# Attosecond Pulse Shaping by Multilayer Mirrors
## 3 Fabrication of Multilayer Coatings  
Various deposition techniques are used to realize advanced multilayer coatings. Every technique has advantages and disadvantages, and one should evaluate the coating priorities according to numerous criteria, such as overall cost, deposition speed, layer density (which is directly connected to damage thresholds), thickness accuracy, number of target materials, availability of target materials, vacuum requirements, in-situ characterization techniques, and coating homogeneity, to name only some of them. Nowadays, the following techniques are used for the realization of multilayer coatings:  
* **Electron beam physical vapor deposition (EBPVD)**[7; 8] is a form of physical vapor deposition in which a target material anode is bombarded with an electron beam. The electron beam arises from a charged tungsten filament under high vacuum. The electron beam causes atoms from the target to transform into the gaseous phase. These atoms then precipitate into solid form, coating everything in the vacuum chamber (within line of sight) with a thin layer of the anode material.
* **Magnetron sputtering**[9; 10; 11] is a plasma vapor deposition (PVD) process in which a plasma is created. The positively charged ions from the plasma are accelerated by an electrical field superimposed on the negatively charged electrode or 'target'. The positive ions are accelerated by potentials ranging from a few hundred to a few thousand electron volts and strike the negative electrode with sufficient force to dislodge and eject atoms from the target material. These atoms will be ejected in a typical line-of-sight cosine distribution from the face of the target and will condense on (substrate) surfaces that are placed in proximity to the magnetron sputtering cathode.
* **A (dual) ion beam deposition (D-IBD)**[12; 13; 14] apparatus typically consists of an ion source, ion optics, and the deposition target. Optionally, a mass analyzer can be incorporated. In the ion source, materials in the form of a gas, an evaporated solid, or a solution (liquid) are ionized. The ions are then accelerated, focused, or deflected using high voltages or magnetic fields. Optional deceleration at the substrate can be employed to define the deposition energy. This energy usually ranges from a few to a few thousand electron volts. At low energy, molecular ion beams are deposited intact (soft landing), while, at a high deposition energy, molecular ions fragment, and atomic ions penetrate further into the material. This process is known as ion implantation. The ion beam current, which is a quantitative measure for the deposited amount of material, can be monitored during the deposition process.
* **Pulsed laser deposition (PLD)**[15; 16; 17] is a physical vapor deposition technique where a high-power pulsed laser beam is focused inside a vacuum chamber to strike the target material that is to be deposited. This material is vaporized from the target in a plasma plume, which deposits the material as a thin film on a substrate. This process can occur in ultrahigh vacuum or in the presence of a background gas, such as oxygen. Oxygen is commonly used when depositing oxides to fully oxygenate the deposited films.  
* **Metalorganic vapor phase epitaxy (MOVPE)**, also known as organometallic vapor phase epitaxy (OMVPE) or metalorganic chemical vapor deposition (MOCVD) [46; 47], is a chemical vapor deposition method used to produce single or polycrystalline thin films. It is a highly complex process for growing crystalline layers to create complex semiconductor multilayer structures. In contrast to molecular beam epitaxy (MBE), the growth of crystals is by chemical reaction and not by physical deposition. This takes place not in a vacuum but from the gas phase at moderate pressures (10-760 Torr). As such, this technique is preferred for the formation of devices incorporating thermodynamically metastable alloys. It has become a major process in the manufacture of optoelectronics.