High-resolution monitoring of the hole depth during ultrafast laser ablation drilling by diode laser self-mixing interferometry

We demonstrate that diode laser self-mixing interferometry can be exploited to instantaneously measure the ablation front displacement and the laser ablation rate during ultrafast microdrilling of metals. The proof of concept was obtained using a 50-μm-thick stainless steel plate as the target, a 120?ps/110?kHz microchip fiber laser as the machining source, and an 823?nm diode laser with an integrated photodiode as the probe. The time dependence of the hole penetration depth was measured with a 0.41?μm resolution.     

Generation of ultrafast mid-infrared laser by DFG between two actively synchronized picosecond lasers in a MgO:PPLN crystal

We report the difference-frequency generation (DFG) of ultrafast mid-infrared laser radiation around 3???m between two picosecond laser pulses with the center wavelengths of 800?nm and 1064?nm in a MgO:PPLN crystal at room temperature. The two laser pulses were generated from the actively synchronized picoseconds Ti:sapphire and Nd:YVO₄ oscillators. We measured the DFG wavelengths tunable from 3.19?C3.29???m and the output power is potential to be several mW. This experiment proves a possible roadmap for ultrafast mid- and far-infrared laser radiation generation and even for the THz radiation.     

Picosecond diode-pumped 1.5 μm Er,Yb:glass lasers operating at 10–100 GHz repetition rate

Stable ultrafast laser sources at multi-GHz repetition rates are important for various application areas, such as optical sampling, frequency comb metrology, or advanced high-speed return-to-zero telecom systems. We review SESAM-mode-locked Er,Yb:glass lasers operating in the 1.5 μm spectral region at multi-GHz repetition rates, discussing the key improvements that have enabled increasing the repetition rate up to 100 GHz. We also present further improved results with shorter pulse durations from a 100 GHz Er,Yb:glass laser. With an improved SESAM design we achieved 1.1 ps pulses with up to 30 mW average output power. Moreover, we discuss for the first time the importance of beam quality deteriorations arising from frequency-degenerate higher order spatial modes in such lasers.     

High-energy temporally shaped nanosecond-pulse master-oscillator power amplifier based on ytterbium-doped single-mode microstructured flexible fiber

We present a versatile master-oscillator power amplifier system at 1053?nm in the few-nanoseconds regime meeting the high-level requirements of high-power laser facility front ends. Thanks to temporal shaping, more than 1.5?mJ pulse energy at 1?kHz with an excellent optical signal-to-noise ratio has been obtained in a single-mode 40?μm core flexible fiber.     

Ultrafast mode switching based on a micro-ring laser

Injection locking and multi-mode switching characteristics of a semiconductor ring laser with the radius of 10 μm are investigated based on a nonlinear time domain multimode rate-equation model. The stable injection locking regions for different target modes are studied as the function of detuning frequency and injection power ratio. The results show that ultra-wide detuning range of ∼100 GHz wide at 5 dB injection power ratio and ultra-low switching power ratio of −27 dB can be realized for this micro-ring laser device. Optimal detuning value and high injection power lead to the minimal switching time. An ultrafast response time of 10 ps indicates that a 10 μm-radius SRL can be utilized for ultrafast all-optical scenarios and high-speed tunable lasers.     

Milliwatt-level mid-infrared (10.5-16.5 μm) difference frequency generation with a femtosecond dual-signal-wavelength optical parametric oscillator

We demonstrate the generation of mid-infrared radiation using a femtosecond dual-signal-wavelength optical parametric oscillator and difference frequency generation in an extracavity gallium selenide or silver gallium diselenide crystal. This system generates up to 4.3?mW of average mid-infrared power. Its spectra can be tuned to between 10.5?μm and 16.5?μm wavelength (952 cm^-1-606 cm^-1) with more than 50 cm^-1 spectral bandwidth. We demonstrate that the power and spectra of this system are temporally very stable.     

Ultrabroadband phase-matched optical parametric generation in the ultraviolet by use of guided waves

We present what is believed to be the first experimental demonstration of guided-wave phase-matched frequency mixing and harmonic conversion in gases. Broad-bandwidth ultrafast pulses, tunable around 270 nm, were generated from an ultrafast Ti:sapphire amplifier system using 2? + 2? - ? parametric wave mixing in a capillary waveguide. We achieved nonresonant phase matching by coupling both the fundamental and the second-harmonic light into the lowest-order mode. The output 3? pulses have an energy of >4muJ at a 1-kHz repetition rate. Simple extensions of this method can generate higher-energy 10-20-fs pulses tunable throughout the vacuum ultraviolet.     

1GHz梳状波调制1.3μmDFB半导体激光器皮秒超短光脉冲产生的实验研究

本文介绍一种采用高重复率梳状波电流调制1.3μm分布反馈(DFB)半导体激光器产生皮秒超短光脉冲的技术。采用1GHz重复率尖脉冲电流直接调制1.3μm半导体激光器产生了最短15ps、输出平均功率为4.5mW的超短光脉冲。     

Pulse synthesis in the single-cycle regime from independent mode-locked lasers using attosecond-precision feedback

We report the synthesis of a nearly single-cycle (3.7?fs), ultrafast optical pulse train at 78?MHz from the coherent combination of a passively mode-locked Ti:sapphire laser (6?fs pulses) and a fiber supercontinuum (1-1.4?μm, with 8?fs pulses). The coherent combination is achieved via orthogonal, attosecond-precision synchronization of both pulse envelope timing and carrier envelope phase using balanced optical cross-correlation and balanced homodyne detection, respectively. The resulting pulse envelope, which is only 1.1 optical cycles in duration, is retrieved with two-dimensional spectral shearing interferometry (2DSI). To our knowledge, this work represents the first stable synthesis of few-cycle pulses from independent laser sources.     

Passive synchronization of all-fiber lasers through a common saturable absorber

We present the synchronization of two all-fiber mode-locked lasers, operating at 1.0?μm and 1.54?μm, coupled through the use of a shared single-wall carbon nanotube absorber. Both lasers operate in the soliton-regime, achieving a synchronized repetition rate of 13.08?MHz. The broadband absorption range of the single-wall carbon nanotubes allows the stable mode-locking behavior at 1?μm and 1.5?μm. The nonlinear coupling effects between two energy states of the carbon nanotube absorber result in stable synchronized pulses for hours of operation, with a large cavity mismatch of 1400?μm.     

High-power, hybrid Er:fiber/Tm:fiber frequency comb source in the 2 μm wavelength region

We present a 2 μm frequency comb based on a reliable mode-locked Er:fiber laser with 100 MHz repetition rate. After shifting the spectrum of the amplified Er:fiber comb to longer wavelengths, a single-clad Tm/Ho:fiber is used as a self-pumped pre-amplifier to generate a coherent and broadband spectrum centered at 1.93 μm. Subsequently, a cladding-pumped Tm:fiber amplifier boosts the system to a maximum output power of 4.8 W at 1.96 μm. After compression in a compact grating compressor, our amplified Er:fiber/Tm:fiber hybrid system delivers as much as 2.9 W with a pulse duration of 141 fs. The system's comb properties are examined via heterodyne measurement.     

Octave spanning supercontinuum in an As₂S₃ taper using ultralow pump pulse energy

An octave spanning spectrum is generated in an As?S? taper via 77 pJ pulses from an ultrafast fiber laser. Using a previously developed tapering method, we construct a 1.3 μm taper that has a zero-dispersion wavelength around 1.4 μm. The low two-photon absorption of sulfide-based chalcogenide fiber allows for higher input powers than previous efforts in selenium-based chalcogenide tapered fibers. This higher power handling capability combined with input pulse chirp compensation allows an octave spanning spectrum to be generated directly from the taper using the unamplified laser output.     

High-power broadband laser source tunable from 3.0 μm to 4.4 μm based on a femtosecond Yb:fiber oscillator

We describe a tunable broadband mid-IR laser source based on difference-frequency mixing of a 100?MHz femtosecond Yb:fiber laser oscillator and a Raman-shifted soliton generated with the same laser. The resulting light is tunable over 3.0?μm to 4.4?μm, with a FWHM bandwidth of 170?nm and maximum average output power up to 125?mW. The noise and coherence properties of this source are also investigated and described.     

Efficient generation of far-infrared radiation in the vicinity of polariton resonance of lithium niobate

We efficiently generated far-infrared radiation at the wavelengths centered at 20.8?μm in the vicinity of one of the polariton resonances of lithium niobate. Such an efficient nonlinear conversion is made possible by exploiting phase matching for difference-frequency generation in lithium niobate. The highest peak power reached 233?W.     

Ultrafast all-optical modulation by near-infrared intersubband transition in n-doped InGaAs/AlAsSb quantum wells

We demonstrate the ultrafast modulation of interband (IB)-resonant light (1.0–1.1 μm) by near-infrared intersubband (ISB)-resonant light (1.55–1.9 μm) in n-doped InGaAs/AlAsSb multiple quantum wells (QWs) using non-degenerate pump–probe spectroscopy. A modulation with an absorption recovery time of 1.0–2.0 ps has been observed in a planer-type modulation device due to ultrafast ISB relaxation of the carriers. The IB carrier relaxation process in the absence of an ISB-resonant light has also been investigated by time-resolved photoluminescence (PL) measurement. The modulation speed is determined by the inter- and intra-subband relaxation of the carriers in the conduction subband. The modulation speed at 1.1 μm due to an ISB-resonant pump light at 1.95 μm has been observed to be 1.4 ps at excitation energy of 500 fJ/μm².     

Diode-pumped Nd:YLF slab master oscillator power amplifier laser system with 655 m J output at 50 Hz repetition rate

A laser-diode-pumped high-pulse-energy Nd:Li YF4 master oscillator power amplifier 1053 nm laser system is demonstrated. We design a home-made pump module to homogenize the pump intensity through the ray tracing method. To increase the extraction efficiency, the pre-amplifier adopts a double-pass amplification structure. At a repetition rate of 50 Hz, 655 m J pulse energy and 12.9 ns pulse width of 1053 nm laser is obtained from the master oscillator power amplifier system. The corresponding peak power is 51 MW. The optical-to-optical efficiency of the system is about 9.7%.     

0.09-terawatt pulses with a 31% efficient, kilohertz repetition-rate Ti:sapphire regenerative amplifier

We present an efficient, ultrafast regenerate amplifier that increases the energy of a laser pulse from 300 pJ to 6 mJ and produces average powers of as much as 9 W in a TEM(00) spatial mode. As an ultrafast amplifier, the system produces 4-mJ pulses with 0.09 TW of peak power.     

Coherent beam combining of two femtosecond fiber chirped-pulse amplifiers

We demonstrate coherent beam combining of two femtosecond fiber chirped-pulse amplifiers seeded by a common oscillator. Using a feedback loop based on an electro-optic phase modulator, an average power of 7.2?W before compression is obtained with a combining efficiency of 90%. The spatial and temporal qualities of the oscillator are retained, with a recombined pulse width of 325?fs. This experiment opens up a way to scale the peak/average power of ultrafast fiber sources.     

Tunable third-harmonic generation in a solid-core tellurite glass fiber

A solid-core tellurite glass fiber with 1.8?dB/m loss at 1.55?μm was made by using the built-in casting preform fabrication method and rod-in-tube fiber drawing technique. Pumping a 10?cm fiber piece with picosecond pulses of 3-5×10(12)?W/cm(2), 0.1% of the fundamental power limited by the coherence length of 0.3-5?μm was converted into visible third-harmonic power tunable over a broad near-IR wavelength ranging from 1500 to 1680?nm. Frequency conversion from the mid-IR to near-IR was found to be even more efficient due to the longer coherence lengths of 12-20?μm in the wavelength range of 2200-2500?nm.