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Basic Laser Facts

The term LASER is an acronym for Light Amplification by Stimulated Emission of Radiation. Lasers emit light that is coherent, directional, monochromatic, and intense. Lasers operate in either Continuous Wave (CW) where the beam is always on or is pulsed.

Modern marking lasers are usually “pumped”, meaning they use a light source to “pump” or energize a crystal rod or gas to generate the laser beam. Each laser type has its own advantages and applications. The four more popular types include:


		Lamp-Pumped (LP) - Crystal (typically Nd: YAG or YVO4) is side pumped using a Krypton arc lamp. LP lasers typically produce higher power outputs than other laser markers, making them excellent choices for general marking. LP lasers are available in a variety of wavelengths including infrared and green. Most LP lasers produce a multimode beam profile but are also offered in TEM00, low order, and other modes. Lamp-pumped lasers use a Krypton lamp as their pumping source. Much of the “white” light generated by the Krypton lamp goes unused by the crystal and becomes excessive heat, requiring an external chiller to keep the laser module at operating temperature. As a general rule, LP lasers have a much larger footprint than either diode-pumped or fiber lasers. Customers may perform their own routine maintenance, including regular lamp replacement every 1,000 hours of operation. Lamp-pumped lasers should be serviced twice annually by a certified field service technician to ensure top performance.
		Diode-Pumped (DP) - Similar in composition to a lamp-pumped laser, DP lasers use a diode pack to stimulate the crystal. The diode packs generate a wavelength closely matching the optimal stimulating wavelength of the YAG or YVO4 crystal. This system is more energy efficient than LP lasers, generating less heat, is more compact, and the diode packs have greater life than Krypton arc lamps. DP lasers are available in infrared, green, or ultraviolet wavelengths. DP lasers of 50 watts or less do not require an external chiller, thus giving DP lasers a smaller “footprint” and less maintenance overall. DP lasers often have better beam quality than LP systems. DP systems should be serviced by certified field service technician once a year.
		CO2- Uses an electrical discharge to excite the CO2 gas. CO2 lasers are extremely popular and low cost laser marker for organic and other materials. The CO2 markers are used extensively by the packaging industry because of their marking speed and low cost. This marker uses a gas cartridge as its lasing medium that can be recharged upon depletion.
		Fiber Laser- Fiber lasers differ greatly from both LP and DP lasers. Fiber lasers use a telecommunications grade diode to pump an optical fiber. Extremely compact and efficient, fiber lasers have superior beam quality and stability over LP and DP system. This virtually maintenance-free laser is available only in IR (1060 – 1070 nm) wavelength at this time. The fiber laser is rated for an estimated 100,000 hours of operation and should be serviced by a certified field service technician as needed.

	Lamp-Pumped	Diode-Pumped	CO₂	Fiber-Pumped

Typical Power Output (Watts)	80	50	35	20

MTTF Light Source (hrs)	600	15,000	20,000	100,000

Cost of Replacement	$110	$11,000	$9,500 - $12,500	$8,500

Typical Power Consumption (kWh)	3.4	2.2	1.5	0.3

Cooling	Ext. chiller	Int. chiller	Air Cooled	Air cooled

The need for marking and coding products has never been greater. Manufacturers mark their products to enhance the product’s appearance and for brand identification purposes. Additionally, many manufacturers must adhere to strict traceability requirements, necessitating the use of bar codes, 2D matrix codes, serial numbers, and other marks. The marking process is further complicated considering the ever-widening array of materials used by manufacturers. Lasers have proven to be the most effective means of marking and have become commonplace in today’s modern manufacturing plants.

Laser marking is a non-contact process relying on heat generated by the laser beam to alter the surface of the work piece. To achieve the desired results, the operator can control the thermal reaction by varying two main variables: power and marking speed.

Power is compromised of two main factors, current and pulse rate. The current acts like the throttle of an automobile. By varying the current the operator can vary the power output of the laser. Lasers are also pulsed, usually with the use of a Q-switch to generate thousands of watts of output. The laser acts like a large capacitor, storing energy until it is released. The Q-switch effectively divides the laser output into pulses of light. A low pulse rate (1kHz) yields higher peak power but longer durations between pulses. A higher pulse rate (50kHz) generates less peak power but shorter durations between pulses.

What does this mean to the material? The high peak power pulses at low frequencies increases the surface temperature very rapidly resulting in material vaporization and minimal heat conduction into the part. At higher repetition rates, the lower peak power produces much less, if any, vaporization but will result in significantly more heat conduction to the material. The Q-switch pulse rate is probably the most important variable for control of the thermal process.

Marking speed, or beam velocity, is another important variable. Power and speed are inversely proportional, i.e. less power requires more time to mark and vice versa. Deep marking (typically >0.002”) each point on the engraved line will require exposure to several pulses to achieve depth and the beam velocity must be reduced until the desired depth is achieved. For shallow marking, the speed may be increased to the system’s maximum velocity or until the separation between pulses is aesthetically unacceptable at the pulse rate setting. As a general rule, pulses should overlap at least 50% to give the appearance for a continuous engraved line.

The advantages of laser for marking and coding are obvious: fewer consumables; permanent, legible marks; flexibility to quickly change the mark as needed; and faster marking speeds. Laser marking with its highly economical performance and product quality sets it apart from conventional marking methods such as mechanical embossing and print processes.

In the laser industry, M² is the most popular parameter used to describe the quality of the laser beam

D is the beam diameter at its waist
Θ is the divergence angle at far field
λ is the laser wavelength

TEMoo Mode

	Gaussian intensity profile (also called “fundamental mode”)
	Diffraction limited beam quality
	Can be focused to smallest spot size
	Achievable maximum power is lower than low order mode or multimode
	Good for ultra fine laser processing but may take more time and more power for desired results
	Output power requirements determined by process and material properties

CrystaLaser Images

Actual laser beam profile, TEMoo mode, Gaussian beam

Selecting the proper wavelength for an application is extremely complex, requiring knowledge gained through years of marking experience. Many factors influence the selection: the size of the character to be marked, the desired marking speed, desired line width, the type of mark, the physical properties of the material to be marked, the color of the material, the power of the laser, the pulse frequency, and other factors. These factors interact with each other in a dynamic manner making the selection process very complicated. The only method to ensure the application is marked using the best wavelength is to run test samples varying the factors accordingly. The chart below is offered as a general guide for wavelength selection. The final selection should be made only after samples have been successfully marked.

Types of Laser Marking

		Surface Etching

		Ability to change the surface finish of a metal thus altering its reflectivity and enhancing contrast
		Penetration depth is typically no more than 0.0001” deep
		One of the most common forms of laser marking

		Engrave Marking

		Vaporization of base material sufficient to produce depth required, typically 0.0001” to 0.005”
		Vaporization process identical to surface etching
		Increased depth of the mark requires repeated passes

		Thermal Marking

		Controls heat using different laser parameters such as marking speed, pulse frequency, power, and focus
		Applied to certain alloys resulting in color variations (i.e. titanium)

		Ablating

		Removes a coating, paint, or other surface treatment from a base material to create contrast without damaging the base material
		Typically done with anodized aluminum, backlit buttons, and painted steel

		Specialty Marking

		Commonly used in plastics
		Contrast can occur naturally in some plastics by heat or coupling with a wavelength causing a chemical change
		Additives can be used with most plastics to achieve different colors

		Surface Annealing

		Draws carbon and/or oxides from the base material to get contrasting mark
		Marking beam produces sharp contrasting line to surrounding area with little or no penetration
		Excellent for applications such as medical implants, bearings, tooling, or other applications where a smooth, undamaged surface and contrast is important

Test Results of a Ytterbium DPSS Fiber Laser

Last Updated: 10/23/2006