Nanosecond Laser, Picosecond Laser, Femtosecond Laser, Can You Tell The Difference?

We are not unfamiliar with laser processing, but you can often hear nanosecond laser, picosecond laser, femtosecond laser, etc, can you distinguish it?

Let's figure out the time unit conversion first

1ms (milliseconds)=0.001 seconds =10-3 seconds

1μs (microsecond)=0.000001=10-6 seconds

1ns (nanosecond)=0.0000000001 seconds =10-9 seconds

1ps (picosecond)=0.0000000000001 seconds =10-12 seconds

1fs (femtosecond)=0.000000000000001 seconds =10-15 seconds

By figuring out the unit of time, we know that the femtosecond laser is an extremely ultra-short pulse laser processing. In the past ten years, ultra-short pulse laser processing technology has made rapid progress.

Ⅰ. The significance of ultra-short pulse laser

There have long been attempts to use lasers for micromachining. However, due to the long pulse width and low laser intensity of the laser caused by the material melting and continuous evaporation, although the laser beam can be focused into a small spot, the thermal impact on the material is still very large, limiting the accuracy of processing. Only by reducing the thermal effect can the processing quality be improved.

When the laser pulse time is applied to the material in the order of picoseconds, the processing effect will change significantly. As the pulse energy rises sharply, the high power density is enough to strip the outer electrons. Due to the short time, the laser interacts with the material, the ions are ablated from the surface of the material before transferring the energy to the surrounding material, and will not bring thermal effects to the surrounding material, so it is also called "cold processing". With the advantages brought by cold processing, short and ultra-short pulse lasers have entered industrial production applications.

Ⅱ. Laser processing: long pulse VS ultra-short pulse

The ultra-short pulse processing energy is injected very quickly into a small area of action, and the instantaneous high energy density deposition changes the mode of electron absorption and movement, avoiding the influence of laser linear absorption, energy transfer, and diffusion, and fundamentally changes the interaction mechanism between laser and matter.

Ⅲ.The wide application of laser processing

Laser processing includes high-power cutting and welding; Micro-machining drilling, marking, cutting, texturing, stripping, isolation, etc., The main uses of various laser processing means are:

1. Drill holes

In circuit board design, people began to use ceramic substrates instead of conventional plastic substrates to achieve better thermal conductivity. In order to connect electronic components, it is generally necessary to drill up to hundreds of thousands of small holes in the board. It is therefore important to ensure that the stability of the substrate is not affected by the heat input during the drilling process, and the picosecond laser is the ideal tool for this application.

The picosecond laser can complete the machining of the hole by percussion drilling and ensure the uniformity of the hole. In addition to circuit boards, Picosecond lasers can also perform high-quality drilling on materials such as plastic films, semiconductors, metal films, and sapphires.

100μm stainless steel sheet, drilled, 3.3ns vs 200fs, 10,000 pulses, near the ablation threshold:

2. Line and cut

Lines can be formed by superimposing laser pulses in a scanning manner. It usually takes a lot of scanning to penetrate deep into the ceramic until the depth of the line reaches 1/6 of the thickness of the material. The individual modules are then separated from the ceramic substrate along these notches. This separation method is called marking.

Another separation method is to use ultra-short pulse laser ablation cutting, also known as ablation cutting. The laser ablates the material, removing it until it is cut through. The advantage of this technique is that there is greater flexibility in the shape and size of the machined holes. All process steps can be completed with a picosecond laser.

Different effects of picosecond laser and nanosecond laser on marking polycarbonate materials.

3. Line ablation (removal of coating)

Another application often seen as micromachining is the precise removal of coatings without damaging or slightly damaging the base material. Ablation can be either a line a few micrometers wide or a large area of removal a few square centimeters.

Because the thickness of the coating is usually much less than the width of the ablation, the heat cannot be conducted on the side. Laser pulses of nanosecond width can therefore be used.

The combination of high average power laser, square or rectangular conduction fiber, and flat top light intensity distribution, these technologies make laser surface ablation can be used in industrial fields. For example, the TrumPF TruMicro 7060 laser is used to remove the coating on the glass of a thin film solar cell. The same laser can also be used in the automotive industry to remove anti-corrosive coatings in preparation for subsequent welding.

4. Surface structure

Structuring can change the physical properties of the material surface. According to the lotus effect, hydrophobic surface structures allow water to flow away from the surface. This property can be achieved by creating submicron structures on the surface with ultrashort pulsed lasers, and the structures to be created can be precisely controlled by changing the laser parameters.

Opposite effects, such as hydrophilic surfaces, can also be achieved, and micromachining can also create larger-size structures. These processes can be used in fuel tanks in engines to create microstructures that reduce wear, or to structure metal surfaces to achieve welding with plastics.

5. Engraving molding

Sculpting is the creation of three-dimensional shapes by ablating materials. Although the size of the ablation may exceed the scope of what is traditionally referred to as micromachining, the precision required makes it classified in this category of laser applications. Picosecond lasers can be used to process polycrystalline diamond tool edges in milling machines.

The laser is the ideal tool for processing polycrystalline diamonds, which are extremely hard materials that can be used to make milling cutter blades. The use of engraving molding technology to process the chip grooves and teeth of the milling cutter, in this case, the benefits of laser non-contact and high machining accuracy.

Micromachining has a very broad application prospect, and more and more daily necessities are entering our field of vision through laser micromachining.

Laser processing is a non-contact processing, with less follow-up process, good controllability, easy integration, high processing efficiency, low material loss, low environmental pollution, and other significant advantages, has been widely used in automotive, electronics, electrical appliances, aviation, metallurgy, and machinery manufacturing industries. It plays an increasingly important role in improving product quality, labor productivity, automation, and reducing material consumption.

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