Stimulated polariton scattering (SPS) is one of the most important non-collinear phase-matching nonlinear process. In SPS, the angle between the THz and pump waves is as large as 65°, so it is necessary to study the spatial intensity distributions of the pump, Stokes and THz waves effected by the non-collinear phase-matching. In this work, we take the injection-seeded terahertz wave parametric generator (is-TPG) as an example to obtain the numerical solutions of the coupled-wave equations. The simulation results are focused on the spatial-temporal intensity distributions and the energy input-output characteristics. It is notable that the spatial intensity distributions of the pump and Stokes beams along the THz-wave propagation direction are not uniform as the inputs. The pump wave is depleted along the THz-wave propagation direction while the Stokes wave is increasing at the same time.
This paper presents the tunable Stokes laser characteristics based on the stimulated polariton scattering in KTiOAsO4 crystal. With a given pumping laser wavelength of 1064.2 nm, discontinuously tunable first-Stokes wave was obtained from 1077.9 to 1079.0 nm, from 1080.1 to 1080.8 nm, from 1082.8 to 1083.6 nm, from 1085.5 to 1085.8 nm, from 1086.8 to 1088.4 nm. With a pumping pulse energy of 125.0 mJ, the maximum first-Stokes laser pulse energy at 1078.6 nm was 24.7 mJ. The second-Stokes wave at 1093.4 nm was obtained and investigated as well.
The mode competition mechanism in concentric 4-core and 7-core fiber lasers with large mode area single mode (SM)
fiber as in-phase supermode selection component is presented. The coupling coefficient between the fundamental mode
in large mode area SM fiber and each supermode in mutlicore fiber is discussed. For individual supermode in multicore
fiber, the coupling coefficient is optimized as a function of the core radius of SM fiber as well as the distance between
multicore fiber and SM fiber. The optimization results demonstrate that only two supermodes are involved in
concentric-type fiber lasing - in-phase and anti-phase supermode, owing to the negligible coupling coefficients of the
other supermodes. Furthermore, to achieve the best in-phase supermode selection, the core radius of SM fiber will be
optimized for maximum coupling coefficient difference between in-phase supermode and anti-phase supermodes. The
numerical results illustrate that in-phase supermode always dominate the output and is the highest when the distance
equals zero. Compared to conventional multicore fiber lasers with Talbot cavity, this all-fiber configuration based on
large mode area SM fiber has higher-order supermodes more efficiently suppressed and high-brightness output may be
achieved.
The dynamic properties of the laser emission are very important in studying the characteristics of the laser and may
reveal the underlying operating mechanism. Here we report a more precise measurement of the build-up time of random
laser pumped by picosecond pulse laser. The build-up time is defined as the time delay from the peak of the pumping
pulse to that of the emission. The random laser is R6G dye solutions with nanometer size TiO 2 as the scatterer. Various
dye concentrations and scatterer density are tried and measured. A specially customized fiber and a streak camera with a
spectrometer are employed to make the simultaneous measurement. The fiber has two branches and the lengths of both
branches are made equal with a difference of much less than 1 mm. The dispersion of the fiber, which introduces much
error in the results, is also measured and later compensated in the following data processing. The streak camera with
spectrometer can catch the random laser pulse and the pumping pulse signal in one shot with a resolution of less than 2
picoseconds. The results show that the build-up time changes evidently with the dye concentration, while it changes a
little along with the scatterer density. The pulse width almost remains the same in our experiment considering the errors.
Absorption coefficience of Tm3+ ions in Tm 3+ /Yb3+ codoped tellurite glass have been analyzed by
using the J-O theory. The J-O parameters are calculated to be Ω2 = 11.11×10-20 cm2, Ω4 = 3.5×10-20
cm2 and Ω6 = 3.6×10-20 cm2. Spontaneous radiative transition probabilities, branching ratios and
radiative life time of Tm3+ ions are also calculated, the calculation results indicate that it is difficult to
get S-band amplification through single 808 nm laser pump in this glass, this is tested by 808 nm
single wavelength pump experiment. The Yb3+ codoping with Tm3+ and energy transfer process
between them make 980 nm single wavelength pump scheme possible to get S-band amplification,
experiment results indicate that 980 nm pump energy absorbed by Yb3+ is transferred to Tm3+,
consequently, the low cost 980 nm pump scheme could make it become promising material for S-band
amplification.
We studied the spectral shift of random lasing in the Rhodamine 6G dye solution with TiO2 nanoscatterers under
picosecond pulses pumping. The red shift, resulting from the re-absorption and re-emission of the dye, indicates a longer
optical path length of the emitted laser traveling inside the medium. Thus the optical paths of the random laser in the
solution can be estimated using the values of red shifts for different dye concentrations and scatterer densities. The
diffusion theory is provided and the theoretical results agree very well with that calculated from the red shifts before the
inflection points appear for increasing scatterer density. The followed increasing scatterer density results in the lights
staying longer in the medium, in contrast to that predicted by the diffusion theory. So it is clear that the inflection point
shows that the system is changing from a diffusion system to a weakly localized one in which the light stay longer
because of the localization.
We present time-resolved measurements of pulse transmission at wavelength 532 nm (60 ps pulse width, 10 Hz
repetition rate) on samples of titanium powders suspended in methanol. The average particle diameter of the powders is
80 nm. We used a streak camera with 2 ps time revolution to record the transmitted signals. When the particle density is
low, the results agreed with the diffusion theory and we obtained the time-independent diffusion constants. By adding
the titanium powders gradually in methanol, we obtained the relationship between the diffusion constant and the particle
density of TiO2 in the suspended solution. When using the TiO2 powders as the sample with a particle density of
1.36x1015 cm-3, the experimental result showed a little deviation from the diffusion theory, which may be the signature of
localization in the random media.
Photonic crystal (PhC) is a new class of material which has a periodic modulation of dielectric constant. PhC will exhibit superprism effect, negative refraction and self-collimating ultra-low group velocity due to the anomalous dispersion of PhC . We can utilize the characters of photonic bandgap(PBG), defect band, pass band and band edge to control the propagation of the light .This research was to investigate the refraction and superprism effect of photonic crystals .The study background and the basic theories of photonic crystals were introduced. The refraction of photonic crystals and superprism effect were discussed with the correlating knowledge and the computing methods. A new theory of light refraction at the surface of a photonic crystal was put forward and simulated. The simulating results of this application for negative refraction and superprism effect were demonstrated by some simulating figures. These may bring about important potential applications in some areas.
Keywords: photonic crystal, superprism effect, simulation
A continue-wave (CW) laser-diode (LD) pumped passively Q-switched intracavity frequency-doubling green laser is reported in this paper. We used 3%at. Nd doped YVO4 with size of 3 X 3 X 1mm as gain medium, Cr4+:YAG as a saturable absorber with small-signal transmission T0=94% for passively Q-switch and periodically poled LiNbO3 (PPLN) with the grating period ? =6. 1 µm as a frequency doubler. The laser cavity was consisted of one face of the Nd:YVO4, coated high-reflectance (HR) coating at 1.06 µm and high transmittance (HT) at 0.808 µ m, and a 50mm radius of curvature output mirror with HR coating at 1.06 1 µm and HT coating at 0.53 µm.. A CW 1W LD and a grading-refractive-index lens were used for the end-pumping. The output energy of the green laser is 0.96 µ J with the pulse-width of 19ns. No green-noise problem exists in the green laser, because both the polarizations of fundamental wave and second harmonic wave are the same. Some theoretical results on the passively Q-switching and intracavity frequency-doubling are also reported.
By using a mirror whose reflectivity is dependent on wavelength as the output coupler of a Cr4+:YAG tunable laser pumped by 1.06 micrometers Q-switched pulses, the dependence of the Cr(superscript 4+$:YAG laser pulse characteristics on wavelength is greatly weakened and the whole efficiency of the laser is greatly enhanced.
In this paper, the stability of laser-diode-pumped passively Q-switched lasers with a Cr4+:YAG as the saturable absorber and an Nd3+:YAG or an Nd3+:SFAP as the gain medium is studied. First, the influence of the transversal mode structure on the stability is investigated. Then, with the laser operating in TEMoo mode, the variations of the pulse energy fluctuation and the repetition rate fluctuation as functions of the repetition rate are measured. Finally, the repetition rate fluctuation and the pulse energy fluctuation are semi-quantitatively and qualitatively analyzed, respectively.
By using a laser-diode as pump source and saturable absorber Cr4+:YAG as passive Q-switch, a KTP as intracavity frequency doubling crystal, we have realized green Q- switched laser output at 0.5295 micrometers from a Nd:S-FAP crystal. The output green laser characteristics, such as the average power, the single pulse energy, the pulse width, the repetition rate for different small-signal transmission of Cr4+:YAG and different pump power, were measured. Meanwhile, the coupling rate equations of intracavity frequency doubling for Cr4+:YAG as passive Q-switch were given and the numerical solution of equations agreed with the experimental results.
This paper presents the experimental results of a CW laser- diode end-pumped passively Q-switched Nd3+:YAG laser with a Cr4+:YAG saturable absorber and two groups of theoretical results. The first group is obtained by numerically solving the passively Q-switched laser rate equations in which the spatial variation of pumping and intracavity laser intensity is taken into account. The second group is obtained from the analytical solutions of Q- switched laser rate equations under the plane-wave approximation. The comparison shows that the first group is more close to the experimental results.
Nd:Sr5(VO4)3F is anew material for efficient and miniature diode-pumped solid-state lasers. By using a laser- diode pump operating at 809 nm, a KTP as intracavity- doubling crystal, the intracavity frequency doubling Nd:Sr5(VO4)3F laser at 0.5325 micrometers has been realized. The TEMoo mode green laser output power is 25.6 mW at 200 mW incident pump power of the diode-laser. An optical efficiency of 12.8 percent and a laser threshold of 13.2 mW have been measured. Meanwhile, the way of improving efficiency is discussed.
Nd:Sr5(PO4)3F, known as Nd:S-FAP, is a new material for low-threshold high-efficiency miniature solid- state lasers. By using a tunable due-laser and a xenon flash lamp as well as a laser-diode pump as pump source, respectively, the performance of low-threshold high- efficiency Nd:S-FAP at 1.328 micrometers has been realized. The threshold energy and slope efficiency for different transmission of output reflector were measured. The characteristics of output laser, such as the emission spectrum, the output power, the output energy, the pulse width and so on, were presented.
Using a xenon flash lamp as pump source, KTP as intracavity- doubling crystal and BDN dye film as passive Q-switch, the green laser output at 0.5295 micrometers from a new crystal Nd:Sr5(PO4)3F has been demonstrated. The green laser output energy and pulse width were measured under the conditions of different resonator length and small-signal transmission of dye film. Meanwhile, the Q-switched coupling wave rate equations for intracavity frequency doubling were given an the experimental results agreed with the numerical solutions of equations.
The performance of Nd:S-VAP mode-locked laser by using iodoethane solution of BDN dye is reported. Pulse train energy is 1.5mJ; pulse width: 200ps; divergence: 0.6mrad.
By means of studding on the characteristics of phase mismatch of Neodymium yttrium aluminum borate [NdxY1-xAl(BO3)4; NYAB] crystal, a method of improving beam profile of NYAB laser was presented. Because of the exist of little, periodically local shortcomings of NYAB crystal, there were different wave-vector mismatch (Delta) Ks at the different locations of NYAB when a wide incident beam passed through it for SHG. According to the phase matching theory of second harmonic generation, there were different conversion efficiencies at the different locations of the incident beam, resulting in inhomogeneous beam profile of second harmonics. We measured the curves of the SHG efficiencies versus phase mismatch angles of NYAB crystals under cases of different diameters (100 micrometers - 2 mm) of fundamental wave beam. The curves showed that the phase mismatch acceptance angle (Delta) (Theta) m was very small for the thin incident beam when a very homogeneous harmonic beam was obtained, while (Delta) (Theta) m was large for a wide incident beam and the profile of the harmonic beam was not homogeneous.
In this paper the lasing performance of a intracavity doubling of CW diode-laser end-pumped Nd3+:Sr5(PO4)3F, Nd:S-FAP, laser with KTP crystal was reported. We measured the single output performance of the green laser: the pumping threshold was 8 mW; when the pumping light of 210 mW was absorbed, the maximum single output at 529.7 nm was 4.4 mW (TEM00 mode), corresponding to a total conversion efficiency 2.1%. The comparison between experimental results and theoretical calculation was also discussed in this paper.
The absorption spectrum of a new crystal Nd:S-FAP is measured, and its broad absorption band and two strong absorption peaks show that it can be suitably pumped with a tunable dye- laser and a Xenon flash lamp. Using both a tunable dye-laser (570 - 600 nm) and a Xenon flash lamp as pump source, respectively, we have realized the free-running and Q-switched output with BDN dye film at 1.059 micrometer. For the tunable dye-laser pump source, a slope efficiency of 49% and a laser threshold energy of only 2.5 mJ have been measured, while for a Xenon flash lamp pump source, the lowest threshold energy is 150 mJ and the highest slope efficiency is 1.25%. Meanwhile, the emission spectrum, the polarization, the output energy and the pulse width are presented.
The absorption spectrum of a new crystal Nd:Sr6(VO4)3F, known as Nd:S-VAP, is measured and its strong absorption peak at 809 nm shows that it can be suitably pumped by laser-diode. By using a laser-diode pump operating at 809 nm, Nd:S-VAP crystal has been successfully lased at 1.065 micrometer. A highest slope efficiency of 43.5% and a lowest laser threshold of only 11 mW have been measured. The theoretical formulas for threshold power and slope efficiency were written, and the theoretical prediction is in agreement with the experimental result.
The Q-switching run and mode-locking run of laser self-frequency-doubling from 1.06 micrometers to 0.53 micrometers have been realized for the first time in self-active and self- frequency-doubling NYAB crystal pumped by an xenon flash lamp. Several MW/cm2 giant pulse outputs at a 0.53 micrometers wavelength and a 0.53 micrometers ultrashort pulse chain of 0.22 mJ energy and 220 ps in duration were obtained, respectively. Meanwhile, the single green light pulse output energy and pulse duration were measured under the conditions of different resonator lengths and pumpings, and the ways of improving the green laser output peak power are proposed. The possibility of obtaining a total-solid NYAB mode-locked laser is discussed.
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