OPTM 4101 Principles of Optics Lecture Notes PDF

1/9/24 OPTM 4101 Principles of Optics The Nature of Light - waves Danuta Sampson, Discipline of Optometry, SAH...

1/9/24 OPTM 4101 Principles of Optics The Nature of Light - waves Danuta Sampson, Discipline of Optometry, SAH [email protected] 1 Acknowledgement of country The University of Western Australia acknowledges that its campus is situated on Noongar land, and that Noongar people remain the spiritual and cultural custodians of their land, and continue to practise their values, languages, beliefs and knowledge. Artist: Dr Richard Barry Walley OAM 2 1  1/9/24 Lecture Objectives 1. Describe the main characteristics of waves and colour. 2. Describe the relationship between wavelength, frequency and colour. 3. Explain the difference between monochromatic and polychromatic waves. 4. Describe the relationship between wavelength and energy and explain its clinical implications. 5. Distinguish between light rays and light waves. 3 3 What is light? Light is a form of energy. It is made up of tiny photons, each contains a lot of energy. Without light, life on our planet would die. - Sun, you are far away – said the Earth. - Not that far, only 147.51 million km. Light travels faster than anything else in the universe. It travels at a speed of 300,0000 km per second in a vacuum. 4 2  1/9/24 Light - facts Light usually travels on a straight path, but it bends – or refracts – when traveling T - Sun, you are far away – said the Earth. through a transparent object. A prism is a good example of refracted light. Place a - Not that far, only 147.51 million km. metal spoon in a transparent glass filled with water. The spoon appears to be bent because of how the light moves through the glass. 5 5 Light – matter interaction Light can travel through some types of matter but not others. Light travels through the air. It can be seen through a glass window -orSun, a sheet offar you are clear plastic away wrap. – said the These types Earth. - Not that far, only 147.51 million km. of matter are transparent. Some objects are translucent, meaning light passes through them, while some light is reflected. Wax paper is a good example. Opaque matter reflects light or bounces it back into the environment. Your book, your pants, or your blanket are all opaque. No light goes through them. 6 6 3  1/9/24 Light – matter interaction Light travels through matter and can reflect, scatter, transmit or be absorbed. - Sun, you are far away – said the Earth. - Not that far, only 147.51 million km. https://medium.com/predict/oh-newton-did-not-know-this-806001819557?source 7 7 Light – matter interaction Sunglasses are made from materials - Sun, you are far away – said the Earth. that absorb visible light and reduce its - Not that far, only 147.51 million km. transmission. 8 8 4  1/9/24 Dual nature of light Can be explained using Can be explained using Phenomenon waves particles Reflection YES YES Refraction YES YES Interference YES NO Diffraction YES NO Polarisation YES NO Photoelectric effect NO YES 9 9 Light – a wave A wave is a disturbance that transmits energy from one point of a medium to another without the medium itself moving noticeably. 10 Credit: https://electroagenda.com/en/waves-in-electronics-and-communications/ 10 5  1/9/24 Light – a wave A wave is a disturbance that transmits energy from one point of a medium to another without the medium itself moving noticeably. A wave transfers energy from one place to another. (Doesn’t transfer any matter). 11 11 Characteristics of EM wave A wave is a disturbance that transmits energy from one point of a medium to another without the medium itself moving noticeably. Wavelength Displacement Direction of travel 12 12 6  1/9/24 Characteristics of EM wave A wave is a disturbance that transmits energy from one point of a medium to another without the medium itself moving noticeably. TIME PERIOD Displacement T Time (seconds) Direction of travel 13 13 Characteristics of EM wave Wavelength [m] Speed of light in vacuum [m/s] # != = #&' $ Frequency of wave [Hz] Period of wave [s] c = 299,792,458 m/s, or approximately 300,000 km/s 14 7  1/9/24 Characteristics of EM wave Wavelength [m] Speed of light in vacuum [m/s] # != = #&' Speed of light in other medium than vacuum [m/s] $ !≤# ! (= ) Refractive index c = 299,792,458 m/s, or approximately 300,000 km/s 15 Light – a ray A light ray is an idealised model of light drawn as a straight line. https://www.telescope-optics.net/reflection.htm 16 16 8  1/9/24 EM wave vs mechanical wave Electromagnetic (EM) wave Mechanical wave Photo credit: EM-Wave.gif, Wikimedia Photo credit: Roger McLassus; Wikipedia 17 Electromagnetic (EM) wave Electromagnetic wave The fundamental disturbance is associated with small oscillations in the electric and magnetic fields. The electromagnetic waves may have many forms, from radio waves to X-rays, and the difference lies in their frequency. 18 9  1/9/24 Polychromatic light Polychromatic light consists of many wavelengths, whereas monochromatic light consists theoretically of a single wavelength. 19 19 Colour Light is a part of the EM spectrum – it stands out because the human eye perceives it as different colours. Dispersion Wavelengths of red (longest), green, and violet (shortest) light 20 Photo credit: Wikipedia 20 10  1/9/24 Colour Light is a part of the EM spectrum – it stands out because the human eye perceives it as different colours. Dispersion Wavelengths of red (longest), green, and violet (shortest) light # != = #&' $ 21 Photo credit: Wikipedia 21 Colour 22 Photo credit: Yousafbhutta; pixabay.com 22 11  1/9/24 What colour is a cucumber? Photo credit: Krzys16, pixabay.com 23 23 What colour is a cucumber? A green cucumber reflects green light. When white light from the sun strikes the cucumber, the green wavelengths are reflected and travel to your eyes, which are detected by the colour-sensitive cones in your retina. The cone photoreceptor cells send a message to your brain – it’s a green cucumber! Photo credit: Krzys16, pixabay.com 24 24 12  1/9/24 What colour is a cucumber? What would happen if we illuminated a cucumber using a blue flashlight instead of sunlight? Photo credit: Krzys16, pixabay.com 25 25 Colour properties HUE COLOURFULNESS BRIGTHNESS + Photo credit: Visual optics CHROMA Colourfulness relative to the brightness LIGHTNESS Relative brightness SATURATION Colourfulness of an area judged in relation to its brightness 26 26 13  1/9/24 Colour mixing Primary additive colours: Red, Green & Blue (RGB). If we mix all additive primaries, we obtain white. Primary subtractive colours: Cyan, Magenta & Yellow. If we mix all subtractive primaries, we obtain black. RED Blue CYAN Yellow Magenta Green https://videohive.net/user/xponentialdesign?ref White Black =xponentialdesign&clickthrough_id&redirect_ba GREEN BLUE MAGENTA YELLOW ck=true Cyan Red 27 Photo credit: Lisa Cianci, https://rmit.pressbooks.pub/colourtheory1/part/additive-and-subtractive-colour/ 27 Colour mixing COLOUR WHEEL COLOUR TRIANGLE Photo credit: Visual optics 28 28 14  1/9/24 Regions of the electromagnetic spectrum Important for optometrists The approximate wavelength, frequency, and energy limits of the various regions of the electromagnetic spectrum. 29 Bibliography and references 1. Hecht, E. (2017). Optics. Pearson. 2. Strong, S. (2023). Introduction to visual optics: a light approach. Elsevier. 3. Schwartz, S.H. (2002). Geometrical and visual optics: A clinical introduction. McGraw-Hill Education. 4. Bennett, A.G. and Rabbett, R.B. (2007). Clinical visual optics. Butterworth- Heinemann. 30 30 15  1/9/24 Thank You 31 16