Virtual Journal of Laser

A linear relationship between concentration of sulfur dioxide (SO₂) and optical parameter (OP) is established using the Beer–Lambert law. The SO₂ measuring system is set up to measure the concentration of sulfur dioxide in the wavelength range 275–315 nm. Experimental
results indicate that the detection limit of the sulfur dioxide measuring system is below 0.2 ppm per meter of path length,
and the measurement precision is better than ±1%. The proposed SO₂ measuring method features limited interference from other gases and dust, and high stability and short response time.

An intense green upconversion (UC) emission (λ
_exc=976 nm) followed by the heating effect in Yb³⁺/Er³⁺ co-doped Gd₂O₃ nanoparticles has been detected. A temperature rise up to 504 K has been observed (on a noteworthy low laser excitation of
290 mW) using fluorescence intensity ratio (FIR) method of the thermalized UC luminescence bands ²H_11/2→⁴I_15/2 and ⁴S_3/2→⁴I_15/2 of Er³⁺ ion. The reported controlled optical heating of nanoparticles and its nano-volume has potential applications in biomedicines
and in the creation of holes in soft materials.

An erbium doped K_0.603Li_0.397Ta_0.428Nb_0.572O₃ single crystal was grown by the step-cooling technique. The crystal has a tetragonal tungsten bronze-type structure at room
temperature with a Curie temperature of 303°C. There are Er ions characteristic absorption bands around 449, 485, 521, 550,
and 652 nm in the visible absorption spectrum. Upconversion fluorescence spectra and power dependence centered at 527 nm,
548 nm, and 660 nm under 975 nm excitation were measured at room temperature. Decay lifetimes of the 548 nm and 660 nm emission
bands are 281 μs and 420 μs, respectively. The lifetime of the 548 nm emission corresponding to the transition of  ⁴
S
_3/2→⁴
I
_15/2 is ten times the lifetime of the same transition of Er³⁺ in LiNbO₃ crystal and twice in KYb(WO₄)₂ crystal. The crystal might become a promising upconversion laser material.

Compact diode end-pumped acousto-optically Q-switched Nd:YLF laser was developed. As in effective CW diode end-pumped lasers,
pump beam was made sufficiently narrower than resonator Gaussian mode to increase efficiency in Q-switched operation. The
dramatic changes of output radiation structure were observed at some resonator lengths. The radiation structure is close to
the Gaussian mode in intervals between these lengths.

We have recently developed a new laser based set-up (Jet-Cooled Laser-Induced Fluorescence) for the analysis of aromatic compounds
generated in flames. This method relies on the extraction of the species from the flame via a thin microprobe and their direct
analysis inside a supersonic free jet by Laser-Induced Fluorescence (LIF). Under the supersonic conditions of the jet, the
vibronic spectra of the molecules become structured as the possibility of electronic transitions is reduced, allowing their
selective detection by LIF. In addition, due to the very low quenching efficiency inside the jet, LIF signals can be directly
related to the population of the probed species and easily calibrated into absolute concentrations. All of the work presented
here has been carried out for naphthalene, which is an important PAH involved in soot formation mechanisms. The calibration
procedure is described in detail.

It is of great interest to investigate a freestanding GaN nanocolumn slab with bottom subwavelength nanostructures. A low-index
buffer layer offers more paths accessible to emit light in air, and the nanostructures break the total internal reflection
condition at the bottom surface to improve the light-extraction efficiency. The GaN nanocolumns and subwavelength nanostructures
can also effectively suppress optical reflection over a broad wavelength range. In this work, the freestanding GaN nanocolumn
slabs with bottom subwavelength nanostructures are implemented with a diameter of 1200 μm by a combination of self-assembly
technique, silicon-on-insulator (SOI) technology, manufacturing of silicon, and epitaxial growth of GaN.

Metals and metal alloys are usually employed as interconnections to guide electrical signals between components into the very
large scale integrated (VLSI) devices. These devices demand higher complexity, better performance and lower cost. Thin film
is a common geometry for these metallic applications, requiring a substrate for rigidity. Accurate depth profile analysis
of coatings is becoming increasingly important with expanding industrial use in technological fields. A number of articles
devoted to LIBS applications for depth-resolved analysis have been published in recent years. In the present work, we are
studying the ability of femtosecond LIBS to make depth profiling for a Ti thin film of thickness 213 nm deposited onto a silicon
(100) substrate before and after thermal annealing. The measurements revealed that an average ablation rates of 15 nm per
pulse have been achieved.

Thermo-optic coefficients dn/dT of anisotropic Nd(3 at.%):KGd(WO₄)₂, KGd(WO₄)₂, Nd(0.4 at.%):YVO₄ and Nd(0.4 at.%):GdVO₄ crystals were measured at 632.8 nm, 300 K by a beam deflection method. For Nd:KGd(WO₄)₂, the values of dn/dT amount to dn
_p/dT=−14.8×10⁻⁶ K⁻¹, dn
_m/dT=−10.1×10⁻⁶ K⁻¹ and dn
_g/dT=−16.0×10⁻⁶ K⁻¹. For vanadate crystals, dn
_e/dT=3.1×10⁻⁶ K⁻¹, dn
_o/dT=8.2×10⁻⁶ K⁻¹ (for Nd:YVO₄) and dn
_e/dT=4.3×10⁻⁶ K⁻¹, dn
_o/dT=5.5×10⁻⁶ K⁻¹ (for Nd:GdVO₄).

Flame-generated soot was heated using a pulsed laser, and temperatures of the irradiated soot were inferred by fitting the
Planck function to spectrally resolved laser-induced incandescence with the temperature as an adjustable parameter. The effect
of the wavelength dependence of the emissivity on the inferred temperatures of the irradiated soot was studied using selected
expressions for the soot emissivity in the fit. Depending upon the choice of the functional form of the emissivity, the maximum
temperature reached by the soot during the laser pulse was calculated to span a range of 341 K (3475–3816 K) at a 1064-nm
laser fluence of 0.1 J/cm² and 456 K (4115–4571 K) at a 1064-nm laser fluence of 0.4 J/cm² with a 1σ standard deviation about the mean of ∼25 K.

In this work, the evidence of SF₆ gas decomposition at the vicinity of SiO₂ glass has been investigated using various laser wavelengths: at 193, 248, 532 and 1064 nm. It was shown that SiF₄ gas and S₂F₁₀ clusters were simultaneously created during ArF excimer laser irradiation, while no by-products were seen in the irradiation
cell using Q-switched Nd:YAG laser. The gas content analysis was carried out using laser breakdown spectroscopy (LIBS) and
Fourier transform IR spectroscopy (FTIR). Moreover, the fluorine penetration into the glass surface was studied by energy
dispersive X-ray (EDX) microanalysis and wavelength dispersive X-ray (WDX) mapping to support the suggested mechanisms.