Given their many applications in material processing, remote sensing, defense, and fundamental science, lasers have undergone a tremendously fast development. This has included a constant increase in output powers, both average and peak power, since a higher output power can significantly enhance the capabilities of lasers. Currently, peak powers can reach the petawatt level with pulsed operation, whereas the average output power remains a few tens of kilowatts due to technical difficulties in reducing waste heat generation attributed to the low pumping efficiency. This useless heat generation can cause thermal stress, lowering beam quality, generating fractures in the gain medium, and leading to the reduction of the operable average power.

In order to optimize average output power with no thermally-induced detrimental side effects, the author of this Applied Optics article devises two simple expressions: a laser material efficiency and a laser material heating parameter for low quantum defect laser materials in a steady state. A laser material efficiency is simply defined as the emitted laser power divided by the absorbed pump power. In the case of a laser material heating parameter, energy conservation is used to derive the parameter by considering the difference between the absorbed power and the emitted power, divided by the emitted power, so that it can be physically understood as the local heat generation rate normalized with the emitted power. It is therefore natural to expect that either maximizing the efficiency or minimizing the heating parameter can lead to a better laser performance. Accordingly, by manipulating the ratio of the pumping wavelength to the laser wavelength within these two expressions the author first finds the suitable conditions that lead to a high laser material efficiency with a relatively low heating parameter for an ideal laser material, where the material is assumed to be perfectly radiative, linear, and optically thin. Then, to apply these conditions to more realistic laser materials, a few loss mechanisms including quenching of the laser excitation, background absorption, and fluorescence reabsorption are implanted in a laser material efficiency and heating parameter, and the author successfully evaluates the influences of the loss mechanisms on the optimization of the laser performance.

In summary, the author successfully designs the theoretical analysis to optimize the laser output power in a steady state by employing a laser material efficiency and heating parameter. By thoroughly understanding the author’s analysis, one gets deeper insights into the fundamental limitations of low quantum defect lasers.

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