ptl) 165-171... 

Aldraibi MS, Touma DJ, Khachemoune A (2007) Hair removal with the 3-mec alexandrite laser in patients with skin types IV-VI efficacy, safety, and the role of topical steroids in preventing side effects. J Drugs Dermatol 6(l) 60-66... 

Fig. 5.72. (a) Level scheme of a tunable four-level solid-state vibronic laser (b) absorption spectrum for two different polarization directions of the pump laser (c) output power Pout (7.) for the example of the alexandrite laser... 

The future importance of these lasers is derived from the fact that many of them may be pumped by diode laser arrays. This has already been demonstrated for Nd YAG and alexandrite lasers, where very high total energy conversion efficiencies were achieved. For the diode laser-pumped Nd YAG laser, values of rj = 0.3 for the ratio of laser output power to electrical input power have been reported (30% plug-in efficiency) [5.132]. 

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