Before discussing Argon ion laser we have to know about ion laser because Argon ion laser is one of the types of ION LASER.

An ion laser is a gas laser in which ionized gas is used as the active or lasing medium. The electrical pumping method is used to achieve the population inversion in an ion laser. The pumping process is a two-step process in ion Laser. In the first step, the electron in the discharge tube makes a collision with neutral atoms of rare gases and thus produces an ion.

In the second step, these ions are excited to a higher energy level. Therefore, the population of higher energy level increase due to the successive collision of the irons with the electrons in the discharge tube. These lasers require high pumping power of the order of several kilowatts. In ion lasers, both Pulsed and continuous laser action have been observed.

For example, Argon ion laser, Krypton ion laser, and mercury in a laser are common ion gas lasers. 

Argon Ion Laser

Definition of Argon Ion Laser

An Argon ion laser is a gas laser in which ionized Argon gas is used as the active or lasing medium.

Construction of Argon Ion Laser

The experimental setup of Ar+ ion laser is shown in the figure :

The Argon ion Laser consists of a long and narrow discharge tube made of beryllium oxide filled with organ gas having two Windows at its ends inclined at Brewster’s angle.

The narrow discharge tube act as an optical resonator or cavity as two Mirrors are placed at each end of the tube facing perpendicular to the length of the tube. One of the mirrors is partially reflecting mirror and the other is 100%  reflecting mirror.

When a high voltage is applied between the cathode and anode, a high current flows. Due to the high current density, the Argon ions migrate continuously toward the cathode and electrons toward the anode.

Ions having low mobility tend to accumulate at the cathode, get neutralized, and diffuse slowly back into the discharge tube. 

The discharge tube consists of a return tube to equalize the distribution of argon iron. The electric field in the discharge accelerates the iron which produces a high temperature of approximately 3,000 degrees Kelvin. Therefore the water cooling system is required. 

The hot ions collide with the tube and may damage it. The wall damage may be reduced by using material such as graphite or beryllia (Beo) having higher thermal conductivity. To increase the pump rate and output power, a static magnetic field is applied in the discharge region parallel to the axis.

This field confines the discharge to the center of the tube and increases the number of electrons near the axis. The Argon ion Laser oscillates simultaneously on two transitions having wavelength 4881Å (blue) and 5145 Å(green).

Oscillation on a single line can be selected by placing a prism inside the cavity. With this laser, High output powers up to 100W can be obtained from a 1 cm diameter tube. 

Working of Argon Ion Laser

The Argon ion Laser is a four-level laser. The various energy level of argon ion is shown in the figure. When electric discharge passes through the tube, the Argon atoms are pumped to energy level E3 by two-step of collision with electrons.

In the first step, neutral argon atoms are ionized and raised to energy level E1 (known as the ground state of argon ions). In the second step, the ion in the ground state is excited to energy level E3.

The excited organ iron in energy labels E3 falls back to energy level E2 either the spontaneous emission or by stimulated emission process. The ions in energy level E2 decay spontaneously to the ground state of argon-ion emitting a photon of wavelength 720Å ( ultraviolet Photon).

In the Argon ion laser, the number of photons of different wavelengths is emitted. For example,, Argon laser generates up to 18 discrete lines (wavelength) ranging from ultraviolet (720 Å) to visible green (5145Å) the majority of the power developed at 4881Å and 5145Å wavelengths.

A Prism is placed in front of one of the mirrors of the cavity to select a particular wavelength for repeated oscillation in the cavity to stimulated identical photons. As such this laser operates at a single wavelength. In the absence of the prism, the organ and Laser are allowed to board band operation ( i.e. Photon of many wavelengths). 

Advantages of Argon ion laser 

• The width of the spectrum of Argon ion laser is large i.e. it emits multiple wavelengths.
• The output of the Argon laser is high as compared to the output of the He-Ne laser.
•  The argon laser is a high-gain system.
•  The divergence of the Argon laser is very small.

Disadvantages of Argon ion Laser

• The cost of an Argon laser is more than that of a He-Ne laser.
• The efficiency of the argon laser is very small.
•  A large amount of power supply is needed to operate an Argon laser.

 Applications of Argon ion laser

• Argon lasers are used to treat glaucoma and diabetic eye diseases.
• They are used in Raman spectroscopy.
• They are used in holography.
• They are used in forensic science.
• They are used as sources for optical pumping.

Krypton Ion laser

In the Krypton ion Iron laser, the active or lasing medium is krypton ions. The population inversion is achieved through the electrical pumping method. 

The working of krypton ion Laser is similar to that of Argon ion Laser. However, the output krypton iron laser has spectral lines in the visible region of the spectrum. On the other hand, the output of the argon-ion laser has a spectral line in the visible region, ultraviolet region, and near-visible region of the spectrum. 

FAQ on Argon Ion Laser