Affordable and Scalable Ultrashort Pulse Lasers (USP) for Material Processing

Material processing with lasers is awesome. Just think of those high power lasers cutting 100s of millimetre thick metal blocks or the sparking material when engraving titanium or stainless steel. Every workpiece is a little fireworks. 

Lasers can do a lot. Cutting, welding, marking and engraving have been the most typical application from early CO2 lasers till todays MOPA (master oscillator power amplifier) designs. Initially CO2 lasers were very inefficient and got replaced by solid state lasers. Solid state lasers were bulky and unreliable so they got replaced the Q-switched fibre lasers. There was a demand for higher quality marks and edges so Q-switched fibre lasers got replaced with MOPAs which can deliver shorter pulses (couple nanoseconds). UV, blue and green lasers have further improved the processing quality with their higher absorption in the material and smaller spot size in focus. However, they cost the reliability through quickly degrading wavelength conversion crystals.  

Recently there is a new trend emerging, namely femtosecond and picosecond lasers starting to replace MOPAs. Shorter pulses are of course one of the reasons - even higher quality processing is made possible with a nanometer heat affected zone. 
While q-switched and MOPA lasers are limited to 10s of kilowatts of peak powers, the ultrashort pulse laser technology brings to peak power to well above the megawatt range. This high power leads to all kind of exciting physical effects, not possible previously with other lasers: 

• The electric field of the laser pulse is so high that it overcomes forces between electrons and atomic nuclei, molecular bonds.
• Basically any material can be broken down / processed with these lasers. Ceramics, metals, organics, plastics, liquids, glasses or gasses - you name it.
• Electrons are accelerated in the laser focus and as they hit the bulk material again they produce x-rays.
• If the intensity is fine tuned it can produce refractive index changes in materials by slightly altering the structure.
• On the surface of the workpiece microstructures can be created through interference or laser beam with itself (laser interference patterning).
• A simple polarized beam with the right intensity in focus will create periodic structures (laser induced periodic surface structures) which work as diffraction gratings.
• Liquids like water can be broken down (like an electrolysis) without using any electrodes which would get consumed.
• Nanoparticles can be generated when a bulk is ablated in a liquid. 3D printing can be done using two photon polymerization.
• Microprocessing of materials can be realized with extremely thin edges (wire mesh or resistor trimming with micrometers thick connections).
• Glass can be cut and cleaved or microchannels can be formed for microfluidics applications

... and this list is not even close to being complete. 

Ultrashort pulse lasers to me are like AI of the photonics world - they will be soon used for many applications which were earlier only limited to a certain group of researcher and companies with deep pockets.

What enables the laser revolution?
If we look back on past changes there is one important factor which enables the switch from one laser technology to another: the price. CO2 lasers required high voltage, gas circulation, large components - the material cost was huge. Recent lasers are based on optical fibre technology which is cheap and widely available due to the developments in the telecom industry. Just like before, the most recent technology is first used in volume production, research labs where the high cost of a single laser is not an issue. But as soon as the price comes down, we get not just workshops but even DIY enthusiasts picking up the pace in their garages.

Let's admit: Ultrashort pulse lasers are currently very expensive. Litilit in Europe is one of the most affordable manufacturer and asking 55kEUR for a femtosecond laser. Chinese alternatives like Y-Laser cost 45kEUR or more. Prices simply don't seem to be possible below these levels. Why is that? Let's dive into that a bit more in detail.

The high price is due to the complexity. To achieve such high peak power levels one needs to use chirped pulse amplification (CPA). The laser can break down any material, so what does it stop it from breaking down itself? The answer is CPA! 

How the usual CPA based lasers work is that a mode-locked laser oscillator generates a lot (e.g. 60 million per second) of low energy and very short pulses. Some of these pulses are selected using a very quick optical switch (pulse picker), then the pulses are stretched. This is required because power is energy divided by time. The longer the pulse the smaller the peak power so it won't damage any of the laser components. 
Once the pulses are stretched they are amplified (usually in a preamp and a power amp configuration). Once amplified, the pulses will need recompression. This needs to be done with a large diameter beam to avoid damage to the compression optics. At the end an optical isolator makes sure that the backreflected pulses from the workpiece don't damage the laser. 
The whole process is complicated which means, many optical and electronics components with precise control and specs are needed. Building and testing the laser requires many work hours, expensive equipment. Development of the product takes long and it's costly. 

The main root cause is complexity. 

To reduce the price considerable one needs to extremely simplify the design and this is exactly our strategy at DIY-Optics. By extremely simplification we can achieve a total material cost of 14kEUR and a build and test time of about a single day. We start with stretched pulses which need only a single amplification stage and no pulse picking. The laser needs power and an on/off input signal. Stripped to the most needed functions while delivering the extremely high peak power to break down any material.

Of course, the limited number of features is not suited for every application but it enables a lot of them. One often forgets about the fact that the material processing optics around the laser can be tailored to the application too. For instance you can increase the spot size by choosing the right focal length or going off-focus, make the pulses longer by passing them though a piece of high dispersion glass, reducing the deposited energy by scanning the beam faster or slower. 

The low complexity comes with many advantages, now just the low price. Fast lead time, easy integration, small size, and scalability are the key words here. Most of these lasers are currently used in volume production applications so high laser cost, long lead times and limited laser production capacity are not an issue. If a million smartphones get the apple engraved on them or a billion resistors are trimmed with a single laser then it doesn't matter if the laser costs 150kEUR - per produced components the cost is negligible. But when it comes to lasers being used at low volume and low duty cycle applications, the price will be very important. For instance, if you produce 50 custom microfluidics cells per week with your system or 30 dental implants a month then the cost becomes a very significant barrier. 
Luckily, these lower volume USP laser applications also have a much wider customer base. Just to stick with these examples, there are certainly much more dental practices and biochemistry labs worldwide than smartphone/semiconductor factories. That means, the laser will need to be produced in a much larger volume. The large volume will further boost price reduction. In physics this process is called a resonance - and the growth in amplitude (or in this case the number of lasers and price reduction) will be exponential. The switch from MOPA to USP will happen quickly as soon as the process starts to take off. 

I'm sure you have a good application in mind or just looking for an affordable laser. Otherwise you wouldn't be reading this blogpost. So, I recommend taking this to the next level! 

Consider pre-ordering our laser or talk to us about your application - we can also design your whole system as we have done for many other partners in the past.

Follow the link to the product page: 

Ultrashort Pulse Laser for Material Processing – DIY-Optics GmbH