[Show abstract][Hide abstract] ABSTRACT: We report experimental results of second-harmonic (SH) generation (SHG) by a quasi-phase-matched periodically poled Mg-doped stoichiometric LiTaO3 crystal for 1030 nm input radiation of 18 ps pulse duration, within the range of peak input laser intensity I = 0.1-9.5 GW/cm2 and under repetition rate 10-20 kHz. For I>3 GW/cm2 SHG efficiency achieves the saturation level of η≈0.35 which can be maintained within a wide range of I = 3-9.5 GW/cm2. The loss of SHG efficiency observed for I>5 GW/cm2 can be recovered to the level of η≈0.35 by using temperature-controlled operation. By applying our experimental data we find the value of two-photon absorption (TPA) coefficient for 515 nm radiation, β≈1.1-2.7 cm/GW, agreeing well with the theoretical estimate β≈2.6 cm/GW. Our analysis suggests that the inhibition of SHG efficiency, its saturation and stabilization are due to a combined mechanism including: (i) non-steady-state ps effect scaled by ≈ζ−2[1-exp(-ζ)]2 as compared with the efficiency for ns pulsed operation (ζ = L/V2τP , L is the crystal length, τP is the pulse duration and V2 is the group velocity of SH); (ii) dephasing caused by the spectral bandwidth of the input radiation (≈300 GHz); (iii) thermal dephasing caused by TPA of SH; and (iv) strong SH attenuation by TPA of order ≈I2−1dI2/dz≈-(0.8-8) cm−1 for I = 1-9.5 GW/cm2.
[Show abstract][Hide abstract] ABSTRACT: The effect of Ce doping on the dielectric relaxation in Sr0.75Ba0.25Nb2O6 single crystal grown by double crucible Stepanov technique has been investigated. It has been observed that the incorporation of Ce ion in the lattice reduces the dielectric maxima. It further increases the degree of diffusiveness and lowers the temperature of dielectric maxima as a result of the introduction of additional random field via created point defects. Both the undoped and Ce doped crystals undergo a non-debye type relaxation. Vogel-Fulcher fitting reveals that the attempt frequency reduced by one order of magnitude on Ce doping.
Journal of Alloys and Compounds 02/2015; 621:26-29. DOI:10.1016/j.jallcom.2014.09.196 · 3.00 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Terahertz waves are generated using a femtosecond laser pulse in a periodically poled stoichiometric lithium tantalate crystal and simultaneously detected via a non-collinear optical parametric interaction inside the same crystal. Real time up-conversion signal between the generated THz and an optic probe pulses is measured depending on the beam overlapped conditions using a general silicon-photodiode for the THz detection. The non-collinear geometry is to facilitate manipulated property of the position-dependent bandwidth at narrow and broad bandwidths of 45 GHz and 3.3 THz, respectively at the one crystal. Furthermore, an aperture effect at the detection part is characterized as the function of size and position owing to the spatial distribution of the frequency conversion signal and it is applied in optimization of the in-situ detection scheme.
Journal of infrared, millimeter and terahertz waves 10/2014; 35(10). DOI:10.1007/s10762-014-0091-y · 1.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Here we report the anomalous electro-caloric effect (ECE) observed in lead-free SrxBa(1−x)Nb2O6 (, 0.61 and 0.75) ferroelectric single crystals. Temperature-dependent hysteresis measurement revealed that the spontaneous polarization of SrxBa(1−x)Nb2O6 single crystals with all the compositions under investigation decreases with a decrease in the temperature below the temperature of the dielectric maxima . As a consequence, these crystals exhibited negative electro-caloric effect at lower temperature along with the usual positive ECE above . The EC coefficient obtained near is 0.21, 0.43 and 0.28 K mm/kV for , 0.61 and 0.75 samples, respectively. The maximum values of in the negative ECE region are −1.4, −0.81 and for 50SBN, 61SBN and 75SBN, respectively.
[Show abstract][Hide abstract] ABSTRACT: 355 nm generation was confirmed by using a novel ferroelectric QPM device, PP-LBGO with Fan-out structure as a third harmonic of 1064 nm light. More than 100 mW was generated without any walk-off.
[Show abstract][Hide abstract] ABSTRACT: Continuous tuning of terahertz waves was demonstrated with seamless change in grating period in a periodically poled stoichiometric lithium tantalite (SLT) crystal. The periodically poled fan-out structure allows wide tunability such as 610 GHz with the bandwidth as narrow as 17 GHz at a carrier frequency of 1.00 THz. Temperature-dependent measurements show a gradual intensity increase of the THz pulses as the temperature decreases. Furthermore, absorption and refractive index of SLT in the THz range were estimated and compared with those of LiNbO3 (LN). The absorption coefficient of the LT crystal at ordinary wave was almost half of that in the LN crystal. SLT could be one of the powerful crystals for high-power THz generation with large optical aperture because of the fewer defects inside the crystal. (C) 2014 The Japan Society of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: Second harmonic UV (350nm) generation was demonstrated by periodically poled LaBGeO5 (PPLBGO) for the first time. PP structures were fabricated with 5.5um periodicity. The phase-matching-wavelength agreed fairly well with the calculation from reported Sellmeier’s equation.
[Show abstract][Hide abstract] ABSTRACT: Simultaneous tunable terahertz wave generation with the frequency range (0.85 ~ 1.59 THz) and the bandwidth range (43 ~ 78 GHz) was demonstrated using a fan-shaped periodically poled stoichiometric lithium tantalate crystal.
Lasers and Electro-Optics Pacific Rim (CLEO-PR), 2013 Conference on; 06/2013
[Show abstract][Hide abstract] ABSTRACT: Frequency and bandwidth of terahertz wave were simultaneously tuned by selectively choosing domain period in a fan-shaped periodically poled stoichiometric lithium tantalate crystal.
Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2013 38th International Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: c-Axis oriented single crystals of relaxor ferroelectric SrxBa1−xNb2O6 (x = 0.61 and 0.75) were investigated
using polarized Raman spectroscopy and the behavior of optical phonon as a function of temperature
across the phase transition from space group P4bm to P¯4b2. Based on the polarized and depolarized
spectra mode assignments were carried out. Modes of symmetry A1(LO), B1, and B2 were identified. From
the detailed line shape fitting of the spectra, frequencies of the prominent modes associated with NbO6
stretching vibration were obtained. In contrast to the earlier reported results, these modes are found to
exhibit discontinuous changes across the transition. The phase transition temperatures are found to be
336 and 322 K for x = 0.61 and 0.75, respectively.
[Show abstract][Hide abstract] ABSTRACT: To clarify whether the thermal diffusivity along the X-axis of a
periodically poled Mg 1-mol %-doped near-stoichiometric
LiTaO3 (PPMgSLT) frequency-conversion device is the same as
that of bulk-MgSLT crystal, we measured the thermal diffusivity along
the X-axis (the direction perpendicular to the domain-wall) of a PPMgSLT
device with a domain-inverted period of 8.0 μm by using a modified AC
calorimetric method (laser-heating Ångström method) at room
temperature. We found that the thermal diffusivity [(1.98±
0.06)× 10-6 m2/s] was almost the same as
that of bulk-MgSLT crystal [(2.09± 0.04)× 10-6
m2/s]. This means that domain-walls are not phonon scattering
centers with respect to thermal diffusivity and that domain-walls do not
affect thermal diffusivity at room temperature. Consequently, the
thermal diffusivity of bulk-MgSLT crystal is acceptable for PPMgSLT
Japanese Journal of Applied Physics 01/2012; 51(1):2601-. DOI:10.1143/JJAP.51.012601 · 1.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report on the method that terahertz generation and detection were simultaneously performed via non-collinear optical parametric interaction in a nonlinear crystals using a Si-photodiode. The bandwidth manipulation between broad 3.3 THz and narrow 45GHz bandwidths was demonstrated at single quasi-phase-matching crystal using the position-dependence of the crystal.
Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2012 37th International Conference on; 01/2012
[Show abstract][Hide abstract] ABSTRACT: Visible light-induced polarization-dependent photochemical deposition of silver nanoparticles (AgNPs) has been demonstrated using Mn-doped congruent LiNbO3 (CLN) single crystals. Mn-doped CLN has a strong absorption over a wide region of the visible spectrum that allowed effective visible light irradiation for photochemical deposition. The AgNPs deposition on Mn-doped CLN was compared with that on non-doped congruent LiNbO3, and together these further confirmed that the photochemical deposition on LiNbO3 is caused by the strong photogalvanic effect.
[Show abstract][Hide abstract] ABSTRACT: Tunable terahertz pulses were generated in fan-out periodically poled structure with QPM period of 50 to 90 μm. Center frequency was tuned from 0.94 to 1.55 THz with as narrow as band-width of 20 GHz.
[Show abstract][Hide abstract] ABSTRACT: Femtosecond optical pulse is used to generate narrow-band terahertz pulses depending on a quasi-phase-matched condition in periodically poled lithium niobate (PPLN) and stoichiometric lithium tantalate (PPSLT) crystals by difference frequency generation. The origin of narrow-band THz generation proved that the two frequency components of the fs pulse contribute to the frequency mixing. By cryogenic cooling, the absorption of THz waves in the crystal is significantly reduced which results in efficient THz generation. Simultaneously generated forward and backward THz pulses were 1.38 and 0.65 THz with as narrow as the bandwidth of 32 GHz in the PPSLT sample. Temperature dependence of the generated THz waveforms had good agreement with the simulation result using one dimensional plane-wave propagation model.
[Show abstract][Hide abstract] ABSTRACT: We present a more-developed method where narrow-band terahertz (THz) waves are simultaneously generated and detected at one quasi-phase matching crystal. For THz detection, we used a photodiode as a THz detector via parametric interaction between THz wave and weak probe beam, compare to the photoconductive antenna or electro-optic sampling methods.
[Show abstract][Hide abstract] ABSTRACT: We investigated the thermal conductivities of non-doped near-stoichiometric LiTaO3 (SLT) and Mg (1mol%)-doped near-stoichiometric LiTaO3 (Mg:SLT) crystals along the X-, Y-, and Z-axes at room temperature. Those of non-doped congruent LiTaO3 (CLT) crystal along the same axes were also estimated to investigate the effect of non-stoichiometric defects. The thermal conductivities were determined by measuring the thermal diffusivity using a laser-flash method and measuring the specific heat using a differential scanning calorimeter. Anisotropy of the thermal conductivities was found for all three crystals. That is, the thermal conductivities along the X-axis were the same as those along the Y-axis and less than those along the Z-axis. The thermal conductivities of the SLT crystal were the highest and were twice those of the CLT crystal. The thermal conductivities of the Mg:SLT crystal were slightly lower than those of the SLT crystal apparently due to the Mg-doping. We also investigated the effect of the difference in domain structure on thermal conductivity using as-grown Mg:SLT crystal with randomly distributed multi-domains and found that it did not affect the thermal conductivity along any axis. These findings regarding thermal conductivity should be useful for designing high-power laser applications using SLT and Mg:SLT crystals.
[Show abstract][Hide abstract] ABSTRACT: Continuous tunable terahertz pulses were generated with a continuous grating-period change from 65 to 90 μm in periodically poled stoichiometric lithium tantalate crystal. Center frequency was tuned from 0.9 to 1.3 THz with as narrow as band-width of 21 GHz at crystal temperature of 130 K.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate the pyroelectric effect induced by a short pulse laser with an intensity up to 6 MW/cm2 which is used to heat the Fe-doped Lithium niobate crystal. 0.2 °C temperature rise induced by a 10 ns laser pulse causes a very large current peak (up to 25 mA) since the rate of temperature rise is extremely large comparing with that induced by using an ordinary heater. On the other hand, the pyroelectric current during the cooling is much smaller because of the slow cooling rate by thermal conduction.