Laser Diodes (LDs) are becoming increasingly attractive as small and reliable laser-beam sources,
with applications that include pumping of solid-state lasers, materials processing, and medicine. However,
because of the poor beam quality of its output beam, which affects its direct applications, thus people pay
much attention on how to shape the beam of the high power laser diode bar effectively. In this paper some
typical beam shaping methods, shaping principles, key techniques and shaping effects are discussed. Based on
geometric optical analysis, the collimation properties of the off-axis light wave through a cylindrical lens and
elliptical cylindrical lens are separately analyzed in detail by rays tracing formulas, the collimation effects of
them are also made a comparison.
The spatial resolution of a space communication system is constrained by the diffraction limit of the telescope aperture.
In a frequency-modulated continuous wave (FMCW), the frequency of the laser is ramped, and the frequency difference
between the reflected wave and a local-oscillator wave is monitored. For maximum performance the frequency ramping
should be linear. Linear frequency modulation (LFM) of the laser emission is a commonly used method for improving
the detection sensitivity. Because of the available technology, techniques that use relatively low modulation frequencies
were implemented first. In the early 1980's, an elegant measurement method based on frequency modulation opened up
new applications for spectroscopy with spectrally modulated laser light. In this paper we analyzed systematically the
principles of saw tooth-wave optical FMCW. For optical FMCW, because all the practical optical waves are from single-mode
lasers, and because the laser beam from a single-mode laser is coherent in space due to the nature of stimulated
emission, the spatial coherence is always satisfied, and therefore only temporal coherence need be considered. The chip
signal, experimental system, and results are analyzed and discussed.
Owing to its compactness, lightness, and low cost, laser diodes (LD) play an important role as a coherent source in
various fields of technology. Because of the waveguide properties of their active areas, laser diodes generate large
divergence-angle beams with elliptically shaped intensity profiles. And the beam of LD has astigmatism. So it is difficult
to collimate LD beams effectively. The binary optical elements are small, light, easy to be copied and able to realize
multi-purpose integrated, especially suits for the beam shaping of laser diode array. Based on accurate far-field model of
high-power laser diode, a design method of binary optical element for laser diode beams, which can correct the
astigmatism of the laser beam, has been developed, and the principle and process has been given in detail. The method is
simple and practical. The relief surface of the element is of multiphase structure. And its theoretical diffraction efficiency
is as high as 95%.
Acoustic landmine detection (ALD) is a technique for the detection of buried landmines including non-metal mines. An
important issue in ALD is the acoustic excitation of the soil. Laser excitation is promising for complete standoff
detection using lasers for excitation and monitoring. Our method is based on a YAG laser at 1.06 um not He-Ne laser or
loudspeaker with acoustic excitation and on an erbium fiber laser at 1.54 um not microphone with LDV detection. An
analysis is given to show the potential and the inherent limitations of the technique. In the present paper we have tried to
answer two questions on locating landmines: (1) too many false alarm; (2) plastic landmine. The answer to the first
question is the LDV with an erbium fiber laser at 1.54 um. The second answer is YAG laser at 1.06 um induce acoustic.