Double-pass Amplifier Research Articles

Single-frequency erbium-doped fiber laser based on self-injection feedback.

In this paper, a single-frequency erbium-doped fiber laser based on self-injection feedback is reported, which uses a high-reflectivity broadband fiber Bragg grating, an ordinary commercial high-doped erbium fiber and a low-reflectivity broadband fiber Bragg grating to form the main resonant cavity, and a stable narrow linewidth single-frequency laser output is achieved by connecting a single-mode fiber and a low reflectivity narrowband fiber Bragg grating to form self-injection feedback. Then, a saturated double-pass erbium-doped fiber amplifier and a saturable absorber were added to the self-injection optical path, which well suppressed the relative intensity noise and phase noise and the relaxation oscillation intensity was well suppressed by about 18.08 dB, and the phase noise was 36.7dBc·Hz-1 suppression, the edge-mode rejection ratio is increased by 13 dB, and the final laser linewidth is about 270 Hz, and the output power is 8.5 dBm.

High power GaSb-based superluminescent diode with cascade cavity suppression waveguide geometry and ultra-low antireflection coating

We report on a GaSb-based superluminescent diode optimized for high-power broadband operation around a wavelength of 2 μm. The high optical power was achieved by the high-quality epitaxial InGaSb/AlGaAsSb type-I quantum well gain material, which was processed into a double-pass amplification configuration. To prevent lasing at high current injection while enabling strong amplified spontaneous emission, a cascade cavity suppression waveguide geometry was designed to connect the vertical rear facet with the reflectivity-suppressed angled front facet. A Ta2O5/SiO2 ultra-low antireflection coating with a minimum reflectivity of 0.04% was applied to the front facet for further cavity suppression. This combination allowed the superluminescent diodes to demonstrate a record high single-transverse-mode output power of up to 152 mW under continuous-wave operation at room temperature, with a broad spectral band of 42 nm full width at half maximum. A 25% promotion in optical power has been realized compared to current state-of-the-art devices in this wavelength range, without sacrificing spectral bandwidth. The high-power spectral density characteristics, along with a good beam quality, are well suited for absorption spectroscopy applications and hybrid integration with silicon technology.

A single-longitudinal-mode Er:YAG laser and MOPA system based on the Faraday effect

We demonstrate a continuously operating Er:YAG single-longitudinal-mode laser and its amplifier with a corner cube retroreflector based on the Faraday effect. A maximum power of 1.02 W, the central wavelength of 1645.46 nm, Er:YAG single-longitudinal-mode laser with a line-width of 204 kHz has been realized. The slope efficiency is 9.38% and the beam quality factors M2 are 1.16, 1.05 in the × and y directions. Additionally, the single-longitudinal-mode laser is amplified to 1.86 W by the double-pass amplifier. The results indicate that the unidirectional operation ring laser in combination with the corner cube prism provides a 1.6 μm continuous-wave single-longitudinal-mode laser with high-power and stability.

Compact all-solid-state femtosecond Yb amplifier using a high-brightness multi-watt tapered laser diode

In this work, we present a novel amplification module based on a high-brilliance tapered pump laser diode. A monolithic distributed Bragg grating permits to stabilize the diode wavelength, that was kept at 978.5 nm with a full-width at half-maximum bandwidth <0.2 nm during our experiments. Such a compact and reliable single laser source achieves a maximum output power of about 6.5 W, in a linearly polarized beam with high spatial quality (M2 < 1.5). This allows to optimize the performance of compact amplification modules designed to maximize the gain-per-Watt of absorbed pump power and the optical-to-optical extraction efficiency. To assess the potential of such pump unit, we designed a single-pass and double-pass amplification module based on a 3-mm-long 9.5%-doped Yb:KYW crystal, seeded by a either a cw or a femtosecond oscillator providing a maximum average power of ∼500 mW with output wavelength tunable between 1025 nm and 1035 nm. By tightly focusing the pump beam and carefully optimizing the mode-matching between the almost TEM00 pump and seed beam we achieved a single pass small signal gain G0 > 7 at about 3.5 W absorbed pump power and a maximum output power of 2.2 W, corresponding to an optical-to-optical extraction efficiency close to 50%. The excellent beam quality of the seeder was very well preserved during amplification, resulting in a measured Mx2× My2 <1.1 both in single and double pass.

Effect of delay time between pre-pulse and main pulse on single-pass and double-pass amplification of 46.9 nm laser

In this paper, the influence of the delay time between the pre-pulse and the main pulse on the double-pass amplified 46.9 nm laser was studied for the first time, to the best of our knowledge, by using a high-precision polished SiC slice as a rear mirror. The temporal and spatial characteristics of the output laser were measured separately to investigate the effect of the delay time on the laser characteristics. The energy of the double-pass amplified laser was between 510 µJ and 890 µJ. In addition, a theoretical model of double-pass amplification was established to analyze the effect of the delay time on the double-pass amplified 46.9 nm laser.

Effects of L-shape and Raman second-order pumping scheme on the performance of double-pass hybrid fiber amplifier

Effects of L-shape and Raman second-order pumping scheme on the performance of double-pass hybrid fiber amplifier

Compact 15 mJ Fiber–Solid Hybrid Hundred-Picosecond Laser Source for Laser Ablation on Copper

We report on a millijoule-level fiber–solid hybrid hundred-picosecond laser system with a stable performance and compact structure. The laser system is based on a master oscillator power amplifier structure containing an all-fiber master oscillator, a quasi-continuous-wave side-pumped Nd:YAG regenerative amplifier, and a double-pass amplifier. By using the filtering effect of fiber Bragg grating and the dispersion characteristics of single-mode fiber stretcher, the spectrum broadening caused by self-phase modulation effect is effectively suppressed. Thus, the gain linewidth of the Yb-doped fiber seed source and Nd:YAG laser amplifiers is accurately matched. The reason for thermally induced depolarization in the solid-state laser amplifier is theoretically analyzed, and a more flexible depolarization compensation structure is adopted in amplifier experiment. Furthermore, the pulse energy of 14.58 mJ and pulse width of 228 ps is achieved at 500 Hz repetition rate. The central wavelength is 1064.1 nm with a 3 dB bandwidth of 0.47 nm. The beam quality factors in the horizontal and vertical directions are 1.49 and 1.51, respectively. This laser system has a simple and compact structure and has a power stability of 1.9%. The high pulse energy and beam quality of this hundred-picosecond laser are confirmed by latter theoretical simulation of copper laser ablation. It is a very practical laser system for material processing and laser-induced damage.

Sub-60-fs, compact 1100-nm fiber laser system based on double-pass pre-chirp managed amplification.

An ytterbium-doped, single-stage, double-pass nonlinear fiber amplification system was fabricated for amplifying an 1100-nm mode-locking fiber laser. Pre-chirp managed amplification (PCMA) was applied in realizing the nonlinear amplification process with an all-polarization-maintaining (PM) fiber construction. The system can deliver 19.8-nJ, 58.7-fs, 24.4-MHz amplified signal pulses with a 10-dB spectral range spanning from 1049 nm to 1130 nm. Further experimental investigations were conducted in exploring the dynamics of the double-pass nonlinear amplification process. This compact 1100-nm ultrafast fiber laser can be implemented for multi-photon microscopy (MPM) with deep penetration depth.

Radially polarized 33 W emission from a double-pass Ho:YAG thin-slab amplifier

The generation of a 33.7 W radially polarized output is demonstrated by way of double-pass amplification in a Ho:YAG thin-slab crystal. The amplifier system was seeded with the radially polarized output beam from a continuous-wave 13.2 W, 2.1 µm Ho:YAG rod laser, which exploited gain medium bifocusing and a ring-shaped pump spot to promote preferential lasing on the radially polarized Laguerre–Gaussian mode. By compensating for both the thermally induced stress birefringence in the thin-slab crystal and the Gouy phase shift resulting from astigmatic focusing of the 13.2 W seed, only marginal beam degradation was observed across the 95 W range of pump power into the amplifier.

100 kHz Narrow-Linewidth Burst-Mode MOPA Laser System With Uniform Envelope

In this study, a 100-kHz narrow-linewidth burst-mode laser system combined with a master oscillator power amplifier (MOPA) structure was reported with a stable pulse burst profile over 2 ms duration. A theoretical model was established to characterize and compensate the variation characteristics of coefficient of variation (COV) within a burst envelope for the double-pass three-stage amplification system, in terms of different parameter factors. Simulated results yielded similar tendency with the measured ones. For a stable burst envelope with a COV of 2.72% and 2.93%, output pulse energy at a 100 kHz repetition rate was scaled up to 1.08 and 4.38 mJ in the case of an input average pulse energy of 8.6 and 116.51 nJ, respectively. Corresponding Mx2 and My2 values with 2.2 and 2.4 were endowed with 1.08 mJ output single-pulse energy and 2.7 and 2.1 for 4.38 mJ pulse energy. The spectral linewidth of amplified pulses was measured to be less than 83.1 and 67.9 MHz, with respect to output pulse duration of 10.3 and 96.1 ns, respectively.

High Stability Industrial-Grade Nd: YVO4 Picosecond Laser Amplifier With High Average Output Power

We demonstrate a high-power Nd: YVO4 picosecond laser amplifier that is capable of generating 51.5 W of average output power at a wavelength of 1,064 nm, with a repetition rate of 70 MHz and a pulse duration of 8.5 ps. This system encompasses three stages of laser diode end-pumped Nd: YVO4 amplification including two double-pass amplifiers and a single-pass amplifier. Laser output with near-diffraction-limited beam quality (M2 &amp;lt; 1.1) was maintained throughout the entire power scaling range of the laser. The system exhibited very high output power stability with a root-mean-square amplitude fluctuation of less than 0.2% over a period of 15 h of continuous operation.

High-repetition-rate, 50-µJ-level, 1064-nm, CPA laser system based on a single-stage double-pass Yb-doped rod-type fiber amplifier

A 1064-nm femtosecond fiber chirped pulse amplification (FCPA) laser system based on a single-stage double-pass Yb-doped rod-type photonic crystal fiber (PCF) amplifier was demonstrated with a pulse repetition rate of 500 kHz, which was specially designed for expected conversion efficiency enhancement of a 10.8 eV source. With a series of Yb:fiber power amplifiers, the average output power was boosted to approximately 35 W. Further, using a transmission gratings-based pulse compressor, an average output power of 27.5 W was achieved, corresponding to a pulse energy of 55 µJ and a compression efficiency of 78.6%. The shortest pulse duration was optimized to be 204 fs, which was also accompanied by obvious pedestal. A pulse duration of 336 fs was also obtained when the pulse quality was at a top priority. To the best of our knowledge, this is the first demonstration of high-repetition-rate high-pulse-energy 1064-nm, instead of 1035-nm, femtosecond laser, based on commercially available Yb-doped rod-type PCF amplifier.

Numerical model of end-pumped Yb:YAG double-pass laser amplifier experimentally validated at 129 W output power

Keywords: solid-state amplifier, thermal effects, depolarization In this work, a double-pass end-pumped Yb:YAG amplifier system was investigated experimentally and numerically. The amplifier was seeded by a fibre-CPA based seed laser FemtoLux 30 (Ekspla). The presented laser system produced 129 W average power and 129 μJ energy pulses at 1 MHz pulse repetition rate, with optical-to-optical efficiency of 32% at room temperature (T = 20°C). The resulting beam quality was M2 ∼ 2.1 and the measured depolarization losses were to 17.9%. After the compression, 441 fs pulse duration was achieved. During the work, comprehensive amplifier modelling was performed using the code written in Matlab. The modelling results matched well the experimental data, providing the tool to predict the performance of laser systems based on ytterbium-doped isotropic crystalline, ceramic and glass laser materials prior to designing and manufacturing.

Single-pass and double-pass USP amplification in heavily alloyed Er/Yb complexed active fiber

Single-pass and double-pass USP amplification in heavily alloyed Er/Yb complexed active fiber

Effect of Delay Time between Pre-Pulse and Main Pulse on Single-Pass and Double-Pass Amplification of 46.9nm Laser

Effect of Delay Time between Pre-Pulse and Main Pulse on Single-Pass and Double-Pass Amplification of 46.9nm Laser

High efficiency, 41.6 W, 10 kHz picosecond output based on a Nd:YAG double-pass multi-folded Innoslab amplifier

We designed a novel structure of double-pass multi-folded partially-end-pumped slab (Innoslab) amplifier, which could effectively improve the extraction efficiency. High efficiency and high power picosecond (ps) radiation was obtained by the Nd:YAG Innoslab amplifier. A 4.5 W seed at a repetition rate of 10 kHz was amplified to 41.6 W under an absorbed pump power of 124.7 W, corresponding to extraction efficiency of 29.8%. The pulse duration was approximately 86.5 ps, and the corresponding peak power was up to 48.1 MW. The beam quality factor M2 at the maximum output power was measured to be 2.28 and 1.52 in the horizontal and vertical directions, respectively. To the best of our knowledge, this study was the first to report high efficiency double-pass multi-folded Innoslab amplifier.

Wideband full double-pass serial hybrid fiber amplifier utilizing L-shape configuration.

In this work, a new, to the best of our knowledge, full double-pass serial hybrid fiber amplifier is simulated on OptiSystem 7.0 software. A wideband flat gain spectrum covered both conventional and long communication bandwidth (C+L) from 1530 to 1590 nm, which is approximately 60 nm with high average gain of 23.6 dB; acceptable noise figure of 7 dB is achieved via the L-shape configuration. The main innovative step in the proposed design is decreasing the cascading amplification effect between the combined amplifiers, by making the individual full double-pass for the input signal in each amplifier stage.

Experimental and theoretical study of the nonlinear birefringence in the formation process of vector solitons in a total polarization control ring cavity bias twist fiber

In this work, we present the numerical and experimental investigation of the polarization dynamics in a free birefringence mode-locked fiber laser. The laser includes a double-pass Erbium-doped fiber amplifier and 20-m long bi-twisted fiber at a twist rate of ± 6 turns m−1 to mitigate both, linear and circular birefringence effects. We found ellipticity changes due to nonlinear birefringence in the 20-m long fiber during pulse formation and propagation. In contrast with previously reported works, the inclusion of bi-twisted fiber allows investigate the nonlinear effects independently from the linear ones. The experimental behavior was confirmed by numerical simulations based on split step Fourier method showing that the polarization changes are generated since the vector soliton formation process.

Demonstration of double-pass amplification of gain saturated 46.9 nm laser

With a SiC plane mirror, we demonstrated the double-pass amplification of gain saturated 46.9 nm laser pumped by capillary discharge. In comparison with the single-pass amplified 46.9 nm laser, the amplitude of the double-pass laser pulse increased about 2.4 times, and the FHWM of the double-pass laser pulse broadened about 0.9 ns. In addition, the single-pass and the double-pass amplified laser spots have similar spatial distributions and peak-to-peak divergences. The double-pass 46.9 nm laser has good practicability because the SiC mirror is hardly damaged by the plasma.

Generation and amplification of a multi-beam sub-nanosecond laser

In this paper, a methodology to produce a multi-beam sub-nanosecond laser is proposed. Laser pulses with a pulse energy of 0.14 mJ and a pulse width of 490 ps are generated in a YAG/Nd:YAG/Cr4+:YAG microchip laser at a repetition rate of 200 Hz. After amplification with a laser diode (LD) side-pumped Nd:YAG module, four laser beams are generated because of the thermally induced birefringence. With a double-pass LD side-pumped amplifier, the single pulse energy of the four laser beams is amplified to 5.23 mJ with a peak power of ∼10.67 MW, and air breakdown with four points is achieved with a 2 × 2 lens array.