Abstract: Focus of a laser optical system can be corrected using a variable radius mirror having a focusing cavity and a separate cooling cavity. Pressure of a focusing material at a sufficiently low mass flow in the focusing cavity deforms a reflective surface mounted to the focusing cavity, changing its radius. Cooling material provided to the cooling cavity cools the variable radius mirror. A laser beam is reflected by the deformed reflecting surface to focusing optics, focusing the reflected laser beam on an EUV-emitting target, and minimizing a laser focus error by one or more of: maximizing a measured EUV power or minimizing a measured laser beam divergence. Providing focusing material at a deformation pressure and at a sufficiently low mass flow, and providing a separate cooling cavity, avoids perturbations in the reflective surface which would otherwise affect laser beam focus.

Abstract: Focus of a laser optical system can be corrected using a variable radius mirror having a focusing cavity and a separate cooling cavity. Pressure of a focusing material at a sufficiently low mass flow in the focusing cavity deforms a reflective surface mounted to the focusing cavity, changing its radius. Cooling material provided to the cooling cavity cools the variable radius mirror. A laser beam is reflected by the deformed reflecting surface to focusing optics, focusing the reflected laser beam on an EUV-emitting target, and minimizing a laser focus error by one or more of: maximizing a measured EUV power or minimizing a measured laser beam divergence. Providing focusing material at a deformation pressure and at a sufficiently low mass flow, and providing a separate cooling cavity, avoids perturbations in the reflective surface which would otherwise affect laser beam focus.

Abstract: A dichroic beam splitter module is disclosed for separating a main pulse laser beam from a pre-pulse laser beam each traversing a common beam path. In one embodiment, two dichroic elements are physically aligned along the beam path and are configured to pass the pre-pulse, a laser light having a first wavelength, to target material located near an irradiation site yet reflect the main pulse, a laser light having a second wavelength. The reflected main pulse is then further reflected by two reflective elements or mirrors from the first dichroic element to the second dichroic element and then on to the irradiation site. In alternative embodiments, the first mirror is deformable to alter beam characteristics of the reflected main pulse beam and the second mirror is adjustable to align the main pulse beam to the irradiation site.

Abstract: A dichroic beam splitter module is disclosed for separating a main pulse laser beam from a pre-pulse laser beam each traversing a common beam path. In one embodiment, two dichroic elements are physically aligned along the beam path and are configured to pass the pre-pulse, a laser light having a first wavelength, to target material located near an irradiation site yet reflect the main pulse, a laser light having a second wavelength. The reflected main pulse is then further reflected by two reflective elements or mirrors from the first dichroic element to the second dichroic element and then on to the irradiation site. In alternative embodiments, the first mirror is deformable to alter beam characteristics of the reflected main pulse beam and the second mirror is adjustable to align the main pulse beam to the irradiation site.