Tunable Picosecond Pulses Research Articles

Generating tunable picosecond pulses at 900 nm directly from the all-fiber structured parametric oscillator

In this work, we present an all-fiber structured parametric oscillator capable of directly generating pulses within the 900 nm wavelength range. Leveraging the four-wave mixing effect within photonic crystal fibers, the oscillator converts the 1030 nm pump light into two distinct sidebands centered at 900 nm and 1250 nm. Employing time-dispersion-tuning techniques, we achieved a remarkable continuously tunable wavelength range spanning 60 nm, from 865 nm to 925 nm. These pulses exhibited a pulse width of 3.2 ps and a peak power of 500 W at 900 nm, with a repetition rate of 30.6 MHz.

Synchronous tunable picosecond surface emitting lasers by optical gain-switching

Generation of sub-100 ps pulses tunable over 48 nm is demonstrated by optically gain-switching a MEMS-vertical-cavity surface-emitting laser (VCSEL). A minimum pulse width of 61 ps and a maximum, unamplified peak power of 28 mW are demonstrated. The polarization stability of the VCSELs allows amplification with a polarization-dependent semiconductor optical amplifier, resulting in pulse compression to 57 ps with a peak power of 932 mW. The low threshold power (average <1 mW) enables simultaneous pumping of multiple lasers for the generation of synchronized, independently tunable picosecond pulses.

BioCARS: Synchrotron facility for probing structural dynamics of biological macromolecules.

A major goal in biomedical science is to move beyond static images of proteins and other biological macromolecules to the internal dynamics underlying their function. This level of study is necessary to understand how these molecules work and to engineer new functions and modulators of function. Stemming from a visionary commitment to this problem by Keith Moffat decades ago, a community of structural biologists has now enabled a set of x-ray scattering technologies for observing intramolecular dynamics in biological macromolecules at atomic resolution and over the broad range of timescales over which motions are functionally relevant. Many of these techniques are provided by BioCARS, a cutting-edge synchrotron radiation facility built under Moffat leadership and located at the Advanced Photon Source at Argonne National Laboratory. BioCARS enables experimental studies of molecular dynamics with time resolutions spanning from 100 ps to seconds and provides both time-resolved x-ray crystallography and small- and wide-angle x-ray scattering. Structural changes can be initiated by several methods-UV/Vis pumping with tunable picosecond and nanosecond laser pulses, substrate diffusion, and global perturbations, such as electric field and temperature jumps. Studies of dynamics typically involve subtle perturbations to molecular structures, requiring specialized computational techniques for data processing and interpretation. In this review, we present the challenges in experimental macromolecular dynamics and describe the current state of experimental capabilities at this facility. As Moffat imagined years ago, BioCARS is now positioned to catalyze the scientific community to make fundamental advances in understanding proteins and other complex biological macromolecules.

Nonlinear Absorption and Refraction of Picosecond and Femtosecond Pulses in HgTe Quantum Dot Films.

We report measurements of the saturated intensities, saturable absorption, and nonlinear refraction in 70-nm thick films containing 4 nm HgTe quantum dots. We demonstrate strong nonlinear refraction and saturable absorption in the thin films using tunable picosecond and femtosecond pulses. Studies were carried out using tunable laser pulses in the range of 400–1100 nm. A significant variation of the nonlinear refraction along this spectral range was demonstrated. The maximal values of the nonlinear absorption coefficients and nonlinear refractive indices determined within the studied wavelength range were −2.4 × 10−5 cm2 W−1 (in the case of 28 ps, 700 nm probe pulses) and −3 × 10−9 cm2 W−1 (in the case of 28 ps, 400 nm probe pulses), respectively. Our studies show that HgTe quantum dots can be used in different fields e.g., as efficient emitters of high-order harmonics of ultrashort laser pulses or as laser mode-lockers.

Wavelength-tunable picosecond laser source based on filtering and amplifying broadband dissipative soliton pulse

A method for obtaining picosecond pulse sources with continuously tunable central wavelengths is demonstrated numerically and experimentally. A dissipative soliton (DS) mode-locked erbium-doped fiber (EDF) laser based on the nonlinear polarization rotation provides the seed pulse with a flat-top spectral profile and a 55 nm spectral bandwidth. Then it is filtered by a wavelength-tunable super-Gaussian bandpass filter and amplified by two segments of EDFs with different doping concentrations. The output DS pulse from the EDF laser can be compressed from 5.532 ps to 0.291 ps by using a single-mode fiber (SMF-28e), while the pulse energy is about 1.6 nJ. Furthermore, the about 4 ps and 6.84 nJ pulses with continuously tunable central wavelengths ranging from 1535 to 1580 nm can be obtained by amplifying the spectrally filtered pulses. The tunable picosecond pulse source based on the extra-cavity filtering method is very useful for many practical applications because of its flexible wavelength control.

Electronically tunable picosecond pulse generation from Ho3+-doped fluoride fiber laser using frequency-shifted feedback.

In this Letter, we demonstrate electronically tunable picosecond (ps) pulse emission from the 5I6-5I7 transition of the Ho3+ ion by using an acousto-optic tunable filter. The holmium- and praseodymium-codoped ZBLAN fiber laser produced sub-50 ps pulses over a 100 nm tuning range, critically reaching a longest wavelength of 2.94 µm, which overlaps with the peak absorption of liquid water. Measured pulse energies of 8.1 nJ well exceed those expected from picosecond solitonic operation, suggesting possible application in ablative medicine. Furthermore, we present harmonically mode-locked operation of the oscillator, which indicates the possibility of expanding the capabilities of mid-infrared frequency shifted-feedback lasers through the ability to achieve higher pulse repetition rates.

Wavelength tunable picosecond pulse bunch laser around 3 µm through PPMgLN –based DFG with temperature insensitive high power scaling

We report a bunch-mode-operated, wavelength-tunable, temperature-insensitive high power, mid-infrared (MIR) laser based on difference frequency generation (DFG) in a periodically poled Magneoisum-oxide doped Lithium Niobate (PPMgLN) chip. Two synchronized fiber lasers each with master oscillator power amplifier (MOPA) structures are utilized as pump and signal sources for the DFG. The pump laser is seeded by a mode-locked Yb fiber laser around 1030 nm with fundamental repetition rate of 16.32 MHz and pulse duration of 8.5 ps. Each pulse of the pump seed is multiplied by a factor of 16, forming the pulse bunch, and then amplified to 27.8 W. A super-luminescent light emitting diode (SLED) around 1580 nm is triggered by the first pulses of the pump bunch and adopted as the signal seed, which is amplified to 4 W afterwards. The pulse duration and spectral bandwidth of the signal are ~ 5 ns and 50 nm, respectively, covering the total duration of the pump bunch in the time domain and signal wavelength tuning range in the spectral domain, respectively, enabling wavelength-tuning DFG with temperature-insensitive power scaling. High power pulse bunch MIR laser can always be realized within the crystal temperature range from 25 to 95 °C with corresponding idler wavelength from 3.03 μm to 2.84 μm. The highest idler power of 4.6 W is achieved at 3.0 μm with pump-to-idler conversion efficiency of ~ 16.5%. It is believed that such a bunch-mode-operated, mid-infrared ps laser source with high output power within the whole temperature-wavelength tuning range are of great value to the evaluation of wavelength dependent laser bio-ablation.

Passively synchronized mode-locked fiber lasers for coherent anti-Stokes Raman imaging.

We have proposed and implemented a polarization-maintaining passively synchronized fiber laser system, which could deliver tunable dual-color picosecond pulses by including a frequency-doubling module and a spectral broadening module. Specifically, the output from the involved Er-doped fiber laser were used to generate second-harmonic pulses at 790 nm with a quadratic nonlinear crystal. In parallel, the amplified pulses from the synchronized Yb-doped fiber laser were launched into a 150-m single mode fiber, which resulted in not only substantial spectral bandwidth broadening from 0.1 to 20.1 nm, but also a significant Raman-induced signal around 1080 nm. Consequently, narrow spectra from 1018-1051 nm and 1070-1095 nm could be continuously tuned via a tunable bandpass filter, corresponding to Raman bonds from 2835-3143 cm-1 and 3312-3525 cm-1. Finally, the achieved tunable synchronized pulses enabled us to microscopically examine mouse ear samples based on coherent anti-Stokes Raman and second harmonic generation imaging. Therefore, our tunable passively-synchronized fiber laser system would be promising to provide a simple and compact laser source for subsequent coherent Raman microscopy.

Efficient and tunable spectral compression using frequency-domain nonlinear optics.

A key requirement in the field of ultrafast vibrational spectroscopy is to efficiently generate intense tunable narrowband picosecond laser pulses synchronized to a broadband femtosecond laser source. Current nonlinear methods for picosecond pulse generation suffer from complexities in both experimental implementation and pulse frequency tunability. We present here a straightforward method for spectral bandwidth compression that produces frequency tunable picosecond pulses with efficient power conversion. Broadband femtosecond laser pulses are compressed to narrowband picosecond pulses using frequency domain sum-frequency generation of spatially chirped pulses, achieving spectral bandwidths of <20 cm-1 and power conversion efficiency of ∼18%. The experimental design of the bandwidth compressor is presented and its application to stimulated Raman spectroscopy is demonstrated.

Tunable narrow linewidth picosecond pulses from a single grating gain-switched Ce:LiCAF laser

We report a gain-switched laser oscillator configuration for generating tunable short and narrow spectral linewidth 290 nm laser pulses from a Ce:LiCAF crystal. Continuous tuning of the laser emission over a range of 18 nm from 281 nm to 299 nm is achieved using a single grating in a low-Q short-cavity oscillator. The shortest pulse duration achieved is 450 ps at 281 nm and the narrowest spectral linewidth is 0.17 nm at 287 nm. The average output energy ranged between 0.5 mJ and 0.8 mJ, resulting to conversion efficiencies of 8%–10%, depending on the output wavelength. The simplicity of our configuration makes aligning easier as well as reduces the loss in laser output energy, thereby leading to improved laser efficiency.

Diode-pumped femtosecond Tm3+-doped LuScO3 laser near 2.1 μm.

We report on the first demonstration, to the best of our knowledge, of a diode-pumped Tm:LuScO3 laser. Efficient and broadly tunable continuous wave operation in the 1973-2141nm region and femtosecond mode-locking through the use of an ion-implanted InGaAsSb quantum-well-based semiconductor saturable absorber mirror are realized. When mode-locked, near-transform-limited pulses as short as 170fs were generated at 2093nm with an average output power of 113mW and a pulse repetition frequency of 115.2MHz. Tunable picosecond pulse generation was demonstrated in the 2074-2104nm spectral range.

Wavelength tunable ultra-short pulses based on a flat broadband spectrum generated in a nonlinear ytterbium-doped fiber amplifier**Project supported by the National Basic Research Program of China (Grant No. 2013CB922404), the National Scientific Research Project of China (Grant No. 61177047), and the National Natural Science Foundation of China (Grant No. 61575011).

We present a nonlinear ytterbium-doped fiber amplifier based on enhanced nonlinear effects that can produce a flat broadband spectrum ranging from 1050–1225 nm with a maximum average output power of 7.8 W at 14 W pump power. Its repetition rate is 89 MHz. Using a pair of gratings and two knife edges as a filter, wavelength tunable picosecond pulses of tens to hundreds of milliwatts can be obtained in the broadband spectrum range. The output power, pulse width, and spectrum (center wavelength and linewidth) are adjusted by tuning the distance of the grating pair and/or the knife edges. Fixing the distance between the two gratings at 15 mm and keeping the output spectrum linewidth at approximately 20 nm, the shortest pulse width obtained is less than 1 ps centered at 1080 nm. The longest wavelength of the short pulses is around 1200 nm, and its output power and pulse width are 40 mW and 5.79 ps, respectively. The generation of a flat broadband spectrum is also discussed in this paper.

Enhanced Supercontinuum Generation in Nonlinear Ytterbium-Doped Fiber Amplifier by Seeding at Short Wavelength

The amplification of a short-pulsed fiber laser along a high-power nonlinear fiber amplifier will undergo nonlinear spectral broadening and temporal distortion with the influence of fiber nonlinear effects. Within the same nonlinear Yb-doped fiber amplifier, we experimentally compared the different spectral and temporal evolution processes of tunable chirped picosecond pulses at different wavelengths (ranging from 1030 to 1070 nm). The comparison results indicate that the generated supercontinuum can be significantly enhanced when the amplifier is seeded at a short wavelength. A comprehensive analysis links the phenomenon to the overlap of Yb $^{3+}$ ion gain and the Raman gain, as well as the additional amplified spontaneous emission seeding effect. The phenomena of nonlinear-effect-induced spectral and temporal center dips were also observed and explained. The proposed conclusion can help to thoroughly understand the nonlinear process in fiber amplifiers and contribute to the development of a high-power spectrally flat amplifier-based supercontinuum source.

Yb-Fiber-Laser-Pumped Ultrafast Frequency Conversion Sources From the Mid-Infrared to the Ultraviolet

We describe the development of versatile, practical, and high-power ultrafast optical sources based on second-order nonlinear frequency conversion in bulk materials pumped by the mode-locked Yb-fiber laser at 1064 nm, and covering spectral regions from the near- to mid-infrared (mid-IR) to the visible and ultraviolet (UV). By exploiting synchronously-pumped optical parametric oscillators (SPOPOs) based on quasi-phase-matched nonlinear materials of MgO:PPLN and MgO:sPPLT, in combination with internal and external single-pass harmonic generation in birefringent crystals of BiB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> and β-BaB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> , we have generated tunable picosecond pulses in spectral regions from above ~4 μm in the mid-IR, into the visible, and down to 317 nm in the UV. The demonstrated sources can deliver average output powers of up to 11.7 W in the near- to mid-IR, 3.5 W in the visible, and 30 mW in the UV, in picosecond pulses at ~80 MHz repetition rate, with high passive stability, excellent output characteristics, and the potential for further power scaling with increased fiber laser pump power. The described sources represent an effective approach for the extension of fiber laser technology across the entire wavelength range from the UV to mid-IR spectrum, and ultimately the THz spectral range.

A broad and tunable 250- to 430-nm source for microscopy and lifetime measurements by frequency doubling of a 78-MHz-picosecond white-light laser

Broadly tunable picosecond pulses in the UV for nonlinear microscopy and lifetime measurements are not yet readily available. Complex synchronously pumped optical parametric oscillators with subsequent frequency doubling are typically used. We show that direct second harmonic generation of a visible picosecond supercontinuum source at 78 MHz renders pulses easily tunable from 250 to 430 nm. We find that an unexpectedly large numerical aperture and the use of thick crystals increase the efficiency of the frequency doubling process dramatically. The observed spectral width and efficiency are nearly two orders of magnitude larger than predicted by conventional theory. With broadband achromatic doubling, a 130 nm wide spectrum is achieved. Pulse durations of 17–35 ps are found in the UV and an average power between 1 and 70 μW. This qualifies the setup for most UV-based microscopic investigations. As first application, the fluorescence lifetime of two differing conformations of 2-(2′-hydroxyphenyl) benzothiazole is measured.

Orange-to-red tunable picosecond pulses by frequency doubling in a diode-pumped PPKTP waveguide

A compact picosecond all-room-temperature orange-to-red tunable laser source in the spectral region between 600 and 627 nm is demonstrated. The tunable radiation is obtained by second-harmonic generation in a periodically poled potassium titanyl phosphate (PPKTP) multimode waveguide using a tunable quantum-dot external-cavity mode-locked laser. The maximum second-harmonic output peak power of 3.91 mW at 613 nm is achieved for 85.94 mW of launched pump peak power at 1226 nm, resulting in conversion efficiency of 4.55%.

Optimization of a distributed feedback dye laser system to generate single tunable picosecond pulses from UV to IR

We report a new configuration of a picosecond distributed feedback dye laser system, which can be pumped by various wavelengths. The optical characteristics of the system are presented. By using a triangle mirror functioned beam splitter and a right-angle prism attached to the front face of the cell in the pumping geometry, continuously and widely tunable laser wavelengths have been obtained for a range of more than 100 nm. A quenching mirror adhered to a face on the side of the cell, functioning as a high-Q cavity shared common gain medium, has been employed to observe single short laser pulses with transform-limited bandwidth.

Rapid vibrational imaging with sum frequency generation microscopy

We demonstrate rapid vibrational imaging based on sum frequency generation (SFG) microscopy with a collinear excitation geometry. Using the tunable picosecond pulses from a high-repetition-rate optical parametric oscillator, vibrationally selective imaging of collagen fibers is achieved with submicrometer lateral resolution. We furthermore show simultaneous SFG and second harmonic generation imaging to emphasize the compatibility of the microscope with other nonlinear optical modalities.

Ultrafast few-fermion optoelectronics in a single self-assembledInGaAs/GaAsquantum dot

We report a comprehensive study of the ultrafast optoelectronic response of a single self-assembled InGaAs/GaAs quantum dot embedded in a $n\text{\ensuremath{-}}i$-Schottky photodiode device. While manipulation of the artificial atom relies on two independently tunable picosecond pulse trains, sensitive all electrical readout is achieved via photocurrent. We apply our methods to probe the temporal evolution of the quantum dot absorption spectrum following coherent optical generation of a $s$-shell exciton. Our measurements reveal the biexciton absorption as well as previously unobserved $p$-shell transitions that appear in the presence of $s$-shell population. Furthermore, time-resolved measurements allow us to directly monitor the picosecond tunneling times of electrons and holes out of the dot. Beyond these incoherent phenomena, we also demonstrate the potential of our techniques for coherent quantum dot manipulations. Beginning with excitonic Rabi oscillations driven by a single pulse tuned to the neutral exciton we move on to demonstrate the coherent generation of the biexciton via a two-photon nonlinearity, before realizing conditional Rabi oscillations in the exciton-biexciton state manifold. The results provide significant potential for realizing and utilizing conditional coherent dynamics in quantum dot nanostructures for all optical, ultrafast quantum information processing.

Narrow-bandwidth tunable picosecond pulses in the visible produced by noncollinear optical parametric amplification with a chirped blue pump

Narrow-bandwidth (approximately 27 cm(-1)) tunable picosecond pulses from 480 nm-780 nm were generated from the output of a 1 kHz femtosecond titanium:sapphire laser system using a type I noncollinear optical parametric amplifier (NOPA) with chirped second-harmonic generation (SHG) pumping. Unlike a femtosecond NOPA, this system utilizes a broadband pump beam, the chirped 400 nm SHG of the Ti:sapphire fundamental, to amplify a monochromatic signal beam (spectrally-filtered output of a type II collinear OPA). Optimum geometric conditions for simultaneous phase- and group-velocity matching were calculated in the visible spectrum. This design is an efficient and simple method for generating tunable visible picosecond pulses that are synchronized to the femtosecond pulses.