Laser beam profile measurement for developers of micromachining systems
Friday, December 20, 2019
The production of modern miniature devices and microsystems requires highly precise micromachining techniques. Laser micromachining, which has grown in popularity in the past decade, has become an essential tool in many industrial and research applications.
This technology has revolutionized the machining industry, opening a range of possibilities regarding the types of materials that can be machined and the range of structures that can be produced.
Laser micromachining has been extensively researched and refined to overcome the limitations of conventional machining techniques. In addition to silicon wafer semiconductors and other microelectronics, laser micromachining also plays a crucial role in the manufacture of medical tools and implant devices. Therefore, as you can see, there is little to no room for error.
A common misconception is that laser beams never change. However, like any other mechanical equipment, lasers can degrade over time, drastically affecting their quality and performance.
Your equipment, therefore, needs to be regularly monitored and calibrated using a laser beam profiler to ensure that your laser performs consistently. In micromachining, two main parameters affect your laser performance: the averaged or instantaneous power, and the spatial distribution of that power.
The output power of your laser determines the effectiveness with which the beam can penetrate the material. Power stability can also have a profound effect on groove widths and achievable tolerances.
High peak power densities typically lead to highly controlled micro-ablation processes, which are ideal for micromachining. This is especially crucial when machining transparent materials, such as quartz and sapphire.
While power is essential for machining purposes, this parameter is also useful for determining the type of power detector you should use. If your laser’s output power exceeds the threshold of the profiler, the equipment can become damaged, thus reducing your measurement accuracy.
Understanding your laser beam’s power is, therefore, a critical aspect of accurate profiling measurement.
In laser machining applications, carefully maintaining the focal position, i.e., the position associated with the smallest waist diameter, is a crucial step in the fabrication process. This ensures that the beam’s focal point (which is usually in the order of a few microns) is concentrated on the object’s surface, making it possible to produce small features.
A laser beam profiler, which measures the spatial distribution of the power across the beam, is therefore essential to ensuring that maximum micromachining resolution is achieved. These devices measure several parameters which are necessary for obtaining tight tolerances, such as beam width, hot spots, ellipticity, and M-Squared.
All laser beam profilers are not created equal. To select the right profiler for your application, you will need to consider several parameters, including the wavelength, beam size, output power, and type of laser beam.
The two most common types of laser beam profiling devices are CMOS cameras and scanning slit beam profilers. CMOS camera profilers are used to produce full two-dimensional images of the laser. They are ideal for both continuous (CW), and low repetition pulse lasers with beam sizes greater than 50 microns.
Cameras, however, are very sensitive. Too much power concentrated on a small area can damage the sensor equipment. Therefore, when using cameras to measure high powered lasers, additional attenuation may be required.
Scanning slit profilers, on the other hand, work by taking tiny samples of the laser beam through a narrow slit to produce a one-dimensional profile. This characteristic allows scanning slit profiles to measure kilowatts of power without any attenuation. This type of laser beam profiler is best suited for pulsed beam systems with femtosecond pulses and beam sizes of less than 50 microns.
Sensitive and highly precise applications, such as micromachining, can greatly benefit from frequent measurement and maintenance periods. However, selecting the right beam profiler for the job is critical. You should, therefore, ensure that the chosen laser beam profiler is appropriate for the wavelength, power, beam size, and type (CW or pulsed) of laser you use.