Sapphire Laser Pumping Research Articles

Polymer optical fiber amplifier based on all-inorganic perovskite quantum dots

The proliferation of polymer optical fibers (POFs) has opened multiple avenues of optical-based networks and sensing applications in the visible spectral range. However, the lack of efficient amplifiers significantly hinders their utilization in practical scenarios. As emerging gain media, halide perovskites have attracted considerable attention in exploring their practical applications. In this Letter, we investigated the optical gain properties of cesium lead bromide quantum dots (CsPbBr3 QDs), and by facet dip-coating, we realized a polymer optical fiber amplifier. Under a 400-nm, 163-fs Ti:Sapphire laser pumping, the amplified spontaneous emission (ASE) thresholds of 1.6 and 20.1 μJ/cm2 were achieved through stripe pumping of a QDs-thin-film and end-pumping of a polymer-fiber facet dip-coated with the QDs, respectively. A gain coefficient of 232.2 ± 22.8 cm−1 was obtained using the variable stripe length method. By coupling a broadband continuous-wave light source into the POF as the signal, the optical gain behavior was studied with varying pump fluence and signal power density. More than 20 dB optical gain was achieved within the ASE wavelength region of 530–540 nm with a predicted theoretical maximum gain of 33.6 dB. The research verifies the feasibility of amplifying continuous-wave signals in the visible spectrum and potentially closing the research gap in visible-light optical-to-optical amplifiers. This opens the avenue for further research and innovations in practical polymer-based optical amplification for a plethora of applications, including all optical processing chips and short-range interconnects, as well as visible-light and underwater communications.

Optimization of a multi-TW few-cycle 1.7-µm source based on Type-I BBO dual-chirped optical parametric amplification.

This paper presents the optimization of a dual-chirped optical parametric amplification (DC-OPA) scheme for producing an ultrafast intense infrared (IR) pulse. By employing a total energy of 0.77 J Ti:sapphire pump laser and type-I BBO crystals, an IR pulse energy at the center wavelength of 1.7 µm exceeded 0.1 J using the optimized DC-OPA. By adjusting the injected seed spectrum and prism pair compressor with a gross throughput of over 70%, the 1.7-µm pulse was compressed to 31 fs, which resulted in a peak power of up to 2.3 TW. Based on the demonstration of the BBO type-I DC-OPA, we propose a novel OPA scheme called the "dual pump DC-OPA" for producing a high-energy IR pulse with a two-cycle duration.

"Mixed" Tm:Ca(Gd,Lu)AlO4 - a novel crystal for tunable and mode-locked 2 µm lasers.

We report on the crystal growth, spectroscopy characterization and first laser operation of a new tetragonal disordered "mixed" calcium aluminate crystal, Tm:Ca(Gd,Lu)AlO4. The introduction of Lu3+ leads to an additional inhomogeneous broadening of Tm3+ absorption and emission spectra compared to the well-known Tm:CaGdAlO4. The maximum stimulated-emission cross-section for the 3F4 → 3H6 Tm3+ transition is 0.91 × 10-20 cm2 at 1813 nm for σ-polarization, and the emission bandwidth is more than 200 nm. A continuous-wave diode-pumped Tm:Ca(Gd,Lu)AlO4 laser generates 1.82 W at 1945 nm with a slope efficiency of 29%. Under Ti:Sapphire laser pumping, a continuous tuning of the laser wavelength from 1836 to 2083 nm (tuning range: 247 nm) is demonstrated. The Tm:Ca(Gd,Lu)AlO4 crystal is promising for tunable/femtosecond lasers at ~2 μm.

Passively Q-switched femtosecond-laser-written thulium waveguide laser based on evanescent field interaction with carbon nanotubes

Surface channel waveguides (WGs) were fabricated in a monoclinic Tm3+:KLu(WO4)2 crystal by femtosecond direct laser writing (fs-DLW). The WGs consisted of a half-ring cladding with diameters of 50 and 60 μm located just beneath the crystal surface. They were characterized by confocal laser microscopy and μ-Raman spectroscopy, indicating a reduced crystallinity and stress-induced birefringence of the WG cladding. In continuous-wave (CW) mode, under Ti:sapphire laser pumping at 802 nm, the maximum output power reached 171.1 mW at 1847.4 nm, corresponding to a slope efficiency η of 37.8% for the 60 μm diameter WG. The WG propagation loss was 0.7±0.3 dB/cm. The top surface of the WGs was spin-coated by a polymethyl methacrylate film containing randomly oriented (spaghetti-like) arc-discharge single-walled carbon nanotubes serving as a saturable absorber based on evanescent field coupling. Stable passively Q-switched (PQS) operation was achieved. The PQS 60 μm diameter WG laser generated a record output power of 150 mW at 1846.8 nm with η=34.6%. The conversion efficiency with respect to the CW mode was 87.6%. The best pulse characteristics (energy/duration) were 105.6 nJ/98 ns at a repetition rate of 1.42 MHz.

Electric-field induced second-harmonic generation of femtosecond pulses in atmospheric air

Electric-field induced second harmonic generation with a femtosecond Ti:sapphire pump laser in atmospheric air is investigated. Phase matching between fundamental and second harmonic waves is achieved via quasi-phase matching, employing periodic electrode arrangements on printed circuit boards with a total length of about 0.5 m. The weak chromatic dispersion of the atmospheric air enables broadband phase matching conditions and makes this method tailorable for frequency doubling broadband femtosecond laser pulses. A maximum energy of 0.13 nJ is observed in a 20 nm bandwidth around 395 nm.

Efficient continuous-wave in-band pumped Nd:KY(MoO4)2 laser

We report on highly-efficient laser operation in the orthorhombic Nd3+:KY(MoO4)2 (Nd:KYMo) double molybdate crystal. 2 at.% Nd:KYMo crystals were grown by the Czochralski method under low temperature gradients. Under Ti:Sapphire laser pumping at 874 nm (in-band, 4I9/2 → 4F3/2 transition), a compact continuous-wave (CW) c-cut Nd:KYMo laser generated 0.43 W at 1067 nm with a slope efficiency of 71% (with respect to the absorbed pump power) and a laser threshold of only 40 mW. For a standard pump wavelength of ~810 nm, the peak output was scaled to 0.55 W in a quasi-CW mode. A negative thermal lens has been detected for Nd:KYMo.

Efficient laser operation of Nd3+:Lu2O3 at various wavelengths between 917 nm and 1463 nm

Even though the first Nd3+-doped sesquioxide lasers have been realized more than 50 years ago, up to now no reports on efficient laser operation of Nd3+:doped sesquioxides can be found. In this work, we review the favorable spectroscopic properties of the sesquioxide Nd3+:Lu2O3 in terms of ground state absorption, stimulated emission, and excited state absorption cross sections as well as the upper level lifetime. Making use of these properties, we achieved efficient laser performance on eight different laser transitions in the wavelength range between 917 nm and 1463 nm under Ti:sapphire laser pumping using state-of-the-art HEM-grown Nd3+:Lu2O3 crystals with good optical quality. At the strongest transition around 1076 nm we determined a slope efficiency of 69%, which represents the highest efficiency ever obtained for a Nd3+-doped sesquioxide. Furthermore, we could generate watt level output powers and high slope efficiencies for seven other transitions. Lasers at 917 nm, 1053 nm, 1108 nm and 1463 nm were realized for the first time and the latter represents one of the longest laser wavelengths obtained on the 4F3/2 → 4I13/2 transition in Nd3+-doped materials.

The Shape of The Exfoliated Surface during Femtosecond Laser Ablation

Femtosecond laser ablation processes on metals are systematically observed using a Ti:sapphire laser pump and the soft x-ray laser probe reflective imaging system. In addition to the dark disk at the femtosecond laser-irradiated spot, an elliptical shadow that expands in the horizontal direction in the nanosecond time domain was observed. We show that the shadow is caused by the exfoliated surface during femtosecond laser ablation. By analyzing the shadow, we can determine the evolution of the exfoliated surface over time. The shape of the film is the result of the relationship between the spatial distribution of the laser beam profile and the ablation threshold of the metal.

Observation of Midinfrared 4-$\mu \text{m}$ Emission in Ho3+-Doped Fluoroaluminate Glasses

Ho3+ activated fluoroaluminate glasses were prepared successfully via melt-quenching method. Not only 2- and 2.85- $\mu \text{m}$ emissions but also 4- $\mu \text{m}$ emissions were observed for the first time by 900-nm Ti: sapphire laser pumping. The optimal midinfrared emissions were obtained when Ho3+ concentration reaches 1 mol%. Spectroscopic properties and energy transfer mechanism of Ho3+ were investigated in detail. Results indicate that the prepared glasses possess high midinfrared transmittance (90%), large emission cross sections at $2~\mu \text{m}$ ( $7.6 \times 10^{-21} $ cm $^{2}$ ), $2.85~\mu \text{m}$ ( $17.6 \times 10^{-21}$ cm $^{2}$ ), and 4 $\mu \text{m}$ ( $6.87 \times 10^{-21}$ cm $^{2}$ ) together with superior gain properties. It is suggested that Ho3+ activated fluoroaluminate glass is an attractive candidate for midinfrared laser materials application.

Observations of complex frequency comb structure in a harmonically-pumped femtosecond optical parametric oscillator

Various schemes allow femtosecond optical parametric oscillators to produce pulses at harmonics of their pump laser repetition frequency, each apparently offering the possibility of generating widely-spaced, tunable frequency combs. Using a 100-MHz Ti:sapphire pump laser, we have compared two alternative optical parametric oscillator architectures, both leading to 300-MHz pulses but one configured in a cavity three times shorter than the pump laser and the other in a cavity one-third longer. Heterodyne measurements between the pump and each of these two systems show that they possess different carrier-envelope offset characteristics, with implications on the coherence and stabilization of the resulting combs.

Dynamic wavelength switching of a remote nitrogen or air laser with chirped femtosecond laser pulses

We experimentally investigate the influence of the chirp of 800 nm Ti:sapphire pump laser pulses on the lasing behaviors of N2+ ions for the transitions between the excited electronic B2∑u+ state (v′ = 0) and the ground X2∑g+ state (v = 0,1) at wavelengths of 391 and 428 nm. We found that as the chirp of the pump laser pulses varies from negative to positive, the intensities of the lasing signals at 391 and 428 nm show different chirp-dependent behaviors. Namely, the coherent emission at 391 nm reaches the maximum when the chirp of the pump pulse is transform-limited; whereas the 428 nm emission becomes strongest when the pump pulse is negatively chirped. This observation is ascribed to different self-generated seed sources produced in the plasma channel, which is verified by introducing an external seed for a pump–probe measurement. Our finding enables switching of wavelengths of remote lasing emissions of N2+ by manipulating the chirp of the pump laser pulses.

Diode-pumped continuous-wave (Ho,Tm):KLu(WO_4)_2 laser with >1 W output power

We studied laser generation of the Ho3+-ion in (Ho,Tm):KLu(WO4)2 crystals pumped by Ti:sapphire and diode lasers achieving output powers up to ~1.2 W. For polarization parallel to the Nm principal axis, the lasers operated at 2078 or 2059-1960 nm depending on the transmission of the output coupler. The maximum slope efficiency with respect to the absorbed power reached ~30% for both types of pump sources. Tuning was studied with Ti:sapphire laser pumping achieving a tuning range of ~180 nm.

Continuous-wave laser performance of Tm:LuVO4 under Ti:sapphire laser pumping

We investigate the cw laser performance of Tm:LuV O4 crystals pumped with tunable polarized source and report a roughly twofold improvement to their efficiency with 1 W of output power and broad tunability at room temperature.

Time-resolved soft x-ray absorption setup using multi-bunch operation modes at synchrotrons

Here, we report on a novel experimental apparatus for performing time-resolved soft x-ray absorption spectroscopy in the sub-ns time scale using non-hybrid multi-bunch mode synchrotron radiation. The present setup is based on a variable repetition rate Ti:sapphire laser (pump pulse) synchronized with the ~500 MHz x-ray synchrotron radiation bunches and on a detection system that discriminates and singles out the significant x-ray photon pulses by means of a custom made photon counting unit. The whole setup has been validated by measuring the time evolution of the L(3) absorption edge during the melting and the solidification of a Ge single crystal irradiated by an intense ultrafast laser pulse. These results pave the way for performing synchrotron time-resolved experiments in the sub-ns time domain with variable repetition rate exploiting the full flux of the synchrotron radiation.

Dual-chirped optical parametric amplification for generating few hundred mJ infrared pulses

An ultrafast high-power infrared pulse source employing a dual-chirped optical parametric amplification (DC-OPA) scheme based on a Ti:sapphire pump laser system is theoretically investigated. By chirping both pump and seed pulses in an optimized way, high-energy pump pulses can be utilized for a DC-OPA process without exceeding the damage threshold of BBO crystals, and broadband signal and idler pulses at 1.4 μm and 1.87 μm can be generated with a total conversion efficiency approaching 40%. Furthermore, few-cycle idler pulses with a passively stabilized carrier-envelope phase (CEP) can be generated by the difference frequency generation process in a collinear configuration. DC-OPA, a BBO-OPA scheme pumped by a Ti:sapphire laser, is efficient and scalable in output energy of the infrared pulses, which provides us with the design parameters of an ultrafast infrared laser system with an energy up to a few hundred mJ.

Broad emission band of Yb^3+ in the nonlinear Nb:RbTiOPO_4 crystal: origin and applications

By means of micro-structural and optical characterization of the Yb:Nb:RbTiOPO(4) crystal, we demonstrated that the broad emission band of Yb(3+) in these crystals is due to the large splitting of the ytterbium ground state only, and not to a complex multisite occupation by the ytterbium ions in the crystals. We used this broad emission band to demonstrate wide laser tuning range and generation of femtosecond laser pulses. Passive mode-locked laser operation has been realized by using a semiconductor saturable absorber mirror, generating ultra short laser pulses of 155 fs, which were very stable in time, under Ti:sapphire laser pumping at 1053 nm.

Continuous-wave laser operation of Tm and Ho co-doped NaY(WO_4)_2 and NaLu(WO_4)_2 crystals

Tetragonal single crystals of NaT(WO(4))(2) (T = Y or Lu) co-doped with Tm(3+) and Ho(3+) ions have been employed for broadly tunable and efficient room-temperature laser operation at around 2 mum. With Ti:sapphire laser pumping at 795 nm, a slope efficiency and a maximum output power as high as 48% and 265 mW, respectively, have been achieved at 2050 nm from a Tm,Ho:NaY(WO(4))(2) crystal. Tuning from 1830 nm to 2080 nm has also been obtained using an intracavity Lyot filter.

Nd:YAG waveguide laser with 1.3 W output power, fabricated by direct femtosecond laser writing

Tracks of modified material were written with femtosecond-laser pulses in neodymium-doped YAG crystals. Due to a stress-induced change of the refractive index, waveguiding beside the tracks and between two adjacent tracks with a distance of approximately 25 μm was observed. Loss measurements resulted in guiding losses of about 1.6 dB/cm for the double track waveguide. Spectroscopic investigations of the 4F3/2→4F11/2 transmission lines of the neodymium ions, which are close to the modified region, revealed a small stress-induced red shift of the lines. Laser oscillation of single-track waveguides and double-track waveguides was demonstrated with Ti:Sapphire laser pumping at a wavelength of 808 nm. Best laser performance with about 1.3 W output power at 2.25 W launched pump power was achieved using a double-track waveguide with a separation of 27 μm at an outcoupling transmission of 95%.

Optical frequency up-conversion by supercontinuum-free widely-tunable fiber-optic Cherenkov radiation

Spectrally-isolated narrowband Cherenkov radiation from commercial nonlinear photonic crystal fibers is demonstrated as an ultrafast optical source with a visible tuning range of 485-690 nm, which complementarily extends the near-infrared tuning range of 690-1020 nm from the corresponding femtosecond Ti:sapphire pump laser. Pump-tosignal conversion efficiency routinely surpasses 10%, enabling multimilliwatt visible output across the entire tuning range. Appropriate selection of fiber parameters and pumping conditions efficiently suppresses the supercontinuum generation typically associated with Cherenkov radiation.

Coherent ultrafast pulse synthesis between an optical parametric oscillator and a laser

We have demonstrated coherent pulse synthesis between the carrier-envelope, phase-locked, second-harmonic pulses from a synchronously pumped femtosecond optical parametric oscillator and those from its self-mode-locked Ti:sapphire pump laser. By using a single nonlinear crystal for parametric and second-harmonic generation, we maximized the common-mode rejection of environmental noise, obtaining a temporal overlap between the pulses with a precision of 30 as (1% of the optical period) in an observation time of 20 ms. Mutual coherence between the two parent pulses was verified optically by spectral interferometry, and synthesis was tested by measuring the autocorrelation of the combined pulses, with and without carrier-envelope phase locking.