Optical parametric oscillators synchronously pumped with 1-µm femtosecond and picosecond lasers are used to generate long-wave mid-infrared radiation using the nonlinear material orientation-patterned gallium phosphide. The output spectra from the femtosecond OPO are measured, demonstrating tuning based on grating period and temperature from 5.5 to 13.0 µm. The picosecond OPO produces 137 mW at 7.87 µm, representing the first picosecond-pumped OPO using orientation gallium phosphide.
By using free-running independent femtosecond OPOs with a repetition-rate difference of 500 Hz we demonstrate methane absorption spectroscopy with spectral coverage simultaneously spanning the methane P, Q and R branches and with a resolution of 0.5 cm. Absolute optical frequency calibration with an accuracy of 0.25 cm (0.27 nm) is achieved from simultaneous repetition-rate and carrier-envelope-offset frequency measurements, without the need for any optical reference. The calibration technique allows registration and averaging of consecutively acquired dual-comb spectra, leading to a high quality and low-noise absorbance measurement in good agreement with the HITRAN database.
The CREMA collaboration is pursuing a measurement of the ground-state
hyperfine splitting (HFS) in muonic hydrogen
(\muμp)
with 1 ppm accuracy by means of pulsed laser spectroscopy to determine
the two-photon-exchange contribution with 2\times10^{-4}2×10−4
relative accuracy. In the proposed experiment, the
\muμp
atom undergoes a laser excitation from the singlet hyperfine state to
the triplet hyperfine state, {then} is quenched back to the singlet
state by an inelastic collision with a H_22
molecule. The resulting increase of kinetic energy after the collisional
deexcitation is used as a signature of a successful laser transition
between hyperfine states. In this paper, we calculate the combined
probability that a \muμp
atom initially in the singlet hyperfine state undergoes a laser
excitation to the triplet state followed by a collisional-induced
deexcitation back to the singlet state. This combined probability has
been computed using the optical Bloch equations including the inelastic
and elastic collisions. Omitting the decoherence effects caused by {the
laser bandwidth and }collisions would overestimate the transition
probability by more than a factor of {two in the experimental
conditions. Moreover,} we also account for Doppler effects and provide
the matrix element, the saturation fluence, the elastic and inelastic
collision rates for the singlet and triplet states, and the resonance
linewidth. This calculation thus quantifies one of the key unknowns of
the HFS experiment, leading to a precise definition of the requirements
for the laser system and to an optimization of the hydrogen gas target
where \muμp
is formed and the laser spectroscopy will occur.
Fiber gratings are among key components in fiber-based photonics systems and, particularly, laser cavities. In the latter, they can play multiple roles, such as those of mirrors, polarizers, filters, or dispersion compensators. In this Letter, we present the inscription of highly reflective first-order fiber Bragg gratings (FBGs) in soft indium fluoride-based (
I
n
F
3
) fibers using a two-beam phase-mask interferometer and a femtosecond laser. We demonstrate an enhanced response of
I
n
F
3
-based fiber to a visible (400 nm) inscription wavelength compared to ultraviolet irradiation at 266 nm. In this way, FBGs with a reflectivity
>
99.7
%
were inscribed at around 1.9 µm with the bandwidth of 2.68 nm. After thermal annealing at 393K, the Bragg wavelength demonstrates stable thermal shift of 20 pm/K in the temperature range 293–373K. These observations suggest a potential extension of
I
n
F
3
fiber-based laser components to an operational range of up to 5 µm.
The Pound–Drever–Hall (PDH) technique is a popular method for stabilizing the frequency of a laser to a stable optical resonator or, vice versa, the length of a resonator to the frequency of a stable laser. We propose a refinement of the technique yielding an “infinite” dynamic (capture) range so that a resonator is correctly locked to the seed frequency, even after large perturbations. The stable but off-resonant lock points (also called Trojan operating points), present in conventional PDH error signals, are removed by phase modulating the seed laser at a frequency corresponding to half the free spectral range of the resonator. We verify the robustness of our scheme experimentally by realizing an injection-seeded Yb:YAG thin-disk laser. We also give an analytical formulation of the PDH error signal for arbitrary modulation frequencies and discuss the parameter range for which our PDH locking scheme guarantees correct locking. Our scheme is simple as it does not require additional electronics apart from the standard PDH setup and is particularly suited to realize injection-seeded lasers and injection-seeded optical parametric oscillators.
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