Laser technology is ubiquitous in the modern world from the optical and atomic clocks that allow satellites to navigate, to the spectrometers used in chemical analysis. As the demand for smaller and more portable devices continues there is increasing pressure on lasers technology to be miniaturised. TOPTICA Photonics are at the forefront of this change and are currently developing miniaturised, visible-range, semiconductor lasers.
AZoOptics spoke to Patrick Leisching, Vice President Research & Development at TOPTICA Photonics, about how they have developed this new technology, the obstacles they have faced along the way and the applications they expect this new generation of lasers to be used in.
What changes have occurred that have made the miniaturization of lasers possible?
To be able to create miniaturized lasers that emitted at visible wavelengths with a high spectral quality we needed miniaturized optical isolators. The optical isolator is necessary to prevent laser backscatter which damages the laser itself. Developing an optical isolator for the visible region was the first challenge that we faced.
In the infrared region of the spectrum (wavelengths above 1,000 nm) miniaturized optical isolators are readily available due to high demand from the materials processing and telecommunications industries. However, as there is lower demand for this technology in the visible region we had to create our own visible-range, miniaturized optical isolators.
Our miniature optical isolators were constructed using CdMnTe as the new isolator material instead of TGG. CdMnTe has been known to have a Verdet constant that is 10 times higher than TGG, which is the current high standard, for over two decades. However only particle physicists have pushed the CdMnTe technology to a commercial level, as they used it to improve their detectors.
This new development has allowed us to create miniature laser systems. We’ve been able to take several cubic meters of lab-based equipment and turned it into a handheld, portable quantum device.
What types of lasers can be miniaturized? Is there any specific type of laser that lends itself easily to miniaturization and hand-hold spectrometers?
Semiconductor-based lasers were an obvious choice. They are the smallest type of laser available meaning that if you want to miniaturize laser technology it is almost mandatory to use a semiconductor-based device.
Other lasers could simply not be used. Although solid state based devices form good lasers they have a low pump and conversion efficiency. Whilst solid state lasers can covert around 5% of the electrons that power them into photons, semiconductor lasers can achieve upwards of 50%.
As semiconductor lasers are so efficient it is possible to create a powerful laser using only a small surface area. This would not be possible using a solid state laser which will never be able to compete with the 50% efficiency.
In addition to this, semiconductor lasers can be tuned to emit light in the visible range, making them an obvious choice. The integration of semiconductor lasers onto photonic integrated circuits is well known from telecom industry at 1550 nm and will allow for hand-hold spectrometer devices.
What are the advantages of having a smaller laser? Are there any particular technologies that this research is aimed towards?
For starters the miniaturization of the technology makes it transportable. This means that laser-based technologies, such as spectroscopy, can now be integrated into portable devices.
For example, if the police have to identify a strange package on the street they need to know if it contains a biological hazard, a chemical hazard such as explosives, or if it is completely harmless.
Currently the only option is to carefully transfer the package to a qualified lab for its analysis. This has its own risks associated with it and means that law enforcement have to wait for a result, which is far from ideal. Whereas, if the police had a handheld spectrometer, using our miniature laser, they would be able to determine at the point of discovery if the package is dangerous or not.
There are many more interesting applications which range from the everyday world, such as a Gravimeter for scanning the earth on a macro scale to find old, underground mining tunnels, to the lab such as scanning materials on a nanoscale to measure tiny magnetic fields. Distributed acoustic sensing using coherent raylight Backscatter to monitor railroads or oil & gas exploration require laser systems with a very narrow line width.
The lasers will also allow portable atomic clocks to be developed and thus enable a quantum accelerometer. These would be really useful in navigation. Atomic clocks would allow a submarine to set off from the coast of Europe and reach New York within an improved accuracy: today's standard with a ring-laser gyroscope is an accuracy of one kilometer per day only. The portable atomic clock can improve this accuracy by orders of magnitude.
Atomic clocks use the electronic transitions of atoms, caused by irradiation with microwaves, to measure the passage of time.
What challenges have you faced whilst developing miniature lasers?
The main challenge that we face is the removal of heat away from the device. Whilst semiconductor lasers are highly efficient to produce the power that we require there is still a lot of heat dissipation. To prevent poor device performance or, at worse, damage to the device itself it is necessary to transport heat away from the device.
As we want to keep the overall device small water cooling is not an option. Instead we are focusing on miniaturizing the electronics and making them more efficient.
This is a similar problem that phone designers, who want efficient electronics to increase the phones battery life, are currently facing. We have taken inspiration from their designs and discoveries to develop a portable laser system with a high watt-level efficiency.
Are your miniature lasers simplified versions of their larger counterparts, or do they have the same levels of complexity?
These days’ lasers use a discrete, modular approach so additional components can be added onto the laser system.
The laser system can be assembled into a 20 cm3 box, which can be shrunk even further, by shrinking the components inside. However, the smaller that these components get the more degrees of freedom are lost which can make the laser less useful in some applications.
There are many different ways in which we can vary the laser. We could make it tunable in the wavelength, tunable in the power, fixed power and so on… To create a particular design, we have to limit the laser in other aspects.
We are currently working on a miniaturized laser which has a helium neon gas cell.
A lser module produced by TOPTICA Photonics.
What applications is your miniaturized gas cell laser designed for?
Helium Neon (HeNe) lasers have been in use for over 50 years so it is a mature technology. As it was one of the pioneer lasers it has its limitations. It cannot be tuned, the power does not scale, it cannot be locked and so on. We wanted an easy target for our first miniaturized laser and, due to their limitations, HeNe lasers with a wavelength of 633 nm were chosen.
High-coherence HeNe lasers, whilst being old, are still used in a huge range of applications. The most common of these is the tracking system used in large scale manufacturing. For example, in the aerospace industry when a large airplane is built tracker systems are used to ensure that parts are positioned and connected with a micrometer accuracy.
These lasers are also used in the semiconductor industry to inspect wafers on a nanometer scale or they can be used in the gyroscopes used for plane navigation for long distance navigation.
What other specialized lasers are TOPTICA currently working on?
We are working on visible range lasers at 780 nm and at 850 nm. We want to make these lasers both tunable and also ultra-stable so we can use them in atomic clocks.
We plan to use the lessons we have learnt developing the 633 nm laser to create our 780 nm and 850 nm lasers.
How prevalent do you expect miniaturized laser technology to become?
We expect the HeNe 633 nm to be very popular. There is already an established market for this type of laser and we expect our high end users to be extremely happy once we offer them a smaller, semiconductor based solution.
It will take a little longer for our other lasers, which we expect to be used in next-generation quantum applications. For starters, they are going to take a little longer to develop and also we want to build a prototype of an atomic clock before introducing them to the public. First commercial applications can include railroad monitoring or oil & gas exploration scenarios via distributed acoustic sensing.
The compact multi-laser spectrometer will most likely find its first application in compact flow-cell spectrometers for clinical applications.
Where can our readers find out more about laser miniaturization and TOPTICA Photonics?
The best place to go would be our website .
We have also recently published articles on laser miniaturization which you can view using the links below;
 Compact single-mode diode laser in the visible spectral range; Christian Nölleke, Patrick Leisching, Gunnar Blume, Daniel Jedrzejczyk, Johannes Pohl, David Feise, Alexander Sahm and Katrin Paschke; Proc. SPIE 10082, Solid State Lasers XXVI: Technology and Devices, 1008225 (February 17, 2017);
 Photonic-integrated circuits for multi-color laser engines; Sebastian Romero-García, Thomas Klos, Edwin Klein, Jonas Leuermann, Martin Büscher, Patrick Leisching and Jeremy Witzens; Proc. SPIE 10108, Silicon Photonics XII, 101080Z (March 2, 2017); doi:10.1117/12.2250758
 633-nm single-mode laser diode module with PM fiber output; G. Blume, D. Jedrzejczyk, J. Pohl, D. Feise, A. Sahm, B. Eppich, C. Nöllecke, P. Leisching and K. Paschke; Proc. SPIE 10100, Optical Components and Materials XIV, 1010018 (February 16, 2017);
About Dr. Patrick Leisching
With his roots in ultrashort laser physics at Technical University Munich, PhD in the THz group of Prof. Kurz at RWTH Aachen, first Post-Doc position in Paris at the Ecole Polytechnique and developing fiber lasers at Max-Born Institute in Berlin, Dr. Patrick Leisching has gained his industrial experience as research scientist, project leader and department head in the telecommunication industry with Siemens and later also at Nokia Siemens Networks.
Dr. Patrick Leisching joined TOPTICA in March 2010 and he is the driving force for the technology development spanning the full width of the TOPTICA product spectrum.
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