Jelinková
The Optica Laser Congress and Exhibition will be held from 19 to 23 October in Prague, Czechia. At the Congress, Helena Jelinková, Czech Technical University (CTU) in Prague, Czechia, will give a plenary talk entitled “Solid-state lasers and their applications at the Faculty of Nuclear Sciences and Physical Engineering, CTU in Prague.” Before the meeting, OPN spoke with Jelinková to get a preview of her talk and her thoughts on developments in the field.
What do you plan to discuss in your plenary talk at the Laser Congress?
I would like to present and explain the best results achieved in our solid-state laser laboratories over the last 60 years. We have designed and constructed many lasers generating in the visible, near- and mid-infrared (IR) spectral regions. I also plan to discuss our investigations into nonlinear optical phenomena like stimulated Raman scattering, harmonics generation, and other optical parametrical processes for radiation generation. Our laboratory is focused as well on generation in various temporal regimes, from continuous-wave down to hundreds of femtoseconds.
In the past, we have concentrated mainly on noncoherent flashlamp pumping. But over the past three decades, we have designed diode-pumped solid-state lasers as well, especially compact laser sources using rare-earth and transition metal ions and microchip systems. I plan to present the main results obtained using active media based on lanthanide ions (Pr³⁺, Nd³⁺, Tm³⁺, Er³⁺, Ho³⁺, Yb³⁺, Dy³⁺) as well as transition-metal ions (Ti³⁺, Cr²⁺, Fe²⁺) embedded in various host matrices. These media enable the generation of radiation in the 0.7–6 µm spectral range across different temporal regimes.
Our parallel research was dedicated to the development of microchip lasers, paying special attention to the generation of short, nanosecond pulses in the near-infrared region, especially around wavelengths of 1.3 µm and 1.44 µm. These lasers were designed as compact monolithic systems, utilizing active Nd:YAG crystals in combination with passive saturable absorbers based on V:YAG. This configuration enabled stable and efficient pulse generation without the need for active modulation.
The lasers developed in our lab have been used in many applications, so I would like to mention some examples, like measuring the distance to artificial Earth satellites or laser systems for industry or medicine. The newly designed mid-IR lasers currently under investigation have potential applications in detection and measurement techniques within optical communication systems.
What do you think are some exciting recent developments in solid-state lasers?
In recent years, several significant and fascinating advancements have emerged in the field of solid-state lasers.
One notable area is in new active materials and broader spectral coverage. Intensive research is being carried out into new active ions (for example, Cr²⁺, Fe²⁺, Dy³⁺) and host crystals that allow the generation of radiation in the mid-infrared region (2–6 µm). This spectral range is particularly important for sensing and spectroscopic applications.
Major progress has been made in advanced diode pumping and miniaturization through improvements in semiconductor laser diodes and their integration with solid-state materials. This has enabled the development of compact, energy-efficient lasers, such as microchip lasers, which are now widely used in scientific, industrial and medical applications.
There has also been progress in passive modulation and ultrashort pulse generation. Advances in techniques such as the generation of femtosecond pulses without complex active components have made it possible to create stable, compact sources for precise measurements and applications in biomedicine and materials research.
Thanks to improved cooling systems, optimized resonator geometries, and power-scaling techniques (such as beam combining), it has become possible to significantly increase the output power of solid-state lasers while maintaining beam quality. This opens new opportunities in areas like cutting, welding, fusion, and even defense technologies.
A new trend is the integration of solid-state lasers into photonic circuits and their use in quantum optics and quantum communication systems, where compact, stable and highly coherent light sources are in high demand.
These developments not only expand the practical applications of lasers but also push the boundaries of fundamental research in physics, optics and materials science.
What applications are you looking at for solid-state lasers in the visible, near-IR and mid-IR regions?
Solid-state lasers operating in the visible, near- and mid-IR spectral regions offer a wide range of potential applications across various fields, and we’re focusing on some key areas.
Lasers generating radiation in the visible region can be used in biomedical imaging and diagnostics; lasers in the visible spectrum are used for fluorescence microscopy and ophthalmology. Precise visible lasers are essential for spectroscopy, atomic physics and optical trapping.
Laser radiation in the near-infrared region can find applications in optical communications. Lasers around 1.3 µm and 1.55 µm are widely used in fiber optic networks due to their low-loss transmission in optical fibers. Also, compact near-IR sources are ideal for distance measurement, 3D mapping and autonomous navigation systems. Near-IR lasers should be used in tissue or other biological treatment.
Mid-IR laser radiation can be used for gas sensing and environmental monitoring. Many gases have strong absorption lines in the mid-IR range, making these lasers ideal for trace gas detection and pollution monitoring. These lasers are also important in optical jamming and defense systems due to their ability to disrupt heat-seeking technologies, as well as in precise material processing, including cutting and drilling of polymers and composites.
Our current research is oriented toward developing compact, efficient and tunable solid-state lasers across these spectral ranges, with the goal of enabling or enhancing these applications through advanced laser technology.
What are some of the challenges in generating laser radiation in these wavelengths?
Generating laser radiation across the visible, near-IR, and especially mid-IR regions presents a range of technical and material challenges.
One key issue is material limitations. Not all dopant ions offer efficient lasing transitions in the desired spectral ranges, especially in the mid-IR, where suitable ions like Cr²⁺, Fe²⁺, or Dy³⁺ are more difficult to integrate into stable host matrices. Such matrices must be transparent, possess low phonon energy and exhibit suitable thermal conductivity.
Another challenge is pumping efficiency. Efficient diode pumping is well-established for the near-IR, but for visible or mid-IR transitions, matching the pump wavelength and absorption bands is more complex.
Nonlinear effects and conversion efficiency can also present issues. Nonlinear optical crystals used for wavelength conversion must be transparent in the desired spectral range and have an acceptably high effective nonlinear coefficient, long-term stability and a high optical damage threshold.
Producing high-quality mirrors, lenses and anti-reflective coatings for mid-IR wavelengths is more challenging due to increased material absorption and fabrication limitations. Additionally, in the mid-IR range, optical components such as isolators, modulators, polarizers and detectors are generally less developed and tend to be more expensive or limited in performance.
Despite these challenges, ongoing progress in materials science, crystal growth, diode technology and nonlinear optics continues to expand the capabilities of solid-state lasers across these spectral regions.
Can you tell us about the transition in your work from solid-state laser transmitters for measuring artificial Earth satellites to medical applications?
Measuring the distances to artificial satellites was one of the tasks undertaken by the solid-state laser group at our department, where our primary responsibility was the development of laser transmitters. The first systems were Q-switched ruby lasers using a rotating prism, with an additional passive switch employed to shorten the pulse duration up to 25 to 30 ns.
To improve the distance measurement accuracy, it was necessary to shorten the transmitted laser pulse. As a result, we developed and implemented systems producing pulse durations of 2 to 5 ns, and eventually down to 25 ps. Using these shorter pulse durations, the precision of the distance measurements reached such a level that further inaccuracies were primarily due to external factors, such as atmospheric effects or the number of retroreflectors on the satellite. Since additional shortening of the pulse length would no longer significantly enhance measurement accuracy, this line of research was concluded.
In parallel with satellite ranging, our laboratories also investigated medical applications of laser radiation. Our group designed a laser scalpel using a continuous-wave Nd:YAG laser emitting at wavelengths of 1.06 µm or 1.3 µm. During these studies, we realized that the same type of laser radiation used for satellite ranging (in the last version of our transmitter) could be effectively applied in ophthalmology—specifically, for removing secondary cataracts following primary cataract surgery. This led to the development of an Nd:YAG laser capable of generating short 25-ps pulses for this purpose, effectively transferring our expertise from laser transmitter design to a medical device.
Building on this foundation, we continued to focus on medical applications. Furthermore, our laboratory has developed a Q-switched ruby laser for the removal of nevi, as well as traumatic and artificial tattoos. Following the introduction of the Er:YAG laser, we also constructed a painless dental drill, further expanding the scope of our laser technologies in medicine.
While satellite ranging and medical laser applications may seem like distinct areas, they share a critical common requirement: The laser systems must be highly reliable. In satellite ranging, scientists relying on our data needed the system to perform flawlessly. In medical contexts, any failure of the laser system could pose a risk to the patient. Thus, regardless of the application, reliability and safety were always overriding.
How has spending your career at the Czech Technical University in Prague influenced your research?
Studying at the CTU in Prague, the Faculty of Nuclear Sciences and Physical Engineering, is what first brought me into contact with lasers. Our faculty offers rigorous theoretical courses that are closely integrated with hands-on laboratory work, often linked to real scientific research tasks. I began working with lasers experimentally in my fourth-year study, and I also dedicated my degree thesis and then Ph.D. thesis to this research.
Today, students gain access to laboratory work even earlier—typically in their third year, the final year of the bachelor’s program. They then continue into the master’s program, where they complete a year-long research project, culminating in their degree thesis.
Is there anything else you’d like to share with our readers?
I would just like to add that working in science—and in my case, in laser physics and technology—is truly exciting. The laws of nature cannot be influenced, which means that we sometimes encounter failure in experimental work. That makes it even more rewarding when an experiment succeeds and our assumptions are confirmed.
