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We have successfully constructed a Kerr lens mode-locked (KLM) Ti:sapphire oscillator to generate ultrashort pulses of ~18 fs. The oscillator consists of only 5 elements including a pair of double-chirped mirrors to balance negative group delay dispersion in the cavity. The bandwidth of the mode-locked laser oscillator spectrum is from 600 nm to 950 nm and pulse energy is 1.5 nJ. Both the output spectrum and the output power were stable against environmental disturbance. For the pulse characterization, a second harmonic generation frequency resolved optical gating method was used.
The motivation for generating ultra-short, intense, high-quality optical pulses comes from many fields of physics and from other areas such as the study of dynamics of chemical reactions or biological processes [1]. We have successfully designed and constructed a-symmetric cavity Kerr lens Mode locked (KML) Ti:sapphire pulsed laser. Cavity design of ultrashort Ti:sapphire oscillator consists of only 5 elements: a gain medium – highly doped Ti:sapphire crystal, a pair of GDD-oscillation compensated double chirped mirrors (DCM), a high reflectivity end mirror and output coupler. Z folded linear cavity has round trip length of about 2.2 m which corresponds to repetition rate of ~136 MHz. The pumping source is the diode-pumped Nd:YAG laser (532 nm, 5 W, @Millennia eV) has high intensity Gaussian beam profile which are the suitable for realization of KLM technique to get shortest pulses [1][3].
We applied the dielectric function method to solve analytically L-NL-L structure problems with negative Kerr nonlinearity. A damped wave in linear and a periodic standing wave in non-linear media had to be matched at boundaries. We gave a formulation of boundary conditions that did not explicitly include a film thickness. The boundary-value of a dielectric function can be expressed through the constant of non-trivial integral of motion. Using it, one generates a family of matched solutions satisfying boundary conditions. Then arbitrary film thickness can be checked against this family of solutions in search of matches. As a result, all fitted solutions are determined straightforwardly.
The Kerr-lens mode-locking (KLM) is known as a suitable method for generation of femtosecond pulses and mode-locked Ti:sapphire laser is now widely used sources of stable, energetic femtosecond pulses. We will present the simulation of KLM in Ti:sapphire laser cavities with a folded-cavity four-mirror by applying the ABCD ray-tracing technique for a Gaussian beam. Simulations will be performed for an asymmetric resonator design. Based on the numerical analysis, we will find the optimum design parameters (slit position, gain cavity spacing, gain medium position) for KLM.
The Kerr-lens mode-locking (KLM) is known as a suitable method for generation of femtosecond pulses and mode-locked Ti:sapphire laser is now widely used sources of stable, energetic femtosecond pulses. We will present the simulation of KLM in Ti:sapphire laser cavities with a folded-cavity four-mirror by applying the ABCD ray-tracing technique for a Gaussian beam. Simulations will be performed for an asymmetric resonator design. Based on the numerical analysis, we will find the optimum design parameters (slit position, gain cavity spacing, gain medium position) for KLM.
Керр-линз мод синхронизация (КМС) известна как подходящий метод генерации фемтосекундных импульсов, а Ti: сапфировый лазер с синхронизацией мод в настоящее время широко используется в стабильных энергичных фемтосекундных импульсах. Мы представим моделирование КМС в резонаторах Ti: сапфирового лазера со свернутым резонатором, применяя метод трассировки лучей ABCD для гауссовского пучка. Моделирование будет работать для асимметричной конструкции резонатора. Будут обсуждаться синхронизация мод с жесткой апертурой и усиление мод с мягкой апертурой. На основе численного анализа мы найдем оптимальные параметры конструкции (положение щели, расстояние между полостями усиления, положение среды усиления) для КМС. Ключевые слова: Самофокусировка, Керр-линз, Чувствительность смещения.
Two different pump-probe (PP) setups were developed successfully with different femtosecond pulse lasers. Using a PP setup with an ultra-short pulse laser, the excitation of coherent phonons in GaAs was measured for a calibration and an accuracy test of the developed setup. The frequencies of the coherent phonon modes were in good agreement with reported values [1, 2]. The setups for ZnSe and GaAs were transmission and reflection–type, respectively. When using the ultra-short pulse laser, the signal in the PP experiment was measured by a balanced photo diode. In the other PP experimental setup, built to measure the transient transmittance of bulk ZnSe, the light source and detector differed from the previous PP setup. A strong pulse laser was successfully used for the spectrally resolved pump probe experimental setup. A broadband, high-resolution spectrometer (HR4000CG-UV-NIR) was used as the detector.
We calculated third order non-linear polarization to estimate the two-photon absorption of non-interacting two-level molecules in the transmission-type degenerate pump–probe geometry. The spectral intensity and the phase changes of the laser pulses when passing through a thin dielectric slab composed of the molecules were considered. We also investigated the effect of the decay rate of the molecules and the chirp of the pulses on their spectral intensity and phase changes.
We calculated the polarization-dependent Raman scattering cross section spectra of LaMnO3 below the A-type magnetic ordering temperature. Two strong peaks appear around the MnO6 octahedra stretching phonon frequency. One mode shows Ag symmetry, while the other mode shows Bg symmetry. We found that the Ag symmetry peak is a Jahn-Teller phonon coupled to the orbital wave and the Bg symmetry peak is an orbital wave coupled to a Q2 phonon mode via the Jahn-Teller electron phonon coupling.
We propose an excitation-probe measurement method utilizing entangled photon pulses. The excitation-probe signal is dominated by stimulated Raman scattering as well as two-photon absorption when the time delay between the excitation pulse and the probe pulse is shorter than the pulse duration. We demonstrate that the two-photon-absorption signal can be suppressed when the photons of the pulses are entangled. The stimulated Raman scattering signal can be composed of many peaks distributed over broad photon energies owing to the transitions between numerous quantum states in complex materials. We show that the desired peaks among the many peaks can be selected by controlling the thickness of the nonlinear crystal, the pump pulse center frequency, and the polarization of the excitation pulse and probe pulse.
Цахилгаан шүүлтүүрт явагдах титэмт ниргэлэг үүсэх болон стример шилжих нөхцөлийг судалж стационар титэмт ниргэлэг явагдаж байх хүчдэл, гүйдлийн хамгийн их ба хамгийн бага утгын хязгаарыг тооцоолов. Түүнчлэн иончлолын коэффициентийн орноос хамаарах хамаарал мэдэгдэж байгаа тохиолдолд титэмт ниргэлгийн асаах хүчдлийн утгыг онолын хувьд гаргах боломжтойг үзүүлж титэмт ниргэлгийн доторхи цахилгаан орон ба ионы түгэлт гаргав.
This paper describes a method to determine the phase retardation of birefringent optical components by combining spectral interferometry and the Fourier transform method. The retardation of each orthogonal polarization component was resolved by using two rotatable linear polarizers in the interferometer. The phase retardation measured by using suggested method was compared to that measured using the conventional polarimetric method. The results of independent methods were well matched, which confirms the validity of the proposed method.
Ultrafast transient optical conductivity of spin-orbital ordered LaMnO3 was investigated theoretically. A quasi-two-dimensional Hubbard Hamiltonian based on a four-site Mn cluster was established to simulate the LaMnO3 system. The time evolution of the transient optical conductivity was numerically calculated. Intensity oscillations of the optical conductivity were observed, which were interpreted as the result of the quantum interference between phonon-coupled orbiton excited states. Also, the photo-induced anisotropy was observed, which revealed the broken orbital symmetry of the optical excited state.
A polarimetric experimental method was developed to determine the Jones matrix elements of transparent optical materials without sign ambiguity. A set of polarization dependent transmittance data of the samples was measured with polarizer - sample - analyzer system and another set of data was measured with polarizer - sample - quarter-wave plate - analyzer. Two data sets were compared and mathematically analyzed to obtain the correct signs of the elements of the matrix. The Jones matrix elements of a quarter-wave plate were determined to check the validity of the method. The experimentally obtained matrix elements of the quarter-wave plate were consistent with the theoretical expectations. The same method was applied to obtain the Jones matrix elements of a twisted nematic liquid crystal panel.
We reportthetransmittance(T) andthepump–probetransmittancechange ðDTÞ of Nd0.5Sr0.5MnO3 (NSMO) thinfilmsgrownonSrTiO3(STO)(100)andSTO(110)substratesin1.3–1.7eVrangeatroom temperature.ThestrainofNSMOwasisotropiconSTO(100)andanisotropiconSTO(110).Both T and DT showednopolarizationdependenceinNSMO/STO(100)buttheintensityof T and DT was anisotropicinNSMO/STO(110).Also DT showedsharpexponentialdecaywithincreasingtimedelay betweenthepumpandprobepulse.Theshorttimedecaybehaviour ðt0:3 psÞ showednosignificant polarizationdirectionandsubstratedependence,whichindicatesthatthecarrier–carrierscatteringrate is notsensitivetothestrainstateinNSMO.
We calculated the infrared conductivity spectrum of orbitally ordered LaMnO3 in phonon frequency and overtone frequency ranges. We considered orbital exchange, Jahn-Teller electron–phonon coupling, and phonon–phonon coupling. The fundamental excitation of the phonon-coupled orbiton was only Raman active, not infrared active, while its overtone modes were both Raman and infrared active. Our calculations reproduced the small peaks near 1300 cm⁻¹ observed both in Raman scattering and infrared conductivity spectra, as consistent with previous experimental results.
