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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].
Surface-plasmon resonance (SPR) effect in thin metal films is highly sensitive to the dielectric refractive index changes in the vicinity of metal interface and the conventional Kretschmann configuration has been widely used in the SPR measurement. In this work we have presented the thickness optimization for a monometallic plasmonic structure using the prism-based Kretschmann configuration in angular and spectral interrogation. He-Ne laser with wavelength of 632.8 nm as an optical source, a thin gold layer deposited onto the glass substrate and a BK7 glass prism were applied for this studies. Based on the numerical analysis with variation of metallic layer thickness, angle of incidence and wavelength we will obtain the resonance parameters, such as reflectivity and phase. Experimentally, the SPR spectra of a pure gold sensing surface has been studied. With functionalizing with specific antigen molecules on the surface of the gold layer, this optimized settings can be further used as biosensing purpose for detection of certain analytes.
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.
We measured time- and frequency-resolved phase changes owing to two-photon absorption induced by ultrashort (10 fs) pulses transmitted through a transparent material (ZnSe crystal), using femtosecond two-photon phase change spectroscopy. The maximal phase change was 0.02 rad when a pulse with the energy density of 1.5 nJ was focused with the focus diameter of 100 μm. The maximal phase change occurred when a probe pulse was delayed with respect to a pump pulse by 64 fs. A calculation assuming two-photon absorption by noninteracting atomic gases was consistent with the experimental observations, which supported the observed phase change of the pulse that is due to the two-photon absorption.
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.
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.
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.
