Holmium Advanced Laser Systems – a Better Choice for Q-switched Operations than Thulium Fiber Laser

Holmium Advanced Laser Systems

Performance of Rare-Earth Ions

Trivalent rare earth ions Tm3+ and Ho3+ show extraordinary results for the high power continuous wave and pulsed laser operation in 2 µ wavelength range. Thulium fiber laser is, in general, better for CW operations, when holmium laser is preferred for pulsed and q-switched lasers operations because of its high gain. However, holmium can be excited around 1.9 µ for an efficient operation at 2.1 µ, or it needs to exploit some energy transfer from thulium or ytterbium.

Evolution of Holmium Laser Products

Before recently, holmium laser products were created as co-doped systems, because there weren’t any laser diodes that could provide wavelength ranges for pumping Ho3+ ions. Mostly, thulium co-doping was used, because its ions cross relaxation process properties. Currently, the most potential option to reach the highest output powers is in-band pumping of Ho:YAG crystals. It is possible in 1.9 µ wavelength range.

Industrial and LIDAR Applications

There are a lot of different applications that need short laser pulses with high pulse energies or high CW powers at the 2.1 µ wavelength, which makes holmium lasers in high demand on the market. Mainly, holmium advanced laser systems are created using thulium crystals or fiber lasers for pumping. Moreover, 2.1 µ wavelength is eye safe, because the emission doesn’t reach the retina, which makes it not dangerous for eyes. This wavelength range makes holmium laser in demand for commercial use, especially for LIDAR systems, which operate similarly to radars. 2 µ wavelength allows one to absorb certain atmospheric gasses (e.g. H2O, CO2, N2O) to detect and to analyse them. One of the key advantages of this laser for LIDAR technology is the capability to detect specific lighter atmospheric gasses and molecules. It has a greater potential than thulium fiber laser in chemical and petroleum industries due to safety and quality control as well as in medicine and environmental research.

Medical Applications

Moreover, holmium laser is very promising in terms of medical applications. High water absorption allows performing extra precise surgeries; 2.1 µ emission coagulation effects minimize bleeding. Ho:YAG penetrates into a soft tissue at the depth of 300 µ. However, thulium fiber laser has its own advantages in performing surgical procedures. Holmium laser systems have a lot of potential and, definitely, require further developments and research. They can be applied in a lot of different industries for various purposes, including spectroscopy, sensing and surgery.

Atomic Cooling: scientific laser systems (laboratory laser, laser equipment)

Atomic Cooling

Principles of Atomic Cooling

Since 1976 scientists have been working on the idea of controlling (cooling, trapping) atoms with laser equipment. The atom trapped in the laboratory laser beam absorbs photons and becomes excited; photons can transmit their impulses to the atom. When atoms are de-excited, they reemit photons in random directions. As a result the atom experiences light pressure in the direction of the laser beam spread. Atoms get excited when the frequency drift is similar to the optical transition.
If an atomic gas is irradiated from each side with the laser frequency that is less than that of an atomic transition, the number of slow atoms grows leading to the temperature decrease.

First Experiments in Atomic Cooling

The first atomic cooling experiment was conducted in the laser spectroscopy department of ISAN. Using the laboratory laser in dilatational cooling the transverse velocity is increased due to the growth of fluctuation atom impulses when laser light photons are absorbed and emitted. At some point of dilatational cooling its speed becomes comparable to that of the transverse one and for further dilatational cooling the transverse cooling of the beam has to be performed. First time it was done in the laboratory in 1984, and the record atom temperature of 0.003 K was reached. This temperature is close to the Doppler cooling.

Impact on Atomic Manipulation

All these experiments with scientific laser systems allowed decreasing the energy of neutral atoms to the levels when their space localization with electric, magnetic and laser fields became possible. This opened new opportunities for sharp decreasing the temperature of the atoms that were already cooled down.

Global Research and Techniques

ISAN was the first laboratory in the world to start experiments with controlling the atomic motion with laser equipment. Today there are dozens of laboratories around the world that work on this aspect using different scientific laser systems.
Different methods exist to cool neutral and excited particles (atoms, molecules and their ions), they are based on various dissipation processes. For example, electric cooling of excited particles is done through the collision of hot atoms and cold electron fluid. However, the most popular and effective way to cool neutral atoms (and localized ions as well) is the collision of those atoms and laser beam photons.