The interaction between visible light and materials is a fascinating topic in physics and is responsible for many of the optical phenomena we observe in everyday life. When visible light interacts with materials, it can be absorbed, transmitted, or reflected, and the behavior depends on various factors, including the material’s composition and the properties of light.
Visible light is a form of electromagnetic radiation with wavelengths ranging from approximately 400 to 700 nanometers, which corresponds to the colors we perceive, from violet to red.
J Tech Photonics diode based lasers are all around 450nm, which is blue in color. You can see the blue light in the picture below as it is cutting the wood.
There are different kinds of lasers which have different wavelengths. One of the more common cutting laser is the CO2 gas laser, which has a much longer wavelength of 10,600nm. CO2 lasers have much different reactions to materials because they are not in the visible spectrum of light. We will discuss specifically J Tech diode lasers in the visible spectrum (450nm blue).
Why do materials react different to the J Tech blue laser?
When this light encounters a material, several processes can occur:
1. Absorption: When light interacts with a material, some of its energy can be absorbed by the atoms or molecules in the material. The energy absorbed can cause the electrons in the atoms or molecules to jump to higher energy states. This process can change the material’s internal energy, which may result in a rise in temperature. The color we perceive in a material is due to the specific wavelengths of light that are not absorbed by the material. Instead, they are reflected or transmitted, and those are the colors we see.
2. Transmission: Transparent materials allow light to pass through them with minimal absorption. In such materials, the atoms or molecules do not significantly absorb the light’s energy, so the light can pass through and emerge on the other side. Materials like glass and water are good examples of transparent materials. The light’s speed may change while passing through a material, which is why we see phenomena like refraction (bending of light) when light travels from one medium to another.
3. Reflection: Some materials have surfaces that do not allow light to pass through easily. When light encounters such a surface, it gets reflected back, obeying the law of reflection. The angle of incidence (the angle at which light strikes the surface) is equal to the angle of reflection (the angle at which light bounces off the surface). This is why we see our reflection in a mirror or see objects around us—they reflect light that reaches our eyes.
The specific interactions of light with materials depend on the material’s atomic and molecular structure, as well as the energy levels of its electrons. These factors determine which wavelengths of light the material will absorb, transmit, or reflect.
Which colors will be best to process with the laser, dark, light, or clear?
Darker colors generally absorb more energy than lighter colors and clear materials. This is because the color of an object is determined by the wavelengths of light it reflects or transmits while absorbing the rest. Dark colors, such as black, absorb a larger portion of the incident light, while light colors (e.g., white) reflect more light, and clear materials (transparent or translucent) allow light to pass through with minimal absorption.
Here’s how the absorption of energy varies between light colors, dark colors, and clear materials:
1. Dark Colors (e.g., Black): Dark-colored materials absorb a significant portion of the incident light, converting it into heat energy. As a result, they tend to absorb more energy than other colors. This is why dark-colored objects, like black pavement on a sunny day, can become much hotter compared to lighter-colored surfaces.
2. Light Colors (e.g., White): Light-colored materials, such as white objects, reflect most of the incident light and absorb only a small amount. Since they reflect more light than they absorb, they tend to absorb less energy compared to dark colors.
3. Clear Materials (e.g., Transparent or Translucent): Clear materials are designed to allow light to pass through them with minimal absorption. As a result, they do not absorb much energy from the incident light. Instead, they either transmit the light through the material or, in the case of translucent materials, scatter the light, allowing some of it to pass through while diffusing the rest.
Takeaway: Dark colors certainly work the best. The more opaque and darker the better. Lighter colors are harder to engrave and cut, and clear just won’t cut at all.
Why do dark materials absorb more blue laser energy?
Dark materials absorb more energy because of their optical properties related to color and light absorption. When light interacts with a material, it can be either absorbed, transmitted, or reflected, depending on the material’s properties and the light’s wavelength.
The color of an object is determined by the wavelengths of light that it reflects or transmits while absorbing other wavelengths. Dark materials, such as black objects, appear dark because they absorb most of the light that strikes them, reflecting very little. Light colors, on the other hand, appear bright because they reflect a significant portion of the incident light, absorbing only a small amount.
Here’s why darker materials absorb more energy:
1. Light Absorption: Darker materials have a higher absorption coefficient for visible light. This means that when light strikes a dark material, a larger proportion of the light’s energy is absorbed by the material’s atoms or molecules, promoting electronic transitions or increasing the material’s internal energy.
2. Color and Wavelengths: The color we perceive is determined by the wavelengths of light that are not absorbed but are instead reflected or transmitted. White objects appear white because they reflect all visible wavelengths of light, while black objects appear black because they absorb most or all visible wavelengths. Therefore, a dark material absorbs a broader range of colors, converting them into heat or other forms of energy.
3. Heat Generation: When light is absorbed, it can convert into heat energy within the material. Dark materials, being good absorbers of light, efficiently convert incident light energy into heat, warming up more than lighter-colored materials under the same light exposure.
4. Energy Dissipation: The absorbed energy may also be dissipated within the material, leading to various effects, such as molecular vibrations, lattice distortions, or photochemical reactions.
5. Temperature Increase: Since dark materials absorb more energy and convert it into heat, they can heat up more quickly and to higher temperatures when exposed to light or other forms of electromagnetic radiation.
As a practical example, consider wearing dark-colored clothing on a sunny day. Dark-colored clothes absorb more sunlight, which is why they can feel significantly warmer than lighter-colored clothes, as they trap more heat close to the body.
In summary, darker materials absorb more energy because of their higher light absorption properties, which lead to more substantial heat generation and temperature increases when exposed to light or other forms of electromagnetic radiation.