Laser-produced plasma (LPP) sources for extreme ultraviolet lithography (EUVL) systems utilize CO<sub>2</sub> lasers operating
with wavelength 10.6μm. Since multilayer-coated optics have high reflectivity for this infrared radiation (IR), a
significant and detrimental amount of IR is passed through the EUVL system. One method to remove the IR from the
system is to utilize a binary diffraction grating. When this grating is applied directly to the surface of the primary
collector optic of the source, the majority of the IR is diverted outside the radius of the exit aperture at the intermediate
focus (IF). This paper will report details on the performance of a full size (410mm diameter) Demonstration Collector
utilizing IR rejection (IRR) technology with the capability to produce over 125X suppression of IR, equaling the
performance of a IR spectral filter. Additional details will be reported on the technology development and use of a
glassy smoothing layer to enable high EUV performance, a weighted average multilayer reflectance of 50.9% for
unpolarized EUV radiation.
Johansson crystals have been known for many decades as x-ray optical elements with a high resolving power and small
foci. However, in the past their use in applications requiring a small focus and a narrow band pass were limited by
imperfections caused by the technologies applied to their manufacture. While high performance Johansson crystals
might have been achieved in some research facilities, such crystals were not commercially available. RIT has developed
a process for fabricating precision Johansson crystals. The fabrication maintains the crystal structure intact. The angular
precision of the bending process of atomic planes and the reflecting crystal surface is better than four arc seconds. In
this paper, we will present the basic aspects of the technology and the achievements with Silicon and Germanium
The flux distributions in the focal plane of Kirkpatrick-Baez optics are investigated as the parameters of the focusing
ellipse of the mirrors are changed from typical laboratory optics to synchrotron beam line optics. This work shows the
effects of the most predominant focusing imperfections that arise from conditions that violate the original assumptions of
Kirkpatrick-Baez systems, including orthogonality of the mirror surfaces and paraxial rays.
Presented is a study of a coaxial, hybrid-stable-unstable resonator for high power lasers. The coaxial configuration
allows the realization of the outcoupling and rear mirror in one mechanical structure with the incorporation of an axicon
mirror with retroreflective characteristics as an intra-cavity folding mirror. The design of the stable direction is
investigated to optimize the set-up for best beam quality and minimized alignment sensitivity. Additionally, the instable
direction is examined to achieve an even heat load on the mirrors. Simulations of the laser structure are performed and
compared to measurements.
Two applications emerge as drivers for higher brightness fiber-coupled diode lasers: advanced solid-state pumping schemes and materials processing. In contrast to the well-established side-pumping schemes of laser rods, advanced pumping schemes for today's solid-state lasers make use of the high brightness of the pump sources to increase the performance and efficiency of the solid-state laser. Materials processing applications such as metal welding and cutting are commonly served with solid-state lasers or CO<sub>2</sub> lasers. Lately, the increased lifespan, reduced systems costs and increased brightness of fiber-coupled diode laser systems make them a new alternative.
In this work, a diode laser system is described that yields 250 wats in a 600 micrometer spot with a numerical aperture 0.2 of the focused beam, corresponding to a F/# of 2.4. The system is based on a single 15 bar stack that operates in cw-mode. For brightness enhancement, it incorporates a measure to increase the fill factor of the emitting aperture and polarization multiplexing. The brightness in the focus spot is 10<sup>5</sup>W/cm<sup>2</sup> with a F# of 2.4 focusing optic and 3x10<sup>5</sup>W/cm<sup>2</sup> with a high speed of F/# of 1.4.
To achieve the required symmetry for fiber coupling, the system incorporates a beam transformer that assimilates the beam quality along the two main axes of the beam profile. A monolithic design is chosen to reduce alignment tolerances and to increase ruggedness.
Today's high power diode lasers achieve spots with dimensions of approximately 1 mm square, delivering intensities breaching 10<SUP>5</SUP> W/cm<SUP>2</SUP> and power levels of up to 4 kW. These lasers can be used for a variety of applications from surface treatment to welding. However, each of these applications require different focus sizes to maximize the benefits of the laser source. Therefore, variable cylindrical optics were designed and manufactured in the scope of this work. They create rectangular spot sizes with adjustable aspect ratios. These optics are used in connection with high power diode laser stacks operating in the multiple kilowatt power range. Two different variable optics were used. The first is designed for surface applications such as hardening, cladding and alloying. The spot size varies from 6.0 mm to 22.0 mm in one direction and stays constant at 2.6 mm in the other direction. The second optic exhibits two ranges of continuously variable spot sizes from 1.2 mm to 6.0 mm and 2.4 mm to 12.0 mm with its second dimension fixed at 1.2 mm or 2.4 mm respectively. This lens is used for applications from surface treatment to welding and cutting.
Commercially available high power diode lasers (HPDLs) with output powers of up to 6 kW have been recognized as an interesting tool for industrial applications. In certain fields of application they offer many advantages over Nd:YAG and CO<SUB>2</SUB> lasers because of their low maintenance, compact design and low capital costs. Examples of successful industrial implementation of HPDLs include plastic welding, surface hardening and heat conduction welding of stainless steel and aluminum. The joining of plastics with an HPDL offers the advantages of producing a weld seam with high strength, high consistency and superior appearance. One example is the keyless entry system introduced with the Mercedes E-class where the microelectronic circuits are embedded in a plastic housing. Other applications include instrument panels, cell phones, headlights and tail lights. Applications in the field of surface treatment of metals profit from the HPDL's inherent line-shaped focus and the homogeneous intensity distribution across this focus. An HPDL system is used within the industry to harden rails for coordinate measurement machines. This system contains a customized zoom optic to focus the laser light onto the rails. With the addition of a temperature control, even complex shapes can be hardened with a constant depth and minimum distortion.
Monolithic linear arrays of diode lasers, also known as diode laser bars, are the basic elements for most high-power laser applications such as solid-state laser pumping or material processing. Cylindrical microlenses used as fast- axis collimators for 10-mm diode bars require very high angles of aperture (up to 100 degree FW1/e2, equivalent to a numerical aperture of approx. 0.8) to capture most of the emitted laser power. For the efficient longitudinal pumping of laser rods, or the narrow focusing of the diode laser radiation (fiber coupling, material processing), high- quality microlenses with small lens aberrations are necessary to avoid power losses and beam quality degradation. A technique for coupling the output of high- power diode laser bars into one multimode fiber with high efficiency, easy alignment requirements and low manufacturing costs is demonstrated using a single fiber with core diameter down to 400 micrometers . This technique comprises two micro step-mirrors for beam shaping. The overall efficiency from one diode-laser bar to fiber is 71% with 20 W cm laser power through the fiber. Coupling of 12 diode laser bars and power of 200 W out of a fiber with core diameter of 0.8 mm and NA equals 0.2 is achievable with this technique.
We developed a compact fiber-coupled high-power diode-laser unit with optical output power up to 40 W cw, coupled into a multimode fiber with 600 micrometers core diameter and NA 0.22. This diode-laser unit is suitable for pumping solid-sate or fiber lasers as well as for material processing. Essential part is a novel beam-shaping system with compact size, high flexibility and low alignment requirements, which uses a pair of micro step-mirrors. The whole unit fits into a housing of approximately 110 X 100 X 90 mm.
A technique for coupling the radiation of a high-power diode laser bar into one multimode fiber with high efficiency, easy alignment requirements and low manufacturing costs is demonstrated using a single fiber with 400 micrometers core diameter. The principal item of the fiber-coupling system is a pair of micro step-mirrors--a novel design for beam shaping. The overall efficiency from diode-laser to fiber is 71% with 20 W cw laser power through the fiber. Polarization and wavelength multiplexing renders the system scaleable to higher output power which makes it highly suitable for material processing and pumping of lasers.