BS ISO 19741:2018 pdf download

BS ISO 19741:2018 pdf download.Optics and photonics — Optical materials and components — Test method for striae in infrared optical materials
1 Scope
This document specifies the principle, apparatus, condition, sample, procedure and data processing of measuring striae in infrared optical materials.
It is applicable to the determination of striae in infrared optical materials, such as infrared optical glass,which is opaque to visible wavelengths and whose transmission optical spectra are beyond 0,78 µm.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 10110-7, Optics and photonics — Preparation of drawings for optical elements and systems — Part 7:Surface imperfections
ISO 10110-8, Optics and photonics — Preparation of drawings for optical elements and systems — Part 8:Surface texture; roughness and waviness
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
3.1 striae
regions of resembling bands, layers or rods formed due to short range severe deviations of refractive index in infrared optical materials, observed only by infrared detecting devices
3.2 striae value
average grey level of striae (3.1) multiplying the percentage of striae area per thickness of infrared optical materials
4 Principle
The principle of this test is to illuminate a sample with collimated infrared radiation and image the material in a Schlieren or projection imaging system. The striae will be imaged and measured, and then the area and the product of striae area percentage to the mean grey level will be calculated. When the projection optical system is adjusted to a beam-contracting telescope system, it is known as a projection measurement system. And when the projection optical system is adjusted to a camera system which utilizes a knife edge device, it is known as a Schlieren measurement system. The schematic diagram of striae measurement in infrared optical materials is shown in Figure 1.
5 Apparatus
5.1 Apparatus arrangement The apparatus consists of a collimating infrared light source system, a sample adjustment stage, a projection optical system, an image sensor, and a computer image collecting, processing and displaying system.
5.2 Collimating infrared light source system
The collimated infrared light source system consists of a light source, a condenser, a light source diaphragm, and an infrared collimating optics. The diaphragm shall be placed at the focus of the infrared collimating optics. The emission spectrum of the system shall cover or be within the transmission spectrum of the sample. The nonuniformity of light intensity distribution shall not be more than 5 %. The radiation intensity of the light source shall meet the requirement of the response of the image sensor. The emergent light aperture of the system should be more than the diameter of the sample.