Hall 4 EXPLORATIONS INTO OPTICS

 

Introduction to the Hall

Welcome to the hall of EXPLORATIONS INTO OPTICS. This hall is divided into four sections: The Unusual World, Geometrical Optics, Physical Optics, and Quantum Optics. Through a series of classic optical experiments, you will gain insights into the very nature of light. The hall covers an exhibition area of 567 square meters, with purple as its dominant color.

Visual Acuity

This exhibit is Visual Acuity. Vision is one of the most important senses through which we perceive the world, and it is influenced by resolution, brightness, and contrast. In front of you are two display screens—choose different samples, then use the knobs to adjust resolution, brightness, and contrast, and observe how the same image changes. Resolution refers to the smallest details the human eye or a camera can distinguish—the higher the resolution, the sharper and finer the image. Brightness describes the intensity of light, or how bright it appears to our eyes. Contrast determines the difference between light and dark areas in an image.

Pinhole Imaging

This exhibit is Pinhole Imaging. The principle of pinhole imaging was recorded as early as the Mo Jing in ancient China. Mozi and his students conducted the world’s first pinhole imaging experiment, verifying the fundamental law that light travels in straight lines. Here you can see a simple experimental setup consisting of a light source, a small pinhole, and a projection screen. Press the button on the cabinet to activate the device, and you will observe an inverted real image formed on the screen.

Refraction, Reflection, and Total Internal Reflection

This exhibit is Refraction, Reflection, and Total Internal Reflection, which introduces the basic laws of geometrical optics. On the table in front of you are three glass blocks, each with a different refractive index. Press the button to operate the setup and observe how light behaves when it enters the blocks at different angles of incidence.

Lenses and Light Rays

Here you see the Lenses and Light Rays exhibit. It demonstrates the imaging principles of convex lenses, concave lenses, convex mirrors, and concave mirrors. By pressing the button, you can move a selected lens or mirror into the light path and observe how light rays form images through different optical components.

Microscopes and Telescopes

Displayed here are optical imaging demonstration systems for both microscopes and telescopes. With a microscope, we can observe biological cells and bacteria; with a telescope, we can clearly view distant objects. Together, these instruments extend the range of human vision. This exhibit allows you to learn in detail about their structure and operating principles.

Electromagnetic Spectrum

This is the Electromagnetic Spectrum exhibit. All around us, space is filled with electromagnetic waves of various frequencies. Arranged in order of increasing wavelength, they include gamma rays, X-rays, ultraviolet light, visible light, infrared radiation, and radio waves. Of these, only visible light can be detected by the human eye. By rotating the dial, you can explore the characteristics of each band of the electromagnetic spectrum.

Interference and Diffraction

This exhibit is Interference and Diffraction, which explains single-slit diffraction, double-slit interference, and multiple-slit diffraction. When two coherent light beams overlap in space, the intensity of the combined light in the overlapping region is not simply the sum of the two beams—it produces alternating bright and dark fringes. This is called optical interference. Diffraction, on the other hand, refers to the phenomenon in which light deviates from straight-line propagation when its wavefront encounters an obstacle or an aperture. Together, interference and diffraction provide strong evidence for the wave theory of light.

Applied Optics

This exhibit is Applied Optics. Through the design of optical systems, instruments such as the microscope, telescope, camera, and projector were invented. You can learn about these four optical imaging systems from the display panels on the wall.

Newton’s Rings

This exhibit is Newton’s Rings, and here you see the experimental apparatus. Newton’s Rings are formed by placing a plano-convex lens with a very large radius of curvature, convex side down, on top of a flat glass plate. When parallel light shines vertically onto the lens, two beams of light are reflected—one from the upper surface and one from the lower surface of the thin air film between the glass and the lens. These beams interfere with each other, creating concentric circular fringes. The first person to discover and analyze this phenomenon was the English physicist Isaac Newton. The Newton’s Rings effect can be used to test the surface quality of optical components, measure the radius of curvature of a lens surface, and determine the refractive index of liquids.

Schlieren Apparatus

This exhibit is the Schlieren Apparatus. A schlieren system makes invisible airflows visible by detecting changes in fluid density through variations in light intensity. Extend your hands close to the center of the mirror—this is the optimal viewing zone—and watch the screen. You will clearly see the airflow patterns around your hands. Rub your hands together or blow gently toward the center of the mirror, and the effect will become even more obvious.

Changes in temperature and airflow speed affect the density of air, which in turn changes its refractive index and bends the path of light. The schlieren system is built on this principle, using a concave mirror, a point light source, a camera, and a knife edge, carefully aligned through precise optical design. Even the slightest disturbance of air in the viewing area can be captured by the camera, making the “invisible airflow” visible. Schlieren imaging is widely applied in aerospace technology, fluid dynamics, and related research fields.

Light and Color

This exhibit is Light and Color. We live in a colorful world—but are these colors related to light? The answer is yes. For a luminous object, the color we see is determined by the light that the object itself emits. For a transparent object, the color is determined by the light that passes through it. For an opaque object, the color comes from the light reflected off its surface.

Michelson Interferometer

Here you see the Michelson Interferometer. Michelson originally designed this instrument to study the speed of light. Its principle is that an incident beam of light is split into two beams, which are reflected back by corresponding plane mirrors and then recombined to interfere. The difference in optical path between the two beams can be adjusted either by changing the length of the interferometer arms or by altering the refractive index of the medium. This produces different interference patterns, such as equal-thickness fringes, equal-inclination fringes, and variations of the fringe distribution. The Michelson interferometer can be used to measure the refractive index of gases and liquids, the thickness of glass, and for various kinds of precision testing.

Measuring the Speed of Light with the Beat Method

Displayed here is the experimental apparatus for measuring the speed of light using the beat method. The speed of light in a vacuum is a fundamental physical constant, closely related to many principles and laws in mechanics, electromagnetism, optics, and modern physics. Determining the exact value of the speed of light is therefore of great importance. The beat-frequency method measures the speed of light by analyzing the spatial distribution of light beats. By determining the optical path difference between two adjacent points of the same phase at the same moment, along with the beat frequency, the speed of light can be indirectly calculated.

Holographic Imaging

This exhibit is Holographic Imaging. Holography differs fundamentally from conventional photography. Ordinary photography produces flat, two-dimensional images, while holography produces three-dimensional images. Holography involves two steps: recording and reconstruction. What is presented here is the reconstruction process, where you can observe the three-dimensional holographic image. Holographic imaging has important applications in large-capacity and high-density data storage, precision measurement, non-destructive testing, and microscopy.

Polarization

This exhibit is Polarization. In 1808, the French physicist Étienne-Louis Malus discovered the phenomenon of polarized light while studying birefringence, and formulated Malus’s Law. Due to the physiological limits of the human eye, we cannot perceive the polarization of light directly without the aid of optical devices. This exhibit combines visual demonstrations to let you directly experience polarization through persistence of vision, color polarization, and Malus’s Law. By rotating the knob to adjust three polarizing plates, you can observe the pigeon changing color, appearing, and disappearing. The color change occurs because light passing through adhesive tape is refracted in two slightly different ways, and the colors you see come from the interference between these refracted rays. Today, polarization has a wide range of applications—for example, in 3D movies, liquid crystal displays, and polarization cameras—and also in optical imaging, detection, sensing, and communications.

Retroreflection

This exhibit is Retroreflection. Retroreflection is a type of reflection in which light rays are returned almost exactly along the path of incidence, back toward the source, regardless of changes in the angle of incidence within a certain range. Here, you can observe the effect for yourself. Put on the headlamp and press the “Light Source” button to turn it on. Align the beam with your line of sight, then look at the two “cat’s eyes” in the display—one made of a retroreflective glass bead, the other of ordinary glass. The retroreflective glass bead appears bright, while the ordinary one looks dim. In daily life, retroreflective materials are widely used in road signs and markings, reflective decals on vehicles, firefighting signs, and many other safety applications.

Optical Tweezers

On the display table is an Optical Tweezers experimental setup. The principle of optical tweezers is based on the interaction between light and matter, as well as the manipulation of light fields. By carefully designing the distribution of the light field, it is possible to create an optical potential well or optical force field, thereby enabling the manipulation of microscopic objects. In the field of medicine, optical tweezers are a high-precision, non-contact optical micromanipulation tool that can manipulate single cells, study their structure, function, and interactions, and play an important role in genetic research. Beyond medicine, optical tweezers are also widely applied in photonics, nanomaterials science, and micro-electro-mechanical systems (MEMS).

Magneto-Optical Rotation

This exhibit is Magneto-Optical Rotation. When linearly polarized light passes through a medium under the influence of a magnetic field, its plane of vibration rotates—this phenomenon is known as magneto-optical rotation. It has important applications in devices such as optical modulators and isolators. On the table is an experimental setup consisting of a light source, a polarizer (P1), a coil, and an analyzer (P2). When no current flows through the coil, the transmission axis of analyzer P2 is set perpendicular to that of polarizer P1, resulting in extinction. Once current flows through the coil and generates a magnetic field, extinction occurs only after rotating the analyzer’s transmission axis by a certain angle—this demonstrates the magneto-optical rotation effect.

Measurement of Luminous Flux

This exhibit is Measurement of Luminous Flux. Luminous flux refers to the amount of visible energy emitted by a light source into the surrounding space per unit time. The common instrument used to measure luminous flux is an integrating sphere, which you see on the display table. Since the light emitted by a source is affected by factors such as its size, shape, and voltage fluctuations, it cannot be perfectly uniform, which can affect measurement accuracy. To address this, the light source is placed inside the integrating sphere, the sphere is closed, and the source is powered on. The light emerging from the output port is then evenly distributed, allowing accurate measurement of luminous flux.

Photoelectric Effect

On the display table is a Photoelectric Effect experimental setup. The photoelectric effect refers to the phenomenon in which light of a certain frequency irradiates a metal surface, causing the metal atoms to absorb photon energy and release electrons. This effect was first discovered by German physicist Heinrich Hertz while studying Maxwell’s electromagnetic theory. Later, Albert Einstein proposed the photon hypothesis, successfully explained the photoelectric effect, and was awarded the Nobel Prize in Physics. In technologies such as film, television, and radio facsimile, photocells are used to convert light signals into electrical signals—these devices operate based on the principle of the photoelectric effect.

The Disappearing Object

This exhibit is The Disappearing Object. When you observe a ruler through the lens system, the middle part of the ruler seems to disappear. Why does this happen? The secret lies in the four lenses with different focal lengths. When arranged in sequence at specified distances, they bend the surrounding light rays and narrow the light path, while ensuring that the background is reconstructed along its original path. As a result, an “invisible zone” is formed. The ruler, placed within this invisible zone, disappears from view. You can follow the optical path diagram on the display table to find this so-called “invisible region.”

Energy Level Transition

This exhibit is Energy Level Transition, a concept first introduced by Niels Bohr. The microscopic particles that make up matter can occupy different energy states, known as energy levels. When a particle transitions from a higher energy level to a lower one, it releases photons of a certain frequency. Conversely, when transitioning from a lower energy level to a higher one, it must absorb photons of a corresponding frequency. Through the multimedia display, you can explore transitions between energy levels in a four-level system and gain a deeper understanding of this fundamental principle in quantum optics.

Laser Voice Transmission

This exhibit is Laser Voice Transmission. Laser voice transmission is a type of acousto-optic modulation technology, with light serving as the carrier of sound. When you speak into the microphone, your voice is encoded onto the laser through the transmitter, becoming a modulated signal. Under the protection of the safety cover, the laser carries the signal to the receiver, where it is decoded and the sound is restored, then amplified and played back.

Press the music button to hear the effect. On the receiving panel, you will see a diffraction pattern of the laser, created as the modulated beam passes through a diffraction grating. By rotating the polarizer to adjust the laser’s energy, you will notice the pattern brightening or dimming—and the sound volume changing accordingly.

An Unusual World

This exhibit is An Unusual World. Here, through illustrated panels and multimedia displays, you can explore questions such as: Why is the ocean blue? What causes morning and evening glow? How does the world appear to someone with color blindness? You can also discover the beauty of light phenomena and optics in practice—for example, the birefringence of calcite crystals and the use of fluorite in lenses—demonstrating the wonder and diversity of the optical world.

Quantum Optics Lecture Hall

You can first watch video materials to learn the basics of quantum optics, and then participate in two interactive quiz zones to test and reinforce your knowledge.

The Hall of Light Exploration ends here. Please proceed to the Hall of the ERA OF OPTICS.