Fundamentals of Optical Technology: The Wave-Particle Nature of Light and Its Application to Non-Contact Measurement

Understanding light requires recognizing its dual nature — both wave-like and particle-like. These properties are directly applied to non-contact measurement and analysis technologies, leading to groundbreaking advancements across various fields.

This article provides a comprehensive overview, from the fundamental properties and historical background of light to practical applications that leverage its wave and particle characteristics. Let’s explore the future potential of optical technology built upon this fascinating duality.

What Is Light? — Its Properties and Historical Background

Here, we take an overview of how light has been defined and studied throughout history.

Light is not only something we see every day, but also a vital element that sustains life. Since ancient Greece, many theories have been proposed about the true nature of light, as people sought to unravel its mysteries through the observation of the sun and stars. With the progress of science and technology, light came to be understood as a type of electromagnetic wave, and later it was revealed that its nature can be described both as a wave and as a particle. This duality has greatly advanced the development of optical technologies and enabled a wide range of applications.

Historically, Isaac Newton regarded light as composed of particles, while Christiaan Huygens proposed a wave theory. Later, through James Clerk Maxwell’s theory of electromagnetism and Albert Einstein’s light quantum hypothesis, discussions about the nature of light led to the establishment of quantum mechanics. These pioneering studies have profoundly clarified the properties of light and are directly connected to today’s non-contact measurement technologies and the development of precision instruments.

Overview and Applications of Optical Technology

Optical technology is utilized across a wide range of fields, but it is important to understand both its fundamental principles and the breadth of its applications.

Built upon basic concepts such as reflection and refraction, optical technology underpins numerous measurement and analysis instruments as well as communication systems. For example, optical fiber communication harnesses total internal reflection to achieve high-speed, high-capacity data transmission. In recent years, the emergence of laser-based processing technologies and advanced imaging systems has expanded its applications into diverse areas including medicine, industry, and the automotive sector. This wide applicability is largely due to the inherent advantages of light—its ease of manipulation, safety, and the ability to achieve highly precise control.

The range of applications extends from medical devices such as endoscopes to large telescopes for astronomical observation. In particular, non-contact measurement technologies, such as optical 3D scanners capable of quickly and accurately measuring dimensions or detecting defects, serve as critical technological foundations. These instruments are designed based on an understanding of light’s wave and particle properties, making them indispensable for realizing advanced analytical techniques in practical applications.

Fundamental Phenomena in Optics: Reflection, Refraction, and Scattering

Reflection is the phenomenon in which light changes its direction when it strikes surfaces such as mirrors or metal. It can be categorized into specular reflection and diffuse reflection. Refraction refers to the bending of light as it passes through the boundary between different media, with the angle of bending determined by the refractive index of the material. Scattering occurs on surfaces with particles or roughness, causing light to spread in complex directions. These phenomena can also be explained by the wave nature of light, and understanding their principles enables the design of various optical components such as mirrors, lenses, and prisms.

Types of Optical Instruments Useful for Non-Contact Measurement

Examples of optical instruments include telescopes and microscopes. Telescopes use mechanisms that collect light through reflection and refraction to magnify and observe distant celestial objects. Microscopes, on the other hand, combine multiple lens systems to visualize minute structures, employing techniques that enhance resolution according to the wavelength of light. In recent years, the integration of laser technology has led to the development of highly precise non-contact measurement instruments and 3D scanners, which are also highly useful in various industrial applications.

Delving Deeper into the Wave Nature of Light

Focusing on the wave nature of light allows us to understand phenomena such as interference and diffraction.

The wave characteristics of light are primarily described in terms of concepts like wavelength and frequency. Evidence that light propagates as a wave is clearly seen in interference fringes observed in the double-slit experiment and in spectroscopic observations using diffraction gratings. These phenomena can be explained within the framework of classical physics, but when combined with quantum mechanics, they enable more precise and wide-ranging applications, which is one of the fascinating aspects of optical technology.

The wave nature of light also greatly contributes to non-contact measurement. By applying the principles of interference, interferometric techniques can sensitively detect minute changes in distance or shape between the measuring device and the target. For example, in semiconductor wafer manufacturing, high-precision thickness measurements based on wavelength standards are indispensable. Such technologies exemplify the practical applications of light’s wave properties.

Mechanisms of Interference and Diffraction, and Practical Examples

Interference refers to the phenomenon in which two or more light waves overlap, resulting in regions of reinforcement or cancellation. A classic example is the double-slit experiment, famous for producing interference fringes that are difficult to explain without considering light as a wave. Diffraction occurs when light bends around obstacles or the edges of an aperture and spreads into the space beyond. Examples of diffraction include the rainbow-colored patterns seen on the shiny surfaces of CDs and DVDs, as well as the iridescent colors that appear on the surface of soap bubbles.

The Relationship Between Wavelength, Frequency, and Energy

To quantitatively describe the wave nature of light, it is essential to understand the relationship between wavelength, frequency, and energy. In general, the shorter the wavelength, the higher the frequency and the greater the energy. On the electromagnetic spectrum, this means that violet light has higher energy. This property is highly useful when selecting light sources for specific applications and directly influences the choice of laser types and spectroscopic analysis methods.

Exploring the Particle Nature of Light

On the other hand, understanding light as particles—photons—requires a quantum mechanical perspective and has led to a wide range of applications.

The particle nature of light is explained through the concept of photons, the smallest units that carry energy and momentum. Unlike the continuous representation of light as a wave, phenomena where light behaves as particles—such as the photoelectric effect—clearly demonstrate this behavior. These effects cannot be fully explained by classical physics and are correctly understood only through quantum mechanics. As a result, controlling light at the single-particle level has opened up new possibilities in cutting-edge technologies, including information communication and quantum computing.

Treating light as particles also allows for detailed explanations of interactions with specific materials that absorb or emit light at targeted wavelengths. Furthermore, the particle concept is applied in non-contact measurement technologies, driving the development of ultra-sensitive sensors such as single-photon detectors. This enables observations in extremely low-light conditions and the detection of subtle effects, significantly improving measurement precision across diverse fields.

Photon Particle Nature as Observed in the Photoelectric Effect

The photoelectric effect is a phenomenon in which electrons are emitted from a material, such as a metal, when it is exposed to light. Einstein explained this phenomenon by describing light as particles—photons—whose energy allows them to overcome the electron’s binding energy. This groundbreaking insight greatly contributed to the development of quantum mechanics and has been directly applied to energy conversion technologies such as semiconductor devices and solar cells.

Understanding Quantum Mechanics and the Dual Nature of Light

In quantum mechanics, it is necessary to simultaneously accept the dual nature of light as both a particle and a wave. This serves as a theoretical framework that most accurately explains experimental results and is considered self-evident in the microscopic world. Understanding this duality of light enables a variety of technological innovations—such as ultra-precise measurements and quantum cryptography—that were not achievable using conventional physical models alone.

Practical Applications of Optical Technology in Non-Contact Measurement

Non-contact measurement and analysis techniques leveraging optical technology are widely used across fields ranging from healthcare to industry.

Non-contact measurement is particularly suited for examining samples quickly without altering their physical properties. Since light can gather information without physically touching an object, it serves as an extremely useful tool for accurately assessing everything from shape to composition. In industrial applications, it is employed for inspecting products on production lines or detecting surface defects on wafers, enabling early identification of flaws and improving overall yield.

In the medical field, non-invasive observation through endoscopy and laser treatments have evolved to minimize patient burden. Additionally, 3D scanners are being used for analyzing the three-dimensional structure of bones and organs, supporting diagnostics and surgical planning. This wide range of applications reflects a comprehensive understanding of light and the careful optimization of measurement conditions, taking into account both its wave and particle properties.

Principles of Interferometric Measurement and Optical 3D Scanners

Interferometric measurement is a technique in which light emitted from a source is split into two or more beams, and the resulting interference fringes formed when these beams recombine are analyzed. This method allows for precise measurement of extremely small displacements or shapes at the nanometer scale, making it a prime example of high-precision, non-contact measurement. In the case of optical 3D scanners, light is projected onto the target object, and the reflected light or changes in projected patterns are captured to obtain three-dimensional information. These scanners are widely used, from product inspection to the digital archiving of cultural heritage.

Laser technology utilized in non-contact inspection

Lasers offer excellent monochromaticity and directivity, as well as the advantage of achieving a high optical energy density. These characteristics enable high-precision non-contact inspections, such as long-distance measurements and the detection of minute defects. For industrial materials like metals and plastics, the wavelength selectivity of lasers allows efficient detection of surface anomalies, contributing to improved quality control efficiency and enhanced reliability.

Applications: From Medical Imaging to Precision Industry

In medical imaging, technologies have advanced that leverage the non-invasive nature of lasers and the scattering and absorption properties of light to visualize conditions within tissues. For example, in laser surgery, cancerous tissues can be precisely removed while minimizing damage to healthy tissue. In the field of precision industry, optical measurement devices are employed to accurately inspect wiring patterns on electronic boards or semiconductor chips and to improve the assembly accuracy of components, contributing to both enhanced safety and productivity.

Summary

Understanding light as both a wave and a particle forms the foundation for further research, development, and ultra-precise measurement technologies.

Many aspects of light remain not fully understood, and with the advancement of quantum mechanics and nanotechnology, new discoveries are anticipated. In the future, technologies that control photons individually and high-resolution imaging that maximally exploits light’s wave properties are expected to advance further, expanding applications in advanced non-contact measurement, high-speed communications, and beyond. In a wide range of industries, including healthcare, innovations centered on optical technologies have the potential to become a major driving force in improving quality of life.