A laser cutter uses a high-energy laser beam to burn, melt, and vaporize various materials like paper, wood, plastics, metals, etc.
How much heat can a laser generate?
Heat is directly proportional to the randomness of the particles (atoms and molecules) of a material, and the amount of laser energy absorbed by the material determines the amount of heat generated.
This article discusses the temperature and heat produced by laser cutters and the science behind it.
The heat generated by a laser depends upon its power. While some low-powered lasers (used in pointers) cannot even burn a piece of paper, high-powered lasers can generate enough heat to vaporize metals like tungsten, which has a melting temperature of 6,177°F (3,414 °C; 3,687 K).
How Hot is a Laser Cutter?
The ability of a laser cutter to burn a material depends upon the type of laser being used.
The laser itself does not carry any temperature but heats the surface of the material it touches by transferring the energy it carries to the material.
The amount of heat generated by the laser depends upon the ability of the material to absorb the laser energy, the power of the laser, and the time for which the laser is in contact with the material.
Different materials absorb lasers of different wavelengths.
A CO2 laser with a wavelength of 9000 - 12000 nm is readily absorbed by non-metals, whereas metals readily absorb fiber lasers with a wavelength of 950 - 1060 nm.
On the other hand, Diode lasers have a wavelength of 450 - 950 nm, which is readily absorbed by both metals and non-metals.
The lasers used in laser pointers are extremely low-powered (around 5 mW) and cannot raise the temperature of the material high enough to cause any significant heating effect.
A 5W diode laser can raise the temperature of a surface high enough to burn various materials ranging from a piece of paper (480 °F) to a sheet of plastic.
Higher power CO2 lasers and fiber lasers can heat the surface enough to burn metals.
Some very high-powered lasers can even melt and vaporize tungsten, the metal with the highest melting temperature of 6,177°F (3,414 °C; 3,687 K).
A high-power laser can heat the air to the degree that the particles of the air ignite and turn into plasma.
The working of a laser cutting machine is based on the similar principle where the laser heats the surface of the material and vaporizes it.
Under certain conditions, when using a fiber laser for cutting metal, a ball of plasma is formed around the cutting area which then enhances the efficiency of the process.
Furthermore, during research at the SLAC National Accelerator Laboratory, scientists fired pulses of an extremely high-powered X-ray laser on a very thin foil of aluminum.
This transformed the aluminum foil into a "hot dense matter" with a record temperature of 3.6 million degrees Fahrenheit, which is hotter than the sun's corona.
Theoretically, even low-powered lasers can generate high temperatures when operated for an infinitely long time.
However, operating the laser for long durations results in mechanical failures of the machine and limits the laser to a certain temperature.
The higher the laser's power, the higher will be the rate of energy transfer, the faster it can raise the temperature of a material.
For example, consider a material that has a melting point of around 1000°C.
A high-powered laser can cut through this material faster as it supplies more energy per unit of time to raise the temperature of the surface of the material.
On the other hand, a low-powered laser will supply less energy per unit time and slowly increase the temperature of the material.
This results in a comparatively longer dwell time for the low-powered laser to perform a similar task when compared to a high-powered laser.
What is a Laser?
LASER stands for Light Amplification by Stimulated Emission of Radiations.
The principle of laser is similar to using a magnifying glass to focus the sun's rays towards a point and generate heat.
However, lasers do not occur naturally and are generated by stimulating a light source such as a semiconductor diode, ruby crystal, CO2 gas, etc.
The light generated by the source is then amplified and converged towards a point to eliminate or minimize the loss of energy by dispersion.
This convergence of the light also increases the energy density of the laser and thereby enables the laser to burn through the material.
Depending on the light source, there are different lasers with different wavelengths.
|Carbon dioxide (gas laser)
|Nd: YAG (solid-state laser)
|Fiber (solid-state laser)
|Krypton KPT 532
|Rhodamine 6G Dye
(Tunable - dye laser)
Various types of lasers
How does a Laser burn a material?
If you are still reading this article, you are probably curious about the question - How does a laser burn the material without itself being hot?
Burning a material requires heat energy to raise the temperature of the material high enough and start a fire.
For example, when using a match stick to burn material, the heat from the fire of the match stick transfers towards the comparatively colder material and raises its temperature to ignite it.
Unlike fire, the laser itself is not hot. Then how does it burn the material?
To answer that, we need to understand the concept of "negative temperature".
Lasers are considered to have a negative temperature, which means that lasers are not hot but have high energy, which they readily transfer to other material when it comes in contact.
This can be demonstrated by the fact that a fiber laser cannot burn various organic materials, or a diode laser cannot burn transparent materials.
Whereas heat transfers from higher temperature to lower temperature regardless of the type or opacity of the material.
The energy transferred by the laser excites the molecules of the material.
These excited molecules undergo random motion and start colliding with each other, thereby increasing the temperature.
In simple terms, as the amount of laser energy absorbed by a material increases, its temperature also increases.
The major difference between heating material by a conventional heat source (like fire) and by a laser is the equilibrium state.
When heating a material with fire, the heat continuously transfers from the fire (source) to the material (target) until the temperature of the material is raised high enough to be equal to that of fire.
This is known as the equilibrium state, and the fire cannot heat the material beyond it.
Whereas in lasers, the material is heated by absorbing the laser energy.
No matter how hot the material gets, the energy of a laser will always be greater than the material.
Therefore, the material keeps heating up, and there is no equilibrium state to limit the laser from heating the material beyond a certain temperature.
However, the ability of the laser to burn the material in less time depends upon the laser power.
The higher the laser's power, the higher the energy absorbed by the material per unit of time and the lesser will be the time taken to burn the material.
Frequently Asked Questions (FAQ)
Does a laser cutter generate more heat than a plasma cutter?
Yes, a high-powered laser cutter can generate more heat than a plasma cutter.
This can be supported by the fact that a plasma cutter melts the metal, and a laser vaporizes it. The heat required for vaporizing a material is higher than the heat required for melting a material.
Is every focused light a laser?
No, not every focused light is a laser. Lasers are not just focused beams of light. Unlike the rays of the sun or the light used in our homes that consists of a mixture of radiations of different wavelengths, the laser is coherent light. Generally, a particular laser consists of radiations of only one wavelength.
What kind of radiation is a laser?
A laser beam is a concentrated beam of electromagnetic radiation. Depending upon the wavelength of the laser, a laser can be ultraviolet, infrared, or even X-ray. The diode lasers generally fall under the visible spectrum of the electromagnetic spectrum and can be considered light radiations. But a CO2 laser falls under the infrared region and is not visible to the human eye and is therefore considered infrared radiation.
Can we use a laser to boil water?
Yes, a laser can be used to boil water.
Scientists have used a high-powered X-ray laser to raise the temperature of water kept at room temperature, to 180032 degrees Fahrenheit (100,000 ºC) in less than 0.001 nanoseconds (millionth of a millionth of a second).