High power simultaneous dual-wavelength CW and passively-Q-switched laser operation of LD pumped Tm:YLF at 1.9 and 2.3 µm.

Simultaneous dual-wavelength laser oscillation of Tm:YLF at 1.9 and 2.3 µm were successfully realized. The three-mirror cavity was exploited to study dual-wavelength laser performance, which is formed by a shared input mirror and two independent output couplers for the two laser wavelengths. Under an absorbed pump power of 15.2 W, the maximum CW output powers of 5.49 W around 1908nm and 1.12 W around 2305 nm were simultaneously obtained, corresponding to a total optical-to-optical conversion efficiency of 43.5%. A Cr2+:ZnSe was further used to passively Q-switch the dual-wavelength laser, generating pulses with pulse widths of 554 ns at 1.9 µm and 4 µs at 2.3 µm. To the best of our knowledge, this is the first report on the dual-wavelength laser operation of Tm3+-single-doped solid-state laser at 1.9 and 2.3 µm. The higher optical conversion efficiency, smaller wavelength competition effect and simultaneous dual-wavelength output make this Tm-doped solid-state laser have potential application in medical surgery.

High-efficiency high-repetition-rate gain-switched operation around 3 µm in Cr2+:CdSe single-crystal laser pumped by fiber-laser-pumped Ho3+:YAG laser.

We report the efficient gain-switched high-repetition-rate Cr2+:CdSe single-crystal laser operating around 3 µm and pumped at 2.09 µm by a fiber-laser-pumped Ho3+:YAG laser. Average power of up to 6 W with the optical-to-optical efficiency of 67% at 2.65-2.85 µm was achieved in the Cr2+:CdSe laser with nanosecond pulses at 8 kHz repetition rate. Wavelength tunability from 2.5 µm to 3.15 µm was demonstrated using a set of cavity mirrors and an intracavity Lyot filter.

Broadband spectral characterization of the phase shift induced by population inversion in Ti:Sapphire.

The spectral phase shift of broadband amplified pulses, induced by population inversion, was measured in Ti:Sapphire at different pump fluence values. The measurement was performed for two orthogonal polarization directions and at two different crystal temperatures of 296 K and 30 K. Zero shifts and sign changes were observed in the spectral phase, which are connected to the gain spectrum of the crystal. The electronic refractive index changes were also numerically calculated by the Kramers-Kronig theory. The results are highly important for achieving sub-10 fs pulse duration and phase stability in the next generation of Ti:Sapphire-based laser systems.

Influence of a backward reflection on low-threshold mode instability in Yb3+-doped few-mode fiber amplifiers.

An influence of backward reflection on spatio-temporal instability of the fundamental mode in Yb3+-doped few-mode polarization maintaining fiber amplifiers with a core diameter of 10 µm was studied experimentally and theoretically. The mode instability threshold was registered to decrease dramatically in the presence of a backward reflection of the signal from the output fiber end; an increase of the signal bandwidth or input power resulted in the increase of the threshold. Numerical simulation revealed a self-consistent growth of the higher-order mode LP11 and a traveling index grating accompanying the population grating induced by the mode interference field (due to different polarizability of the excited and unexcited Yb3+ ions). The presence of the backward-propagating wave resulted in four-wave mixing on the common index grating induced by the interference field of pairs of the fundamental LP01 and LP11 modes.

Highly efficient 2 µm CW and Q-switched Tm3+:Lu2O3 ceramics lasers in-band pumped by a Raman-shifted erbium fiber laser at 1670 nm.

Highly efficient laser oscillations at 2 µm were investigated in Tm:Lu2O3 ceramics in-band pumped at 1670 nm by a Raman-shifted erbium fiber laser. Both 23 W CW and 15 W active Q-switched oscillations with 40 ns pulse duration and 15-30 kHz repetition rate were achieved in a high-quality beam. The evolution of two generated waves at 1966 and 2064 nm in dependence on pump power was studied.

Hybrid booster at 1940 nm based on Tm:Lu2O3 ceramics implementing fiber combined signal and pump sources.

A novel concept of a booster amplifier for a pulsed Tm fiber laser at 1940 nm based on Tm:Lu2O3 ceramics and implementing fiber-combined signal and pump was examined. The pumping emission of the ceramics at 1678 nm was obtained from Raman-shifted Er fiber laser radiation. The hybrid fiber-ceramics amplifier with a gain factor of up to 6 dB and a pulse energy of more than 650 µJ with single-mode output was demonstrated.

Low-threshold mode instability in Yb3+-doped few-mode fiber amplifiers.

Spatio-temporal instability of the fundamental mode in Yb(3+)-doped few-mode PM fiber amplifiers with a core diameter of 8.5 µm was registered at 2-30 Watts pump power. Both experimental and theoretical analysis revealed the nonlinear power transformation of the LP(01) fundamental mode into high-order modes. Numerical simulation revealed self-consistent growth of the higher-order mode and traveling electronic index grating accompanying the population grating induced by the mode interference field (due to different polarizability of the excited and unexcited Yb(3+) ions). Experimental results and numerical calculations showed the increase of the instability threshold along with an increase of the signal frequency bandwidth.

2-µm Tm:Lu2O3 ceramic disk laser intracavity-pumped by a semiconductor disk laser.

A proof-of-principle study of a 1.97-µm Tm:Lu2O3 ceramic disk laser, intracavity pumped by a 1.2-µm semiconductor disk laser, is presented. The demonstrated concept allows for improved pump absorption and takes advantage of the broad wavelength coverage provided by semiconductor disk laser technology. For thin disk lasers the small thickness of the gain element typically leads to inefficient pump light absorption. This problem is usually solved by using a complex multi-pass pump arrangement. In this study we address this challenge with a new laser concept of an intracavity pumped ceramic thin disk laser. The output power at 1.97 µm was limited to 250 mW due to heat spreader-less mounting scheme of the ceramic gain disk.

Broadly tunable femtosecond Tm:Lu2O3 ceramic laser operating around 2070 nm.

Femtosecond mode locking of a Tm-doped Lu2O3 ceramic laser is reported. Transform-limited pulses as short as 180 fs are generated at 2076 nm with an average output power of 400 mW and a pulse repetition frequency of 121.2 MHz. An output power up to 750 mW can be reached at the somewhat longer pulse duration of 382 fs. Femtosecond pulse generation is realized in the 2030-2100 nm spectral range. Passive mode locking was achieved using an ion-implanted InGaAsSb quantum-well-based SESAM.

All-fiber coherent combining of Er-doped amplifiers through refractive index control in Yb-doped fibers.

We propose a simple all-fiber solution for coherent beam combining of Er-doped fiber amplifiers. This method, which we believe to be a new method, employs the effect of refractive index changes in Yb-doped fibers induced at approximately 1.55 microm by optical pumping at approximately 980 nm, which is performed for an active phase control in the fiber configuration. An algorithm based on population inversion in a two-level system supports the straightforward implementation of the effect into a feedback loop. Combining two 500 mW Er-doped amplifiers in a single-mode fiber is successfully demonstrated with control by approximately 120 mW laser diode. The method is shown to operate against the acoustic phase noise within the range of approximately pi rad and with a rate of approximately 2.6 pi rad/ms that potentially serves combining of at least 50 amplifiers similar to those used in practical work.

Dynamics of pump-induced refractive index changes in single-mode Yb-doped optical fibers.

We quantify the refractive index changes (RIC) in single-mode ytterbium-doped optical fibers induced by optical pulses at 980 nm and, for the first time, report details of the effect dynamics. The RIC dynamics is shown to follow that of the population of the excited/unexcited ion states with a factor proportional to their polarizability difference (PD). The absolute PD value is evaluated in the spectral range of 1460-1620 nm for different fiber samples and is found to be independent on the fiber geometry and on the ion concentration. The PD dispersion profile indicates to a predominant far-resonance UV rather than near-resonant IR transitions contribution to the RIC.

Efficient continuous-wave generation in a self-organizing diode-pumped Nd:YVO4 laser with a reciprocal dynamic holographic cavity.

A diode-pumped Nd:YVO4 laser is demonstrated that has a reciprocal self-intersecting loop cavity with self-organization by formation of a dynamic holographic grating induced by the generating beam. Continuous-wave high spatial quality generation (M2 < 1.2) with 9.6 W of power and 32% optical efficiency is obtained. Spectral compositions and temporal dynamics are investigated as functions of diode-pumping power.