With graphene as saturable absorber, an Nd:KLu(WO4)2 eye-safe laser operating at 1,425 nm is demonstrated. To the best of our knowledge, this is the first demonstration that an Nd:KLu(WO4)2 laser operates at the eye-safe 1.4-μm region. A maximum total average output power of 170 mW is obtained under the pump power of 9.6 W, corresponding to an optical–optical efficiency of 1.77 %. The minimum pulse width and the highest pulse repetition rate are 153 ns and 97 kHz, respectively. Also the characteristics of the graphene used as saturable absorber for a 1.4-μm laser were studied for the first time.
An intracavity pumped SrWO4 anti-Stokes Raman laser is realized by placing an inclined SrWO4 Raman cavity in a Q-switched Nd:YAG fundamental cavity. This structure is used to achieve non-collinear phase matching between the fundamental, the first-order Stokes and the first-order anti-Stokes waves. The maximum forward and backward first anti-Stokes outputs are 0.683 and 0.667 mJ, respectively, and the corresponding first anti-Stokes pulse widths are both 3.3 ns. A rate equation model is set up to simulate the output energies and temporal characteristics of these pulses. The stimulated results are in agreement with the experimental ones on the whole.
Kerr self-focusing of high-power ultrashort laser pulses in atmosphere may result in a structure or structures of high intensity that can propagate over long distances with little divergence. Filamentation has garnered significant interest in the nonlinear optics community due to its unique properties. Salient features of filaments include a central region of intense laser power (greater than the ionization threshold of the propagation medium) and a low temperature plasma column that lasts up to nanoseconds in duration after the passage of the laser pulse. Steel and titanium samples are ablated by filaments and by sharply focused sub-picosecond laser pulses. We then performed metrology on the samples to compare the ablation features in addition to modeling of the plasma ablation process. Ablation with filaments leads to a wider range of material responses as compared to ablation with sharply focused pulse. This results in potential complications for applications of filament ablation that depends on the rate of material removal and spectroscopic analysis.
Faraday modulation/rotation spectroscopy (FAMOS/FRS) is a spectroscopic technique for detection of paramagnetic species in gas phase. Although the prevailing theoretical description predicts fully symmetric lineshapes, experiments do not in general provide such. This work shows that asymmetries in FAMOS can have at least two origins; (1) a frequency-dependent laser intensity and (2) polarization imperfections, which both are scrutinized here. A general analytical description for the latter, derived under the assumption that both the polarization imperfections and the relative absorption are small, is presented, conveniently expressed in terms of 1st Fourier coefficients of modulated dispersion and absorption lineshape functions. The resulting expression, which is thus an extension to the conventional FAMOS expression, can thereby be swiftly evaluated and allows for online fitting to measured asymmetric FAMOS signals. Curve fits to experimentally obtained data from nitric oxide measured both in the ultraviolet and the mid-infrared regions demonstrate the applicability of the methodology.
Generation of dual-wavelength continuous-wave (cw) radiation with independent and arbitrarily tuning, and indefinitely close spacing, using two cw optical parametric oscillators (OPOs) coupled with an anti-resonant ring interferometer is reported. The singly resonant OPOs, based on identical 30-mm-long MgO:sPPLT crystals, are pumped by a single cw laser at 532 nm. Two pairs of signal and idler wavelengths can be independently and arbitrarily tuned, with each signal (idler) pair tuned through degeneracy and beyond. Frequency separation between two distinct resonant signal waves from 7 down to 0.8 THz is demonstrated, and their overlap at 951 nm providing a frequency difference as small as ~220 MHz is shown. The OPOs independently provide a signal (idler) wavelength coverage across 870–1,000 nm (1,040–1,370 nm) and simultaneously generate idler powers of >1 W.
To study the role of the solvent and of the laser fluence in the matrix-assisted pulsed laser evaporation (MAPLE) process, we used a soft polymer (polydimethylsiloxane—PDMS) as “sensing surface” and toluene as solvent. Thin films of the PDMS polymer were placed in the position of the growing film, while a frozen toluene target was irradiated with an ArF laser at the conventional fluences used in MAPLE depositions (60–250 mJ/cm2). Apart the absence of solute, the MAPLE typical experimental conditions for the deposition of thin organic layers were tested. The effects on the PDMS films of the toluene target ablation, at different fluences, were studied using atomic force microscopy and contact angles measurements. The results were compared with the effects produced on similar PDMS films by four different treatments (exposure to a drop of the solvent, to saturated toluene vapors and to plasma sources of two different powers).
An eye-safe Raman laser is realized with BaTeMo2O9 (BTM) nonlinear crystal for the first time. By using a diode-end-pumped acousto-optically Q-switched Nd:YVO4 laser as the pumping source, the BTM crystal converts the fundamental laser at 1,342 nm to first-Stokes laser at 1,531 nm successfully. With an incident power of 10.8 W and a pulse repetition rate of 25 kHz, the average output power at 1,531 nm is obtained to be 0.83 W, corresponding to a diode-to-Stokes conversion efficiency of 7.7 %. The pulse width is 11 ns, and the peak power is 3.0 kW.
Self-starting and stable mode-locking of an Yb:KYW laser in the picoseconds pulse regime has been achieved by exploiting a positive cascaded Kerr lens in periodically poled KTP. The use of a volume Bragg grating (VBG), for locking the output spectrum of the laser, was essential to achieve a stable mode-locked operation in this wide gain bandwidth laser material. The laser emitted stable, nearly transform-limited pulses with a duration of 16 ps, at a repetition rate of 210 MHz, and with an energy of 3.2 nJ. The mode-locked spectrum was centred at 1,029.1 nm and featured a FWHM bandwidth of 85 pm, which was effectively determined by the VBG. Combination of a large cascaded Kerr nonlinearity with spectral limiting by a VBG represents so far the best opportunity for stable mode-locking of a broadband laser to produce near-transform-limited picosecond pulses.
We introduce the basics of an apodized 2f/1f wavelength modulation method for the spectroscopy of the R(9) transition line in the first overtone band of carbon monoxide (12C16O) in near-infrared (NIR) region around 2.33 μm. Performance of the method is investigated for high gas concentrations beyond the optically thin limit to generalize common 2f/1f wavelength modulation spectroscopy (WMS) reported by Rieker et al. (Appl Opt 48:5546, ). Numerical simulations are performed based on real experimental parameters associated with a NIR spectrometer designed in our laboratory. The results primarily show a more linear response and less error than occurred in the common WMS-2f/1f method for an optically thick sample. It is also theoretically shown that the apodized method enables sharpening the spectrum without peak displacement compared to the common WMS-2f/1f method.
We carried out experimental and numerical study of the ultrafast supercontinuum generation by filamentation of 120 fs, 800 nm laser pulses in sapphire under variable focusing conditions. We demonstrate that the supercontinuum spectra produced in loose focusing conditions have much larger infrared extent, while the spectral blueshift remains fairly the same. Our numerical simulations reproduce the experimental results in great detail and disclose that the input beam focusing conditions affect only the nonlinear propagation of the leading sub-pulse, which emerges after the pulse splitting event, and which is responsible for the redshifted spectral broadening.