Continuous-wave Mode-locked Laser Research Articles

CW mode-locked fiber laser by improved all-polarization-maintaining figure-9 cavity at 1064 nm

In order to realize broadband continuous wave (CW) mode locking by figure-9 fiber laser at 1064 nm, we propose an improved all-polarization-maintaining figure-9 cavity structure by adding gain fiber to both the loop and the linear arm in the laser. When the two sections of gain fiber are pumped simultaneously, the CW mode locking regime can be obtained. In this work, noise-like mode-locked pulses are generated with a central wavelength of 1064 nm and a chirped fiber grating (CFBG) is used for dispersion management. The net dispersion of the cavity is about 0.01 ps2 and the output power is 234 mW. The noise-like pulses are validated by autocorrelator, the peak duration on the autocorrelation trace pedestal is about 261 fs, and the pedestal duration is about 103 ps. Numerical simulations are performed on the noise-like pulses, which agree with the experimental results. This study has inspiration for mode-locked lasers with a central wavelength of 1064 nm, and has potential application value in fields such as supercontinuum generation, fiber sensing, laser microfabrication, and laser ablation.

Stable continuous-wave mode-locked laser from a 1645 nm Er:YAG ceramic oscillator

We demonstrate stable continuous-wave mode-locking (CWML) pulses around 1645 nm by employing a homemade Er:YAG ceramic. By using a fiber laser and semiconductor saturable absorber mirror (SESAM) with a modulation depth of 1.2%, we get ML pulses with an output average power up to 815 mW, a pulse width shortened as ∼4 ps, and a peak power of ∼1.8 kW. With the SESAM of the modulation depth of 2.4%, second-order harmonic ML pulses were also obtained. As far as we know, this is the first report of CWML from Er3+-doped ceramics and also the shortest pulse duration in Er3+-doped solid-state oscillators.

Nanosecond and femtosecond lasers based on black arsenic-phosphorus alloys saturable absorber

In this paper, the high-repetition-rate passively Q-switched (PQS) and the femtosecond continuous-wave mode-locked (CWML) lasers are successfully obtained with 2D black arsenic-phosphorus (b-AsP) nanosheets as saturable absorber (SA) at 1 μm for the first time, to the best of our knowledge. The saturable absorption properties and ultrafast carrier dynamics of the 2D b-AsP SA are explored by Z-scan and pump-probe techniques. Moreover, according to the measurement of desired nonlinear optical characteristics of the relaxation time of 27 ps and the modulation depth of 7.14%, the PQS and CWML lasers are demonstrated with the highest repetition rate of 2.26 MHz in the PQS laser and the pulse width of 470 fs in the CWML laser. The results show 2D b-AsP SA has enormous potential for pulse modulation in solid-state bulk lasers.

Nonlinear optical response of a monolayer WS2 and the application of a hundred-MHz nanosecond laser.

High quality monolayer WS2 was successfully fabricated by chemical vapor deposition method. The nonlinear optical response of monolayer WS2 is demonstrated for the first time. Due to the relatively low modulation depth of 1.4% and saturable intensity of 68.6 kW/cm2 of monolayer WS2, a robust continuous-wave mode-locked (CWML) nanosecond laser with a repetition rate of 93.1 MHz is obtained. To the best of our knowledge, this is the highest repetition rate of nanosecond pulses generated from CWML lasers. This work provides an effective approach to obtaining nanosecond pulsed lasers with repetition rates of hundred-megahertz.

575-fs passively mode-locked Yb:CaF2 ceramic laser**Project supported by the National Natural Science Foundation of China (Grant Nos. 11974220, 61635012, and 51902234).

A Yb-doped CaF2 transparent ceramics was successfully fabricated by the hot-pressed method and its laser characteristics were studied. A broad tuning performance and mode-locked laser operation were demonstrated in this ceramics for the first time, to our best knowledge. A 60-nm continuous-wavelength tunable laser from 1019 nm to 1079 nm was obtained with a birefringent filter. By employing a semiconductor saturable absorber mirror without additional dispersion compensation elements, a continuous-wave mode-locked laser with pulse duration as short as 575 fs was delivered, at a central wavelength of 1048.5 nm. The oscillator is operated under a repetition rate of 55 MHz. These results indicate that the Yb:CaF2 transparent ceramics is an ideal candidate for the development of ultrafast lasers in the near-infrared regime.

Diode-pumped passively mode-locked Nd:GYSGG laser at 1061 nm with periodically poled LiNbO3 nonlinear mirror

ABSTRACTWe report a nonlinear-mirror mode-locked diode-pumped solid-state Nd:GYSGG laser operating at 1061 nm. The nonlinear mirror comprises a periodically poled LiNbO3(PPLN) crystal and a dichroic mirror. Continuous-wave mode-locked laser with an output power of 450 mw is obtained under a diode pump power of 5.5 W at 808 nm. The repetition rate of the mode-locked laser is 97.1 MHz and the bandwidth of spectral is 1.3 nm. Considering the group velocity mismatch (GVM) of PPLN, we estimate the minimum pulse width is about 9 ps.

Flexible picosecond burst generation in a mode-locked Nd:YVO4 laser with a compound cavity

We present the generation of picosecond bursts with controllable pulse number in a passively mode-locked Nd:YVO4 laser with a compound cavity. This is the first time to use a compound cavity with additional SESAM to generate pulse burst. The device is constructed by inserting an HWP in the cavity, which reflects part of light in the main cavity into the auxiliary cavity and then the reflected beam is sent back after a delay in the auxiliary cavity. By controlling the power reflected into the main cavity from the auxiliary cavity, a series of bursts can be created with a selectable pulse number and adjustable temporal separation between the pulses. The temporal separation between two adjacent picosecond pulses in the burst can be adjusted by changing the length difference between two cavities. The temporal width of the burst can be adjusted from picosecond to nanosecond, and the repetition rate of the burst is the same as that in continuous wave mode-locked laser. The generation of the burst is presumably attributed to the temporal addition of laser pulses from the two cavities. This work provides a useful method for generating controllable picosecond laser burst.

Kerr-lens mode-locked Pr3+:LuLiF4 laser.

We demonstrate the Kerr-lens mode-locked Pr3+:LuLiF4 (Pr:LLF) laser pumped by a blue laser diode (LD). By theoretical calculation of the group velocity dispersion in the laser gain, the compensation was employed for the realization of the continuous-wave mode-locked laser at the wavelength of 604nm with the pulse width of 1.1ps which, to the best of our knowledge, is the shortest pulse width in the Pr3+ ion doped crystal lasers pumped with LDs. It can be believed that the present Pr:LLF laser should provide some inspiration for the development of the blue LD pumped visible lasers, especially in the mode-locking laser operation.

Diode-Pumped Passively Mode-Locked YVO4/Nd:YVO4 Composite Crystal Laser

We report on a passively mode-locked YVO4/Nd:YVO4 composite crystal laser using a semiconductor saturable absorber mirror. At a pump power of 21.39 W, we achieve a 3.51 W average output power from a continuous wave mode-locked laser with a repetition rate of passively mode-locked pulse of 89 MHz and a pulse width of 38.3 ps. The pulse energy and peak power are 39.4 nJ and 1.03 kW, respectively. Our experiment results show that a composite crystal is an excellent laser crystal for mode locking.

Passively mode-locked Nd:YVO4/PPLN green laser using molybdenum disulfide as a saturable absorber

A molybdenum disulfide (MoS2) saturable absorber (SA) was fabricated via the liquid-phase exfoliation method. The optical properties of MoS2 were systematically characterized and the modulation depth was measured to be 6.2%. A laser-diode-end-pumped, passively mode-locked Nd : YVO4 / PPLN green laser with a SA based on few-layered MoS2 was successfully demonstrated. The pulse width of the stable continuous-wave mode-locked laser operating at 532.1 nm was 3.5 ps, and the pulse repetition frequency was 87.2 MHz. The maximum average output power of 757 mW was obtained under an absorbed pump power of 8.62 W. The calculated single pulse energy and peak power were 8.7 nJ and 2.49 kW, respectively.

Threshold decrease in intracavity optical parametric oscillator synchronously pumped by mode-locked laser

An intracavity optical parametric oscillator (IOPO) pumped by a continuous-wave (CW) mode-locked laser is experimentally realized. The fundamental cavity and optical parametric oscillator cavity are designed to satisfy synchronous pumping. The output characteristics of signal and idle light are measured. Because of higher fundamental photon intensity in IOPO, the threshold of IOPO is lower than that of an extra-cavity optical parametric oscillator. The spectroscopy of signal light is obtained and the wavelength of idle light can be estimated to be 3.298 μm from noncritical phase matching. Based on the intensity fluctuation mechanism of fundamental locking, the dynamical model for IOPO pumped by a CW mode-locked laser is developed. The simulated results for the temporal shape of three lights are calculated from the derived rate equations. Because of dispersion, the signal pulse width of the theory is smaller than that of the experiment with the same pump energy.

Fabrication of a saturable absorber WS2 and its mode locking in solid-state laser

We report on a passively mode-locked Nd : LuVO4 laser using a type saturable absorber of tungsten disulfide (WS2) fabricated by chemical vapor deposition method. At the pump power of 3.3 W, 1.18-W average output power of continuous-wave mode-locked laser with optical conversion efficiency of 36% was achieved. To the best of our knowledge, this is the highest output power of passively mode-locked solid-state laser based on WS2. The repetition rate of passively mode-locked pulse was 80 MHz with the pulse energy of 14.8 nJ. Our experimental results show that WS2 is an excellent type of saturable absorber.

Order of multiphoton excitation of sulfonium photo-acid generators used in photoresists based on SU-8

Multiphoton lithography (MPL), Z-scan spectroscopy, and quantum chemical calculations were employed to investigate the order of multiphoton excitation that occurs when femtosecond laser pulses are used to excite two sulfonium photo-acid generators (PAGs) commonly used in photoresists based on the cross-linkable epoxide SU-8. The mole-fractions of the mono- and bis-sulfonium forms of these PAGs were determined for the commercially available photoresist SU-8 2075 and for the PAGs alone from a separate source. Both were found to contain similar fractions of the mono- and bis-forms, with the mono form present in the majority. Reichert's method was used to determine the solvatochromic strength of the SU-8 matrix, so that results obtained for the PAGs in SU-8 and in solution could be reliably compared. The PAGs were found to exhibit a minimal solvatochromic shift for a series of solvents that span across the solvatochromic strength of SU-8 itself. Sub-micron-sized features were fabricated in SU-8 2075 by MPL using amplified and continuous-wave mode-locked laser pulses. Analysis of the features as a function of average laser power, scan speed, and excitation wavelength shows that the PAGs can be activated by both two- and three-photon absorption (2PA and 3PA). Which activation mode dominates depends principally upon the excitation wavelength because the average laser powers that can be used with the photoresist are limited by practical considerations. The power must be high enough to effect sufficient cross-linking, yet not so high as to exceed the damage threshold of the material. When the laser pulses have a duration on the order of 100 fs, 3PA dominates at wavelengths near 800 nm, whereas 2PA becomes dominant at wavelengths below 700 nm. These findings are corroborated by open-aperture Z-scan measurements and quantum chemical calculations of the cross-sections for 2PA and 3PA as a function of wavelength.

Nonlinear mirror mode-locked Pr:YAlO3 laser

Mode-locking of a praseodymium based solid-state laser by a nonlinear mirror is reported, for the first time to the best of our knowledge. Pr:YAlO3 crystal having 0.6 at.% of Pr3+ ions was used as an active medium. For mode-locking, a nonlinear BBO crystal together with a properly designed dichroic mirror were employed to form an output coupler with intensity dependent reflection. A continuous-wave mode-locked laser operation with a mean output power of 100 mW was achieved under 3.5 W InGaN laser diode pumping. The laser emitted 250 ps pulses with a repetition rate of 105 MHz at a center oscillation wavelength of 747 nm.

Femtosecond Pulses Generation From a Diode-Pumped Yb:CaNb2O6 Disordered Crystal Laser

We experimentally demonstrated a diode-pumped femtosecond Yb:CaNb2O6 disordered crystal laser. Pumping by a 978-nm fiber coupled laser diode and assisting by a semiconductor saturable absorber mirror, stable continuous-wave mode-locked laser pulses with a width of 170 fs at the central wavelength of about 1038 nm were obtained. The laser pulses had an average output power and a repetition rate of 135 mW and 80 MHz, respectively. To the best of our knowledge, this is the shortest laser pulses generated from Yb:CaNb2O6 disordered crystal lasers.

759 fs pulse generation with Nd3+-doped CNGS ordered crystal based on a semiconductor saturable absorber mirror.

A diode-pumped passively continuous wave mode-locked laser at 1064.2 nm based on an ordered Nd:CNGS crystal has been experimentally investigated (for the first time, to our knowledge). Stable mode-locked pulses with a duration of 759 fs were produced at a repetition rate of 43.2 MHz. It is the shortest pulse generation of mode-locked lasers based on Nd3+-doped ordered crystal, as far as we know. A maximum average mode-locked output power of 133 mW was obtained at the absorbed pumped power of 6.7 W, and corresponding single-pulse energy and peak power were determined to be 3.1 nJ and 4.1 kW, respectively. The results indicate that the Nd:CNGS as an ordered crystal is indeed a potential candidate as a femtosecond laser gain medium.

High-power femtosecond pulse generation in a passively mode-locked Nd:SrLaAlO4 laser

A high optical quality Nd:SrLaAlO4 (Nd:SLA) crystal was grown using the Czochralski method and showed broad fluorescence spectrum with a full width at half maximum value of 34 nm, which is beneficial for generating femtosecond laser pulses. A stable diode-pumped passively mode-locked femtosecond Nd:SLA laser with 458 fs pulse duration was achieved for the first time at a central wavelength of 1077.9 nm. The average output power of the continuous-wave mode-locked laser was 520 mW and the repetition rate was 78.5 MHz.

High-peak-power single-oscillator actively Q-switched mode-locked Tm3+-doped fiber laser and its application for high-average output power mid-IR supercontinuum generation in a ZBLAN fiber.

A single-oscillator actively Q-switched mode-locked (QML) thulium-doped silica fiber laser is presented and used to pump a ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber for mid-infrared (mid-IR) supercontinuum (SC) generation. The fiber laser provided high-peak-power levels directly from the oscillator delivering single mode-locked pulse energies up to 48 μJ, being 2-4 orders of magnitude higher than conventional continuous wave mode-locked lasers. By pumping a ZBLAN fiber specially designed for high-output-power SC generation, 7.8 W have been achieved in all spectral bands with a spectrum extending to 4.2 μm.

SESAM mode-locked red praseodymium laser.

We present the first semiconductor saturable absorber mirror (SESAM) mode-locked praseodymium solid-state laser. The laser is based on a Pr(3+):LiYF(4) crystal as gain medium and a GaInP-quantum well-based SESAM. Self-starting continuous-wave mode-locked laser operation with an average output power of 16 mW is achieved at a center wavelength of 639.5 nm. The laser operates at a repetition rate of ∼85.55 MHz and emits pulses with a duration of ∼18 ps.

Typing of Polymorphic Human Genes by Picosecond-Resolved Förster Energy Transfer

By analyzing, on a picoseconds time scale, the fluorescence decay of a donor undergoing Förster resonance energy transfer in a suitable donor-acceptor system we can reveal DNA sequences that are specific of genetically correlated diseases. Since we use picosecond excitation from a continuous-wave mode-locked laser and time-correlated single-photon detection, we achieve such a high acquisition rate, sensitivity, and temporal resolution that we can perform the measurements on the human genomic DNA contained in cells that were simply lysed. We show that, in few minutes, we identify an individual, even heterozygote, carrying the sequences of the DQB1 gene that confers susceptibility to the development of insulin-dependent diabetes mellitus with no need of DNA extraction, purification, PCR amplification.