Virtual Journal of Laser

There are significant benefits to medical laser surgeries performed with mid-infrared wavelengths, including the ability to select laser parameters in order to minimize photochemical and thermal collateral damage. It has been shown that a wavelength of 6.1 μm is optimal when high ablation efficiency and minimal collateral damage is desired in biological soft tissues. Historically, free electron lasers were the only option for ablating tissue at this wavelength due to their ample pulse energy and average power. In recent years, new sources are being developed for this wavelength that can successfully ablate tissue. These alternative sources have different pulse structures and pulse durations than free electron lasers, motivating investigation of how these parameters affect the ablation process. Here, we present the pulse duration dependence for mid-IR laser ablation of biological tissues at a wavelength of 6.1 μm on a tissue phantom of cooked egg white. The crater shape, depth, and volume all changed in a significant, nonmonotonic manner as the laser pulse duration was increased from 100 ns to 5 μs.

The cancer burden is increasing worldwide and there is a need to develop new technologies for cancer diagnosis. Confocal laser endomicroscopy (CLE) is a minimally invasive optical technique that enables in vivo confocal imaging of tissue structures. With the use of fluorescent dyes, the technique allows confocal fluorescence endomicroscopy of tissue from surface to subsurface layers. CLE has been applied to the surveillance and diagnosis of cancer in numerous clinical studies recently, and also holds potential for optical and guided biopsy procedures. The first part of this mini review is focused on the application of CLE for cancer detection and surveillance. The second part is focused on the application of CLE to imaging of the oral cavity. We have previously demonstrated the potential of CLE for diagnostic imaging of oral cavity lesions. To move toward real-time 3-D imaging, we interfaced an endomicroscope to an embedded computing system. The prototype system is capable of automated image acquisition and real-time volume rendering. Rendering results provide topographical and depth information.

Tissue destruction from electrical injury is devastating and hard to treat. Unfortunately, the pathophysiology of electrical trauma is still not well understood. We have developed a suite of tools aimed at investigating damage due to high voltage shock on the skin using a rat model. Electrical injuries were created with a custom made high-tension shock system and a spectroscopic system, based on spatial frequency domain imaging, was used to determine optical properties of electrically injured tissues. The extrapolated values of absorption and scattering coefficients at six different wavelengths were then utilized to monitor parameters of interest such as tissue oxygen saturation, methemoglobin volume fraction, and hemoglobin volume fraction at four time intervals post injury. An FLIR thermal camera was used to record skin temperature during the electrical shock. Finally, a laser Doppler imaging apparatus was used to assess tissue perfusion. In this paper, the results of experiments conducted on a rat model and discussions on the systemic changes in tissue optical properties before and after electrical shock are presented.

Recent progress in the development of femtosecond-pulse fiber lasers with parameters appropriate for nonlinear microscopy is reviewed. Pulse shaping in lasers with only normal-dispersion components is briefly described, and the performance of the resulting lasers is summarized. Fiber lasers based on the formation of dissipative solitons now offer performance competitive with that of solid-state lasers, but with the benefits of the fiber medium. Lasers based on self-similar pulse evolution in the gain section of a laser also offer a combination of short pulse duration and high pulse energy that will be attractive for applications in nonlinear bioimaging.

Laser immunotherapy (LIT) is an in situ autologous cancer vaccine (inCVAX) that induces a systemic immune responses through a local intervention. The effect of LIT depends on two major interactions: a selective photothermal interaction and an active immunological stimulation. The selective photothermal interaction can help release tumor antigens, which can stimulate specific antitumor immunity in the host. The elevated expression of heat-shock protein and the local application of immunoadjuvant further enhance the immune responses. The safety and effectiveness of LIT have been tested in preclinical studies and in preliminary clinical trials. Tumor samples from breast cancer patients treated by LIT were analyzed using histochemical methods. Preliminary results showed a change in T cells after LIT treatment, indicating strong induced immune responses. LIT may be proven to be a feasible treatment modality for metastatic cancers.

Operational and environmental stability of ultrafast laser systems is critical for their applications in practical biophotonics. Mode-locked fiber lasers show great promise in applications such as supercontinuum sources or multiphoton microscopy systems. Recently, substantial progress has been made in the development of all-fiber nonlinear-optical laser control schemes, which resulted in the demonstration of highly stable monolithic, i.e., not containing any free-space elements, lasers with direct fiber-end delivery of femtosecond pulses. This paper provides an overview of the progress in the development of such all-fiber mode-locked lasers based on Yb-fiber as gain medium, operating at the wavelength around 1
$mu$m, and delivering femtosecond pulses reaching tens of nanojoules of energy.

We report a high-speed time-multiplexing dual wavelength band swept laser source based on an optical parametric amplifier. A dual-band swept-source optical coherence tomography (OCT) system is implemented to demonstrate the advantage of a second wavelength band for fast spectroscopic OCT (SOCT). The innovative time-multiplexing architecture greatly reduces the complexity of the coupling and detecting configuration in comparison with the previous dual-band swept-source setup. We demonstrate the optical parametric amplification’s characteristics as a dual-band generator and applied the source to firstly achieve the SOCT around 1550 nm.

In this paper, we compare the sensitivities of the two optical modalities, laser pulse time-of-flight (TOF) and optical coherence tomography (OCT), in regard to glucose sensing within the range of 0–1000 mg/dL in flowing blood and tissue-mimicking liquid (Intralipid). We show that TOF technique is more sensitive than OCT, as well for blood as for Intralipid measurements. In the case of TOF technique, glucose sensitivity in Intralipid is higher than in blood. We speculate that all this is associated with longer pathlengths of detected photons in TOF than in OCT, which is confirmed by comparison with Monte Carlo simulations.

The 23 papers in Part 1 of this special issue on biophotonics can be divided into the following sections: advanced bioimaging and microscopy; novel approaches in biophotonic diagnostics and therapeutics; multimodal biosensing techniques; advanced nanobiophotonics; and novel laser, fiber-optic, and electro-optic biophotonic tools and devices.

Cancer therapy utilizing the molecular layer deposition (MLD) and the self-organized lightwave network (SOLNET) is proposed. The MLD is a growth method, in which different kinds of molecules are sequentially provided to a substrate to synthesize organic tailored materials with designated molecular arrangements. The first proposal is the selective delivery of multifunctional materials, containing luminescent molecules for imaging, sensitizers for photodynamic therapy, paramagnetic agent, and so on, to cancer cells by the MLD. The second proposal is the in situ synthesis of drugs, especially, large and toxic ones, at cancer cell sites by the MLD to deliver the drugs efficiently deep inside the cancer without attacking normal cells. The third proposal is the SOLNET-assisted laser surgery. After luminescent molecules are adsorbed in cancer cells by the MLD, a write beam is introduced from an optical fiber into the area containing cancer cells through photoinduced refractive index increase materials to construct self-aligned optical waveguides of the SOLNET connecting the optical fiber to the cancer cells. Surgery laser beams are guided to cancer cells by the SOLNET.