Laser Wavelength: Wavelength Factors, How Does It Vary?

The wavelength of a laser is its most fundamental characteristic, determining its properties, material interactions, and applications. The laser wavelength is usually measured in nanometers (nm), one nanometer being 10-9 meters. Laser wavelength is the inverse of frequency (units: Hz, kHz, MHz). Different laser technologies emit light at varied wavelengths, and the selection of wavelength depends on the specifics of the application and desired characteristics.

This article will examine laser wavelength, its factors, and how they vary.

What Is Laser Wavelength?

The wavelength of a laser refers to the spatial period of the electromagnetic wave produced by the laser. It is the distance between consecutive peaks (or troughs) of the wave that is one embodiment of the emitted light.

In the analysis of laser light, the wavelength is the most fundamental property that determines the color or frequency of the laser light. Most lasers emit on a very narrow spectrum, i.e., they are monochromatic. Different emitter chemicals/mechanisms emit light at particular wavelengths related to their chemical and electromagnetic properties. The wavelength of emission has significant implications for the laser's behavior, interactions with materials, and therefore appropriate applications.

How Does Laser Wavelength Work?

A laser is a device that emits light through optical amplification. The emitted light is generally of a very narrow frequency range, being essentially monochromatic. This light is internally amplified by stimulated emission. Each photon triggers the emission of multiple photons of the same wavelength in a cascade process that is generally partially emitted from the device through a filter or half mirror.

The wavelength of the emitted light depends entirely on the electromagnetic and electro-optical behavior of the laser source. Ruby, for example, will be stimulated by red light in a narrow frequency band, introduced from a source such as a xenon flash tube (the “pump source”). That light will trigger stimulated emission and the emitted light will have a coherent direction resulting from the crystalline structure of the ruby.

To learn more, see our full Laser Beam guide.

What Does the Laser Wavelength Indicate?

The most immediate and visually noticeable indication of the laser wavelength is the color of the emitted light, when in the visible range. Wavelengths correspond directly to color in the electromagnetic spectrum. Shorter wavelengths are associated with violet and blue colors (moving into invisible UV), while longer wavelengths are associated with red (trending into the invisible infrared).

The energy of individual photons in the laser beam is directly related to the wavelength. Shorter wavelengths correspond to higher energy, and longer wavelengths correspond to lower-energy photons. The wavelength of laser light determines how it interacts with target materials. All materials absorb, reflect, and transmit light at characteristic wavelengths. These interactions are crucial and definitive in laser applications.

The wavelength is a direct result of the core-stimulated emission technology used to originate the light. Some materials can undergo stimulated emission at multiple frequencies, but in general, lasers are used in monochromatic—i.e., single-wavelength operational modes.

To learn more, see our full guide on Laser Power.

Why Does the Laser Wavelength Vary?

The variation in laser wavelength is a result of design choices, technological considerations, and application requirements. This variation is often intentional and controlled to tune the emitted light to suit specific applications. Typical laser types and their output wavelengths are shown in Table 1 below:

Lasers are based on various laser-emission media and source/amplification technologies. The choice of laser medium, such as gas, solid-state, semiconductor, or fiber can influence the achievable wavelengths. For example, gas lasers like helium-neon lasers emit in the visible spectrum, while semiconductor lasers (diode lasers) can emit in the visible, infrared, or near-ultraviolet ranges, depending on the dopants used. The stimulated emission or gain (amplification) medium within the laser system determines the specific wavelengths that can be amplified. The properties of the gain medium, such as energy levels and transitions, dictate the available emission wavelengths. Adjusting the composition or doping of the gain medium can influence the laser's wavelength moderately.

Some lasers incorporate tuning mechanisms that allow for the adjustment of the output wavelength. Quantum-cascade lasers are an example of this. Tunable lasers can be tuned manually or electronically to emit light at different wavelengths within a certain range. This tunability is useful for applications in which several wavelengths are required and multiple devices are impractical. In certain laser systems, non-linear effects can lead to the generation of harmonics or other wavelengths not directly produced by the laser medium. Non-linear optical processes, such as frequency doubling or parametric processes can result in the generation of shorter or longer wavelengths. These are usually considered undesirable and will be filtered out.

The choice of pump source used to excite the gain medium can influence the wavelengths produced by a laser. For example, the use of different pump sources in solid-state lasers can lead to variations in the output wavelengths. Techniques such as mode-locking and Q-switching can influence the temporal characteristics of laser pulses, which can indirectly affect the spectral output. These techniques are often used in ultrafast lasers for applications such as femtosecond and picosecond pulse generation.

What Are the Factors That Affect the Laser Wavelength?

The following factors can influence the wavelength of a laser:

1. Lasers are based on various laser media, such as: gases, solids, semiconductors, or doped-fibers. Each type of laser medium has characteristic properties that influence the possible emission wavelengths.
2. The gain medium is the active material within the laser system that undergoes stimulated emission. Properties of the gain medium, such as energy levels, electronic transitions, and bandgap, determine the wavelengths that can be amplified.
3. The pump source is responsible for supplying initiation energy to the gain medium to commence the laser process. Pump-source wavelength can affect the excitation and energy levels of the gain medium, influencing the emitted wavelengths.
4. Some lasers incorporate tuning mechanisms that allow for the adjustment of the output wavelength, altering emitted wavelengths within a certain range. 
5. The design of the laser cavity, including the mirrors and other optical elements, can impact the wavelength selection, by altering the resonance modes and the conditions for constructive interference.
6. Non-linear optical effects, such as frequency doubling, sum or difference frequency generation, and parametric processes can lead to the generation of harmonics or new wavelengths not directly produced by the laser medium.
7. Factors such as temperature and pressure can influence the laser wavelength, especially in gas lasers. Thermal effects on the gain medium can cause shifts in the emitted wavelength.

How Is the Laser Wavelength Measured?

The wavelength of a laser is measured in meters (nanometers, micrometers, millimeters, etc.). It is generally derived by calculating the inverse of frequency, which is found by pulse counting.

In a grating setup, the wavelength can be derived from some simple distance measurements. The equation is:

λ = (Y x Z) / S

Where: 

Y = distance between the slits in the diffraction grating

Z = fringe peak distance

S is the distance between the screen and the grating

Frequency can be measured using several techniques, and the choice of method often depends on the requirements for a particular application. 

For more information, see our full guide on Laser Power Measurement.

What Laser Wavelength Is Required To Cut an Aluminum?

The choice of laser wavelength for cutting aluminum depends primarily upon the absorption spectrum of the aluminum being cut. Different wavelengths offer some relative advantages in terms of absorption, material interaction, and processing characteristics. 

Fiber lasers operating around 1.06 μm are commonly used for cutting aluminum. This wavelength is well-suited for materials with high reflectivity and is extremely effectively absorbed by solid aluminum and molten aluminum.

CO2 lasers, operating at a wavelength of approximately 10.6 micrometers, can also be used for laser cutting aluminum. While CO2 lasers are often associated with cutting non-metallic materials, they can provide efficient cutting for aluminum with increased power levels. This is because the wavelength of a CO2 laser is relatively poorly absorbed by solid aluminum. However, the melt can be commenced with sufficient power, and then this laser light is well absorbed. CO2 lasers offer high power at a relatively low CAPEX cost.

How Do Different Wavelengths Affect Laser Applications?

The choice of laser wavelength has a profound impact on various laser applications. It influences how laser light interacts with materials and therefore the effectiveness of the processes. Materials have varying absorption characteristics in wavelengths. The choice of laser wavelength is generally tailored to match the absorption, reflection, or transmission characteristics of specific materials. Laser material-processing applications, such as: cutting, welding, and engraving, require strong absorption, which determines the efficiency of the process.

What Are the Uses of Lasers in the Visible Light Spectrum?

Lasers in the visible light spectrum have a wide range of applications across various industries. The visible light spectrum ranges from approximately 400 nanometers (violet/blue) to 700 nanometers (red). Lasers operating within this range offer unique properties that make them valuable in different fields. Their uses include:

1. Laser pointers are common devices that use low-power visible lasers, typically in the red (around 635–670 nm) or green (around 532 nm) wavelengths.
2. Visible light communication (VLC) for data transmission. This is a complementary communication method to traditional radio-frequency-based systems, for tight-beam comms.
3. Entertainment, including laser-light shows at concerts, festivals, and events.
4. 3D laser scanning and imaging systems, for mapping objects or environments.
5. Biomedical imaging techniques such as confocal microscopy and fluorescence microscopy.

What Are the Different Types of Lasers?

Lasers come in a diverse and growing number of types and subcategories, such as:

1. Gas lasers such as helium-neon (HeNe).
2. Solid-state lasers such as neodymium-doped yttrium aluminum garnet (Nd:YAG) and erbium-doped yttrium aluminum garnet (Er:YAG).
3. Semiconductors or diode lasers.
4. Fiber lasers.
5. Dye lasers.
6. Excimer lasers.
7. Free electron lasers.
8. Quantum cascade lasers.
9. Carbon dioxide (CO2) lasers.
10. Ruby lasers.
11. Helium-cadmium (HeCd) lasers.

To learn more, see our guide on What Are the Different Types of Lasers.

What Is the Importance of Laser Wavelength in Specific Applications?

The importance of laser wavelength in a specific application is significant and directly impacts the performance and effectiveness of the laser system for that particular task. Different materials have varying absorption characteristics at different wavelengths. The choice of laser wavelength is crucial in all applications and is selected for the properties of the interaction (or non-interaction) between the light and the target. These interactions are: absorption, reflection, and transmission or selective transmission.

What Is the Laser Wavelength for Diode Lasers?

The wavelength of a diode laser is primarily determined by the energy bandgap of the semiconductor material employed. The majority of commercial diode lasers operate in the near-infrared (NIR) spectrum. Common wavelength ranges include:

1. Visible-NIR diodes: 635 to 670 nanometers (red) or 532 nanometers (green).
2. Infrared diodes: 780 nanometers (infrared) and 850 to 980 nanometers.

Some diode lasers operate in the blue and violet regions of the spectrum:

1. Blue diode lasers: 405 to 450 nanometers.
2. Violet diode lasers: 375 to 400 nanometers.
3. Mid-infrared (MIR) and terahertz (THz) diode Lasers: 30 micrometers to 3 mm.

How Does Laser Wavelength Influence Energy and Penetration Depth?

The laser wavelength is crucial in determining how energy is absorbed by materials and how deeply the laser light penetrates the material. The relationship between laser wavelength, energy absorption, and penetration depth is influenced by the material's properties and the specific interaction mechanisms involved.

The absorption of laser energy by a material depends on the material's absorption behavior at the specific wavelength of the laser. When the laser wavelength matches a strong absorption peak of the material, the energy absorption is more efficient. Penetration depth refers to how deeply laser light can penetrate a material before being significantly absorbed. The penetration depth is inversely proportional to the absorption coefficient.

Does the Wavelength's Effect on Laser Influences the Safety and Regulations?

Yes, the laser wavelength plays a significant role in determining the safety considerations and regulatory requirements associated with laser systems. Lasers of various wavelengths interact with biological tissues and materials in distinct ways, influencing the potential hazards and safety measures needed.

The absorption characteristics of various tissues influence the depth of penetration and the potential for thermal damage. Lasers in the ultraviolet (UV) and certain infrared (IR) ranges are more readily absorbed by tissues, leading to potential risks of burns or other injuries. The penetration of laser light into the skin depends on the wavelength. Longer wavelengths in the near-infrared range may penetrate deeper into tissues, potentially reaching internal structures. This penetration can have implications for laser safety, especially in medical and cosmetic applications.

How Can Xometry Help With Your Laser Cutting Projects?

Xometry is a manufacturing coordination and supply-chain partner that can fulfill your laser cutting service needs, from paper to exotic alloys, from film/foil to plate. Talk to us and we’ll show you how we can advance your project with low-friction and cost-effective service.

We work with top-tier suppliers and Fortune 500 manufacturers to simplify the supply chain and proactively and dynamically enable manufacturing capacity. 

You can consider us as providing production capacity by turnkey — your JIT supply chain for our data-driven age. Leading companies and startups work with Xometry to build scalability in demand-ready supply chains to get to market faster.

We have expertise in all aspects of manufacture, from injection molding, CNC machining, sheet metal fabrication, and 3D printing to electronics and PCBA mass production.

Summary

This article presented laser wavelength, explained it, and discussed the various factors that affect it. To learn more about laser wavelength, contact a Xometry representative.

Xometry provides a wide range of manufacturing capabilities, including laser cutting and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.

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