Ti:Sapphire, Mixed Glass & OPCPA
There are three primary amplification methodologies used to create PW-class laser systems; Ti:Sapphire, Mixed Glass and OPCPA. National Energetics is unique in that we are the only commercial company with experience all three types. This gives us a unique perspective in choosing the right medium based on the requirements of the end user facility.
Ti:Sapphire has a broad bandwidth in excess of 200nm, supporting amplification of very short pulses. It also has favorable thermal properties lending it to high repetition rate systems. Typical mJ energy level systems operate at 1-10 kHz and tabletop TW systems can deliver >200TW at 10 Hz.
With an upper state lifetime of only 3.2µs, Ti:Sapphire is typically pumped by a ns laser. Indirect pumping adds cost and complexity to the system and limits repetition rate to that of the pump laser at very high energies. In addition, Ti:Sapphire is not readily available with open apertures above 50mm, limiting scaling to higher energies without the use of multiple beamlines.
Nd:Glass was used in the first CPA systems built in the mid to late 1980s. Nd:Glass remains a commonly used material in high energy laser systems mainly because large aperture, high optical quality rods and discs are easily fabricated in glass. The long upper state lifetime of Nd:Glass allows direct pumping by either flashlamps or laser diodes. This simplifies system design and lowers costs through improved efficiency.
The biggest drawback of using Nd:Glass is the narrower gain spectrum when compared to Ti:Sapphire, which limits the pulsewidth to approximately 500fs. Use of silicate-based and phosphate-based Mixed Glasses in the same amplifier chain increases the overall gain bandwidth of the system and hence shorter pulses – as short as 100fs is possible today.
To date, Nd:Glass lasers have been repetition rate limited to 1 shot/20 minutes or even longer due to the poor thermal properties of glass and the fact that large disc laser systems are radiatively cooled. National Energetics has solved this problem with our new disc laser technology and repetition rates of 1 shot/minute or even faster are a reality.
OPCPA: A salient aspect of the technology we deploy is the active implementation of Optical Parametric Chirped Pulse Amplification (OPCPA) in our designs. OPCPA has become the technology of choice in high power CPA research lasers worldwide. In fact every major petawatt laser project around the world now employs OPCPA to some extent in the front end of the system.
The use of OPCPA in our designs yields a number of important advantages in the performance as well as promoting simplicity, reliability and ease of use in applications and experiments.
Advantages of National Energetics OPCPA based lasers:
- Front-end amplification in OPCPA eliminates the need for complex regenerative amplifiers, replacing CPA front ends with very simple, high gain, single pass amplifiers.
- OPCPA has inherent high pulse temporal contrast.
- OPCPA exhibits lower B-integral and the subsequent formation of mirror prepulses as seen in traditional Ti:Sapphire front end architectures.
- OPCPA offers wavelength flexibility, enabling new wavelengths beyond the traditional 800 nm band of Ti:Sapphire, including near to mid IR CPA systems at 1.5 µm.
Putting it all together
The graph below shows some of the major ultra-intense laser systems installed globally based on energy and pulsewidth. As laser systems in all categories approach or exceed the 1PW milestone, we will begin to see which technologies continue to scale and which technologies begin to reach their limits.
The National Energetic team brings some very unique qualifications to the design and construction of custom CPA lasers. Our team built the Texas Petawatt laser in Austin, a mixed glass OPCPA hybrid system and at 1.3PW, one of the highest power lasers in the world. We also have extensive experience with classic Ti:Sapphire CPA systems as well.
We are unique in our experience as experimentalists using these high energy CPA systems, which gives us the vision and expertise needed to design a laser which not only meets the initial desired specifications but a laser which can serve as a long term, reliable, easy to use target shooter in the lab.
The importance of this aspect of our laser designs cannot be overstated. There is an enormous gulf between the performance of a laser that simply meets the desired specs upon delivery and a laser that is a useful tool for research day in and day out. We can deliver a laser that will get work done.