The development of laser technologies defined the novel quality demands to optical interference coatings. For many technological applications is very important to use lasers with equal distribution of laser intensity across the beam. Gradient mirrors is one of the most simple and convenient means to manage spatial distribution of laser radiation, and can be used in various lasers and laser devices. These mirrors are used as output coupler in the laser cavity to form radiation close to the Gaussian distribution which using radially varying thickness that have been proved the most practical. Multilayer dielectric mirrors with a smooth changing reflection are used in various types of laser resonators. However, in practice, not equal distributions take place especially for Q-switch lasers. It can be arise due to as mode structure of laser irradiation, as optical defects of rod. So, application of such mirrors, permit realize the selection of transverse modes in which the minimal losses possess the transverse mode with amplitude distribution close to distribution of mirror reflection. This paper presents the methodology of fabricating multilayer dielectric mirror with altering over surface parameters of reflectance.
Interference polarizers can be successfully used in lasers and laser devices as independent optical element substituted crystal polarizers. Today, the use of crystal polarizers in some cases can lead to definite difficulties in accordance with peculiarities of laser cavity construction. The novel laser technologies and design of laser elements defined the new demands to optical coatings. In modern lasers interference polarizer can be considered as one of the main element that operates laser radiation. According to special optical outline and the requirements to optical characteristics of laser polarizers can be bryuster or mirror-type. The stable of spectral characteristic at a definite angle is one of the most important parameter. It was shown how optical thickness of each layer influence on angle stability. On the other hand high stable was achieved by using electron-beam ion assisted deposition. The coatings were deposited on the surface of optical glass BK-7 or quartz. Generally, refractory oxides were used. The achievement of the condensation layers structure was provided by active O2 + ions. It was shown, that smooth cleaning by neutral ions as before the evaporation definite separate layer, as after stabilized the optical properties of polarizer. Moreover, the using of ion source allowed increase laser damage threshold. It can be underline that some advantages of ion source revealed during evaporation materials in visible and especially ultra violet region. Also, laser strength was rather more at 1535 nm for ion-assisted deposited films. The average parameters were: minimum transmission efficiency TP < 97%, extinction ratio TP/TS <500, laser damage more than 10 J/cm2, 10 nanosecond pulse at 1064 nm in laser spot 200 μm.
The technology of producing interference coatings for nonlinear crystals has some peculiarities depending on certain properties of such crystals. Besides, the otpical properties of these coatings depend on laser beam irradiation, temperature, and intracavity or extracavity conditions. Temperature in the vacuum chamber, reactive gas pressure, energy of charged particles, conditions of evaporated materials influenced not in the same way as on usual substrates. It was noted that the ion beam acted on pure surfaces of crystals improving adhesion and reducing mechanical stress of the dielectric film. The ion beam sources were used for pre-cleaning just before deposition as assistance in the deposition process. Adhesion, mechanical stress and laser damage threshold depend on the ion beam energy. The optical properties of pure and coated crystals were tested in relation to the ion beam energy. The threshold has been defined. Besides, the degradation of films has been investigated after exposure to the laser beam. Undoubtedly, the antireflection coatings are of the most interest for such crystals. In this work the following aspects of the Ar coatings have been considered: (i) calculation of the optimum construction of optical coatings for a specific spectral range; (ii) production of the required parameters of the films; (iii) study of the optical parameters; (iv) influence of the ion beam on the spectral characteristics of the AR coatings for LBO and BBO crystals. It was noted that only monoenergetic low-energy beams can improve the optical properties for these crystals having AR coatings. As a result of this work, the AR coatings have been produced at one, two or three wavelengths simultaneously.
The obtaining and investigations of interference coatings in deep ultra violet at 193 nm for medical applications are considered. For successful using in excimer medical system each optical elements must have anti-reflective or high- reflective interference coatings that can be satisfied to medical setup. The general problem is how to produce the event distribution of primary laser irradiation at the nearest distance from eye behind the optical system with minimum losses. Besides all types of coatings must provide a high strength under laser irradiation. The conditions of producing interference coatings in this spectral region have some peculiarities: a limiting factor of the evaporation materials, film homogeneous along the surface of optics, and high laser strength. The processes of interaction between excimer laser photons and optical coatings influenced both on substrate and on film. In this connection the optical properties of some evaporated materials and pure substrates are observed. All films were produced by electron-beam evaporation. Optical absorption and laser strength of coated optics was analyzed as influence and variations of energies of ion-beam source.
The results of obtaining and investigations coated optics in deep ultra violet (UV) at 193 nm are considered. For successful using in excimer lasers and medical systems the separate optical elements must provide either a good transmission for laser irradiation or enough high reflection. This can be achieved by anti-reflective (AR) or high- reflective (HR) interference coatings. Numerical design and obtaining of UV dielectric coatings are strongly influenced by the material properties in this wavelength region, that differ from those in visible and near infrared. The peculiarities for thin films in this region are: a limiting factor of the evaporation materials, homogeneous along the surface of optics, and high laser strength. The interaction between excimer laser photons and optical coatings can be determined as two combined process of high repetition rates and high energy densities. These processes influence both on substrate and on film. In this connection the investigations of optical properties of oxides (Al2O3, SiO2) and fluoride (MgF2) films are observed. Besides some new aspects in investigation of pure substrates are obtained. All films were produced by electron-beam evaporation and ion-beam influence was analyzed as variation of optical absorption and laser damage threshold (LDT) of coated optics.
Recently much success has been achieved in the field of dielectric interference coatings. However, the appearance of new types of lasers (for example, diode-pumped solid-state lasers) required development of the high quality low loss coatings for various spectral regions. These coatings may be divided into two groups, antireflective coatings and cut-off filters. We have investigated the various aspects of these coatings. There are choice of the optimum construction of the optical coatings to obtain the required parameters in the specific spectral region, development of the production process to obtain the reproducing results when assembling lasers, study of optical parameters. As a result, the technology for making the following coatings has been developed: (1) the AR coatings for Nd:YAG crystals with the coefficient of residual reflection ((rho) ) less than 0.1% of one surface at 1.06 micrometer; (2) the AR stable coating for LiJO3 crystals with the same parameters; (3) the AR coating for KTP crystals with (rho) less than 0.1% of one surface at 1.06 and 0.53 micrometer simultaneously; (4) the AR coating for the BK-7 substrates with (rho) less than 0.3% at 0.809 and 0.53 micrometer simultaneously; (5) the cut-off filter for the BK-7 or Nd:YAG crystal with high reflection (HR) greater than 99.9% at 1.06 micrometer and high transmission (HT) greater than 95% at 0.809 and 0.53 micrometer; (6) the cut-off filter with HR greater than 99.9% at 1.34 micrometer and HT greater than 95% at 0.67 micrometer; (7) the cut-off filter with HR greater than 99.9% at 1.08 micrometer, HR greater than 90% at 0.53 micrometer and HT greater than 85% at 0.355 micrometer. All types of the optical coatings have been tested in the assembly of the lasers. Now these coatings are successfully used in the commercial lasers.
The technology of obtaining the interference coatings for the nonlinear crystals has some peculiarities depending on the specific properties of these crystals. Temperature, pressure of reactive gas and energy of charged particles do not affect principally the optical properties of the nonlinear crystal. In this paper the various aspects of thin dielectric films for crystals are presented. There are calculations of the optimum structure of the optical coating for specific spectral region, obtaining the required parameters of the films having the optical properties that would not impair the own properties of the crystal parameters of the films having the optical properties. As a rule, the coatings of these crystals that could be coated without heating in a vacuum chamber. As the result of this work the various types of the interference coatings have been obtained. There are the AR coating at a single wavelength in the spectral range of 0.24...1.5 micrometers , the broad-band AR coatings, the AR coating with two AR spectral regions simultaneously.
Some aspects of obtaining high reflective (HR) dielectric mirrors with high damage threshold (LDT) for high-power solid-state near IR region (NIR) lasers are considered. Optical properties of these mirrors were investigated as properties of each alternate layer evaporated with high- index (H) or low-index (L) materials as multilayer system that depends on mirror construction, parameters of evaporation, ion-beam influence, substrate materials and quality of substrate surface. Refractory oxides ZrO2,HfO2, Ta2O5, Al2O3 and SiO2 were used as starting materials for evaporation. Ion-beam influence was estimated as changing of optical absorbance at a wavelength 1.064 micrometers by laser modulated photo-thermal radiometry. Besides the quality of various work-up substrate surface was controlled by this method also. It was noticed that substrates with different surface roughness had different absorption. It was noticed that band edge of absorption of pure substrate in UV region influenced on laser damage threshold of mirrors. Optical properties of evaporated mirrors were tested as the ability of strength for laser irradiation as cavity-mirrors of high power lasers. ZrO2/SiO2 mirrors had the most high laser strength. Estimated value of laser density was 3.6 GW/cm2.
The appearance of new types of lasers (for example, diode- pumped solid-state lasers) required development of the high quality low loss coatings for various spectral regions. These coatings can be divided into following groups: antireflective, high-reflective and cut-off filters. Various aspects of producing these coatings have been investigated. There are choice of the optimum construction of the optical coatings to obtain the required parameters in the specific spectral region, development of the production process to obtain the reproducing results when assembling lasers, study of optical parameters. All types of the optical coatings have been tested in the assembly of the lasers. Now these coatings are successfully used in the commercial lasers.
The results of obtaining and investigations coated optics in deep ultra violet (UV) at 193 nm are considered. For successful using in excimer lasers and medical systems the separate optical elements must provide either a good transmission for laser irradiation or enough high reflection. Numerical design and obtaining of UV dielectric coatings are strongly influenced by the material properties in this wavelength region. The peculiarities for thin films in this region are: a limiting factor of the evaporation materials, homogeneous of the film along the surface, and high laser strength. The interaction between excimer laser photons and optical coatings can be determined as two combined process of high repetition rates and high energy densities. These processes influence both on substrate and on film. In this connection the investigations of optical properties of oxides and fluoride films are observed. Besides some new aspects in investigation of pure substrates are obtained. All films were produced by electron-beam evaporation and ion-beam influence was analyzed as variation of optical absorption and laser damage threshold of coated optics.
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