RESUMEN
Single-shot optical imaging based on ultrashort lasers has revealed nonrepetitive processes in subnanosecond timescales beyond the recording range of conventional high-speed cameras. However, nanosecond photography without sacrificing short exposure time and image quality is still missing because of the gap in recordable timescales between ultrafast optical imaging and high-speed electronic cameras. Here, we demonstrate nanosecond photography and ultrawide time-range high-speed photography using a spectrum circuit that produces interval-tunable pulse trains while keeping short pulse durations. We capture a shock wave propagating through a biological cell with a 1.5-ns frame interval and 44-ps exposure time while suppressing image blur. Furthermore, we observe femtosecond laser processing over multiple timescales (25-ps, 2.0-ns, and 1-ms frame intervals), showing that the plasma generated at the picosecond timescale affects subsequent shock wave formation at the nanosecond timescale. Our technique contributes to accumulating data of various fast processes for analysis and to analyzing multi-timescale phenomena as a series of physical processes.
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Wavefront distortion in temporal focusing microscopy (TFM) results in a distorted temporal profile of the excitation pulses owing to spatio-temporal coupling. Since the pulse duration is dramatically changed in the excitation volume, it is difficult to correct the temporal profile for a thick sample. Here, we demonstrate adaptive optics (AO) correction in a thick sample. We apply structured illumination microscopy (SIM) to an AO correction in wide-field TFM to decrease the change in the pulse duration in the signal detection volume. The AO correction with SIM was very successful in a thick sample for which AO correction with TFM failed.
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We experimentally demonstrate programmable multimode phase-sensitive amplification multiplexed in the frequency domain for flexible control of parallelly generated squeezed states. We utilize the unique phase-matching condition of a type-II periodically poled potassium titanyl phosphate (PPKTP) crystal and pulse shaping technique to fully control the frequency-domain parallel generation of squeezed states in the optical telecommunication band. We experimentally verify that the independent programmability of phase-sensitive optical parametric amplification (OPA) for the modes corresponding to different frequency bands can be achieved by shaping the pump laser pulse from optical parametric gain measurements using a coherent probe light generated by a degenerate synchronously pumped optical parametric oscillator.
RESUMEN
To fully utilize the functions of a center-wavelength-sweeping pulse train generated by a free-space angular-chirp-enhanced delay optical layout for a probe laser pulse in sequentially timed all-optical mapping photography (STAMP), we introduced an integral field spectroscopy (IFS) method using a microlens array (MLA) to produce hyperspectral images, referring to the technique as lens array (LA)-STAMP. Compared with the previous STAMP utilizing spectral filtering where a bandpass filter generated hyperspectral images, LA-STAMP achieved much higher optical throughput. In a prototype setup, we used a 60×60 MLA and demonstrated single-shot burst imaging of a femtosecond laser-induced ablation process on a glass surface with 300 ps frame intervals in a 1.8 ns time window. Each frame image was constructed by assembling spectrally dispersed 36×36 monochromatic segments distributed by each lenslet on 5×5 pixels of a CCD camera. The spatial resolution was â¼4.4µm, which was determined by the MLA's pitch and the magnification of the microscope lens. We limited the number of frames to seven in this prototype setup, although it can be scaled to â¼24 with a spatial resolution of â¼1µm by designing IFS with a fine pitch MLA.
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We demonstrated the regenerative amplification of picosecond laser pulses generated by a gain-switched laser diode at 640 nm with a Pr:YLF crystal that was continuously pumped by a multimode blue laser diode. A 0.7-pJ seed pulse energy sufficiently suppressed the self-oscillation in the amplifier. The amplified pulse energy reached 33 µJ at a repetition rate of 10 kHz. The spatial beam quality was nearly TEM00. We also demonstrated second- and third-harmonic generation and obtained 320- and 213-nm pulse energies of 18 and 0.83 µJ at 10 kHz.
RESUMEN
We investigated whether Pr:YAlO3 and Pr:Y3Al5O12 (YAG) can work as gain media for high-power visible lasers and replace trivalent praseodymium (Pr)-doped fluoride crystals, with particular focus on thermal loading resistivity. Pr:YAlO3 exhibits a high laser gain at 747 nm, and we obtained a maximum output power of 1.2 W and a slope efficiency of 26.7% with high-power GaN laser diode pumping. Excited state absorption and large phonon energy hinder laser oscillation of Pr:YAG at room temperature. We obtained 616 nm laser oscillation of Pr:YAG at 40 K. Furthermore, we achieved a visible laser with Pr:YAG ceramics for the first time. The maximum output power is â¼30mW with a slope efficiency of â¼0.7%.
RESUMEN
We achieved single-shot 2D-burst imaging with a â¼22ps temporal resolution in a nanosecond time window using sequentially timed all-optical mapping photography with a spectral filtering (SF-STAMP) scheme, where a single snapshot of spectral images measured with a linear frequency chirped laser pulse forms time-resolved snapshots. We combined a pulse-stretching scheme of a free-space angular-chirp-enhanced delay (FACED) composed of a pair of tilted mirrors and a 4f-system. With a 4f-FACED system, we generated collinearly propagating burst laser pulses with a different center wavelength and a tunable time interval and demonstrated single-shot burst imaging with a 303 ps interval in a 1.5 ns time window by an SF-STAMP with spectrally sweeping probe pulses.
RESUMEN
We demonstrated the power scaling of a passively Q-switched Pr3+:LiYF4 (YLF) laser at 523, 607, and 640 nm with a Co2+:MgAl2O4 (MALO) saturable absorber and analyzed the experimental results with a numerical simulation based on rate equations. A maximum pulse energy of 33.5 µJ was obtained with a pulse width of 30.9 ns and a repetition rate of 64.0 kHz at 640 nm. We demonstrated ultraviolet pulse generation at 261 and 320 nm by intracavity frequency doubling and obtained 63.3-ns pulses with a pulse energy of 7.0 µJ and a repetition rate of 64.6 kHz at 320 nm as well as 356-ns 261-nm pulses with a pulse energy of 0.2 µJ at a repetition rate of 82.0 kHz. To the best of our knowledge, a 261-nm pulse is the shortest wavelength laser directly generated from the intracavity second-harmonic generation of passively Q-switched lasers.
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We report the construction of diagnostics for ultrafast surface plasmon polariton (SPP) pulses that evolve spatiotemporally in femtosecond and nanometer scales. We constructed two types of scanning near-field optical microscopes (SNOMs) and verified that the temporal waveform of ultrafast SPP pulses can be measured by combining spectral interferometry (SI). In the illumination-collection (I-C) mode SNOM, which uses a single fiber probe to excite samples and collect optical responses, a lock-in detection scheme using a lock-in camera detects SI fringes even for extremely weak signal light pulses. With this I-C SI-SNOM scheme, we measured the complex plasmon response functions of gold (Au) nanorods on Ge2Sb2Te5 thin film, both in the crystal and amorphous phases. For a dual-probe SNOM (DSNOM), a dual-band modulation technique was introduced to independently control the probe-sample and probe-probe distances. With the DSNOM and by employing femtosecond SPP pulse excitation, we successfully measured the temporal waveform of an ultrafast SPP pulse that is propagating on an Au thin layer.
RESUMEN
We demonstrated regenerative laser pulse amplification at 640 nm for the first time, to the best of our knowledge, with a mode-locked Pr3+-doped LiYF4 (Pr3+:YLF) oscillator as a picosecond seed pulse. A regenerative amplifier with a Pr3+:YLF crystal was continuously pumped by a multimode InGaN diode laser. At an absorbed pump power of 3.1 W, we obtained amplified pulse energy of 13 µJ at 10 kHz with an excellent spatial beam quality of M2â¼1.1, demonstrated second-harmonic generation, and obtained a 320 nm pulse energy of 5.9 µJ.
RESUMEN
We demonstrate the high-power continuous-wave operation of a Pr3+:YLF laser end pumped by blue laser diodes. As the pump source, we used four 5 W single-emitter blue laser diodes and a >20 W fiber-coupled module. In single-emitter-diode pumping, we obtained pump-limited output powers of 6.7 and 3.7 W at 640 and 607 nm, respectively. We successfully suppressed thermal aberration and obtained an output power of 3.4 W at a slope efficiency of 25% at 640 nm with good beam quality in the fiber-coupled module pumping.
RESUMEN
Ultrafast surface plasmon polariton (SPP) nanofocusing on a plasmonic metal tapered tip with femtosecond laser pulses enables background-free localized excitation beyond the diffraction limit. We demonstrate simultaneous nanofocusing of ultrafast SPP pulses at 440 and 800 nm, which were coupled with a common diffraction grating structure fabricated on an aluminum (Al) tapered tip, to the tip apex with a radius of â¼35 nm. We achieved selective coherent anti-Stokes Raman scattering (CARS) microscopy that combined an 800 nm (ω) SPP pump pulse, which achieves selective vibrational excitation by spectral focusing, and a 440 nm (2ω) SPP probe pulse. Raman intensity of this novel 2ω-CARS increased by a factor of 3.96 at the G-band and 4.00 at the 2D-band compared with that with ω-CARS for the monolayer graphene. The 2ω-CARS imaging method was applied for imaging a multiwalled carbon nanotube at the D-, G-, and 2D-bands. This dual-wavelength nanofocusing will open up new nanoscale microspectroscopy and optical excitation at the tip apex, such as sum frequency mixing, two-photon excitation.
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We experimentally reveal the pump-induced loss in a Ti:sapphire laser crystal with 451-nm indium gallium nitride (InGaN) laser diode pumping and show that 478-nm pumping can reduce such loss. The influence of the pump-induced loss at 451-nm pumping is significant even for a crystal that exhibits higher effective figure-of-merit and excellent laser performance at 520-nm pumping. We demonstrate the power scaling of a Ti:sapphire laser by combining 478- and 520-nm InGaN laser diodes and obtain CW output power of 593 mW.
RESUMEN
We attain stable mode-locking of an InGaN laser-diode-pumped Pr3+:YLF laser with a pump power of 2.8 W using a semiconductor saturable absorption mirror. A maximum averaged output power of 65 mW was obtained with a 45-ps pulse width at a pulse repetition rate of 108 MHz. We also attempted Kerr-lens mode-locking by employing an SF57 glass in a cavity as a Kerr medium.
RESUMEN
We demonstrate intracavity second-harmonic generation at 320 nm of a diode-pumped praseodymium-doped YLF laser Q-switched by a Cr4+:YAG crystal. By employing two 3.5-W high-power blue InGaN diode lasers as the pump source, we obtained 50-ns Q-switched pulses with a pulse energy of 1.54 µJ at a repetition rate of 50 kHz. A rate equation analysis shows good agreement with the experimental results.
RESUMEN
We propose and experimentally demonstrate a new method called SF-STAMP for sequentially timed all-optical mapping photography (STAMP) that utilizes spectral filtering. SF-STAMP is composed of a diffractive optical element (DOE), a band-pass filter, and two Fourier transform lenses. Using a linearly frequency-chirped pulse and converting the wavelength to the time axis, we realize single-shot ultrafast burst imaging. As an experimental demonstration of SF-STAMP, we monitor the dynamics of a laser ablation using a linearly frequency-chirped broadband pulse (>100 nm) that is temporally stretched up to ~40 ps. This imaging method is expected to be effective for investigating ultrafast dynamics in a diverse range of fields, such as photochemistry, plasma physics, and fluidics.
RESUMEN
We numerically and experimentally demonstrate photon-number squeezed state generation with a symmetric fiber interferometer in an 800-nm wavelength and compared with an asymmetric fiber interferometer, although photon-number squeezed pulses have been generated only with asymmetric interferometers. Even though we obtain -1.0dB squeezing with an asymmetric fiber interferometer, since perfect spectral phase and intensity matching between displacement and signal pulses are achieved with a symmetric fiber interferometer, we obtain better squeezing of -3.1dB. We also numerically calculate and clarify this scheme's usefulness at a 1.55-µm wavelength.
RESUMEN
We measure the absorption recovery time, the ground- and excited-state absorption cross sections of a Cr4+:YAG crystal at 640 nm for the first time. A pump-probe measurement reveals the existence of two recovery times of 26 ns and 5.6 µs. By a Z-scan experiment, the ground- and excited-state absorption cross sections are estimated to be 1.70 - 1.75 × 10(-17) and 0.95 - 1.00 × 10(-17)cm2, respectively. The adequacy of the proposed model and the accuracy of the estimated parameters of the saturable absorber are verified by reproducing the experimentally obtained performance of a passively Q-switched Pr3+:YLF laser with the Cr4+:YAG saturable absorber from rate equation analysis.
RESUMEN
We demonstrate and theoretically analyze the two-dimensional spatiotemporal focusing of femtosecond pulses by utilizing a two-dimensional spectral disperser. Compared with spatiotemporal focusing with a diffraction grating, it can achieve widefield illumination with better sectioning ability for a multiphoton excitation process. By utilizing paraxial approximation, our analytical method improves the axial confinement ability and identifies that the free spectra range (FSR) of the two-dimensional spectral disperser affects the out-of-focus multiphoton excitation intensity due to the temporal self-imaging effect. Based on our numerical simulation, a FSR of 50 GHz is necessary to reduce the out-of-focus two-photon excitation by 2 orders of magnitude compared with that in a grating-based spatiotemporal focusing scheme for a 90-fs excitation laser pulse. We build a two-dimensional spatiotemporal focusing microscope using a virtually imaged phased array and achieve an axial resolution of 1.3 µm, which outperforms the resolution of conventional spatiotemporal focusing using a grating by a factor of 1.7, and demonstrate better image contrast inside a tissue-like phantom.
RESUMEN
The Talbot cavity is one promising method to synchronize the phase of a laser array. However, it does not achieve the lowest array mode with the same phase but the highest array mode with the anti-phase between every two adjacent lasers, which is called out-phase locking. Consequently, their far-field images exhibit 2-peak profiles. We propose intra-Talbot-cavity frequency-doubling. By placing a nonlinear crystal in a Talbot cavity, the Talbot cavity generates an out-phased fundamental wave array, which is converted into an in-phase-locked second harmonic wave array at the nonlinear crystal. We demonstrate numerical calculations and experiments on intra-Talbot-cavity frequency-doubling and obtain an in-phase-locked second harmonic wave array for a Nd:YVO4 array laser.
