Many ordinary hydrocarbon molecules absorb light in the middle infrared range – and this often makes them candidates for working environments lasers emitting in this part of the spectrum. List of application is wide – from medical diagnostics to registration of certain substances in the exhaled gases to the notorious ill, but still far from the introduction of the system of identification of drunk drivers.
… So, it seems to us, science has succeeded to make a big step forward on this path.
Favor of such methods is difficult to deny. Acetone, for example, characterizes the breath of diabetics and formaldehyde can give breast cancer in the early stages, while varying the concentration of carbonyl sulphide – supporting liver condition.
Lasers in the middle of IR-range – hope surgery because they provide less scatter on fabrics and thus less damage to the area around the notch. And, of course, do not forget your favorite entertainment humanity like killing their own kind: the military, too, dream of efficient systems in this range – from target illumination at night to dazzle missiles with IR guidance.
But while it is rather a potential: lasers for this part of the spectrum of crystals cumbersome and expensive, and the fiber can be either on quartz, rather murky in the middle-IR range, or a zirconium fluoride – and even from these two words is obvious why this not the most practical option …
In addition, the transitions leading to the emission of photons in the ions of rare earth elements, is much higher than the ground state – that is, between the wavelength of the emitted laser light and the pump light is a big difference. And overall efficiency suffers greatly from this.
Besides, going into the excited state of the ion has a long and goes bad, what can stop the generation of radiation in general (the emission of a photon to the next energy level shift is difficult to say) or drop it even more effective.
Physicists from the University of Adelaide (Australia), headed by Ori Henderson-Sapir ( Ori Henderson-Sapir ) tried to apply a double pumping of such lasers. First, not very energetic, takes a long-lived low-energy ions in the excited state. And only the second ion pump raises to a higher energy level, in which he stays long, but gives the desired wavelength radiation.
The advantage of this scheme is that, when the ions of the desired photon emission after returning to a lower energy state (such as after the first pump), they are ready for immediate excitation to the second stage. As a result, during the first experiment was designed fiber laser radiation giving 0.26 W at a wavelength of 3.5 microns. Not impressed? In vain, because it is a powerful fiber laser operating at room temperature without the use of non-linear effects, and at the same time and still champion wavelength lasers operating in such an environment.
If previously the efficiency of lasers, which operated in the middle infrared range does not exceed 3%, then this time failed to reach 18%, with no significant rise in price and complexity of the scheme. However, we are not very accurately put it: in fact, it was cheaper. The fact that the two pump means applied cost less than the conventional one, since each of them had a significantly lower power.
Although it is the laser power is sufficient only for diagnostic applications in medicine and too small for the military or laser surgery, fiber lasers inherent scalability gives reason to believe that in the coming years, double pump lead them to an effective level in these areas.
To further simplify the diagnostic use of your device, the researchers are now working on its customizability, intending to reach controlled change in the wavelength of the emitted wavelength range 3.3-3.8 microns, which allow the detection of different molecules – indicators of diseases with the same instrument.