Nd:YAG-Laser

An Nd: YAG laser (short for neodymium - doped yttrium -aluminum-garnet ) laser is a solid state laser, which is used as active medium, a neodymium -doped YAG crystal and usually infrared radiation at wavelength 1064 nm is emitted. Other transitions exist at 946 nm, 1320 nm and 1444 nm

Pros and Cons

An advantage over the CO2 laser also frequently used is that the laser beam is guided through a fiber optic cable due to its lower wavelength.

The radiation of the laser or the scattered radiation is dangerous for services from Laser Class 3R for the eye and skin. In the eye, they will be less damaging the lens, but more the retina. The damage is noticed by the injured person or not until later (skin), since the radiation penetrates far into human tissue and does not cause thermal or optical irritant reactions.

It is possible with this laser to achieve high power (up to 10 kW in series lasers ). It is both continuous (CW, ENGL. Continuous wave ) and pulsed operation possible. Pulse operation is achieved either by pulsed pumping ( flashlamp ), Q-switching or mode-locking. With Q-switched peak powers of a few hundred megawatts to be achieved. Exciting the neodymium ions occurs either with gas discharge lamps ( arc lamps or flash with xenon or krypton - filled ) or laser diode at a wavelength of 808 nm, the average lifetime of the excited electrons of neodymium ions is around 230 microseconds. Due to this relatively long time, it is possible to store energy in the crystal, which then in a short pulse can be (10 to 100 ns) retrieved ( Q-switching ).

In lamp-pumped systems, the efficiency is about 3 to 5 percent, since only a small part of the radiation spectrum within the pumping level. For example, a laser with 3 kW of optical power 60 kW input power, it must be 57 kW dissipated as heat. By excitation with diode lasers (wavelength 808 nm) is pumping efficiency and beam quality can be significantly increased and the overall efficiency increases to about 25 to 50 %.

Applications

Drilling weld, cut

Originally Nd: YAG laser for micro holes for precision cutting of thin sheet metal and welding of single -point connections in use. Meanwhile, also prevailed cutting of thicker plates and welding as competition continues to frequently used carbon dioxide laser due to the increased efficiency and beam quality at high powers. Here comes into play that the beam can be coupled into a fiber and then simply welding robot can be equipped. This then wear a 1D, 2D or 3D appearance.

Material testing

Another application of the Nd: YAG laser is non-destructive acoustic material testing with ultrasound in hot or moving parts. Here is generated using the photoacoustic effect of ultrasound. The abrupt rise in temperature by a laser light pulse leads to thermoelastic effects that stimulate a wide range of ultrasonic waves.

Of increasing importance is the Nd: YAG laser in Raman spectroscopy.

Select / Highlight

In Q-switched operation, the Nd is: YAG laser because of its high peak power for identifying very many materials. He is often done this with a mirror scanner. The permanent laser engraving of tools, components and devices has gained in the course of quality assurance and traceability in importance. Plastics can contain special pigments that have a visible color change effect during laser marking ( eg computer keyboards).

A special Markieranwendung is the glass engraving. With a diode-pumped Nd: YAG lasers, the wavelengths of both 1064 nm and 532 nm, can be in pulsed operation with an average output power of about 1-2 W, two-dimensional as well as three-dimensional structures in the interior of transparent materials (e.g. glass produce ). Since glass is transparent to the laser wavelength, can be used only with Q-switched lasers - the pulse performance is so high that the damage threshold of the glass may be exceeded at the focal point.

In addition, the Nd wins: YAG laser increasingly in electrical engineering importance. The relatively new MID method in which an injection-molded, three-dimensional plastic parts of electronic circuit substrate is simultaneously - boards are superfluous in this technology - the laser to the conductor track activation and also in the ablative copper patterning is used.

Medicine

In medicine, a Nd: YAG laser in the treatment of hemangiomas ( hemangiomas ), since their wavelength is well absorbed by red Hämangiomgewebe and poorly from the water is an essential part of the surrounding tissue.

In ophthalmology it applies to perforate the iris ( iridotomy ) in the context of glaucoma or to remove a cataract. By means of frequency doubling he can replace an argon laser and are used for the treatment of retinal diseases or to improve water drainage in glaucoma ( trabeculoplasty ).

The Nd: YAG laser is used in the surgery, for example, metastases during the resection of lung metastases. More common in medicine and dentistry, however, Er: YAG laser - in contributing to the strongly absorbed by water- containing tissue wavelength of 2.8 microns and can be used in the Q-switched mode for tissue removal without adjacent tissue thermal damage.

Furthermore, the Nd: YAG laser for the disintegration of kidney stones used. For this medical laser applications, since the mid -1990s and the holmium laser (see below) established.

Other applications

Also in the research of the Nd: YAG laser are often used. He may well be frequency doubled ( it creates the highly visible wavelength 532 nm) and can be partially used as a substitute for the argon -ion laser at laser projectors and show purposes. Also green laser pointers are often frequency-doubled Nd: YAG laser. The frequency doubled (532 nm) or tripled (355 nm ) by means of non-linear crystals in the connection to the resonator is an efficient method to laser radiation of shorter wavelengths to produce, resulting in a variety of applications arise in which the absorption of the original wavelength of 1064 nm is not given is.

In the optical flow measurement technique pulsed, frequency-doubled Nd have due to their high power output and excellent beam quality flash lamp or diode pumped, : YAG laser at the so-called Particle Image Velocimetry enforced.

Also suitable are the Nd: YAG laser in the removal of tattoos used.

Military are, inter alia, Nd: YAG laser - so-called ' Dazzler ' - used as blend weapon.

Operation

By supplying energy / light which excites electrons within an atom to several energy levels. The transition to a lower energy level is characterized by the emission of light (for example: infrared light having a wavelength of 1064 nm). When light is on the Nd: YAG crystal sent, one speaks of the pumps. The neodymium atoms are excited. The light used is from a gas discharge tube or a diode laser.

Other dopants

Yttrium - aluminum garnet may be doped for the purpose laser with many other ions, such as found in the ytterbium Yb: YAG laser use, wherein the advantage is the higher maximum doping and thus a higher energy density and smaller slice thickness. The wavelength with which Yb: YAG emitting laser is 1030 nm

Widely used is the holmium laser, which must be fully described as chromium thulium - holmium -YAG lasers. The laser is the trivalent ion holmium ion, while chrome and thulium the absorption and transfer of the flashlamp excitation are the holmium ion. The emission wavelength of the holmium laser is 2123 nm

Nd: Cr: YAG laser or Nd / Cr: YAG - laser is additionally doped with chromium in order to absorb the radiation for its excitation in a wider wavelength range can. This makes it well suited for solar- pumped lasers. Only optical concentrators (eg concave mirror ) is used, and you can completely do without the detour via photovoltaics.