CTH:YAG Laser Crystal as a Spontaneous Incoherent Source in the SWIR

CTH:YAG is a laser medium know for many years [1]. The atmospheric transmission properties and eye safe nature of this laser emitting at $2.1\ \mu \mathrm{m}$ make it attractive for many applications. Thanks to efficient energy transfer between Cr ³⁺ , Tm ³⁺ and Ho3+, CTH:YAG has often been pumped in the visible by flashlamps [2]. CTH:YAG has also a remarkable broadband spectrum spanning from $1.7\ \mu \mathrm{m}$ to $2.15\ \mu \mathrm{m}$ (with a maximum for the longest wavelengths around $2.1\ \mu \mathrm{m}$ as shown in fig. 1b green curve). Sensing and inspection applications are growing with the emergence of low-cost image sensors in the SWIR (Short Wavelength InfraRed) range. Illumination sources in this wavelength band are limited: halogen, black body or low power LEDs as direct emission sources, and supercontinuum or thulium ASE as fiber sources. The purpose of this work is to show that CTH:YAG opens opportunities for innovative, high-brightness, spectrally-broadband and incoherent sources in the SWIR.