Femtosecond fiber laser for medical one-photon confocal reflectance microscopy and multiphoton tomography

So far, medical confocal reflectance microscopy is based on continuous wave (cw) laser diodes operating at 830 nm, and medical multiphoton tomography (MPT) is conducted with tunable water-cooled 80 MHz femtosecond titanium:sapphire lasers with mean powers less than 50 mW. The femtosecond laser beam is guided through an optical arm. The major application is high-resolution label-free skin imaging ("optical virtual biopsy") to detect skin cancer. MPT has also been used to test anti-aging and pharmaceutical components in situ. Here, we report on the use of an ultracompact femtosecond fiber laser for high-resolution tissue imaging. In particular, the development of the PRISM AWARD 2024 winning multimodal multiphoton tomograph based on an ultracompact air-cooled 50/80 MHz fiber laser operating at 780 nm is presented. The 18x9x3.5 cm³ laser head, consisting of a pulse compression unit and a SHG crystal, is positioned inside the 360° imaging head. An optical arm or a fiber delivery for transmitting the ultrashort near-infrared laser beam is no longer required. Interestingly, the femtosecond laser pulses, used for two-photon autofluorescence and SHG imaging, are also employed to realize simultaneous high-resolution (submicron) one-photon confocal microscopy. In addition, optical metabolic imaging (OMI) by time-correlated single photon counting and fluorescence lifetime imaging (FLIM) of autofluorescent coenzymes can be performed. The fifth imaging modality of this multimodal device is white LED far-field imaging for dermoscopy and to define regions of interest for confocal and multiphoton analysis. The novel "green" 230 W femtosecond fiber laser tomograph can be operated by batteries and charged by sunlight due to the reduced power consumption by 75 % when using the fiber laser system compared to the tunable titanium:sapphire laser. High-resolution confocal and multiphoton imaging with compact fiber lasers in remote areas and on the bedside of the patient becomes a reality.