33 research outputs found
10 THz Ultrafast Function Generator - generation of rectangular and triangular pulse trains-
We report the synthesis of arbitrary optical waveforms by manipulating the
spectral phases of Raman sidebands with a wide frequency spacing line-by-line.
Trains of rectangular and triangular pulses are stably produced at an ultrahigh
repetition rate of 10.6229 THz, reminiscent of an ultrafast function generator.Comment: 7 Pages, 5 Figure
Freely designable optical frequency conversion in Raman-resonant four-wave-mixing process
Nonlinear optical processes are governed by the relative-phase relationships among the relevant electromagnetic fields in these processes. In this Report, we describe the physics of arbitrary manipulation of Raman-resonant four-wave-mixing process by artificial control of relative phases. As a typical example, we show freely designable optical-frequency conversions to extreme spectral regions, mid-infrared and vacuum-ultraviolet, with near-unity quantum efficiencies. Furthermore, we show that such optical-frequency conversions can be realized by using a surprisingly simple technology where transparent plates are placed in a nonlinear optical medium and their positions and thicknesses are adjusted precisely. In a numerical simulation assuming practically applicable parameters in detail, we demonstrate a single-frequency tunable laser that covers the whole vacuum-ultraviolet spectral range of 120 to 200 nm
Arbitrary manipulation of amplitude and phase of a set of highly discrete coherent spectra
We describe the attractive optical nature of highly discrete coherent spectra. We show that the relative amplitude and phase of such spectra can be almost arbitrarily manipulated by simply placing three fundamental optical elements—namely, a waveplate, polarizer, and dispersive plate—on an optical axis and then controlling their thicknesses. We also describe the relevant physical mechanism. Furthermore, as a typical application of this optical nature, we demonstrate arbitrary optical waveform generation in a numerical experiment, and we discuss its limitations as an optical-wave manipulation technology and how we can overcome these limitations
Coherent phonon induced optical modulation in semiconductors at terahertz frequencies
The coherent modulation of electronic and vibrational nonlinearities in atoms
and molecular gases by intense few-cycle pulses has been used for high-harmonic
generation in the soft X-ray and attosecond regime, as well as for Raman
frequency combs that span multiple octaves from the Terahertz to Petahertz
frequency regions. In principle, similar high-order nonlinear processes can be
excited efficiently in solids and liquids on account of their high nonlinear
polarizability densities. In this paper, we demonstrate the phononic modulation
of the optical index of Si and GaAs for excitation and probing near their
direct band gaps, respectively at ~3.4 eV and ~3.0 eV. The large amplitude
coherent longitudinal optical polarization due to the excitation of
longitudinal optical (LO) phonon of Si (001) and LO phonon-plasmon coupled
modes in GaAs (001) excited by 10-fs laser pulses induces effective amplitude
and phase modulation of the reflected probe light. The combined action of the
amplitude and phase modulation in Si and GaAs generates phonon frequency combs
with more than 100 and 60 THz bandwidth, respectively.Comment: 15 pages, 11 figure
Generation of five phase-locked harmonics by implementing a divide-by-three optical frequency divider
We report the generation of five phase-locked harmonics, f_1: 2403 nm, f_2:
1201 nm, f_3: 801 nm, f_4: 600 nm, and f_5: 480 nm with an exact frequency
ratio of 1 : 2 : 3 : 4 : 5 by implementing a divide-by-three optical-frequency
divider in the high harmonic generation process. All five harmonics are
generated coaxially with high phase coherence in time and space, which are
applicable for various practical uses.Comment: 6 pages, 6 figure
Generating arbitrary polarization states by manipulating the thicknesses of a pair of uniaxial birefringent plates
We report an optical method of generating arbitrary polarization states by
manipulating the thicknesses of a pair of uniaxial birefringent plates, the
optical axes of which are set at a crossing angle of {\pi}/4. The method has
the remarkable feature of being able to generate a distribution of arbitrary
polarization states in a group of highly discrete spectra without spatially
separating the individual spectral components. The target polarization-state
distribution is obtained as an optimal solution through an exploration. Within
a realistic exploration range, a sufficient number of near-optimal solutions
are found. This property is also reproduced well by a concise model based on a
distribution of exploration points on a Poincar\'e sphere, showing that the
number of near-optimal solutions behaves according to a power law with respect
to the number of spectral components of concern. As a typical example of an
application, by applying this method to a set of phase-locked highly discrete
spectra, we numerically demonstrate the continuous generation of a vector-like
optical electric field waveform, the helicity of which is alternated within a
single optical cycle in the time domain.Comment: 7 pages, 5 figure
Generation of five phase-locked harmonics by implementing a divide-by-three optical frequency divider
We report the generation of five phase-locked harmonics, f1:2403  nm, f2:1201  nm, f:801  nm, f4:600  nm, and f5:480  nm with an exact frequency ratio of 1:2:3:4:5 by implementing a divide-by-three optical frequency divider in the high harmonic generation process. All five harmonics are generated coaxially with high phase coherence in time and space, which are applicable for various practical uses