A laser unit may include a laser chamber including a pair of discharge electrodes that are opposed to each other in a first direction with an electrode gap interposed in between and are configured to provide a discharge width in a second direction, orthogonal to the first direction, smaller than the electrode gap; and an optical resonator including a first optical member and a second optical member that are opposed to each other in a third direction orthogonal to both the first direction and the second direction with the discharge electrodes interposed in between, and configured to amplify laser light generated between the discharge electrodes and output amplified laser light, the optical resonator satisfying the following expression to configure a stable resonator in the second direction:

0<G1.Math.G2<1

where G1 is a G parameter of the first optical member, and G2 is a G parameter of the second optical member.

Online calibration of laser performance as a function of the repetition rate at which the laser is operated is disclosed. The calibration can be periodic and carried out during a scheduled during a non-exposure period. Various criteria can be used to automatically select the repetition rates that result in reliable in-spec performance. The reliable values of repetition rates are then made available to the scanner as allowed values and the laser/scanner system is then permitted to use those allowed repetition rates.

A light emitting sealed body includes: a housing which stores a discharge gas and is provided with a first opening to which first light is incident along a first optical axis and a second opening from which second light is emitted along a second optical axis; a first window portion which hermetically seals the first opening; and a second window portion which hermetically seals the second opening. The housing is formed of a light shielding material which does not transmit the first light and the second light. An internal space is defined by the housing, the first window portion, and the second window portion and the internal space is filled with the discharge gas. The first opening and the second opening are disposed so that the first optical axis and the second optical axis intersect each other.

A chamber for a gas laser device includes a first main electrode and a second main electrode arranged along a predetermined direction as being apart from and facing each other in the internal space, a window arranged at a wall surface of the chamber and transmitting light from the internal space, and a first preionization electrode arranged beside one side of the first main electrode. Here, the first preionization electrode includes a first dielectric pipe, a first preionization inner electrode arranged in the first dielectric pipe and extending along the first dielectric pipe, and a first preionization outer electrode extending along the first dielectric pipe and including a first end portion facing the first dielectric pipe with a first gap with respect to the first dielectric pipe. At least a part of the first gap is larger than 0 mm and equal to or smaller than 0.9 mm.

In a chamber of a gas laser apparatus, a distance from an imaginary axis extending along a predetermined direction to a first end portion between first and second primary electrodes increases from one side toward the other side in the predetermined direction, and a distance from the imaginary axis to a second end portion decreases from the one side toward the other side in the predetermined direction.

In a method, energy is supplied to a first gas discharge chamber of a first stage until a pulsed amplified light beam is output from the first stage and directed toward a second stage. While the energy is supplied to the first gas discharge chamber: a value of an operating parameter of the first gas discharge chamber is measured; it is determined whether to adjust an operating characteristic of the first gas discharge chamber based on the measured value; and, the operating characteristic of the first gas discharge chamber is adjusted if it is determined that the operating characteristic of the first gas discharge chamber should be adjusted. After it is determined that the operating characteristic of the first gas discharge chamber no longer should be adjusted, then an adjustment procedure is applied to an operating characteristic of a second gas discharge chamber of the second stage.

A resonator for a laser includes a first resonator wall and a second resonator wall with a lasing medium disposed in a gap therebetween. The resonator further includes a first mirror disposed at a first end of the first and second resonator walls and a second mirror disposed at a second end of the first and second resonator walls. The mirrors cooperate to form an intra-cavity laser beam that travels along a plurality of paths through the lasing medium. Furthermore, the first mirror and the second mirror form a laser resonator for a parasitic laser mode. A parasitic mode suppressor is located within the superfluous region.

An impedance matching circuit for a gas-laser excitation system includes a high-frequency connection line configured to be connected at a first connection point to a power source and at a second connection point to a gas-laser electrode. The impedance matching circuit is characterized in that an impedance of at least one section of the high-frequency connection line changes by a change to a configuration of the high-frequency connection line, in particular to at least one parameter of the high-frequency connection line in the at least one section.

A gas laser excitation system with an integrated impedance matching circuit, comprises a gas laser electrode, a high-frequency connection line connectable to the gas laser electrode and configured for transmission of high-frequency power to the gas laser electrode, and a shield configured to shield the high-frequency power to be transmitted. The shield is arranged between the high-frequency connection line and the gas laser electrode. The high-frequency connection line interacts with the gas laser electrode and/or the shield in such a way that the resulting impedance changes at least across a section of the high-frequency connection line.

One or more operating characteristics of a light source are adjusted by estimating a plurality of extreme values of operating parameters of the light source while operating the light source under a set of extreme test conditions. For each extreme test condition, a group of pulses of energy is supplied to a first gas discharge chamber of the light source while operating the first gas discharge chamber under the extreme test condition to produce a first pulsed amplified light beam; a group of pulses of energy is supplied to a second gas discharge chamber of the light source while operating the second gas discharge chamber under the extreme test condition to produce a second pulsed amplified light beam. An extreme value of an operating parameter for the extreme test condition is measured to thereby estimate the extreme value of the operating parameter.