Some applications of ultrashort laser pulses in biology and medicine

Abstract

Ultrashort laser pulses are finding increasing applications in biology and medicine. Such pulses can be used directly or after non-linear modification. Direct utilization includes propagation studies in scattering media with applications in optical mammography, dosimetry for photodynamic therapy and species concentration assessment. Intense continua of electromagnetic radiation of very brief duration are formed in the interaction of focused ultrashort and intense laser pulses with matter. Two different kinds of experiment using such radiation are described, employing visible radiation and x-rays, respectively. Focusing into water leads to the generation of a light continuum through self-phase modulation. The propagation of the light through tissue was studied, addressing questions related to specific tissue chromophore absorption. When terawatt laser pulses are focused onto a solid target with high nuclear charge Z, intense x-ray radiation of few ps duration and with energies exceeding hundreds of keV is emitted. Biomedical applications of this radiation are described, including differential absorption and gated-viewing imaging.

Microwave Frequency Comb Generation by Gain-Switching Versus Relaxation Oscillations

“…T HE generation of short optical pulses by semiconductor lasers (SL) is of interest in communications, spectroscopy, plasma formation, medicine, and elsewhere [1]- [3]. If the pulses are periodically spaced, the power spectral density of the photodetected optical intensity I(t) forms a microwave (MW) frequency comb (MWC).…”

Theoretical and experimental study of blurring of a femtosecond laser pulse in a turbid medium

“…Study of propagation of the pulsed optical radiation in a random medium is topical for various ladar problems [1][2][3][4][5][6][7][8]. Modern medical interest in optical diagnostics of live systems and organisms as well as creation of compact sources of femtosecond radiation in the near infrared range (radiation wavelength λ = 700-1000 nm) determine the development of noninvasive optical methods of observing biological tissues with high spatial resolution, among which multiphoton fluorescent microscopy should be emphasized [9][10][11].…”

Non-invasive imaging of optical parameters of biological tissues

“…THE DEVELOPMENT of laser-based diagnostic techniques has made a significant contribution to the non-invasive, early diagnosis and demarcation of malignant mmours (KESSEL, 1987;SVANBERG, 2001) and the investigation of blood and tissue oxygenation dynamics (COPE and DELPY, 1988;LIU et al, 2000). These applications of lasers are primarily based on the interaction of light with biological tissues (TUCHIN, 1997), leading to their scattering and absorption within the medium (WILSON, 1995).…”