Argon Ion Lasers

Definition: gas lasers based on light amplification in ionized argon in a gas discharge

Argon ion lasers are powerful gas lasers, which typically generate multiple watts of optical power in a green or blue output beam with high beam quality.

The core component of an argon ion laser is an argon-filled tube, made e.g. of beryllium oxide ceramics, in which an intense electrical discharge between two hollow electrodes generates a plasma with a high density of argon (Ar⁺) ions. A solenoid around the tube (not shown in Figure 1) can be used for generating a magnetic field, which increases the output power by better confining the plasma.

Figure 1: Setup of a 20-W argon ion laser. The gas discharge with high current density occurs between the hollow anode and cathode. The intracavity prism can be rotated to select the operation wavelength.

A typical device, containing a tube with a length of the order of 1 m, can generate 10 W or 20 W of output power in the green spectral region at 514.5 nm, using several tens of kilowatts of electric power. The dissipated heat must be removed with a water flow around the tube; a closed-circle cooling system often contains a chiller, which further adds to the power consumption. The total wall-plug efficiency is thus very low, usually below 0.1%. There are smaller air-cooled argon ion lasers, generating some tens of milliwatts of output power from several hundred watts of electric power.

The laser can be switched to other wavelengths such as 457.9 nm (blue), 488.0 nm (blue–green), or 351 nm (ultraviolet) by rotating the intracavity prism (on the right-hand side). The highest output power is achieved on the standard 514.5-nm line. Without an intracavity prism, argon ion lasers have a tendency for multi-line operation with simultaneous output at various wavelengths.

There are similar noble gas ion lasers based on krypton instead of argon. Krypton ion lasers typically emit at 647.1 nm, 413.1 nm, or 530.9 nm, but various other lines in the visible, ultraviolet and infrared spectral region are accessible.

Other types of ion lasers are mentioned in the article on gas lasers.

Applications

Multi-watt argon ion lasers can be used e.g. for pumping titanium–sapphire lasers and dye lasers, or for laser light shows. They are rivaled by frequency-doubled diode-pumped solid-state lasers. The latter are far more power efficient and have longer lifetimes, but are more expensive. Argon tubes have a limited lifetime of the order of a few thousand hours. An argon laser may thus be preferable if it is used only during a limited number of hours, whereas a diode-pumped solid-state laser is the better solution for reliable and efficient long-term operation.

Laser safety issues arise both from the high output power of typical ion lasers and from the high voltage applied to the tube.