COVID-19 and Tinnitus.

Coronavirus disease 2019 (COVID-19) is an infectious respiratory disease caused by the severe acute respiratory syndrome coronavirus 2, brings with it a plethora of health concerns. Although most people have mild symptoms, which are respiratory in nature, some experience neurological symptoms, central nervous system manifestations, peripheral nervous manifestations, and skeletal muscle manifestations. But the damaging impact of COVID-19 virus on the hearing organs in the inner ear is a new finding yet to be explored. Currently, there is little evidence published connecting novel coronavirus and tinnitus directly. But according to the American Tinnitus Association, preexisting behavioral conditions make it more likely for patients to experience tinnitus due to the stress and depression associated with social isolation and infection avoidance. Hearing loss and Tinnitus is a common pathology seen in otolaryngology and there are numerous papers in literature describing its associations with other infections. However, this is the first reported case of hearing loss and tinnitus in a COVID-19 patient, in the State of Qatar, and this case report strives to contribute to the ocean of literature highlighting the need for otorhinolaryngologists to be aware of its correlation with COVID-19 virus.

Narrow line width operation of a 980 nm gain guided tapered diode laser bar.

We demonstrate two different schemes for the spectral narrowing of a 12 emitter 980 nm gain guided tapered diode laser bar. In the first scheme, a reflective grating has been used in a Littman Metcalf configuration and the wavelength of the laser emission could be narrowed down from more than 5.5 nm in the free running mode to 0.04 nm (FWHM) at an operating current of 30 A with an output power of 8 W. The spectrum was found to be tunable within a range of 16 nm. In the second scheme, a volume Bragg grating has been used to narrow the wavelength of the laser bar from over 5 nm to less than 0.2 nm with an output of 5 W at 20 A. To our knowledge, this is the first time spectral narrowing has been performed on a gain guided tapered diode laser bar. In the Littman Metcalf configuration, the spectral brightness has been increased by 86 times and in the volume Bragg grating cavity the spectral brightness has been improved over 18 times when compared to the free running operation. These schemes could be also extended for other wavelengths of interest in the future.

16 W output power by high-efficient spectral beam combining of DBR-tapered diode lasers.

Up to 16 W output power has been obtained using spectral beam combining of two 1063 nm DBR-tapered diode lasers. Using a reflecting volume Bragg grating, a combining efficiency as high as 93.7% is achieved, resulting in a single beam with high spatial coherence. The result represents the highest output power achieved by spectral beam combining of two single element tapered diode lasers. Since spectral beam combining does not affect beam propagation parameters, M2-values of 1.8 (fast axis) and 3.3 (slow axis) match the M2-values of the laser with lowest spatial coherence. The principle of spectral beam combining used in our experiments can be expanded to combine more than two tapered diode lasers and hence it is expected that the output power may be increased even further in the future.

Spectral beam combining of a 980 nm tapered diode laser bar.

We demonstrate spectral beam combining of a 980 nm tapered diode laser bar. The combined beam from 12 tapered emitters on the bar yielded an output power of 9.3 W at 30 A of operating current. An M2 value of 5.3 has been achieved along the slow axis. This value is close to that of a free running single tapered emitter on the bar at the same current level. The overall spectral beam combining efficiency was measured to be 63%.

980 nm high brightness external cavity broad area diode laser bar.

We demonstrate off-axis spectral beam combining applied to a 980 nm high power broad area diode laser bar. The experiments yielded 9 W of optical power at 30 A of operating current and the measured M2 values of the combined beam from 12 emitters were 1.9 and 6.4 for the fast and the slow axis, respectively. The slow axis beam quality was 5-6 times better than the value obtained from a single emitter in free running mode. A high brightness of 79 MW/cm2-str was achieved using this configuration. To our knowledge, this is the highest brightness level ever achieved from a broad area diode laser bar.