A ring laser gyroscope uses interference of laser light within a bulk optic ring to detect changes in orientation and spin. It is an application of a Sagnac interferometer. Interference of two circular waves - Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right). ... Lasers range in size from microscopic diode lasers (top) with numerous applications, to football field sized neodymium glass lasers (bottom) used for inertial confinement fusion, nuclear weapons research and other high energy density physics experiments. ... The Sagnac effect manifests itself in an experimental setup called ring interferometry. ...

Ring laser gyros (RLG) can be used as the stable elements (for one degree of freedom each) in an inertial reference system. The advantage of using a RLG is that there are no moving parts. Compared to the conventional spinning gyro, this means there is no friction, which in turn means there will be no inherent drift terms. Additionally, the entire unit is compact, lightweight and virtually indestructible, meaning it can be used in aircraft. Unlike a mechanical gyroscope, the device does not resist changes to its orientation. Physically, an RLG is composed of segments of transmission paths configured as either a square or a triangle and connected with mirrors. One of the mirrors will be partially silvered, allowing light through to the detectors. A laser is launched into the transmission path in both directions, establishing a standing wave resonant with the length of the path. As the apparatus rotates, light in one branch travels a different distance than the other branch, changing its phase and resonant frequency with respect to the light travelling in the other direction, resulting in the interference pattern beating at the detector. The angular position is measured by counting the interference fringes. A gyroscope is a device for measuring or maintaining orientation, based on the principle of conservation of angular momentum. ...

RLGs, while more accurate than mechanical gyros, suffer from an effect known as "lock-in". When the ring laser is rotating very slowly, the frequencies of the counter-rotating lasers become very close to each other. At this low rotation, the nulls in the standing wave tend to "get stuck" on the mirrors, locking the frequency of each beam to the same value, and the interference fringes no longer move relative to the detector, which causes the device to no longer track angular position.

This effect is compensated by adding dithering. The entire apparatus is twisted and untwisted about its axis at a rate convenient to the mechanical resonance of the system, thus ensuring that the angular velocity of the system is usually far from the lock-in threshold. Typical rates are 400Hz, with a peak dither velocity of 1 arc-second per second.

A related device is the fiber optic gyroscope which operates similarly to the ring gyro, but implementing transmission paths with a coiled fiber optic cable. A ring laser gyroscope uses interference of laser light within a bulk optic ring to detect changes in orientation and spin. ...

Primary applications include navigation systems on commercial airliners, ships and spacecraft, where RLGs are often referred to as Inertial Reference System. In these applications, it has replaced its mechanical counterpart, the Inertial guidance system. An inertial guidance system consists of an Inertial Measurement Unit (IMU) combined with control mechanisms, allowing the path of a vehicle to be controlled according to the position determined by the inertial navigation system. ...

See also

• Laser applications
• Laser construction
• Laser science
• List of lasers
• Active laser medium
• Inertial guidance system

Lasers were used in the 2005 Classical Spectacular concert Soon after the invention of the laser in 1960, it was described as a solution in search of a problem. However, since that time, the laser has found a place as a useful tool in many scientific, military, medical and industrial... A laser system generally consists of three important parts: An energy source (usually referred to as the pump or pump source); A gain medium or laser medium; A mirror, or system of mirrors, forming an optical resonator. ... Laser science is a branch of optics that describes the theory and practice of lasers. ... The following is a list of laser types, their operational wavelengths, and their applications. ... Within a laser, the active laser medium is the material that exhibits optical gain. ... An inertial guidance system consists of an Inertial Measurement Unit (IMU) combined with control mechanisms, allowing the path of a vehicle to be controlled according to the position determined by the inertial navigation system. ...

External links

• Stedman Review of the Sagnac Effect - link broken
• Sperry Marine MK 39 Ring Laser Gyro

Examples of manufacturers of RLG based systems:

iMAR Navigation GmbH, Germany

Northrop Grumman, USA

Honeywell Inc., USA