This paper describes the development and implementation of 3 μm lasers for myringotomy and microsurgery. Two different lasers were investigated. The first, an Er-doped, CW zirconate glass fiber laser optically pumped by a 970 nm diode laser, emitted > 1 W of CW power at 2.76 μm with concomitant green incoherent emission that served as a convenient visible illumination beam. The second, a 1 W CW Er:YAG solid-state laser also optically pumped by a 970 nm diode laser, emitted > 1 W of CW power at 2.94 μm, coincident with the strongest infrared water absorption peak. Running CW, both lasers are expected to avoid the loud acoustical shocks associated with pulsed lasers. Myringotomies were carried out with the Er:YAG laser on anaesthetized guinea pigs and the effects of the laser were documented. Laser ablated samples of tympanic membrane, soft tissue and bone were histologically examined. Histology results indicated that the CW Er:YAG laser is a potential candidate for a new myringotomy tool and possibly for otologic microsurgery, but deliverable power levels need to be increased to the 2 W (or higher) level. This work was funded under NIH SBIR Grant No. 5R44DC004899.
Multiphoton microscopy is a powerful technique for high spatial resolution thick tissue imaging. In its simple version, it
uses a high repetition rate femtosecond oscillator laser source focussed and scanned across biological sample that contains fluorophores. However, not every biological structure is inherently fluorescent or can be stained without causing biochemical changes. To circumvent these limitations, other non-invasive nonlinear optical imaging approaches are currently being developed and investigated with regard to different applications. These techniques are: (1) second harmonic generation (SHG), (2) third harmonic generation (THG), and (3) coherent anti-Stokes Raman scattering
(CARS) microscopy. The main advantage of the above mentioned techniques is that they derive their imaging contrast
from optical nonlinearities that do not involve fluorescence process. As a particular application example we investigated
collagen arrays. We show that combining SHG-THG-CARS onto a single imaging platform provides complementary information about the sub-micron architecture of the tissue. SHG microscopy reveals the fibrillar architecture of collagen arrays and confirm a rather high degree of heterogeneity of χ<sup>(2)</sup> within the focal volume, THG highlights the boundaries between the collagen sheets, and CH<sub>2</sub> spectroscopic contrast with CARS.
We report an application of the combined third order microscopy techniques to reveal structure and morphology of the
peripheral nerve in mice. The resonant Coherent Anti-Stokes Raman Scattering (CARS) and third harmonic generation
(THG) techniques have been applied to visualize structure of the myelinated peripheral axon. While CARS was quite
efficient in selective imaging of the cladding layer via characteristic Raman active vibrations of dense lipid structures
constituting the layers, the THG microscopy helped to clearly reveal the degree of optical and nonlinear optical
inhomogeneity of the axon core (that may have further important implications).