mW Average Output Power Research Articles

High-power supercontinuum generation in the mid-infrared pumped by a soliton self-frequency shifted source.

We report the demonstration of a fiber-based supercontinuum source delivering up to 825 mW of average output power between 2.5 and 5.0 µm generated in all-normal dispersion regime. The pumping source consists of an amplified ultrafast Er3+:ZrF4 fiber laser providing high peak power femtosecond pulses at 3.6 µm with an average output power exceeding the watt-level. These pulses are spectrally broadened through self-phase modulation using commercial chalcogenide-based step-index fibers. Al2O3 anti-reflection coatings were sputtered on chalcogenide fiber tips to increase the launching efficiency from 54% to 82%, making this record output power possible, and thus confirming that such coatings can support watt-level pumping with intense femtosecond pulses. To the best of our knowledge, this result represents the highest average output power ever achieved from a As2Se3-based mid-IR supercontinuum source with the potential of a high degree of coherence.

Passively Q-switched Nd:GdLaNbO4 laser based on 2D PdSe2 nanosheet

In this work, a novel two-dimensional palladium diselenide (PdSe2) nanosheet was synthesized by chemical vapour deposition method and used as a saturable absorber (SA) for generation of Q-switched laser pulses. The microstructure and optical properties of PdSe2 nanosheet were investigated. For laser emission, a newly developed Nd:GdLaNbO4 mixed crystal was used as the gain medium, while the pump was done with fiber-coupled diode laser at 879 nm, directly into the 4F3/2 emitting level. The Q-switched Nd:GdLaNbO4/PdSe2 laser yielded 405 mW average output power for 8.8 W absorbed pump power at 879 nm. The laser runs at 164 kHz with 2.47 μJ energy per pulse; pulse duration was 340 ns, indicating a pulse peak power of 7.26 W. These first results prove that PdSe2 nanosheet can be used as SA in passively Q-switch laser devices.

Graphene mode-locked Tm,Ho-codoped crystalline garnet laser producing 70-fs pulses near 21 µm

Bilayer graphene synthesized by chemical vapor deposition is successfully applied as a saturable absorber (SA) for the passive mode-locking of a Tm,Ho:CLNGG laser at 2093nm. Near transform-limited pulses as short as 70 fs, i.e., 10 optical cycles, are produced at a 89 MHz repetition rate with 69 mW average output power. To the best of our knowledge, these are the shortest pulses ever reported from graphene-SA mode-locked Tm, or Ho-lasers in the 2 µm spectral region, including bulk and fiber lasers.

Tightly locked optical frequency comb from a semiconductor disk laser.

Ultrafast semiconductor disk lasers (SDLs) passively modelocked using semiconductor saturable absorbers mirrors (SESAMs) generate optical frequency combs (OFCs) with gigahertz line spacings - a regime where solid-state and fiber lasers struggle with geometrical and Q-switching limitations. We stabilized both the frequency comb spacing and the offset without any additional external optical amplification or pulse compression. The overall noise performance is competitive with other gigahertz OFCs. A SESAM-modelocked vertical external-cavity surface-emitting laser (VECSEL) at a center wavelength around 1 µm generates 122-fs pulses with 160 mW average output power and we only needed 17-pJ pulse energy coupled into a silicon nitride (Si3N4) waveguide for supercontinuum generation (SCG) and OFC offset stabilization.

Graphene and SESAM mode-locked Yb:CNGS lasers with self-frequency doubling properties.

We report on mode-locking of an Yb:Ca3NbGa3Si2O14 laser, which is pumped by a fiber-coupled single-mode laser diode. The shortest pulse duration obtained with a semiconductor saturable absorber mirror is 52 fs, with 75 mW of average output power. Sub-60 fs operation tunable between 1055 and 1074 nm is achieved by employing semiconductor absorbers with different characteristics. We also demonstrate passive mode-locking results with transmissive graphene saturable absorber, reaching an 85 fs pulse duration with 23 mW output power. Moreover, we present the non-phase-matched self-frequency doubling properties of this non-centrosymmetric crystal in the femtosecond regime.

Stable Q-Switched Mode-Locking of 2.7 μm Er:Y2O3 Ceramic Laser Using a Semiconductor Saturable Absorber

This paper studies synchronous Q-switch and mode-locking of an 2.7 μm Er:Y2O3 ceramic laser pumped with a high brightness 976 nm fiber laser and using a semiconductor saturable absorber mirror. The Er:Y2O3 ceramic is home-developed with Er3+ doping concentration of 7 at.%. The laser generated ~92 mW of average output power with stable mode-locked pulses of 100% modulation depth and 130 MHz repetition rate embedded inside Q-switched envelopes of ~1.2 μs width. Repetition rates of the Q-switched pulse envelopes are tunable from 5.1 kHz to 29 kHz with the width varying from 2.7 μs to 1.2 μs.

Compact THz time-domain spectroscopy based on pre-chirped pulses from mode-locked Yb-doped fiber laser

Abstract We report on a compact terahertz (THz) time-domain spectroscopy (TDS) system based on fiber-integrated log-spiral low-temperature-grown InGaAs photo-conductive antenna (PCA) modules pumped by pre-chirped pulses from a 1.03-μm mode-locked Yb-doped fiber laser. A mode-locked Yb-doped fiber laser based on a birefringent spectral filter was produced with 240 mW average output power and 2.68-ps pulse duration. The output pulse had high chirp because the mode-locked fiber laser was implemented in the normal dispersion region. Therefore, the 733-fs output pulse was pre-chirped using two parallel diffraction gratings to facilitate its use as an optical pump source with THz radiation. After propagating in the single-mode fiber, the pulse-width of the pre-chirped pulse was compressed to 331 fs and injected into fiber-integrated PCA modules to generate a THz wave. We successfully obtained a THz emission bandwidth of over 2.5 THz for 120 mm in free space using the compact THz measurement setup. THz radiation was achieved by easily aligning two fiber integrated PCA modules. Absorption lines for water vapor were observed at room temperature. We also observed absorption lines from a 30% α-lactose sample. We confirmed that the fiber-integrated PCA modules and mode-locked Yb-doped fiber laser have potential applications in compact and portable THz-TDS systems.

High Power and Short Pulse Width Operation of Passively Q-Switched Er:Lu2O3 Ceramic Laser at 2.7 μm

Using a low non-saturable loss Bragg-reflector-based semiconductor saturable mirror, a passively Q-switched Er:Lu2O3 ceramic laser at 2.7 μm demonstrated short pulse-width and efficient operation, generating stable pulses of 70 ns pulse-width and ~71 kHz repetition rates. Over 692 mW of average output power was measured, corresponding to a pulse energy of ~9.8 μJ. In a modified resonator design of reduced round-trip time, pulses of 32 ns duration were generated. The achieved results suggest that Er:Lu2O3 ceramic could be a promising gain medium for efficient and high power pulsed laser generation at 2.7 μm. The prospects for further improvement in laser performance at this wavelength are discussed.

Carrier-Envelope Offset Frequency Stabilization of a Fiber Laser by Cross Gain Modulation

We present the first carrier-envelope offset (CEO) frequency stabilization of a fiber laser by cross gain modulation. The Yb-doped fiber laser is mode-locked by nonlinear polarization evolution and emits 32-nm wide dissipative solitons at a repetition rate of 125 MHz with 150 mW of average output power. A continuous wave laser signal at a wavelength of 1025 nm is used as an intracavity power modulator. A low power of only 200 μW of modulator signal is coupled into the fiber laser and amplified in the gain segment. This signal cross modulates the laser gain, achieving 40 times larger modulation bandwidth of the intracavity laser power than with standard pump-current control. A tight CEO lock is demonstrated with 361 mrad of residual integrated phase noise (from 1 Hz to 1 MHz). The method allows easy implementation in many existing fiber laser frequency combs based on various saturable absorbers and fiber configurations.

High-Power Sub-300-Femtosecond Quantum Dot Semiconductor Disk Lasers

Self-assembled quantum dots (QDs) as active media for ultrafast semiconductor disk laser offer large gain bandwidths, fast gain dynamics, and high temperature stability. We report on the shortest pulses and the highest pulse peak power from an optically pumped vertical external cavity surface emitting laser (VECSEL) based on QDs and optimized for passive modelocking at 1035 nm using a semiconductor saturable absorber mirror. We demonstrate 216-fs pulses with an average output power of 269 mW at a pulse repetition rate of 2.77 GHz and 396 W peak power. At a lower pulse repetition rate of 1.67 GHz, we achieve 193-fs pulses with 112 mW of average output power. We remark a higher optical-to-optical pump efficiency compared to our previous QW VECSELs in the sub-300-fs regime. This is further confirmed by a comparative analysis of the saturation recovery which reveals longer carrier lifetimes for the QD compared to QW VECSELs.

Actively Q-switched laser with novel Nd:YAG/YAG polygonal active-mirror

In this work, we demonstrate an efficient actively Q-switched laser based on a novel crystal Nd:YAG/YAG polygonal active mirror. A passively cooled crystal Nd:YAG/YAG polygonal active mirror with an end pump scheme was used as the gain medium. For the overlap between the TEM00 laser mode and large gain profile, a cavity was carefully designed with a large fundamental mode volume. With a maximum absorbed power of 3.1 W, a 685 mW average output power with a pulse repetition of 5 kHz was attained, and the corresponding optical–optical and slope efficiency were 22.1% and 27.7%, respectively. The pulse width was 133.9 ns. The beam quality (M2) was 1.561 in the horizontal direction and 1.261 in the vertical direction.

High peak power ultrafast Yb:CaF2 oscillator pumped by a single-mode fiber-coupled laser diode.

We demonstrate a high peak power mode-locked Yb:CaF2 oscillator pumped by a single-mode laser diode. The laser operated in hybrid Kerr-lens and SESAM mode-locked regime. Its performance was optimized by varying the output coupler ratio. Pulses as short as 65 fs were generated with 0.4% transmission. Employing 5% output coupler enabled generation of 77 fs pulses with 46 kW of peak power (262 mW of average output power). We believe that such high peak powers can open a way to practical applications of single-mode diode-pumped ultrafast ytterbium lasers.

5.9 GHz graphene based q-switched modelocked mid-infrared monolithic waveguide laser.

A high repetition rate Q-switched modelocked ~2.1 µm monolithic waveguide laser is reported. Ultrafast laser inscription is used to fabricate 3D depressed cladding channel waveguides in holmium doped yttrium aluminium garnet. This results in a transversely single mode waveguide laser. With the use of a graphene based saturable output coupler, Q-switched modelocking was achieved with a pulse repetition frequency of 5.9 GHz and up to 170 mW of average output power. This first demonstration of multi-GHz repetition rate operation from a Ho3+:YAG laser provides a compact and convenient source for a number of applications.

High power continuous-wave dual-wavelength alexandrite laser

A high power dual-wavelength alexandrite (Cr:BeAl2O4) laser using a single plate birefringent filter (BRF) was demonstrated. Using a 6 mm thick BRF, dual-wavelength output at 745.2 nm and 756.2 nm (5.9 THz of frequency difference) with 850 mW of average output power was achieved as well as with 16.8% optical-to-optical and 24.2% slope efficiency. The tunability of dual-wavelength separation was also demonstrated by employing the 4 mm and 2 mm thick BRFs with similar output powers. To the best of our knowledge, this is the first demonstration of a dual-wavelength alexandrite laser.

Increased mid-infrared supercontinuum bandwidth and average power by tapering large-mode-area chalcogenide photonic crystal fibers.

The trade-off between the spectral bandwidth and average output power from chalcogenide fiber-based mid-infrared supercontinuum sources is one of the major challenges towards practical application of the technology. In this paper we address this challenge through tapering of large-mode-area chalcogenide photonic crystal fibers. Compared to previously reported step-index fiber tapers the photonic crystal fiber structure ensures single-mode propagation, which improves the beam quality and reduces losses in the taper due to higher-order mode stripping. By pumping the tapered fibers at 4 μm using a MHz optical parametric generation source, and choosing an appropriate length of the untapered fiber segments, the output could be tailored for either the broadest bandwidth from 1 to 11.5 μm with 35.4 mW average output power, or the highest output power of 57.3 mW covering a spectrum from 1 to 8 μm.

Passively Q-switched Nd:YVO4 laser with MoS2/GaAs saturable absorber

The molybdenum disulfide (MoS2) nanosheets adhered on GaAs wafer is employed as MoS2/GaAs saturable absorber (SA) in the Q-switched Nd:YVO4 laser. The MoS2/GaAs SA is successfully fabricated by liquid-exfoliated method of transferring a few-layer MoS2 to 350 μm-depth GaAs wafer. Under the absorbed pump power of 1.77 W, the pulses with 321.6 mW average-output power, 51.3ns pulse duration and 769.7 kHz repetition rate can be obtained, which reveals the potential of MoS2/GaAs heterostructure in generation of short pulse duration. The pulse energy and the peak power are 417.8 nJ and 8.14 W respectively, under the same absorbed pump power. It is promising that the heterostructure SAs with two-dimentional nanomaterials and traditional SAs can be used in optical modulation to get shorter pulse duration.

Carrier envelope offset frequency detection and stabilization of a diode-pumped mode-locked Ti:sapphire laser.

We demonstrate the first diode-pumped Ti:sapphire laser frequency comb. It is pumped by two green laser diodes with a total pump power of 3 W. The Ti:sapphire laser generates 250 mW of average output power in 61-fs pulses at a repetition rate of 216 MHz. We generated an octave-spanning supercontinuum spectrum in a photonic-crystal fiber and detected the carrier envelope offset (CEO) frequency in a standard f-to-2f interferometer setup. We stabilized the CEO-frequency through direct current modulation of one of the green pump diodes with a feedback bandwidth of 55 kHz limited by the pump diode driver used in this experiment. We achieved a reduction of the CEO phase noise power spectral density by 140 dB at 1 Hz offset frequency. An advantage of diode pumping is the ability for high-bandwidth modulation of the pump power via direct current modulation. After this experiment, we studied the modulation capabilities and noise properties of green pump laser diodes with improved driver electronics. The current-to-output-power modulation transfer function shows a bandwidth larger than 1 MHz, which should be sufficient to fully exploit the modulation bandwidth of the Ti:sapphire gain for CEO stabilization in future experiments.

Highly stable self-pulsed operation of an Er:Lu2O3 ceramic laser at 2.7 µm

We report on the highly stable self-pulsed operation of a 2.74 µm Er:Lu2O3 ceramic laser pumped by a wavelength locked narrow bandwidth 976 nm laser diode. The operating pulse repetition rate is continuously tunable from 126 kHz to 270 kHz depending on the pump power level. For 12.3 W of absorbed diode pump power, the Er:Lu2O3 ceramic laser generates 820 mW of average output power at a 270 kHz repetition rate and with a pulse duration of 183 ns. The corresponding pulse-to-pulse amplitude fluctuation is estimated to be less than 0.7%. In the continues-wave (CW) mode of operation, the laser yields over 1.3 W of output power with a slope efficiency of 11.9% with respect to the 976 nm pump power.

Widely tunable all-fiber SESAM mode-locked Ytterbium laser with a linear cavity

We present a widely tunable all-fiber mode-locked laser based on semiconductor saturable absorber mirror (SESAM) with a linear cavity design. An easy-to-use tunable bandpass filter based on thin film cavity technology is employed to tune the wavelength. By tuning the filter and adjusting the polarization controller, mode-locked operation can be achieved over the range of 1023nm–1060nm. With the polarization controller settled, mode-locked operation can be preserved and the wavelength can be continuously tuned from 1030nm to 1053nm. At 1030nm, the laser delivers 9.6mw average output power with 15.4ps 10.96MHz pulses at fundamental mode-locked operation.

Femtosecond Kerr-lens mode-locked Alexandrite laser.

The generation of 170 fs pulses at 755 nm from a Kerr-lens mode-locked Alexandrite laser was demonstrated. The laser was pumped at 532 nm and produced 780 mW of average output power with 9.8% of optical-to-optical efficiency. To the best of our knowledge, these are the shortest pulses that have been produced from a mode-locked Alexandrite laser to date.