Objective Lens

The objective lens is a critical optical component within an interferometric optical head, responsible for collecting light from the measurement surface and focusing it onto the interferometer's detector. It determines the system's resolution, working distance, and field of view, enabling precise non-contact surface measurement through interference patterns. This directory entry covers objective lenses used in optical interferometry, typically employed in surface metrology, profilometry, and other precision measurement applications. The lens is designed to work with visible light (400–700 nm) and is available in focal lengths from 10 to 50 mm, numerical apertures from 0.10 to 0.90, and working distances from 0.5 to 20 mm. The clear aperture ranges from 5 to 30 mm, and the lens achieves a transmittance of at least 95% over the specified wavelength range. Surface flatness is specified as λ/10 (peak-to-valley) at 632.8 nm, and surface quality is 20-10 scratch-dig per MIL-PRF-13830B, with reference to ISO 10110. Centration error is limited to 3 arcminutes or less. The lens operates in a temperature range of -40°C to 85°C and can be stored between -50°C and 100°C in non-condensing conditions. Weight varies from 50 to 200 g depending on size and material. The mounting thread is M25×0.75 per ISO 68-1. Materials on file include optical glass and fused silica. These specifications are typical ranges; actual values must be confirmed for the specific model and application. The objective lens is a component, not a complete system, and requires integration into an interferometric optical head. For procurement, verify model-specific parameters and standards with the legal manufacturer or supplier.

The objective lens operates by refracting incoming light rays to converge at a focal point. In interferometric systems, it collects light reflected from the target surface and directs it to combine with a reference beam, creating interference fringes that encode surface height information. The lens's numerical aperture and focal length determine the system's resolution and depth of field. A higher numerical aperture improves resolution but reduces depth of field, while a longer focal length increases working distance but may reduce magnification. The lens must be properly aligned to minimize centration error, which affects measurement accuracy. The working principle relies on the wave nature of light; any deviation in the optical path due to surface features alters the interference pattern, allowing precise height measurement. The lens is designed for use in a controlled environment, and its performance may degrade outside the specified operating temperature range. Regular inspection for surface quality and cleanliness is essential to maintain measurement integrity.