Neodymium-YAG lasers

Figure 8.16 illustrates the energy levels of Nd in yttrium aluminium garnet (Y3AI5O12), which are involved in the laser action of this crystal (known as the neodymium YAG laser). Describe the processes that occur when the laser is working. 

Fig. 1. Some useful laser sources in the visible and ultraviolet spectrum. For infrared lasers and also a more complete listing of laser lines see, for example, ref. 1. YAG (II) and YAG (III) signify the second and third harmonics, respectively, of the neodymium YAG laser. KDP, potasium dihydrogen phosphate, and KPB, potassium pentaborate, are frequency doubling crystals.

Geyer O. Management of large, leaking, and inadvertent filtering blebs with the neodymium YAG laser. Ophthalmology 1998 105 983-987. 

FIGURE 20.19 The neodymium-YAG laser operates between two excited states of the neodymium ions. 

In Figure 20.19 we sketch the operation of the neodymium-YAG laser. The laser medium is a crystal of yttrium-aluminum-garnet doped with neodymium ions. This laser has the advantage over the ruby laser that the laser action occurs between two excited states, and the population inversion is consequently easier to maintain. The Nd-YAG laser is widely used in science and technology. One major application is to pump the so-called dye lasers in which the medium is intensely colored dye molecules (usually with conjugated double bonds) dissolved in... 

All these problems can be prevented as much as possible by using modern lasers as light source for Raman spectroscopy, for example, Neodymium-YAG laser. The intensity of the light can often be around 0.5 Watts. This laser device is installed in most modern Raman spectrometers. 

Variations of the above apparatus are used in a number of laboratories. Several experiments utilize a type II KDP crystal to generate the third harmonic at 353 nm instead of the fourth harmonic at 264 nm. To obtain a higher repetition rate at a sacrifice in temporal resolution, the glass laser can be replaced with a mode-locked neodymium YAG laser. 

Of course, a TCSPC system works effieiently only with a high-repetition-rate excitation source. Diode lasers ean be built with any repetition rate up to about 100 MHz and are available with 375 nm, 405 nm, 440 nm, and 473 nm emission wavelength. Diode lasers are cost-effieient and ean be multiplexed at ps rates see Excitation Wavelength Multiplexing, page 87. For shorter wavelengths, frequency-doubled or frequency-tripled titanium-sapphire or neodymium-YAG lasers can be used. 

In metabolic cytometry, cells are incubated with a substrate that is tagged with a highly fluorescent dye we prefer tetramethylrhodamine because of its excellent spectroscopic properties and its compatibility with the frequency-doubled neodymium YAG laser. This substrate is prepared at high concentration and undergoes chromatographic purification to eliminate fluorescent impurities. 

Most of the interest in Y3AI5O12 (YAG) has been in its application as a host material for rare-earth ion lasers. As of 1981, Kaminskii, in his book Laser Crystals, lists 45 rare-earth ion lasers with YAG as the host material. The neodymium YAG laser is, beyond a doubt, the most popular solid-state laser in existence today (of the 45 lasers listed by Kaminskii, 23 are with neodymium). 

For the highest peak powers (at lower-pulse repetition rates and average powers), the dye laser is pumped (and mixed) with harmonics of the g-switched neodymium-YAG laser. Higherpeakpowers resultfrom a more efficient pump wavelength (green, 532 run) for rhodamine dyes, coupled with a shorter pump pulse length (of 5-9 nsec). 

FL, flashlamps DL, diode laser ArL, argon ion laser D-YAG, doubled neodymium YAG laser. 

---