Color has been associated with thin films of materials for longer than we know, but, although the effect was known and observed, it was not fully understood until comparatively recently. It was the 19th Century before the interference effects in thin films that are responsible for their color, were properly recognized. Then the subjective, human response that is color, had to wait until the 20th Century before objective methods of defining it were accepted. Nowadays, there are many applications where the color of an optical coating is its most important attribute. This talk will survey some of the history of the struggle to understand and master the color of optical coatings. This is inextricably mingled with the history of color itself and so much of this account deals with the general problem of color.

An apparatus for localized transmittance measurements of optical coatings with spatially non-uniform performance is presented. The setup allows spectral acquisition in the range of 400–1000 nm with spatial resolution higher than 20 μm. Examples of its implementation for the characterization of linearly variable optical components of portable spectrometers are given.

Total loss test of the high-reflective (HR) film coated on super-smooth silica substrate by dual ion beam sputtering (DIBS) is based on the well-established cavity ring-down technique. Scattering and transmittance are tested by integral scattering and transmittance measuring apparatus, after which absorption is calculated. At 632.8 nm wavelength, the magnitude and distribution of thin film loss are researched for both s- and p-polarization, and the reflectivities are 0.99986, 0.99997, and 0.99962, respectively. Based on the analysis, the tested scattering is less than its real value.

An explicit model from the matrix method is utilized to describe the measurement sensitivity of the photothermal detuning technique dependent on the polarization of the probe beam. Numerical results show that the optimal probe wavelengths and the slope of the main spectral band edges are different for both s- and p-polarized beams with the same incident angle. Compared with the random polarized probe beam at the larger incident angle, the measurement sensitivity can be improved approximately twice over with the p- and s-polarized probe beams under the optimal condition.

A novel large-stage atomic force microscope (AFM) for nondestructive characterization of optical thin films is built. An open sample stage and a probe unit are employed to measure samples with large size and weight. Three optical thin films with large areas are imaged using this AFM without needing to cut the pieces apart. Experimental results show that the maximum scanning range for one single image can reach 20×20 (μm) while keeping a high resolution laterally and vertically. The maximum possible size of a sample is 600×1000 (mm). The new AFM is capable of performing wide-range and high-resolution characterizations of large samples such as large-area optical thin films.

Spectroscopic imaging ellipsometry (SIE) is used to characterize a nanofilm pattern on a solid substrate. The combination of a xenon lamp, a monochromator, and collimating optics is utilized to provide a probe beam with diameter of 25 mm, a charge-coupled device (CCD) camera with an imaging lens set and a lateral resolution in tens of microns is used as the detector. The sampling is approached by a rotating compensator at 8 seconds per wavelength. An 8–35-nm-thick stepped SiO2 on Si substrate is characterized in the range of 400–700 nm with a thickness resolution of approximate 0.2 nm.

The current and potential applications of reststrahlen bands in optical surfaces and components are reviewed. This type of interval with metallic-like high reflectance has been used for monochromatization in infrared and when wavelength-selective low emittance is needed for frost prevention or infrared signature reduction. Associated features, including a narrow reflectance minimum for a wide range of angles of incidence, are potentially useful.

Different approaches to the design of dispersive mirrors (DMs) for ultrafast applications are considered. High efficiency and good quality of solutions are achieved due to a completely analytical approach to the computations of all DM characteristics and a modern version of the needle optimization technique. Different means to suppress group delay dispersion (GDD) oscillations are demonstrated. Alternatively, design approaches not based on GDD optimization are described, including time-domain design approaches based on direct optimization of pulse energy concentration.

New or optimized-mixed evaporation materials of PIZOLIN, ALVIRIT, ROMA, and TiO53[1] on the basis of high-index pure substances of TiO2, Nb2O5, CeO2, ZrO2, and Ta2O5 are developed with the aim of identifying dielectric materials with specific refractive indices, reduced film stress, better wear or humidity resistance, and improved ultraviolet (UV) blockage compared to pure substances. Materials are tested in conventional and slightly ion-assisted deposition using process windows typical for coating polymeric substrates. Films with refractive indices in the range of 2.08–2.40, as well as tunable film stress below values for pure substances, are observed. In some cases, the admixture leads to a shift in absorption edge or improvement in moisture resistance of films. Individual results based on the new formulation on film materials with blue colour in transmission (OLIVIN P) in metal and metal oxide mixtures are presented.

Two chalcogenide films with composition Ge25-xSb10+xS65 (x=0, 10) and Te20As30Se50, called 2S1G and TAS, respectively, are studied. These materials have high linear and nonlinear refractive indices and present interesting photosensitive behavior toward bandgap light. Further, these chalcogenides glasses can be deposited in an amorphous thin film for optical coatings or waveguides. Their properties and limitations, including their photoinduction e?ects, nonlinear Kerr effect, photodiflusion of silver, and aging, are discussed.

Optical grade thick diamond films are polished on two sides by electron discharge machining (EDM) are with a mechanical method. The infrared transmittivities of Y2O3/diamond films are investigated in detail. Results indicate that the average infrared transmittivity is improved from 68.82% to 82.42% after deposition of Y2O3 at 10-μm central wavelength, and from 67.98% to 82.45% at 8–12-μm wave-band. The coated films meet the demands of infrared window applications. Therefore, the performance of the optical-class diamond thick films used in an actual infrared window can provide reliable application for basic research.

SnO2 thin films with good orientation are prepared on a glass substrate by radio frequence (RF) reactive sputtering. The phases of the thin films before and after annealing are analyzed by X-ray diffraction (XRD) spectroscopy, and the surface morphologies of the thin films before and after annealing are analyzed by atomic force microscopy (AFM). The result shows that the crystalline quality of the films markedly improved, the grains grow a little, and the orientation is more consistent after annealing in the air at 400℃ for 60 min. After modular multi-grating spectrometer measurement, the average transmittance in the air is found to be 80%. By the scanning electron microscopy (SEM), the energy spectrum shows that the ratio of Sn and O is close to 1:2.

VOx films fabricated by direct currect (DC) magnetron sputtering using a high pure vanadium metal target (99.99%) are reported. The impact of the temperature coefficient of resistance (TCR), the effects of Ar/O2 ratio on the deposition, the sputtering power, the gas pressure, and the annealing temperature and time are analyzed through the design of an orthogonal experiment. The result shows that VOx films prepared by this method have a relatively high TCR. The the annealing temperature and time of the VOx films are studied using the RTP-500. The relationships between TCR and annealing temperature and time are obtained. It illustrates that rapid annealing results in an optimized TCR in the range from –2%/K to –3.6%/K.

Before going into the background of challenges imposed by modern laser technology on coated optical components, this letter reviews the major aspects of coating production and control. Current deposition techniques and characterisation methods for high power optical components applied in modern laser systems are summarised and discussed. In this context, methods are considered especially for the precise control of the spectral transfer properties of optical coatings during production. Also, a short review is presented regarding laser damage in optical coatings and the corresponding measurement techniques. In addition, the outlook includes recent developments in laser technology and corresponding trends in thin film production.

We report on the development of highly dispersive mirrors for chirped-pulse oscillators (CPOs) and amplifiers (CPAs). Low-loss and alignment-insensitive all-dispersive-mirror compressors can take over the role of prisms and gratings in conventional CPA systems, with the added benefit of shorter pulse duration due to high-order dispersion control and absence of self-phase modulation. The evolution of dispersive dielectric multilayer mirror technology within the last 15 years now allows us to report a new generation of low-loss and alignment-insensitive high-dispersion mirrors (HDMs). In this proof-of-concept study, we demonstrate the usability of highly dispersive multilayer mirrors for high-energy femtosecond oscillators, namely for a chirped-pulse Ti:Sa oscillator and an Yb:YAG disk oscillator. In both cases, a group delay dispersion (GDD) in the order of 2×10⁴ fs² was introduced, accompanied with an overall transmission loss as low as about 2%. This unprecedented combination of high dispersion and low loss over a sizeable bandwidth with multilayer structures opens the prospects for femtosecond CPA systems equipped with compact, alignment-insensitive all-mirror compressors, which provide compensation of GDD and higherorder dispersion.

A high-energy broadband chirped mirror is designed for sub-10-fs high-energy chirped-pulse oscillators and amplification systems. This mirror consists of TiO2/SiO2 quarter-wave coatings for a broad bandwidth and optimized HfO2/SiO2 chirped coatings for increasing the laser-induced damage threshold (LIDT). The calculated results show that the mirror has low group delay dispersion (GDD) oscillation and can withstand high-energy chirped pulse laser in a wide range of 720-880 nm.

The strong absorption of materials in the extreme ultraviolet (EUV) above ~50 nm has precluded the development of efficient coatings. The development of novel coatings with improved EUV performance is presented. An extensive research was performed on the search and characterization of materials with moderate absorption, such as various lanthanides. Based on this research, novel multilayers based on Yb, Al, and SiO have been developed with a narrowband performance in the 50–92 nm range. Furthermore, procedures for the design of multi-material multilayers with absorbing materials have been derived, which resulted in multilayers with enhanced reflectance.

A recent development of mirrors is reviewed in this letter. For some applications, such as the hard X-ray telescope, polarization measurements in synchrotron radiation facilities, extreme ultraviolet (EUV) solar observations, and dense plasma diagnostics in China, a series of non-periodic novel multilayers with special performance are developed. X-ray supermirror, EUV broadband polarizer, EUV wide-angular mirror, and double period Kirkpatrick-Baez (K-B) mirror are successfully designed by using different multilayer stack structures.

Mo/Si and SiC/Mg period multilayer mirrors are investigated for solar He-II radiation at 30.4 nm. The optical stabilities of these multilayers are measured before and after space environment simulation tests for the purpose of potential application in space extreme ultraviolet (EUV) observations. All these multilayers are deposited by magnetron sputtering method on microcrystalline glass substrates. Then thermal cycling stability and radiation exposure experiments are performed to simulate the space environment. The testing results indicate that the Mo/Si multilayer is more stable than the SiC/Mg multilayer. The reflectivity of the SiC/Mg multilayer decreases slightly.

A fine layer structure in the Ni/C multilayer (3-4 nm/6-7 nm) is deposited by magnetic sputtering by combining soft X-ray resonant reflectivity curve at 4.48 nm and grazing incidence X-ray reflectivity (GIXR) curve at 0.14 nm. It is found that the thickness of Ni-on-C interface is much rougher than C-on-Ni interface. By analyzing the optical constants, it shows that the interface in the Ni/C multilayer that of system is a mixture of Ni and C atoms; the Ni and C in multilayer system have excellent stability, and no interlayer is formed.

A multilayer Laue lens with a 15-nm outermost zone width is designed for an incident X-ray beam with an energy of 8 keV. WSi2/Si multilayer Laue lens with 324 layers and a total thickness of 7.9 \mu m is successfully fabricated using direct current magnetron sputtering method. After deposition, the multilayer is sliced and polished to achieve the ideal aspect ratio. Characterization results show that the multilayer structure is kept intact and the surface roughness is approximately 0.9 nm after slicing and repeated polishing.

A technology based on plasma etching has been developed to produce antireflective surface structures. By choosing thin initial layers and variable plasma conditions, a broad range of nanostructures can be obtained on various polymers. Specifically, a broadband antireflective effect can be achieved, which is less sensitive to incident angles of light compared to multilayer interference coatings. In addition, plasma etching of antireflective structures has been proven highly cost-effective during replication, especially for mass production, and may be a suitable alternative to common coating procedures.

Three types of dispersion mirrors are designed and discussed. The first type is the complementary chirpedmirror pair used for providing smooth group delay dispersion (GDD) in the wavelength range of 550-1050 nm. Such mirrors are obtained by shifting the GDD oscillation period. The second type of mirror combines the characteristics of chirped mirrors and Gires-Tournois interferometer mirrors. It provides a high dispersion compensation of about -800-fs² GDD in the range of 780-830 nm and about -1150-fs² GDD in the range of 1020-1045 nm. The third type is a protected silver mirror with high reflectivity and low dispersion in the range of 650-1000 nm at 45°.

Optical filters for the use in space instruments must not only satisfy the optical requirements but also contribute to the reduction of mass and size of the instrument itself. Moreover, they must survive in space conditions, specifically at low temperatures and with exposure to irradiation by various particles. Two examples of narrowband transmission filters dedicated to Earth observation are described.

Silicon carbide (SiC) is a promising candidate for large-scale mirrors due to its high stiffness and thermal stability. However, it is very challenging to obtain a super smooth surface for high precision optical telescopes due to the intrinsic defects of SiC. In this letter, a super smooth surface with a roughness lower than 1 nm and a surface profile of \lambda/50 is achieved by depositing a uniform and dense silicon surface modification cladding by plasma ion assisted deposition (PIAD) on a lightweight concave reaction bonded (RB) SiC mirror, followed by a polishing procedure. Characterization data from the high resolution optical microscope, WYKO profilometer, Zygo interferometer, and nanoindentation are further discussed. The thermal shock resistance test indicates that the surface modification cladding is very stable and shows firm adherence. A reflectance of over 98% in the visible light region is obtained on the spectrometer after being coated with the silver-enhanced coatings.

An in situ process monitor for the CuInxGa1?xSe2 (copper indium gallium selenide) (CIGS) coating system is a very important tool that produces repeatable, high-quality CIGS coatings. This letter provides an overview of the current state of application of in situ process monitor systems for co-evaporation CIGS coatings. A comparison between different in situ monitoring systems is given and a novel multiple-elements rate monitor system is introduced.

The combination of fiber optics with nanostructure technologies offers great potential for the realization of novel sensor concepts. Miniature optical fiber sensors based on the Fabry-Perot (F-P) structure are presented. The transducer deposited on the fiber end face is multilayer coating consisting of a stack of nanoporous dielectric TiO2 and MgF2 films of optical thickness \lambda/4, forming a F-P filter with a typical reflection minimum at about 1300-nm wavelength. The reversible adsorption and desorption of water molecules in the porous films depend on water vapor, which would shift the reflected minimum wavelength of the F-P filter. Therefore, the humidity sensing is correlated with the central wavelength change of the F-P filter. A 14-nm shift in central wavelength is observed when the relative humidity increases from 0 to 100%. The central wavelength response to relative humidity is 0.9969 in linearity, which means that the proposed F-P thin-film sensor is very promising as a relative humidity sensor.

We propose and demonstrate two types of narrowband multi-channel filters: transmittance-integrated narrow-bandpass filter arrays and reflectance narrowband multi-channel filters. We develop a combinatorial etching technique possessing 32 elements on a single substrate with which to fabricate these integrated narrow bandpass filters. Double-chamber integrated optical filter arrays are fabricated by use of this etching technique. Reflectance can be achieved by combining metal and dielectric materials. These narrowband multi-channel filters and narrow bandpass filter arrays show good filtering features and can be utilized in many optical applications.

Advances in optical coating technology over the past decade have made it possible to produce high-performance Raman spectroscopy filters with better reliability and at lower costs. The performance and characteristics of three typical Raman filters and an ultraviolet resonance Raman filter are introduced. Some applications of surface-enhanced Raman scattering (SERS) biosensors for the detection and identi-fication of tissues, cells, proteins, nucleic acids, drugs, and chemical pathogens are reviewed.

Antistatic and antireflection (ASAR) coating using indium tin oxide (ITO) by magnetron reactive sputtering (MRS) technique is presented. The relationship between sheet resistance and optical transmittance of ITO prepared by MRS is investigated, and the optimum ITO parameters by MRS are studied through the variation of oxygen flow, temperature, argon flow, and sputtering power. The optical constant of ITO is modeled by combining a single Lorentz oscillator and a Drude free-electron component in the range of 300-1500 nm, which fits well with the experimental data. ASAR coating is designed using ITO based on the optimized parameters, and is implemented by MRS. Experimental results show that ASAR coating by MRS displays high transmittance of up to 99.2%, and low sheet resistance of less than 1.1 k-.

We focus on a more difficult kind of beam splitter in a cemented cube. The specification is that when the incident angle is 45°, the reflectivity in the visible range is 70%±2%, and the reflectivity at 1570 nm is not less than 90%. The film is thick, so cracking and peeling often occur after coating without ion assisted deposition on a vacuum-coating plant made in China. Some experiments are conducted after changing the beam splitter’s design, coating material, evaporation technique, and so on. Final results show that the beam splitter has good properties and can pass humidity, temperature, salt spray fog, and other kinds of environmental tests.

With the great development of laser standard systems and high-precision laser measurement systems, demands of optical systems have resulted in a dramatic increase in performance requirements for thin film optical filters. In this letter, the analysis and manufacture of the double-layer structure of the ultra-low residual reflectance for a single wavelength are reviewed. From a manufacturing standpoint, the manufacture and analysis of these coatings, which satisfy the requirements mentioned, pose as major problems. The coatings are characterized according to ellipsometry analyses and adjustment of the center wavelength of the antireflection (AR) coating Ta2O5/SiO2 double layers. AR coating is deposited on silica substrates by ion beam sputtering (IBS) technique, thus, achieving residual reflectance of less than 0.005% at \lambda 0=632.8 nm.

We present the advantages of experimental design in the sensitivity analysis of optical coatings with a high number of layers by limited numbers of runs of the code. This methodology is effective in studying the uncertainties propagation, and to qualify the interactions between the layers. The results are illustrated by various types of filters and by the influence of two monitoring techniques on filter quality. The sensitivity analysis by experimental design of optical coatings is useful to assess the potential robustness of filters and give clues to study complex optronic systems.

A wet chemical etching process for lead zirconate titanate (PbZrxTi1?xO3 or PZT) thin films is reported. The influences of the etchant compositions, temperatures, and concentrations on the etching rate are studied, and the patterning of PZT thin films is successfully attained using the wet chemical etching process. The relationship between the etching ratio and the ratio of lateral to thickness of less than 1:1.07 is obtained. Furthermore, there is no residue on the pattern. The selectivity of etchant for the photosensitive resist mask and Pt electrode is shown to be good. This process is suitable for the patterning of PZT thin film, of which line width reaches the micrometer range.

A new technique for rapid 3D microstructure preparation using micropipette is investigated. The tool electrode is made by Pt-Ir wire directly inserted into one or several glass micropipettes arrayed together. This electrode is used as anode, and copper plate or indium tin oxide (ITO) film is used as cathode. Both of them are placed in mixed electrolytes of CuSO4 and H2SO4 for electrochemical microdeposition. To apply voltage between the electrodes, copper microcolumn with controllable diameter and height is successfully deposited into the cathode substrate by lifting the anode in Z direction. Moreover, micropatterns can be made by moving the anode on XY plane, sustaining a gap of a few microns from the substrate. Experiments are carried out to check the feasibility of this method. Microcolumns 50?150 μm in diameter with aspect ratio (height/diameter) that can be greater than 50 are fabricated. Several copper microcolumns that grow simultaneously are obtained. Moreover, lines with micro-width are also fabricated on ITO film. The experimental results indicate that this method is simple, fast, efficient, and can be mass-produced. It can be widely used for micro/nano deposition and processing.

In the process of silicon wet etching, the SiO2 film formed by thermal oxidation is firm and compact, and it is an excellent mask material. However, there are some difficulties in its patterning process. Considering the high density of the SiO2 film, its etching time is so long that the protective layer photoresist wrinkles and floats. In this letter, a novel way is used to achieve the graphical process resorting to the MgO film. A layer of the MgO film as the protective layer is deposited on the surface of the SiO2 film, and inductively coupled plasma etching is used to etch the SiO2 film. Then the chip is put in the KOH solution to fabricate the Si V-groove. The results show that the patterning process is easy to control.

The critical technology for fabrication of the micro-bridge structure based on amorphous silicon (a-Si) films is studied. As a key technology in the fabrication of the micro-bridge structure, the sacrificial layer technology, including the preparation of polyimide thin films (i.e., curing, wet etching, and plasma etching processes), is systematically researched, and a series of key parameters are obtained. An improved process °ow of self-supporting micro-bridge structure is established. Experimental results and scanning electron microscope (SEM) images show that the fabrication technology presented is simple and feasible. A 160×120 micro-bridge array is successfully fabricated using this method.

The Segall-Mahan theory is employed to calculate both one and two longitudinal-optical (LO) phonon sidebands of free excitons of zinc oxide (ZnO) in a wide temperature range. The energy spacing from the zero-phonon line to 1 LO and 2 LO phonon sidebands deviates gradually from their characteristic LO phonon energy with increaseing the temperature. The experimental results are good agreement with the theoretical calculation. Only one adjustable parameter is taken into account in this calculation, which determines the range of values of the hole effective mass in ZnO.

Multilayer dielectric thin films have polarization effects at non-normal incidence. In this letter, specifications include s- and p-polarization transmittance (Ts,(p) ≥ 95% at 790—808 nm), s- and p-polarization reflectance (Rs,(p) ≥ 95% at 814—860 nm), angle of incidence (AOI) = 45°, air as incident medium, and BK7 glass as substrate. Based on the two chosen materials (Ta2O5 and SiO2), non-polarized edge filters are carried out using the design methods of the detuned multiple half-wave filters (exact design) and the needle optimization (numerical design). Exact design has a total of 112 layers and 12 cavities; optical thickness is 126 quartwaves at 860 nm. Numerical design has a total of 107 layers and 8 cavities; optical thickness is 91 quartwaves at 850 nm. Hence, the numerical design has less layers and thickness, thus meeting the same specifications of the exact design.

A new design of shallow-etched multilayer dielectric grating (MDG) exhibiting a diffraction efficiency (DE) of approximately 100% in the –1st order at 1064-nm wavelength in Littrow mounting is reported. Particle swarm optimization algorithm and Fourier modal method are used to design MDG and calculate the DE of MDG. The thickness of the grating layer is less than 80 nm which is much shallower than that in the currently reported MDG design for a high DE, which is greatly helpful for the MDG etching process. Meanwhile, the bandwidth of DE which is more than 97.5% of MDG is 60 nm, and it is a meaningful result for MDG to be used in ultrashort pulse compression system.

Color filters used in white light-emitting diode (LED) displays are composed of alternating high-index ZnS and metallic Ag layers. Such a filter has low polarization or angle effect. If this filter is used in the case of oblique incident or large cone angles, the wavelength shift can be reduced significantly, and good filter characteristics can be maintained. Therefore, these filters can meet the needs of white LED color displays.

Antireflection coatings are very important for high-efficiency solar cells. An ideal antireflection structure should lead to zero reflection loss on solar-cell surfaces over an extended solar spectral range for all angles of incidence. Based on the optical thin-film theory, two multilayer structures are adopted as initial stacks in two conditions, respectively. With the aid of a conjugate graduate optimized method, the incident angles of antireflection coating are 0°–60°, the working wavelength range is 400–1200 nm, and two broadband and wide-angle antireflections are designed. The results show that they can all evidently reduce residual reflection.

Thin film optical coatings tailor light reflected or transmitted from an optical element in a desired way. An optical coating chamber is a complex system in which multiple subsystems operate together to fabricate such coatings. For physical vapor deposition processes, such as evaporation and sputtering, the active parts of the subsystems are located within a vacuum chamber. One example is the source system that provides vapor from which films are formed. A gas delivery subsystem may add process gases either in their ground or excited states. Rotary motion and masking subsystems may be used to achieve better uniformity. In addition, a subsystem that ensures accurate layer thickness control may be utilized. Precision optical coatings require that individual layer thicknesses be controlled to within a few percent of the design target or less to achieve accurate placement of a spectral feature. Systems for manufacturing precision optical coatings demand the use of the subsystems that operate within tight tolerances. In this letter, we illustrate subsystem requirements by examining three examples in detail. We then discuss spectral placement impact resulting from height variations of the substrate mounting, thermal gradients on a substrate, and process instabilities from a moving anode. Finally, we conclude by providing a few examples of the performance attainable using a precision coating platform, when all subsystems work properly.

Current developments in optical multilayer design and computation make it possible to calculate filters that satisfy the most demanding optical specifications. Some of the designs are highly sensitive to manufacturing errors and require accurate monitoring and control during thin film deposition. Ellipsometric monitoring enables the accurate deposition of any thickness, including very thin layers, and in situ measurement of both refractive index and thickness of the layers during deposition, which facilitate the subsequent real-time design reoptimisation. In this letter, a number of complex multilayer designs with the aid of ellipsometric monitoring are presented, including a laser notch plus band-blocker filter, dichroic filter, beamsplitter, and a wide-range broadband multiplayer antireflection coating.

A plasma source utilizing direct current (DC) voltage between an anode and a hot hollow cathode is employed to create high-density plasma. Plasma spatial distribution, ion energy, plasma neutralisation, and current densities are found to be separately tunable. Ion current densities >0.5 mA/cm² have been demonstrated over coating areas > 1 m diameter. The primary advantage of plasma, as opposed to the ion source approach, is its ability to fill in the vacuum chamber and the couple with evaporant. This induces partial evaporant ionisation, providing uniform ion-assisted deposition over extended coating areas. Optical thin film properties deposited using the adapted high ion current plasma source are likewise described.

Atomic layer deposition (ALD) is under active research for its many emerging applications. In the optical field, ALD opens fundamentally new research paths, providing extreme conformality and capacity to engineer new materials. ALD enables coatings which are undoable or difficult through physical vapor deposition (PVD), like films inside tubes, highly repeatable sub-nanometer thick films, double-sided deposition, large-area accurate coatings, and three-dimensional coatings that require extreme conformality. We describe ALD from the practical and manufacturing viewpoint.

Plasma ion-assisted deposition (PIAD) process for ultraviolet (UV)-induced transmission and full dielectric thin-film filters in the 200–400 nm spectral region is described. The design and manufacturing method of the UV filters are introduced. The UV filters exhibit deep blocking (> optical density (OD)5–OD6), high transmittance, and stable environment durability. These UV filters pass 10 cycles in an aggravated temperature-humidity test, according to ISO9022-2 and MIL-STD-810F standards.

The challenge in rapid production of high-precision optical coatings is the need to realize a variety of complex coating designs in one process environment. Two approaches to enhance a stable deposition process are presented. First, a virtual deposition system is applied for a pre-selection of coating designs that result in increased process stability using optical broadband monitoring strategies. Second, optical broadband monitoring is combined with additional quartz crystal sensors to realize a hybrid process control for improving layer thickness accuracy. Finally, a successful combination of both approaches is demonstrated by comparative studies on virtual and real deposition processes.

Optical coatings based on multilayers are prepared. The dependence of the refractive index of SiO2, TiO2, HfO2, and ZrO2 on the conditions during thin film evaporation (e.g., oxygen partial pressure, substrate temperature) and upon post-annealing are investigated in detail. For coatings to be stable under intensive laser irradiation, post-heating of the evaporated films is necessary. The correlation between mass density and refractive index is analysed on the basis of a model comprising compact grains (i.e., amorphous or crystalline) and pores filled with air or water. The properties of the whole film are discussed on the basis of an effective-medium model, whereas the properties of a single grain are derived from a general refractivity formula valid for homogeneously distributed dipoles.

The basic form of a mirror as a cast metal object, with a highly polished reflective surface and relief decorations at the back, has remained unchanged throughout most of China’s history. The earliest known Chinese mirrors date back to approximately 2000 BC. For almost a hundred years, advancements in the broad area of optical coatings have been used to shape mirror reflectivity in an inconceivable manner. For example, mirrors for deep ultraviolet (193 nm) and extreme ultraviolet (13.5 nm) are considered, playing a positive effect in lithography. Substantial improvements are expected in the efficiency of layer systems with regard to both optical performance and overall stability.

For single layers of SiO2, Nb2O5, and Ta2O5 that are deposited by plasma-assisted reactive magnetron sputtering (PARMS), we present measurement results for basic optical and mechanical properties, in particular, optical index, intrinsic film stress, thermal shift of spectral transmittance, and microroughness. We find high refractive indices combined with low intrinsic film roughness, moderate compressive stress, and almost a vanishing shift, indicate high potential for the production of high-performance optical coatings. The high thickness accuracy and process stability are exemplified by the measured spectral performance of multilayer stacks with about 200 single layers.

Until now, there are few reports on the effect of process conditions on abrasion resistance, which is the most important mechanical property of optical films. Broadband antireflective (AR) films composed of SiO2and TiO2, whose bands are from 620 to 860 nm and whose reflectivity is less than 0.5%, are prepared by electron-beam evaporation (EBE) at different temperatures, ion beam energies, and cooldown times. The structural properties of the films are investigated by atomic force microscopy, including the surface roughness, crystallinity, shape, uniformity, and compactness of the grain. The abrasion resistance of the samples is tested according to MIL-C-48497A4.5.5.1 standard. We discuss the relationship between abrasion resistance and the structural properties produced under different process conditions, such as preparation temperature, energy of the ion beam, and cooldown time. Grain shape and surface roughness are indicated to codetermine the abrasion resistance of the film. Further, the AR film with triangular grain and moderate roughness shows good abrasion resistance.

Al2O3 films are deposited using ion beam sputtering (IBS), ion beam reactive sputtering (IBRS), and electron beam evaporation (EBE). The properties of the films, such as optical identity, surface roughness, microstructures, and crystalline phase, are investigated. The single layer of alumina is discussed using the IBS method. It has a high refractive index and a perfect microstructure as well as a high ultraviolet (UV) absorption. The roughness of the Al2O3 film deposited using EBE is larger than that of the substrate surface, but it is in an acceptable range. The film deposited using EBE is dominated by the amorphous gamma phase, while the ones deposited using IBS and IBRS are an intermixture of the alpha alumina and the gamma alumina phases.

High precision, single-wavelength optical monitoring of reflectance was shown to be useful in the study of initial oxidation of very thin metal films by low pressure oxygen at room temperature. Thin films of Al, Ni, and Hf metal were sputter-deposited on silicon substrates and their subsequent oxidations were observed at low oxygen partial pressure using a temperature-stabilised laser diode reflectometer. Based on the derived properties of the appropriate metal and oxide films, optical monitoring data were fitted as a multilayer stack comprised of oxide/metal/SiO2/Si. The fitting results show that the exposure to oxygen at a partial pressure of 0.04 Pa forms a certain finite thickness of oxide film on the metal surface. A range of kinetic models such as Deal-Grove, Massoud, and Cabrera-Mott are commonly used to describe the surface oxidation process. However, these models cannot be applied to the initial stage of oxidation, which occurs when a pure metal surface is exposed to oxygen as measured here. Instead, simple chemical reaction kinetics is used to model the time-dependent experimental results of the early stages of oxidation, thus we obtain the equation d(t) = do[1-exp(-t/τ )] and d(t) = do[1-1/(1+t/τ )] for the gas environments of this investigation.

Pure Ge is grown on Si substrate to control the release of the strain in the heterostructure, which is due to the 4.2% lattice misfit between Ge and Si. In this letter, an innovative approach of multi-buffer layers is proposed for the epitaxial growth of high quality Ge thin films on Si (001) substrates in a molecular beam epitaxy system. The multi-buffer layers, including the low temperature Ge seed layer and the Si-Ge alloy intermediate layer fabricated under different temperatures, serve as defect gathering and annihilating sites to reduce the dislocation density in the top layers. The result reveals that the total thickness of the whole structure is less than 400 nm, with a low threading dislocation density of less than 5×10⁵ cm^-2 in the top layer and a root mean square surface roughness of 1.5 nm.

An optical feedback cavity ring-down technique (OF-CRD), in which the retro-reflection of the ring-down cavity (RDC) is re-injected into the oscillator cavity of a Fabry-Perot diode laser and causes the spectral fluctuation of the diode laser, is developed for ultra-high reflectivity measurement of optical mirrors. Due to the optical feedback-induced spectral fluctuation, the spectral line of the diode laser is occasionally in resonance with one or more RDC modes, resulting in an enhancement of the coupling efficiency of the laser power into the RDC and the occurrence of resonance peaks in the amplitude of the CRD output signal. These resonance peaks are employed in a CRD experimental setup for high reflectivity measurement of optical mirrors at 1064 nm. In the CRD setup, a pair of cavity mirrors, with reflectivities higher than 99.99%, is used. The reflectivity of both cavity mirrors is determined to be 99.99606% with an uncertainty of only 0.00003%. With a folded cavity configuration, the reflectivities of three mirrors with incident angles of 0, 22.5, and 45 degrees, are measured, and the results are 99.9459±0.0004%, 99.9755±0.0005%, and 99.9621±0.0006%, respectively.

A dispersive white-light spectral interferometer for precise measurements of the phase properties of multilayer thin film structures is built. A novel wavelet-based differentiation approach that considerably resists measurement error of group delay (GD) and group delay dispersion (GDD) is introduced. Versatile applications beyond phase measurement of the apparatus are demonstrated, including piezoelectric coefficient determination and physical thickness retrieval. With the increase of demand for thin film structures with specific phase properties, this white-light spectral interferometer can play an important role in future thin film industry.