A narrow linewidth mid infrared laser, including a pumping laser diode with a fast-axis compressor and a pumping wavelength λ.sub.o; and an optical resonator arranged to receive the pumping wavelength λ.sub.o, the optical resonator including a laser crystal with a lasing wavelength λ.sub.p, a dichroic mirror, and a nonlinear crystal to generate an idler wavelength λ.sub.i.

The present invention describes a laser system for eliminating astigmatism to produce an elliptical laser beam that has an ellipticity between about 0.9 to 1.0. The laser system described herein allows for increased conversion efficiency and output powers. on-linear optical elements in the laser system eliminate astigmatism. The laser system comprises one or more cavities with wavelength splitters that act as dual-minor chambers for single-pass light transmission through the non-linear optical elements to reduce cavity size or as beam splitters for double-pass light transmission through the non-linear optical elements to increase laser output power. The laser system may also include a birefringent filter and/or etalon in the first cavity for polarization and wavelength tuning. The laser system may also generate a high-power, deep-ultraviolet laser output. The laser system may also be devoid of curved mirrors and non-normal incidence reflection to eliminate astigmatism.

A radiation source arrangement causes interaction between pump radiation (340) and a gaseous medium (406) to generate EUV or soft x-ray radiation by higher harmonic generation (HHG). The operating condition of the radiation source arrangement is monitored by detecting (420/430) third radiation (422) resulting from an interaction between condition sensing radiation and the medium. The condition sensing radiation (740) may be the same as the first radiation or it may be separately applied. The third radiation may be for example a portion of the condition sensing radiation that is reflected or scattered by a vacuum-gas boundary, or it may be lower harmonics of the HHG process, or fluorescence, or scattered. The sensor may include one or more image detectors so that spatial distribution of intensity and/or the angular distribution of the third radiation may be analyzed. Feedback control based on the determined operating condition stabilizes operation of the HHG source.

A current control device supplies a current to a semiconductor laser in order to output laser light to the semiconductor laser, and includes a current commander and a supplier. The current commander outputs a command value corresponding to a current value by increasing the command value with a lapse of time until reaching a target command value corresponding to a current value for outputting the laser light with a predetermined strength. The supplier supplies a current with a size corresponding to the command value output by the current commander to the semiconductor laser.

A laser adjustment method includes a first adjustment step and a second adjustment step. In the first adjustment step, using a light detector detecting a second harmonic light, optical intensity and wavelength of the second harmonic light is detected and a first temperature adjuster is adjusted to adjust temperatures of a Nd:YVO.sub.4 crystal and a KTP crystal such that the detected wavelength of the second harmonic light approaches a desired wavelength and such that the optical intensity of the second harmonic light reaches at least a predetermined value. In the second adjustment step, after the first adjustment step, a temperature of an etalon is adjusted by a second temperature adjuster such that the detected wavelength of the second harmonic light approaches the desired wavelength and such that the optical intensity of the second harmonic light reaches at least a predetermined value.

A laser adjustment method includes a first adjustment step and a second adjustment step. In the first adjustment step, using a light detector detecting a second harmonic light, optical intensity and wavelength of the second harmonic light is detected and a first temperature adjuster is adjusted to adjust temperatures of a Nd:YVO.sub.4 crystal and a KTP crystal such that the detected wavelength of the second harmonic light approaches a desired wavelength and such that the optical intensity of the second harmonic light reaches at least a predetermined value. In the second adjustment step, after the first adjustment step, a temperature of an etalon is adjusted by a second temperature adjuster such that the detected wavelength of the second harmonic light approaches the desired wavelength and such that the optical intensity of the second harmonic light reaches at least a predetermined value.

An optical crystal can be mounted to a mounting block configured to receive the crystal. A base portion on the mounting block utilizes two walls forming a corner and a single biasing spring clip to secure the crystal. The spring clip applies forces in two different directions substantially orthogonal to the two walls. The spring clip is based off a symmetrical geometry which applies nearly the same force application in both directions. The spring also features bend regions that contact the crystal in such a way as to reduce the presence of point loads or stress risers. The length of contact along the crystal is maximized, allowing for proper force distribution and a sufficient surface are contact for static holding capabilities.

An optical crystal can be mounted to a mounting block configured to receive the crystal. A base portion on the mounting block utilizes two walls forming a corner and a single biasing spring clip to secure the crystal. The spring clip applies forces in two different directions substantially orthogonal to the two walls. The spring clip is based off a symmetrical geometry which applies nearly the same force application in both directions. The spring also features bend regions that contact the crystal in such a way as to reduce the presence of point loads or stress risers. The length of contact along the crystal is maximized, allowing for proper force distribution and a sufficient surface are contact for static holding capabilities.

A laser system is described, the laser system comprising: an optical cavity defined by at least first and second at least partially reflecting elements; and a gain system. The gain system comprising at least first and second gain media located within the optical cavity. The first and second gain media are configured to generate optical radiation of at least first and second wavelength ranges in response to pumping energy.

A laser system is described, the laser system comprising: an optical cavity defined by at least first and second at least partially reflecting elements; and a gain system. The gain system comprising at least first and second gain media located within the optical cavity. The first and second gain media are configured to generate optical radiation of at least first and second wavelength ranges in response to pumping energy.