Treatment of murine cutaneous melanoma with near infrared light.

Treatment of cutaneous melanoma (M-3 and B16-F10 implanted in mice) with rapidly-scanned, tightly-focused near infrared light elicits selective destruction of tumor tissue. A single laser treatment yielded complete eradication in >90% of B16-F10 tumors with thicknesses of approximately 3 mm; amelanotic M-3 tumors proved less responsive (ca 25% clearance rate). In addition to local tumor destruction, laser treatment of B16-F10 tumors in immunocompetent mice stimulated enhanced cytokine levels (interleukin-2 and interleukin-10) within treated tumor tissues and rejection of tumor cells upon a subsequent challenge dose. Such an antitumor immune response may lead to improved outcomes at both the treatment site and at sites of distant metastasis.

Simultaneous two-photon activation of type-I photodynamic therapy agents.

The excitation and emission properties of several psoralen derivatives are compared using conventional single-photon excitation and simultaneous two-photon excitation (TPE). Two-photon excitation is effected using the output of a mode-locked titanium: sapphire laser, the near infrared output of which is used to promote nonresonant TPE directly. Specifically, the excitation spectra and excited-state properties of 8-methoxypsoralen and 4'-aminomethyl-4,5,8-trimethylpsoralen are shown to be equivalent using both modes of excitation. Further, in vitro feasibility of two-photon photodynamic therapy (PDT) is demonstrated using Salmonella typhimurium. Two-photon excitation may be beneficial in the practice of PDT because it would allow replacement of visible or UV excitation light with highly penetrating, nondamaging near infrared light and could provide a means for improving localization of therapy. Comparison of possible laser excitation sources for PDT reveals the titanium: sapphire laser to be exceptionally well suited for nonlinear excitation of PDT agents in biological systems due to its extremely short pulse width and high repetition rate that together provide efficient PDT activation and greatly reduced potential for biological damage.

Coherent-burst laser ranging: decoupling resolution and unambiguous range.

A novel signal encoding and decoding method for laser ranging is proposed and experimentally demonstrated. The coherent-burst method uses a quasi-continuous interrupted burst of modulated laser radiation to achieve high-precision ranging at all distances. Both time of flight and phase shift are determined based on an amplitude-modulation pattern that has electronic coherence with a master oscillator. High-frequency modulation provides high absolute precision, while measured temporal delay from transmission to reception eliminates potential uncertainty from aliasing. The method is demonstrated with low-power diode lasers that can be modulated at frequencies in excess of 250 MHz.

Exchange of oxygen isotopes in carbon dioxide-phosphoric [correction of phosporic] acid systems.

The rate of exchange of isotopes of oxygen between solutions of concentrated phosphoric acid and CO2 was measured as a function of temperature, acid strength (pressure of water in equilibrium with the solution), pressure of CO2, and surface area of the reaction vessel. At 75 degrees C, significant exchange was found to occur even for the "anhydrous" phosphoric acids, those in which the nominal percentage of H3PO4 in solution is equal to or exceeds 100%. Exchange is much slower at 25 degrees C, but isotopic shifts as large as 0.1% can be observed in 95% H3PO4 at equilibration times approaching 1000 hr. Rates of exchange were found to be dependent upon the vapor pressure of water in equilibrium with the acid solutions. Exchange was found to occur primarily on the surface of the reaction vessel above the solution, with no dependence on total CO2 pressure. These observations indicate that phosphoric acids with nominal concentrations of H3PO4 approaching 105% are preferable for the minimization of exchange between CO2 samples and acid solutions during phosphorolyses of carbonate materials. Moreover, with such acids, significant time--temperature trade-offs are possible, allowing rapid preparation of CO2 at elevated temperatures.