An Yb fiber laser oscillator with sub-30 fs pulses compressed by MIIPS is tested for multiphoton
microscopy. It leads to greatly improved third harmonic generation images. Multiphoton fluorescence,
second and third harmonic generation modalities are compared on stained microspheres and unstained
We demonstrate three-dimensional Airy-Bessel optical wave packets that propagate without broadening in time or space.
We also demonstrate the non-dispersive and the self-healing nature of the Airy pulse. Since the propagation of an Airy-
Bessel wave packet does not critically depend on the material properties, we believe the Airy-Bessel wave packet will
find its usage in applications as practical devices.
Recent work has shown that stable, highly-chirped pulses can be generated by all-normal-dispersion fiber lasers. Pulses
in the ~100-ps range but with bandwidth to support ~500-fs pulses are produced, with energies of tens of nanojoules and
at repetition rates of 1 MHz and below. The chirped pulses can be compressed to near the transform limit. Lasers that
produce pulses with such giant chirp should greatly simplify chirped-pulse fiber amplifiers. After a brief review of fiber
lasers based on dissipative solitons, recent developments will be summarized.
A femtosecond fiber system based on nonlinear chirped-pulse amplification is investigated. It is the first investigation on
pulse properties from all-normal-dispersion fiber laser after amplification. Nonlinearities due to fibers are carefully
managed. The system generates up to 5-μJ pulses, and delivers near diffraction-limit beam (M<sup>2</sup> < 1.1), polarization
extinction ratio (40 dB) and polarization extinction ratio (36 dB).
This article will review several new modes of pulse formation and propagation in fiber lasers. These modes
exist with large normal cavity dispersion. Self-similar evolution can stabilize high-energy pulses in fiber lasers,
and this leads to order-of-magnitude increases in performance: fiber lasers that generate 10-nJ pulses of 100-fs
duration are now possible. Pulse-shaping based on spectral filtering of a phase-modulated pulse yields similar
performance, from lasers that have no intracavity dispersion control. These new modes feature highly-chirped
pulses in the laser cavity. Instruments based on these new pulse-shaping mechanisms offer performance that is
comparable to that of solid-state lasers but with the major practical advantages of fiber.
In the past 30 years major advances in medical imaging have been made in areas such as magnetic resonance
imaging, computed tomography, and ultrasound. These techniques have become quite effective for structural
imaging at the organ or tissue level, but do not address the clear need for imaging technologies that exploit
existing knowledge of the genetic and molecular bases of disease. Techniques that can provide similar
information on the cellular and molecular scale would be very powerful, and ultimately the extension of such
techniques to in vivo measurements will be desired. The availability of these imaging capabilities would allow
monitoring of the early stages of disease or therapy, for example.
Optical techniques provide excellent imaging capabilities, with
sub-micron spatial resolution, and are noninvasive.
An overall goal of biomedical imaging is to obtain diagnostic or functional information about
biological structures. The difficulty of acquiring high-resolution images of structures deep in tissue presents a
major challenge, however, owing to strong scattering of light. As a consequence, optical imaging has been
limited to thin (typically ~0.5 mm) samples or superficial tissue. In contrast, techniques such as ultrasound and
magnetic resonance provide images of structures centimeters deep in tissue, with ~100-micron resolution. It is
desirable to develop techniques that offer the resolution of optics with the depth-penetration of other techniques.
Since 1990, a variety of nonlinear microscopies have been demonstrated. These include 2- and 3-photon
fluorescence microscopy, and 2nd- and 3rd-harmonic generation microscopies. These typically employ
femtosecond-pulse excitation, for maximum peak power (and thus nonlinear excitation) for a given pulse
energy. A relative newcomer to the group is CARS microscopy , which exploits resonant vibrational
excitation of molecules or bonds. The CARS signal contrast arises from intrinsic elements of cells, and thus
CARS offers the major advantages of a label-free technique. In contrast to other nonlinear microscopies, CARS
imaging is best performed with excitation pulses in the 2-7 ps range, which overlap spectrally with the desired
Raman resonances. Two synchronized excitation pulses are required at different wavelengths, and these beat to
excite the vibration.
The compensation of nonlinear phase shifts by dispersion in femtosecond fiber amplifiers is explained. Contrary to previous understanding, a chirped-pulse fiber amplifier with mismatched stretcher and compressor can out-perform a matched system when the pulse acquires a significant nonlinear phase shift.