We developed a THz bandwidth quantum memory using a photon echo technique in InAs quantum dot ensemble with a large inhomogeneous broadning. To improve photon echo generation efficiency, we applied Adiabatic Rapid Passage (ARP) technique to quantum manipulation of quantum memory. In addition, we developed pulse pumped up conversion single photon detector (UCSPD) which enables us to achieve the femtosecond scale temporal resolution and we successfully demonstrated femtosecond time bin photon echo signals.
We have developed a quantum memory using quantum dots with a photon echo method for the storage of ultraweak femtosecond pulses. This quantum memory has a large bandwidth of 7.2 THz, which can be achieved due to the large inhomogeneous broadening of quantum dots. We successfully demonstrated femtosecond timebin pulse transfer to photon-echo-based quantum memory using quantum dots. We also succeeded in measuring the retrieved time-bin pulses as a photon echo from the quantum memory using a pulse-pumped frequency upconversion single-photon detector (UCSPD) with a temporal resolution of 429 fs. It is found that the retrieved time-bin photon echo pulse maintains the sub-picosecond time duration and the relative phase.
LiNbO3 and LiTaO3 are frequently used in second harmonic conversion of continuous-wave light from the infrared to the visible regions. Optical damage of LiNbO3-type crystals is a crucial issue in the high-average-power laser systems. The optical damage by a light-induced heating is investigated. We have proposed a light-induced heating by the accumulated long-lived states like polarons or self-trapped excitons. In addition to the long-lived states, point defects as color centers are created by a radiation. A new model includes these states. As a results, it is shown that a creating rate of the color center becomes a important parameter on the determination of critical power.
Compressing the temporal correlation of two photons to the monocycle regime (3.56 fs, center wavelength: 1064 nm)
is expected to open up new perspectives in quantum metrology, allowing applications such as submicron quantum
optical coherence tomography and novel nonlinear optical experiments. To achieve this, the two-photon state must
essentially be ultra-broadband in the frequency domain and ultra-short in the time domain. Here, we report the successful generation of such ultra-broadband, frequency-correlated two-photon states via type-0, cw-pumped (532 nm) spontaneous parametric down conversion using four PPMgSLT crystals with different chirp rates of their poling periods. For the collinear condition, single-photon spectra are detected using a Si-CCD and an InGaAs photodiode array with a monochromator, while for a noncollinear condition, an NbN meander-type superconducting single photon detector (SNSPD) and an InP/GaAs photomultiplier tube (PMT) with a laser line Bragg tunable bandpass
filter are used. The broadband sensitivity of the SNSPD and PMT in the near-infrared wavelength range enable singleshot observations with a maximum bandwidth of 820 nm among the four samples. Such spectra can in principle achieve a temporal correlation as short as 1.2 cycles (4.4 fs) with the use of appropriate phase compensation, which can be measured using the sum-frequency signal. We also discuss several detection strategies for measuring coincidence counts in the presence of wavelength-dependent optical elements as a step towards frequency correlation measurements.
Coherent all-solid-state light source of a wavelength below 200nm is attracting a lot of attention for industrial
applications such as semiconductor processing, eye surgery, and micro machining. Multi-stage wavelength conversion
from a high power infrared solid-state laser is a promising solution. We have developed a technology for quasi-phasematching
(QPM) in crystalline quartz that utilizes stress-induced twinning. In the present paper, we report a novel stressmaintaining
module that suppresses back-switching of twinning and enables QPM-SHG in the vacuum ultraviolet (VUV)
region. We demonstrated the fabrication of finest periodic twins with a period of 9.6 μm and performed QPM-SHG
experiment. Vacuum ultraviolet 193.4 nm light of 17 mW was generated from 177 mW fundamental light. To the best of
our knowledge, this is the shortest emission wavelength ever obtained with QPM technology.
Passive mode-locking of Nd-lasers operating on the 4F3/2 → 4I13/2 transition is problematic for semiconductor saturable
absorber mirrors (SESAMs) not only because of difficulties in their fabrication process but also in relation to the
achievable parameters and damage resistivity. We investigate an alternative approach based on second-order nonlinearity
inside the laser cavity which utilizes negative χ(2)-lens formation in a SHG crystal assisted by nonlinear reflection of the
so-called "frequency-doubling nonlinear-mirror" (FDNLM). This approach has been previously employed only for
mode-locking of Nd-lasers emitting at 1.06 μm. Here we demonstrate passive mode-locking of a diode-pumped
Nd:YVO4 laser operating at 1342 nm based on negative χ(2)-lensing assisted by the FDNLM effect. Using a 7-mm-long
BiB3O6 (BIBO) nonlinear crystal or 10-mm-long and 1-mm-thick periodically-poled Mg-doped stoichiometric lithium
tantalate (PPMgSLT) crystal and output couplers highly-reflecting at the second-harmonic with optimized transmission
at the fundamental, we achieve average output powers in the steady-state mode-locked regime of the order of 1 W at
pulse durations in the 4-7 ps range. Such a combination of high output power and short pulse duration is superior with
respect to the results previously reported with SESAM mode-locked Nd-lasers operating on this transition. Higher
average powers have been obtained for this laser transition only by the complex additive mode-locking technique. In our
case the average power limit is set by the maximum power achievable in the fundamental transversal mode in the
continuous-wave (CW) regime. The shortest pulses (FWHM of 3.7 ps) can be very well fitted by sech2 temporal shape
assumption.
Undoped and Mg-doped stoichiometric LiTaO3 with concentrations of 0.5, 0.7, and 1.0 mol % were grown by the double-crucible Czochralski method, and their photorefractive effect was investigated by measuring light-induced birefringence changes. Periodically poled Mg-doped stoichiometric lithium tantalate (PPMgSLT) were fabricated for QPM optical parametric oscillator, whose properties, including slope efficiency and threshold, were measured to investigate influence of photorefractive effect on optical parametric oscillator. The results showed that a concentration of 1 mol % MgO in the melt was enough to suppress photorefractive effect at tens of MW/cm2, and the OPO performance of PPMgSLT doped with 0.5 mol % MgO is only 6 % lower than that of PPMgSLT doped with 1 mol % MgO at room temperature, even though light-induced birefringence existed for the crystal doped with 0.5 mol % MgO.
Computational study of nanosecond pulse laser radiation in periodically poled LiNbO3 and LiTaO3 crystals reveals the complex spacio-temporal evolution of the 1.064 μm fundamental harmonic (FH) and second harmonic (SH) energy fields with associated temperature fields, leading to the thermal dephasing and inhibition of second harmonic generation (SHG). The investigated range of the laser input power is W0=0.5-50 W (with the pulse energy Q0=0.01-1 mJ/pulse and repetition rate of 50 kHz). For input laser powers W0>10 W the FH and SH energy fields are found to strongly couple with non-uniform temperature field leading to significant thermal dephasing and SHG efficiency loss. Heat generation and temperature distributions also exhibit very significant non-uniformities along and across the laser beam, maximizing at the rear or inside the crystal, depending on the input power. Performed study shows the feasibility of the effective thermal control with temperature gradient along the crystal allowing one to maintain (i) the irradiated zone within the temperature tolerance range and (ii) high SHG efficiency under high input laser powers.
Coherent all-solid-state light source in deep ultra-violet (DUV) region is widely required for many applications that include sensing and imaging. One of the promising candidates is a combination of an infrared solid-state laser and nonlinear optical crystals that enable DUV generation. Recently, crystal quartz is remarked as a nonlinear optical material of quasi-phase matching (QPM) in addition to the existing nonlinear optical crystals. It is an excellent optical material that has good transparency to 160nm and high damage threshold to laser light. It also has the χ(2) coefficient that allows optical second harmonic generation (SHG). Previously, it is not recognized as a practical nonlinear material due to the impossibility of the birefringent phase matching (BPM). In this work we fabricated a 125 mm-period twin structure for third-order QPM-SHG of 1064nm and performed the SHG experiments.
A novel design for a quasi-three level, microchip high-power laser is proposed. The design uses a Yb:YAG core surrounded by an undoped YAG region of slab shape that could be pumped from one or from both slab sides. Theoretical descriptions of the pumping optimization, pump-beam distribution, and output-to-input power characteristics are presented. The simulations show that from a composite Yb:YAG chip, which consists of a Yb:YAG core of 2.0-mm diameter and 13.0-at.% Yb concentration surrounded by an undoped YAG slab of 5.0-mm width and 0.8-mm thickness, a TEM00 output beam of 100 W continuous-wave power could be obtained. The expected optical-to-optical efficiency is 39%.
The SHG interference microscope was applied to the observation of the ferroelectric 180 degree(s) domain structure along the axial direction in a y-cut MgO:LiNbO3. Using four different SHG interference images with phase difference of 0, (pi) , +(pi) /2, and -(pi) /2, the special functions of the SHG intensities were calculated in the so- called (eta) -plane, from which the 3D domain structure was successfully obtained.
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