Evolution of DiPOLE

With decades of experience as a world class laser facility, the CLF formed the Centre for Advanced Laser Technology and Applications (CALTA) team to bring on the next generation of lasers. The team saw an opportunity to:

  • enhance one of the great advantages of laser technology, which is a relatively compact size with scope for scalability and flexibility
  • combat one of its limitations, which is the fact that the higher the power of the laser pulse, the lower the repetition rate, resulting in less efficient experiments

CALTA recognised that tackling these challenges could result in advanced, high-performance laser systems with the ability to push the boundaries of laser science and break world records. The result of this concept is DiPOLE, which stands for “Diode-Pumped Optical Laser for Experiments”. It is a scalable laser system that uses laser diodes for pumping, and cryogenic cooling of the gain media to deliver an efficient, high-average-power operation.

CALTA has since been commissioned to deliver DiPOLE systems to some of the top international research facilities in Europe, as well as building the heart of the CLF’s one-of-a-kind laser, EPAC.

The Pioneer DiPOLE10

The Pioneer DiPOLE10 was constructed to demonstrate the concept of a scalable laser system capable of delivering some energy pulses of laser light that could be produced several times a second. This is difficult because, due to overheating, the higher the energy of pulse you produce usually limits the number of pulses you can fire over a certain period. This lengthens the time it takes to conduct experiments, driving up costs and limiting the number of experiments year.

The DiPOLE concept can be thought of in two main systems: the front end, which generates a seed pulse, and the main amplifier.
The DiPOLE front end starts as a fibre seed source, producing an initial laser pulse of a few nJ. Also contained in the seed source is a device that allows you to alter the shape of the pulse, which is especially important for certain applications as it enables precise control over how the energy is distributed over time within each pulse.

The seed pulse is then amplified in two stages, increasing its energy from a few nJ to around 100mJ. The beam is expanded and spatially shaped from 3mm circle into a 20mm square beam before moving into the main amplifier, which contains four slabs of the laser gain medium with two different doping concentrations. After passing through the amplifier head six times, the laser pulse can end up being as powerful as 10J. All this happens 10 times a second (10Hz) thanks to cryogenic cooling, without which the system would overheat and break.

DiPOLE10 has been running for almost 15 years and is still used as an experimental system. It has been fundamental in:

  • improving the efficiency of second and third harmonic generation: a process used to change the colour of the light from infrared to green to UV
  • testing new technologies including software control of devices
  • developing laser shock peening

Higher Energy Systems

Having demonstrated on DiPOLE10 the ability to deliver 10J of energy, the DiPOLE concept began picking up international interest. The next step was to prove that the system was indeed scalable to higher powers; building a system with two amplifier heads in series. Using the same principles, this system can be thought of in three sections; a front end, a 10J amplifier and a 100J amplifier.

DiPOLE 100 for HiLASE
DiPOLE 100X for the European XFEL
DiPOLE for EPAC

The second DiPOLE system, which was commissioned by the HiLASE facility in Prague, had a similar front end to DiPOLE10. Each of the amplifier heads are cryogenically cooled and pumped with the laser diodes. The 10J amplifier head houses four gain medium slabs with two different doping concentrations. Here, the beam size is approximately 20mm square. The 100J amplifier houses six gain medium slabs with three different doping concentrations, with the size of the beam at 75mm square. This increase in size is to ensure the components in the system are not damaged by the high energy of the laser pulses.

The DiPOLE 100 laser system demonstrated 100J of laser energy in each pulse of light in 2016, which set a new world record. Under normal operations each pulse is 10ns long and the system operates with a repetition rate of 10Hz.

The DiPOLE 100 system was delivered to the HiLASE facility in Prague where it continues to set new world records.

A second 100J system has been constructed for the European XFEL (X-ray free electron laser) in Germany. The main challenge here was the space available at the European XFEL. It was very different to that available at HiLASE, and it required the CALTA team to find a way to essentially fold the DiPOLE system in on itself. Thanks to DiPOLE’s modular nature, this was possible.

A third 100J system has been constructed as a pump laser in EPAC for a titanium-doped sapphire (Ti:S) laser system. This required improvements in the efficiency of converting the colour of the beam. The process to change an infrared beam into a green beam can result in energy losses. The CALTA team managed to achieve an impressive 80% conversion efficiency for EPAC.

Read more about DiPOLE for EPAC

Higher Repetition Rate Systems

The DiPOLE 100Hz laser system represents the next evolution in the DiPOLE family. This next-generation system increases the repetition rate tenfold, from 10 shots per second to 100 shots per second, while maintaining a high pulse energy of 10J and delivering an impressive 1kW average power. The DiPOLE 100Hz system demonstrated stable operation at full specification, 10J at 100 Hz, over millions of shots without user intervention.

DiPOLE 100Hz is particularly attractive for industrial applications that demand high throughput and reliability. Its compact design and stable long-term operation make it ideal for:

  • advanced materials processing
  • laser machining and microfabrication
  • optical component testing
  • scientific research requiring high average power

This tenfold increase dramatically enhances throughput for both scientific and industrial applications opening the door to experiments requiring high data rates, improved statistical accuracy, and greater temporal resolution.

The first DiPOLE 100Hz system was delivered to HiLASE in 2023. A second DiPOLE 100Hz system will remain housed at the CLF.