Virtual Journal of Laser

We demonstrate the effect of inversion population ratio mediated by 980 nm pumping band on the gain spectra of a gain-flattened
Erbium-doped fiber amplifier. The gain equalizing filter was designed at 977 nm and the amplifier was built in the four-stage
arrangement. In the pumping structure, the 1480 nm lasers were maintained in the final gain block while the 980 nm band lasers
were utilized in the first three blocks. These laser sources were arranged at several combinations of 977 and 980 nm wavelengths.
Within these 3 nm spectrum, an absorption cross-section difference around 0.32 × 10⁻²⁵ m² contributed to a dispensable gain variation up to 3-dB. These inequalities were the results of variations in population inversion
induced by the pump wavelength discrepancy. The findings show the importance of designing a filter at the specific absorption
wavelength to allow the operation of consistent gain level.

The influence of binding of nanomarkers of fluorescein family to HSA on secondary structure of this protein at different values
of pH was investigated by Raman spectroscopy method. The greatest changes in secondary structure of HSA, consisting in decreasing
of α-helix sites, at binding of fluorescein to HSA occur at pH 5–6. The greatest changes in secondary structure of HSA, consisting
in decreasing of α-helix sites, at binding of eosin or erythrosin to HSA take place at values of pH, smaller 5. The differences
in changes in secondary structure of HSA at binding of these three nanomarkers are explained by dependences of binding of
nanomarkers to HSA on pH which determined by value of electronegativity of atoms of lateral radicals in structural formulas
of nanomarkers and, therefore, by value of pK of their ionized groups.

A miniature Cr⁴⁺:YAG Q-switched, repetitive operation, conductive cooling Nd:YAG laser with a retroreflecting corner cube prism is demonstrated.
The corner cube prism which is insensitive to misalignment in any direction makes it useful for the laser to adapt to the
violent change of ambient temperature and also makes the laser cavity insensitive to the variation of thermal lens of the
crystal. The laser has excellent stability of the average output pulse energy and the threshold voltage under different ambient
temperature of −40, 25, and 55°C.

The soliton molecule is achieved in nonlinear polarization rotation fiber laser. The structure of soliton molecule is heterogeneous
diatomic molecule. The soliton molecule originates from the splitting of the high energy soliton. The dips of the soliton
molecule spectra show that there is the interaction between the constituents of the soliton molecule, resulting in that the
constituents are in the bound state as a unit. The laser bias can change the fine structure of the soliton molecule, which
can be observed in the autocorrelator and oscilloscope.

In order to solve the hard problem of laser instability, a miniature Cr⁴⁺:YAG Q-switched Ce:Nd:YAG laser with a retroreflecting corner cube prism is demonstrated. The corner cube prism is insensitive
to misalignment in any direction. Laser cavity with the prism is found to meet the condition of violent change of environment
temperature and the variation of thermal lens of laser crystal by our experiment. Compared with flat-flat cavity, stability
of the laser with a retroreflecting corner cube prism is improved remarkably.

The purpose of study is to quantify and compare diffusion of propylene glycol, glucose, glycerol in the human skin in vivo
noninvasively. Optical coherence tomography (OCT) was utilized in the functional imaging of optical cleaning agents for monitoring
and quantifying the permeability coefficients (PCs) of them. Our experiments showed that the permeability coefficient of 40%
propylene glycol from different subjects was averaged and found to be (2.52 ± 0.02) × 10⁻⁶ cm/s, the permeability coefficient of 40% glucose was (1.94 ± 0.05) × 10⁻⁶ cm/s, and the permeability coefficient of 40% glycerol was (1.82 ± 0.04) × 10⁻⁶ cm/s. The results indicated that the diffusion of propylene glycol solutions was faster than that of glucose solution, and
the diffusion of glucose solutions was faster than that of glycerol solutions.

In this paper, it is the first time to experimentally demonstrate the second harmonic generation (SHG) of temporal phase modulated
broadband laser. The SHG conversion efficiency and the characteristic of SHG spectrum are investigated in detail and the relation
between SHG conversion efficiency and incident fundamental light intensity is obtained. The highest efficiency of nearly 70%
is achieved at the fundamental pulse intensity of 1.6 GW/cm². The experimental results show that the SHG spectrum widths under high and low intensity are both half of the incident fundamental
lights, and don’t result in the spectrum narrowing. The obtained results are very useful for operation at the second harmonic
wavelength in inertial confinement fusion (ICF) laser facility.

A diode-end-pumped high repetition rate, high peak power acousto-optical (AO) Q-switched 946 nm Nd:YAG laser was demonstrated
in this paper. In our experiments, a 20 mm miniature acousto-optical Q-switch was employed in a 45 mm linear laser cavity
for generating the short laser pulse. At a repetition rate of 10 kHz, a maximum average output power of 2.9 W was achieved
with a pulse width of 24.4 ns, giving a peak power of 11.9 kW. To the best of our knowledge, this is the highest peak power
946 nm Nd:YAG laser at high repetition rate operation. Moreover, pulse train with good stability was also obtained at the
repetition rate of 50 kHz. At an incident pump power of 22.3 W, up to an average output power of 3.5 W pulsed 946 nm laser
was generated at 50 kHz with a pulse width of 69 ns, corresponding to an optical conversion efficiency of 15.7% and an average
slope efficiency of 24.1%, respectively.

An increase in the dental caries prevalence on root surfaces has been observed mainly in elderly. This research assessed,
in vitro, the effectiveness of a pulsed CO₂ (λ = 10.6 μm) laser associated or not with fluoride, in reducing human root dentine demineralization in conditions that mimic
an oral high cariogenic challenge. After sterilization, root dentine specimens were randomly assigned into 6 groups (n = 30), in triplicate. The groups were Control (C), Streptococcus mutans (SM), Fluoride (F), Laser (L), Fluoride + laser (FL), and Laser + fluoride (LF). Except for the control group, all the specimens
were inoculated with SM and immersed 3 times a day in a 40% sucrose bath. After a 7-day cariogenic challenge, the mineral
loss and lesion depth were evaluated by transverse microradiography and fluoride in the biofilm was determined using an ion-selective
electrode. Results were statistically analyzed by analysis of variance, at 5% of significance level.

A novel wavelength switchable all-fiber comb filter based on a dual-pass Mach-Zehnder (M-Z) interferometer is proposed and
demonstrated. The proposed filter consists of a rotatable polarizer and a standard dual-pass M-Z interferometer composed of
two 3-dB fiber couplers with a polarization controller (PC) in one arm. When the PC is properly set, the wavelength switchable
operation is achieved by adjusting the polarization state of the input light. Theoretical calculation is verified by the experimental
results. As applications, the proposed comb filter is incorporated into a fiber ring laser to generate wavelength switchable
multiwavelength lasing.