C Time Conversion
Let's start by converting time units.
- 1 millisecond (ms) = 0.001 seconds = 10 -3 seconds
- 1 microsecond (μs) = 0.000001 seconds = 10 -6 seconds
- 1 nanosecond (ns) = 0.000000001 seconds = 10 -9 seconds
- 1 picosecond (ps) = 0.000000000001 seconds = 10 -12 seconds
- 1 femtosecond (fs) = 0.000000000000001 seconds = 10 -15 seconds
With this understanding of time units, we can see that femtosecond lasers produce extremely short pulses.
In recent years, ultrashort pulse laser processing technology has seen rapid advancements.
The Basics: Nanosecond vs Picosecond vs Femtosecond Lasers
Lasers have a variety of applications across many industries and their effectiveness is differentiated by pulse duration. In this context, we will discuss three types of lasers differentiated mainly by their pulse durations: nanosecond, picosecond and femtosecond lasers.
Nanosecond lasers exhibit a pulse duration of 10 -9 seconds. These lasers have been in use for a long time and are suitable for many material processing applications. However, its longer pulse duration can lead to thermal damage in certain scenarios.
Picosecond lasers have a shorter pulse duration of 10 -12 seconds. The reduced pulse duration minimizes thermal damage and leads to more precise material processing. As a result, they are preferred for applications that require greater precision and less thermal impact on the material being processed.
Femtosecond lasers offer the shortest pulse duration of 10 -15 seconds. Its ultrafast pulses offer unique material processing opportunities as the laser pulse duration is shorter than the conduction time of the target material. This feature allows for a “cold” processing technique, where the material is removed by sublimation without causing heat-induced damage.
These three laser types fall into the category of pulsed lasers, known for their ultra-short pulse durations. The main advantages of ultrafast lasers are the ability to minimize the effects of heat and increase precision in material processing.
In summary, nanosecond, picosecond, and femtosecond lasers are distinguished by their pulse durations (10 -9 10 -12 and 10 -15 seconds, respectively). Each type has its merits and applications, with femtosecond lasers offering the highest precision and minimal thermal impacts due to their extremely short pulse duration.
Ultrashort Pulse Laser Meaning
For a long time, people have tried to use lasers for micromachining.
However, the long pulse width and low laser intensity of traditional lasers caused the material to continually melt and evaporate.
Although the laser beam could be focused to a small spot, the resulting thermal impact on the material was still significant, limiting machining accuracy.
To improve the quality of processing it was necessary to reduce the effect of heat.
When a picosecond-scale laser pulse acts on the material, the processing effect changes drastically.
With a sharp increase in pulse energy, the high power density is sufficient to remove the outer electrons.
The interaction between the laser and the material is so short that ions are removed from the material's surface before the energy is transferred to the surrounding materials, avoiding thermal impact.
This is why the process is also known as “cold working”.
Thanks to the benefits of cold working, short- and ultrashort-pulse lasers have found their way into production and industrial applications.
Laser Processing: Long Pulse vs Ultrashort Pulse
In ultrashort pulse processing, energy is injected quickly into a small area of action.
The high energy density deposited instantly changes the mode of electron absorption and movement, avoiding the effects of linear laser absorption, energy transfer and diffusion. This fundamentally changes the interaction mechanism between the laser and the material.
Position after long pulse laser processing
Position after ultrafast laser pulse processing
Wide application of laser processing
Laser processing covers high-power cutting and welding.
The various laser processing methods such as drilling, tracing, cutting, texturing, pickling and isolation are mainly used in micromachining for the following purposes:
| Classification | Wave continues (CW) |
Almost continuous （QCW） |
Short pulse （Q-Switched） |
Ultrashort pulse （Locked mode） |
|---|---|---|---|---|
| Output form | Continuous output | Millisecond-Microsecond （ms-μs） |
Nanosecond (ns) | Picosecond ~ Femtosecond （ps-fs） |
| Application | laser welding laser cut Laser cladding |
laser drilling Heat treatment |
Laser marking laser drilling medical laser treatment Laser rapid prototyping |
Micro nano machining Medical thin laser Precision drilling Precision cutting |
1.D well
In circuit board design, ceramic substrates are increasingly being used as replacements for traditional plastic substrates due to their better thermal conductivity.
To connect electronic components, it is typically necessary to drill hundreds of thousands of micrometer-sized holes in the board.
Therefore, it is essential to ensure that the stability of the substrate is not affected by the heat generated during the drilling process.
Picosecond lasers are an ideal tool for this application.
When using impact drilling, picosecond lasers can complete hole processing and maintain hole uniformity.
In addition to circuit boards, picosecond lasers can also be used to drill high-quality holes in materials such as plastic films, semiconductors, metallic films and sapphires.
For example, when drilling a 100 micrometer thick stainless steel sheet using 10,000 pulses of 3.3 nanosecond or 200 femtosecond lasers close to the ablation limit:
2. Write, cut
Lines can be generated by scanning and superimposing laser pulses.
By performing multiple sweeps, it is possible to penetrate deep into the ceramic material until the line depth reaches 1/6 of the material thickness.
The modules are then separated from the ceramic substrate along these marked lines, a process known as marking.
Another separation method is ultrashort pulse laser ablation cutting, also known as ablation cutting.
In this process, the laser removes material through ablation until the material is cut.
An advantage of this technology is its greater flexibility in terms of shape and size of the machined hole.
All processing steps can be carried out using a picosecond laser.
It is also important to note the differences in the effects of picosecond and nanosecond lasers on polycarbonate materials.
4. Line ablation (lining removal)
Another common application in micromachining is the precise removal of coatings without causing damage to the base material.
The ablation can range from a line a few microns wide to a large area covering several square centimeters.
Because the coating thickness is generally much thinner than the ablation width, heat cannot be conducted to the sides. In this case, a laser with a nanosecond pulse width can be used.
The combination of high average power laser, square or rectangular conductive fiber and flat light intensity distribution makes laser surface ablation suitable for industrial applications.
For example, the Trumpf company's Trumicro 7060 laser is used to remove the glass coating from thin-film solar cells.
The same laser can also be used in the automotive industry to remove anti-corrosion coatings and prepare for subsequent welding.
5. Recording
Engraving involves creating three-dimensional shapes through the ablation of materials.
Although the size of the ablation may exceed the traditional scope of micromachining, its required precision still places it within the realm of laser applications.
Picosecond lasers can be used to process the edges of polycrystalline diamond tools for milling machines.
Lasers are an ideal tool for machining polycrystalline diamonds, which are extremely hard materials used to make milling cutter edges.
The benefits of using lasers include non-contact processing and high machining precision.
Micromachining has a wide range of applications and is increasingly being used to produce a variety of everyday needs.
Laser processing is a non-contact method and offers several significant advantages, including fewer post-processing steps, good controllability, ease of integration, high processing efficiency, low material loss and minimal environmental impact.
It has become widespread in industries such as automobiles, electronics, household appliances, aviation, metallurgy and machine manufacturing, playing an increasingly important role in improving product quality, labor productivity and automation, while reducing material consumption .
Conclusion
Nanosecond, picosecond, and femtosecond lasers differ primarily in their pulse durations. A nanosecond (ns) is 10 -9 seconds, a picosecond (ps) is 10 -12 seconds, and a femtosecond (fs) is 10 -15 seconds. These ultrashort pulse durations are critical in determining the applications and capabilities of these lasers.
Femtosecond lasers are suitable for applications in ophthalmology and precise materials processing due to their extremely short pulses and reduced thermal damage. Picosecond lasers are similar, offering high precision in tasks such as micromachining or tattoo removal. Nanosecond lasers, with longer pulse durations, are used in applications where more energy transfer is required.
In summary, the choice between nanosecond, picosecond, and femtosecond lasers depends on the specific requirements of various applications. These ultrafast lasers offer a range of possibilities when it comes to precision, energy transfer and thermal damage reduction, making them indispensable tools in countless industries and fields.
