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We analyze how optical distortions in deep imaging or dense scattering media influence three-dimensional interferometric temporal focusing (3D-ITF) imaging, and derive the distorted point spread function (PSF) and optical transfer function (OTF). Upon this, we find that 3D-ITF microscopy is less affected by optical distortions in terms of spatial resolution, artifacts and sectioning ability. Temporal focusing (TF) illumination supports a robust spatial modulation in 3D-ITF microscopy with distorted optics. As the modulation spatial frequencies are unique, they offer a redundancy in 3D-ITF microscopy. The redundancy in the spatial frequency of 3D-ITF images compensates for the loss of spatial frequency caused by the optical distortion in the emission OTF. The redundancy recovers the high spatial frequencies to prevent the degradation of spatial resolution. Moreover, the redundancy recovers the distortion in the emission OTF spectrum, which causes distorted shapes in the PSF such as side lobes and double peaks. Thus, there is a relatively lossless OTF spectrum in 3D-ITF compared to TF, and this leads to better trade-off between remaining noise artifacts and resolution after the Wiener filter correction.

As a method of quantum pulse gating in a quantum simulator, we experimentally demonstrate arbitrary mixing of multimode quantum states prepared in the frequency domain.

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 ∼ 4.4 µ m , 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 ∼ 24 with a spatial resolution of ∼ 1 µ m by designing IFS with a fine pitch MLA.

We investigated whether

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 T E M 00 . 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.

We demonstrated real-time, in-situ operation of a single-shot, frequency-time-encoding burst imaging method of sequentially timed all-optical mapping photography utilizing spectral filtering (SF-STAMP) by employing a high-speed camera with the frame rate of a 1000 fps as a detector. We obtained single-shot burst images of a pulse-by-pulse femtosecond laser ablation of a glass by a chirped probe laser pulse with a 1–2-ps frame interval or by a spectrally sweeping burst laser pulse train with a 300-ps interval. We observed burst images of plasma generation during the early stage of laser ablation in a glass with a short frame interval by a chirped probe laser pulse. We also captured burst images of plume and shock-wave generation in air with a 1.5-ns observation time window by a spectrally sweeping probe laser pulse train.

We propose an extension of the single-shot burst imaging scheme STAMP by introducing a lenslet array-based integral field spectrograph to improve light utilization efficiency and achieve better matching with spectrally sweeping burst probe pulses.

We generate spectral multimode squeezed states and demonstrate quantum mode mixing, a method to arbitrarily mix the spectral multimode quantum states of light using a type-II PPLN waveguide, which is applicable to quantum simulators.

We experimentally examine the characteristics of a continuous wave Ti:sapphire laser pumped by a 449-nm diode-laser at cryogenic temperatures, including the temperature dependence of the pump laser absorption and the fluorescence efficiency.

Multi-photon holographic patterned illumination using temporal focusing (TF) pulses provides 10 μm multi-spots with an axial confinement of 5 μm, enabling parallel photo-stimulation of multi-target cells in three dimensions. However, interference fringes and speckles degrade the uniformity of the spots, causing spatio-temporal fluctuations in photoactivation. Here, we demonstrate fringe- and speckle-free holographic patterned illumination using multifocal time-multiplexed (TM) TF pulses even when the multi-spots overlap spatially. The uniform patterned illumination enabled the expansion of the field-of-view of TM-TF microscopy by more than fivefold and enhanced the axial resolution to 1.3 μm.

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.

Temporal focusing (TF) microscopy has a trade-off between temporal resolution, optical sectioning capability, and field of view. To improve this trade-off, we demonstrate time-multiplexed multi-line temporal focusing (TM-ML-TF) microscopy, which combines the time-multiplexed TF technique with multi-line focusing using a digital micromirror device. Compared with those for TF microscopy, the optical sectioning capability and the signal-to-background ratio were improved by factors of 2.5 and 4.17, respectively. In addition, by applying post-processing for structured illumination microscopy to TM-ML-TF microscopy, the optical sectioning capability and the signal-to-background ratio were further enhanced by factors of 1.2 and 4.63, respectively.

We demonstrated the power scaling of a passively Q-switched Pr

High-power picosecond lasers in the visible and ultraviolet wavelength hold a lot of advantages in various applications. The high absorption efficiency in the various metals leads to the higher removal rates, and the shorter pulse widths can suppress thermal influence during the material processing. Recently, the significant progress in the output power of indium gallium nitride (InGaN)-based laser diodes (LDs) has developed the compact high-power lasers which oscillate directly in the visible wavelength. For example, a continuous-wave laser output power of >6.7 W at the fundamental wavelength of 639 nm was reported with a praseodymium-doped LiYF 4 crystal (Pr:YLF) [1]. Moreover, mode-locked picosecond lasers were also reported using a SESAM saturable absorber with Pr:YLF lasers [2,3]. Further scaling of visible picosecond laser pulse requires an amplifier, but only few experiments were reported on the visible laser amplifiers [4]. For example, the maximum amplification factor of 10 was demonstrated at 478 nm [5]. In this paper, a 639-nm picosecond-pulse regenerative amplifier using a Pr:YLF crystal is demonstrated for the first time.

Beam splitters and phase shifters compose linear photonic circuits and are the most fundamental elements in photon-based quantum information processing. While integration of these linear components on a chip for spatial modes has been dramatically developed in recent years [1], there is another approach for integrated quantum circuits : wavelength division multiplexing (WDM). The degrees of freedom of light allow photons exhibiting different wavelengths to exist independently in the same space, therefore using such characteristics can allow further integrating of photons and modes in a small space.

To capture ultrafast non-repeatable phenomena, we had developed two methods of single-shot ultrafast two-dimensional (2D)-imaging of sequentially timed all-optical mapping photography (STAMP) [1] and STAMP utilizing spectral filtering (SF-STAMP) [2, 3]. In these STAMP schemes, spectral images measured by a linearly frequency-chirped laser pulse corresponds to time-resolved snapshots. So far, we achieved single-shot burst imaging of ultrafast phenomena in picosecond time windows with sub-picosecond temporal resolutions. However, it is not straightforward to extend the time window beyond 10 ps by a conventional method to chirp the probe laser pulse using material dispersion. Currently, we applied a new scheme of free-space angular-chirp-enhanced delay (FACED) [4] composed of a tilted pair of mirrors to SF-STAMP and achieved a sub-ns time window [5]. In this work, we generated spectrally sweeping burst pulses with a 300-ps-pulse interval by FACED, and captured single­shot ultrafast 2D-burst images with a few-nanosecond time window. Furthermore we combined a 1-kfps fast camera. Repetitive laser ablation was captured with 10-frame, 300-ps interval images at every 1 ms.

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.

We experimentally investigate crystals doped with tetravalent chromium or divalent cobalt as saturable absorbers for passive Q-switching of visible solid-state lasers. The recovery time of the ground-state and excited-state absorption cross sections are determined by pump-probe and Z-scan measurements, respectively. We provide saturation intensities, useful wavelength ranges of the investigated materials, and advices to realize passive Q-switching of visible lasers using these crystals as saturable absorbers.

We achieved single-shot 2D-burst imaging with a ∼ 22 p s 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 4 f -system. With a 4 f -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.

We investigated whether P r : Y A l O 3 and P r : Y 3 A l 5 O 12 (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. P r : Y A l O 3 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 ∼ 30 m W with a slope efficiency of ∼ 0.7 % .

We demonstrate the high-power continuous-wave operation of a Pr

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 ∼35 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.

We generate 1.57-μm squeezed vacuum pulses by degenerate spontaneous parametric down conversion (DSPDC)and observe 3.5dB anti-squeezing and −0.48dB squeezing using local oscillator pulses generated from a degenerate synchronously pumped optical parametric oscillator.

We propose a multistage quantum pulse gate which efficiently mix multimode quantum states in the frequency domain. Furthermore we introduce a practicable quantum simulator for calculating Frank Condon factors.

We demonstrate selective CARS measurements of a monolayer graphene and multi-walled carbon nanotubes (MWCNT)at the D-, G-, and 2D-bands with nanofocused SPP pulses at 800 and 440 nm using an aluminum tapered tip.

We generate a spectrally sweeping 100-ps-interval pulse train for ultrafast burst imaging. Adopting those pulses to sequentially timed all-optical mapping photography utilizing spectral filtering (SF-STAMP), we realize single-shot burst imaging with a sub-nanosecond time window.

We demonstrate a continuous-wave Pr3+:YLF laser pumped by blue laser diodes, and obtain the output power of 6.7 and 3.7 W at 640 and 607 nm, respectively. The Pr3+:YLF laser is extended to passive Q-switching by utilizing a Co2+: MgAl 2 O 4 spinel saturable absorber and its intracavity second harmonic generation at DUV.

For capturing ultrafast phenomena in sub-nanosecond (10−10 s) time region in a single-shot basis, we modified STAMP (Sequentially timed all-optical mapping photography) utilizing spectral filtering (SF-STAMP). Our SF-STAMP system consists of a 25-beam-generating diffractive optical element (DOE), a band-pass filter (BPF) or BPF-array, and two Fourier transform lenses. This system duplicates 25-multispectral images simultaneously. Therefore, a linearly frequency-chirped pulse makes spectrally and temporally resolved snapshot-images with the temporal resolution determined by the bandwidth of the wavelength selected by the BPFs. The combination of the DOE and BPF enables to select bandwidth of ∼40 nm for each flame, and the BPF-array chooses the entire spectrum ranging from 660 to 810 nm. The observation time window in a single-shot can be tuned from sub-picosecond (10−13 s) to sub-nanosecond (10−10 s) by controlling the second-order dispersion added to the laser pulse. In this work, we demonstrate 25-frame SF-STAMP system with two-kinds of BPF configuration (a tilted single BPF or BPF-array) and a frequency-chirped laser pulse broadened from 650 to 900 nm. Ultrafast 2D-burst images of crystalline-to-amorphous phase transition of Ge 2 Sb 2 Te 5 and laser ablation process are captured with sub-picosecond to sub-nanosecond time windows.

Supercontinuum (SC) optical pulse generation using solid nonlinear media is demonstrated for a femtosecond laser pulse with relatively narrow initial spectrum width of ∼20 nm (50 fs, FWHM). We propose two methods for obtaining SC pulses with good beam quality. The first method is to increase the number of thin fused silica plates and optimize their position arrangement along the optical path using SPIDER measurements. The second method is to employ induced-phase modulation by the second-harmonic pulses in the thin plates. We obtain SC pulses ranging from 450 to 900 nm, which is comparable to pulses generated by a rare-gas filled hollow core fiber.

Titanium-doped AI2O3 (Ti:sapphire) laser can be directly pumped by recently developed green and blue indium gallium nitride (InGaN) laser diodes (LDs), and mode-locking operations of the laser with these pump sources have already been reported from several groups. Rohrbacher et al. achieved an average output power of 460 mW using two 2.9-W LDs at 450 nm, and a pulse width of 82 fs was obtained by semiconductor saturable absorber mirror (SESAM) mode-locking [1]. However, the 450-nm pumping has been reported to induce an absorption loss in Ti:sapphire crystals, called pump-induced loss, by Roth et al. According to their qualitative experiment, the pump-induced loss was not observed when pump wavelength was longer than 456 nm [2]. A pumping at green wavelength was more efficient than the 450-nm pumping due to not only the lack of the pump-induced loss but also the higher Stokes and absorption efficiencies. However, the available output power from a single green LD (∼520 nm) is lower than that at 450-nm. Sawai et al. demonstrated the first green-diode-pumped Ti:sapphire laser [3], and recently, Gurel et al. reported a successful power scaling resulting 650-mW output power in continuous-wave (CW) operation, and an average output power of 450 mW with a pulse width of 39 fs by Kerr-lens mode-locking, using two overdriven 520-nm LDs [4]. Toward further power scaling, we investigated the characteristics of Ti:sapphire laser pumped by different wavelength.

Many trivalent rare earth ions, such as praseodymium (Pr), samarium (Sm), terbium (Tb) and dysprosium (Dy), have radiative transitions in the visible wavelength region, and those visible lasers have been reported [1]. Especially, Pr3+-doped lasers are successful so far as one of the most efficient approaches for visible lasing thanks to the development of indium gallium nitride (InGaN) diode lasers.

Optical linear circuit is one of the most important parts for optical quantum computing. The optical circuit, which consists of mode mixers and phase shifters, has been used in various quantum protocols: cluster state generation, Boson sampling, and quantum random walk. To realize a large-scale linear circuit, waveguide-based quantum circuits have experimentally been demonstrated by some groups [1, 2]. However, such a waveguide-based circuit cannot overcome issues of flexibility and loss.

A supercontinuum (SC) laser pulse, which is generated through third-order nonlinear process, is valuable light for various applications such as optical coherence tomography (OCT), and spectral measurement. Coherence of a SC pulse is one of the most important properties because the accuracy and sensitivity of these measurements are determined by its noise property. Recently, the second-order coherence property has been revealed by some numerical simulations and experiments [1, 2]. According to these previous reports, the coherence of the SC pulse has been almost lost through the spectral broadening process. However, the depletion of the coherence has been studied only in two bases: time and frequency. Thus, we experimentally study the coherent basis from noisy modes of the SC pulse by utilizing multimode quantum theory [3, 4].

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.

We demonstrate a power scaling of a continuous-wave Pr3+:YLF laser at 640 and 607 nm, by utilizing a 20-W level fiber-delivered blue laser diode (LD) module, and 3.5-W single emitter blue diodes. In the fiber-delivered-LD pumping, we successfully suppress a thermal aberration, and obtain an output power of 3.1 W at a slope efficiency of 23% with a beam quality of M2~1.6. In the single emitter diode pumping, we achieved an output power 4.8 and 2.1 W at 640 and 607 nm, respectively.

We experimentally confirm a pump-induced loss in a Ti:sapphire laser pumped by 451-or 478-nm laser diode. Such loss is significant even for a crystal producing better output performance at 520-nm pumping. We demonstrate a power scaling of a CW Ti:sapphire laser using two 520-nm green diodes and two 478-nm blue diodes, and obtained an output power of 593 mW at an absorbed pump power of 2.5 W.

UTokyo Research掲載「世界最高速の連写カメラ」 URI: http://www.u-tokyo.ac.jp/ja/utokyo-research/research-news/worlds-fastest-burst-mode-camera/

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.

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.

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 M2∼1.1, demonstrated second-harmonic generation, and obtained a 320 nm pulse energy of 5.9 μJ.

We demonstrate pulse laser operation of a 4-cm-long Pr3+-doped fluoride-glass fiber laser pumped by InGaN laser diodes (444 nm) using an acousto-optic modulator. We obtained maximum laser peak power of 105.6 W (2.1 μJ/pulse) with a pulse width of 20 ns at an 8.3-kHz repetition rate for a 607-nm wavelength. Employing a prism tuning cavity, we obtained wavelength tunable Q-switch pulse laser oscillation in the visible region (488–491, 520–526, 601–624, 631–644 nm).

We theoretically reveal the potential of the parallelism of squeezed state generation by nonlinear pulse propagation in an optical fiber. Starting from a nonlinear Schr\"odinger equation coupling with phonon modes that cause Raman noise, we develop a multimode quantum theory of nonlinear propagation in an optical fiber. Based on our proposed method, we numerically simulate fiber nonlinear propagation in two conditions: solitonlike and zero-group-delay-dispersion (zero-GVD) propagation. As a result, we find that zero-GVD propagation enables the large-scale parallel generation of squeezed states relative to solitonlike propagation owing to the broadband phase matching of the four-wave mixing process.

We attain stable mode-locking of an InGaN laser-diode-pumped Prsup3+/sup: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.