Nd: YAG laser is a type of solid-state laser that is widely used in various fields such as material processing, medical applications, and scientific research. It is based on the principle of stimulated emission of radiation, where a population of atoms is excited to higher energy levels, and when they return to their ground state, they emit photons of a specific wavelength.
The construction of the Nd: YAG laser involves a host crystal of yttrium aluminum garnet (YAG) doped with neodymium (Nd) ions. The Nd ions are usually introduced into the YAG crystal through a process called ion doping. The crystal is then optically pumped using a flashlamp or a diode laser, which provides energy to excite the Nd ions.
When the Nd ions are excited, they absorb energy and transition to higher energy levels. The Nd ions can be excited to different energy levels, depending on the amount of energy provided by the pump source. When the Nd ions return to their ground state, they release energy in the form of photons. These photons bounce back and forth between the mirrors at the ends of the laser cavity, creating a coherent beam of light.
The working principle of Nd: YAG laser involves the following steps:
Pumping: The Nd: YAG laser crystal is pumped with high-intensity light, usually from a flash lamp or laser diode. The energy from the pump source excites the neodymium ions in the crystal, raising them to a higher energy level.
Absorption: The excited neodymium ions absorb light energy at a specific wavelength, usually 808 nanometers.
Stimulated emission: As the neodymium ions relax back to their ground state, they emit light energy at a longer wavelength of 1064 nanometers. This is the primary output of the Nd: YAG laser.
Amplification: The emitted photons stimulate other excited neodymium ions in the crystal to emit more photons of the same wavelength, creating a chain reaction of amplified light.
Output: The amplified light is then reflected between two mirrors at the ends of the laser crystal, producing a coherent, directional beam of light. This output can be adjusted by changing the reflectivity of the mirrors.
Nd: YAG lasers are known for their high power, high energy, and long pulse duration, making them ideal for applications that require precision and accuracy, such as laser cutting, welding, and drilling. They are also commonly used in medical applications, such as laser surgery and dermatology.
The energy level diagram of the Nd: YAG laser is shown below:
The Nd ions are excited from the ground state E1 to the excited state E3 by absorbing energy from the pump source. From the excited state E3, they quickly transition to the metastable state E2 through a non-radiative process. When a photon of the correct energy interacts with an ion in the metastable state E2, it can stimulate the emission of another photon with the same energy and phase, causing the emission of a coherent beam of light at a specific wavelength. This process is known as stimulated emission and is responsible for the laser's high intensity and narrow spectral linewidth.
In summary, the Nd: YAG laser is constructed from a YAG crystal doped with Nd ions and optically pumped with a flashlamp or diode laser to create a coherent beam of light. The energy level diagram shows the different energy levels of the Nd ions and the processes involved in the stimulated emission of photons.
