High repetition rate green-pumped supercontinuum generation in calcium fluoride

We compare supercontinuum generation in $$\hbox {CaF}_2$$ CaF 2 crystal under tight and loose focusing of 150 fs, 515 nm second harmonic pulses from an amplified Yb:KGW laser at a repetition rate of 10 kHz. It is demonstrated that supercontinuum generation geometry applying loose focusing ($$\hbox {NA}=0.004$$ NA = 0.004 ) of the pump beam into a long (25 mm) $$\hbox {CaF}_2$$ CaF 2 sample is advantageous in terms of supercontinuum spectral extent and durability of damage-free operation of the nonlinear material as compared to a commonly used supercontinuum generation setup which employs tight focusing ($$\hbox {NA}=0.012$$ NA = 0.012 ) into a short (5 mm) sample and to setup which uses tight focusing into a long (25 mm) sample. More specifically, loose focusing into a long sample showed remarkably longer (20 min) damage-free operation of the nonlinear material, which was not translated with respect of the pump beam, while in tight focusing condition the sample is damaged just within 2 min of operation, leading to a complete extinction of the supercontinuum spectrum. The evolution of optical degradation of the nonlinear material in time and its impact to supercontinuum spectrum is studied in terms of filament-induced luminescence due to self-trapped exciton emission and light scattering at the pump wavelength indicating the onset of optical damage. Our findings are supported by the numerical simulations which compare relevant parameters related to filament propagation in tight and loose focusing conditions.

LiSAF: an efficient and durable nonlinear material for supercontinuum generation in the ultraviolet

We have experimentally studied supercontinuum generation in an undoped LiSAF crystal using ultraviolet, visible and near infrared pump pulses provided by fundamental and second harmonics of amplified femtosecond Ti:sapphire and Yb:KGW lasers. We have found that the optical degradation of the crystal, manifested by gradual narrowing of the supercontinuum spectrum, starts much faster using infrared pump pulses. This is attributed to the role of impact ionization, which increases with increasing the pump wavelength. The most reliable operation is achieved with the shortest pump wavelength of 400 nm (the second harmonic of a Ti:sapphire laser), where LiSAF produces a stable, almost 1.3 octave-spanning supercontinuum spectrum with a short-wavelength cut-off at 252 nm and shows no apparent optical degradation for one hour of continuous operation at 500 Hz repetition rate without crystal translation.

Numerical Analysis of Supercontinuum Generated Microstructured Optical Fiber with all Normal Chromatic Dispersion

A micro-structured photonic crystal fiber (M-PCF) with all normal chromatic dispersion has been proposed for supercontinuum spectrum generation which is applicable in optical transmission and optical coherence tomography applications. Calculations of its different properties using finite difference method have shown that the proposed M-PCF has a high nonlinear coefficients at 1.06 μm, 1.30 μm and 1.55 μm wavelength with flattened chromatic dispersion, low confinement losses and broad supercontinuum spectrum. Moreover, it has been shown that the proposed design obtain high power and short fiber length at 1.06 μm, 1.30 and 1.55 μm center wavelengths by propagating sech2 picosecond optical pulses with 1.0 ps pulse width at a full width at half maximum.

Accurately Shaping Supercontinuum Spectrum via Cascaded PCF

Shaping is very necessary in order to obtain a wide and flat supercontinuum (SC). Via numerical simulations, we accurately demonstrated shaping the SC using the fiber cascading method to significantly increase the width as well as the flatness of the spectrum in silica photonic crystal fiber (PCF). The cascaded PCF contains two segments, each of which has dual zero-dispersion frequencies (ZDFs). The spectral range of the SC can be expanded tremendously by tuning the spacing between the two ZDFs of the first segmented cascaded PCF. Increasing the pump power generates more solitons at the red edge, which accelerates solitons trapping and improves the spectral flatness of the blue edge. Furthermore, cascading the second segmented PCF by choosing appropriate fiber parameters ensures the flatness of the red end of SC. Therefore, a cost-effective alternative method for broad and flat supercontinuum generation in the near-infrared range is proposed here, which can be implemented easily in any photonics laboratory, where dual ZDFs PCFs are commonly found.

Numerical Analysis of Supercontinuum Generated Microstructured Optical Fiber with all Normal Chromatic Dispersion

A micro-structured photonic crystal fiber (M-PCF) with all normal chromatic dispersion has been proposed for supercontinuum spectrum generation which is applicable in optical transmission and optical coherence tomography applications. Calculations of its different properties using finite difference method have shown that the proposed M-PCF has a high nonlinear coefficients at 1.06 μm, 1.30 μm and 1.55 μm wavelength with flattened chromatic dispersion, low confinement losses and broad supercontinuum spectrum. Moreover, it has been shown that the proposed design obtain high power and short fiber length at 1.06 μm, 1.30 and 1.55 μm center wavelengths by propagating sech2 picosecond optical pulses with 1.0 ps pulse width at a full width at half maximum.

All-Fiber-Based All-Normal Dispersion Supercontinuum Source Using a Femtosecond Fiber Laser with Hollow-Core Fiber Pulse Compression

We develop and thoroughly characterize an all-fiber-based all-normal dispersion supercontinuum source pumped with a femtosecond fiber laser at 1036 nm using hollow-core fiber pulse compression. Pulse length, supercontinuum spectrum, and noise are measured.

Enhancing high harmonic generation by the global optimization of a two-color chirped laser field

Enhanced high harmonics are generated by local and global optimization approaches to achieve a supercontinuum spectrum.