Hole Burning Research Articles

Microscopic model of spin flip-flop processes in crystals doped by rare-earth ions

Flip-flop processes due to magnetic dipole-dipole interaction between neighboring ions in crystals doped by rare-earth ions are one of the mechanisms of relaxation between hyperfine levels. Modeling of this mechanism has so far been macroscopic, characterized by an average rate describing the relaxation of all ions. Here, however, we present a microscopic model of flip-flop interactions between individual nuclear spins of dopant ions. Every ion is situated in a unique local environment in the crystal, where each ion has different distances and a unique orientation relative to its nearest neighbors, as determined by the lattice structure. Thus each ion has a unique flip-flop rate and the collective relaxation dynamics of all ions in a bulk crystal is a sum of many exponential decays, giving rise to a distribution of rates rather than a single average decay rate. We employ this model to calculate flip-flop rates in ${\mathrm{Pr}}^{3+}$:${\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}$ and show experimental measurements of population decay of the ground state hyperfine levels at $\ensuremath{\sim}2$ K. We also present a method to measure rates of individual transitions from hole burning spectra that requires significantly fewer fitting parameters in theoretical rate equations compared to earlier work. Furthermore, we measure the effect of external magnetic field on the flip-flop rates and observe that the rates slow down by two orders of magnitude in a field of 5--10 mT.

In vivo ultrasound modulated optical tomography with a persistent spectral hole burning filter.

We present in vivo ultrasound modulated optical tomography (UOT) results on mice, using the persistent spectral hole burning (PSHB) effect in a Tm3+:YAG crystal. Indocyanine green (ICG) solution was injected as an optical absorber and was clearly identified on the PSHB-UOT images, both in the muscle (following an intramuscular injection) and in the liver (following an intravenous injection). This demonstration also validates an experimental setup with an improved level of performance combined with an increased technological maturity compared to previous demonstrations.

Self-mixing interference in a thin-slice solid-state laser with few feedback photons per observation period

Formation of a peculiar lasing pattern leading to a TEM00-like mode accompanied by a nonzero bright outer-ring emission (namely, a modified TEM00 mode) was observed in a 300-\mu m-thick LiNdP4O12 (LNP) laser with reflective flat end mirrors that was pumped with a laser diode whose focused spot size was larger than the lasing beam spot size determined by the thermal lens effect. The photon lifetimes of the laser oscillations were found to be greatly shortened to \tau_{p} = 6.74 ps as compared with those in pure TEM00 mode operation, while the fluorescence lifetime was \tau = 130 \mu s. The formation of the peculiar transverse mode was theoretically treated in terms of the pump-intensity-dependent thermal lens effect, which yields the lasing beam spot sizes in the resultant optical cavity. In addition, transverse spatial hole burning of population inversions due to the preceding transverse eigenmode intensity and the associated anti-guidance of the pure TEM00 field leading to formation of the TEM00 with an emergent outer ring emission was shown to appear with increasing pump power through the electric lens (i.e., population lens) effect, in which almost all of the population inversion contributes to lasing with a pronounced effective modal gain. Self-mixing laser Doppler velocimetry (LDV) experiments and numerical simulations revealed that spontaneous emission factors in the peculiar mode oscillations were greatly decreased in comparison with those in pure TEM00 mode operation. The present thin-slice solid-state laser possessing a large fluorescence-to-photon lifetime and decreased spontaneous emission factor enabled us to detect LDV signals in the regime of few feedback photons per observation period.

Upraising wavelength exactitude in laser array with spatial hole burning suppression based on the reconstruction-equivalent-chirp technique.

An equivalent corrugation pitch modulated distributed-feedback semiconductor multiwavelength laser array (MLA) with two equivalently assisted phase shifts (EAPSs) based on the reconstruction-equivalent-chirp technique is theoretically studied and experimentally demonstrated. The simulated results show that the longitudinal photon density distribution of the studied MLA is much more uniform than that of the MLA without EAPSs. Accordingly, the longitudinal spatial hole burning of the proposed MLA is therefore suppressed more effectively. The experimental results show that the studied MLA has good single-longitudinal-mode performance. The highest side mode suppression ratio (SMSR) is even up to 52.63dB. Meanwhile, the tunable wavelength range of the investigated MLA is 25.94nm under the thermal tuning scheme from 15.12°C to 46.93°C. All channels are within a wavelength deviation of ±0.001n m. The SMSRs are all above 38dB.

Single-Mode Laser With Chirped Photonic Crystal Structure Based on Standard Photolithography

A single-mode laser has been proposed and fabricated by standard photolithography, based on the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> -level chirped photonic crystal. Side-mode suppression ratio (SMSR) over 45 dB and direct-modulation bandwidth up to 16.63 GHz has been exhibited by a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$400~\mu \text{m}$ </tex-math></inline-formula> -long laser with the slope efficiency of about 0.22 mW/mA and the output power of about 33 mW. The device has a flat optical field distribution and can effectively suppress the longitudinal space hole burning effect along the cavity. A cost-effective solution is provided for the bulk production of the single mode laser.

Graphene saturable absorber mirror for passive mode-locking of mid-infrared QCLs

Passive mode-locking in quantum cascade lasers (QCLs) remains one of the huge challenges because of the fast relaxation time of the excited carriers which is typically in the range of sub-picoseconds. The use of conventional techniques such as the semiconductor saturable absorber mirror is inefficient because the spatial hole burning effect dominates the carrier dynamics. To overcome this effect, longitudinal transition structures with relaxation time around $$50~\mathrm {ps}$$ were proposed. However, mode-locking is assured with an external modulation at a cavity roundtrip frequency. In this paper, we demonstrate that a single-layer graphene used as a saturable absorber permits to generate stable pulses in such structures. The graphene is integrated with a highly reflective mirror to increase the internal electric field and achieve the saturation intensity. The dynamic of the QCL is modeled with Maxwell-Bloch equations while Maxwell-Ampere equation is used for the graphene layer by considering a nonlinear conductivity. This system of equations is solved using the one-dimensional Finite-Difference Time-Domain ( FDTD) method. To model the single-layer graphene of a $$0.33~\mathrm {nm}$$ thickness, a specific sub-cell is implemented based on Maloney method. Simulation results of a $${\mkern 1mu} 6.2~\mu {\text{m}}$$ QCL with a diagonal radiative transition show a generation of isolated pulses with a peak electric field of $$80~\mathrm {MV.m^{-1}}$$ and a duration of $$51~\mathrm {fs}$$ . The mode-locking remains stable for QCLs with a vertical transition having a relaxation time below $$5~\mathrm {ps}$$ .

High Rejection and Frequency Agile Optical Filtering of RF Signals Using a Rare Earth Ion-Doped Crystal

While photonics is broadly considered as a leading solution for analog RF processing, photonic RF filters often show a limited out-of-band rejection. In this work we demonstrate a high rejection and high steepness photonic RF bandpass filter based on spectral hole burning in a rare earth ion-doped crystal. The filter is obtained by programming a frequency-selective absorption grating in the crystal. With an experimental and theoretical study we identify the optimal parameters for this filter. We achieve a remarkable rejection of 60 dB and a rejection of 45 dB at 50 MHz from the edge of the filter, compliant with most demanding applications.

Wave mixing efficiency in InAs/GaAs semiconductor quantum dot optical amplifiers and lasers

The nonlinear features of both semiconductor optical amplifiers (SOAs) and semiconductor lasers, which are made from the same InAs/GaAs quantum dot (QD) wafers, are investigated in detail. By employing pump-probe driven four-wave mixing as an experimental tool, the wave conversion process shows notably different profiles for the two types of devices. Due to the contributions of ultrafast, sub-picosecond mechanisms, such as carrier heating and spectral hole burning, the pump-probe frequency can be easily tuned to the THz range. SOAs generally benefit more from sub-picosecond carrier dynamics, hence exhibiting a higher conversion efficiency (CE) in the THz range, compared to their laser diode counterparts. The discrepancy even exceeds 10 dB. In addition, laser experiments yield some differences from the amplifier ones, hence leading to a higher nonlinear CE at small detuning ranges. These results strongly improve our insight into the fundamental nonlinear properties of InAs/GaAs QD material, and contribute to the conception of novel devices for future on-chip applications in all-optical communication networks, such as signal wavelength conversion, mode-locking, and optical frequency comb generation.

Active Modelocking Improvement of MIR-QCL by Integrating Graphene as a Saturable Absorber

The active mode-locking technique of quantum cascade lasers is highly affected by the bias current level and the magnitude of the modulated signal because of the spatial hole burning effect. The laser generates a stable pulse train near the threshold current and for a high modulation magnitude. We show in this paper an improvement of these conditions with an integration of a single-layer graphene which works as a saturable absorber. The light-matter interaction in the laser active region is described by the two-level Maxwell-Bloch equations and in graphene layer by the Maxwell-Ampere equation and Maxwell-Bloch equations. These system equations are solved using the Finite-Difference Time-Domain (FDTD) method which has the main advantage of not involving any approximation. The weakly coupled splitting scheme is adopted for the time discretization of Maxwell and Bloch equations. The graphene saturable absorption is modelled by a saturable conductivity in Maxwell-Ampere equation and with the dipole moment and carrier density in Maxwell-Bloch equations. For a QCL structure with a gain recovery time of 50 ps, simulation results show better stability of the mode-locking over a broad range of injection current and for smaller magnitude of the modulated signal. QCL structure with gain recovery time close to 1 ps reveals the generation of two pulses per roundtrip linked to spatial hole burning. The carrier grating strength can be reduced by changing the boundary conditions of the cavity such as with a high reflectivity mirror in front of graphene layer.

Investigation of Factors Influencing Rise in Needle Temperature to Enhance the Production and Seam Performance –part I

ABSTRACT The most recent industrial sewing machines are designed and developed to give high production and quality. These machines are capable to operate at very high speed. On the other hand, the sewing machines operated at high speed are facing the challenge of very high needle temperature generation which leads to seam damages like burnt holes, stiff seam, molten seam etc. Such seam damages are serious issue and affects the performance of the garment produced. An attempt was taken to analyze the factors influencing the rise in needle temperature change during sewing to derive exact solution to the problem. Thermal camera was set up in the sewing machine and change in needle temperature under varying influencing parameter was recorded and taken for analysis. From this study, it is found that twill fabric and interlock fabric with superimposed seam of four layers and high needle tension produced higher needle temperature. The other factors such as sewing thread, stitch density, needle size etc falls in next level of contribution.

Cavity spectral-hole-burning to boost coherence in plasmon-emitter strong coupling systems

Significant decoherence of the plasmon-emitter (i.e., plexcitonic) strong coupling systems hinders the progress towards their applications in quantum technology due to the unavoidable lossy nature of the plasmons. Inspired by the concept of spectral-hole-burning (SHB) for frequency-selective bleaching of the emitter ensemble, we propose ‘cavity SHB’ by introducing cavity modes with moderate quality factors to the plexcitonic system to boost its coherence. We show that the detuning of the introduced cavity mode with respect to the original plexcitonic system, which defines the location of the cavity SHB, is the most critical parameter. Simultaneously introducing two cavity modes of opposite detunings, the excited-state population of the emitter can be enhanced by 4.5 orders of magnitude within 300 fs, and the attenuation of the emitter’s population can be slowed down by about 56 times. This theoretical proposal provides a new approach of cavity engineering to enhance the plasmon-emitter strong coupling systems’ coherence, which is important for realistic hybrid-cavity design for applications in quantum technology.

Ultraviolet and infrared spectra of mono-, di- and tri-hydrated clusters of protonated noradrenaline – Solvation and conformational variations

Ultraviolet (UV) and infrared (IR) spectra of hydrated clusters of protonated noradrenaline (NAdH+) are measured by the electrospray – cold ion trap laser spectroscopy. NAdH+-(H2O)1,2 show complicated UV transitions, while NAdH+-(H2O)3 gives simple and blue-shifted spectrum. Conformer-selected IR spectra and the IR-UV hole burning spectra reveal that 4, 3 and 2 conformers coexist in hydrated complexes of n = 1 ∼ 3, respectively. Gauche conformations for all observed conformers are assigned from the comparison to the theoretical IR spectra obtained by the DFT calculations. The blue shift in NAdH+-(H2O)3 is rationalized by the πσ*interaction between the third water to OH in catechol.

Comparison of contrast-to-noise ratios of different detection methods in ultrasound optical tomography.

Ultrasound optical tomography (UOT) is a hybrid imaging modality based on interaction between ultrasound and light, with a potential to extend optical imaging capabilities in biological tissues to depths of several centimeters. Several methods have been developed to detect the UOT signal. To better understand their potential for deep tissue imaging, we present a theoretical contrast-to-noise comparison between the spectral hole burning, single-shot off-axis holography, speckle contrast, and photorefractive detection methods for UOT. Our results indicate that spectral hole burning filters have the potential to reach the largest imaging depths. We find that digital off-axis holography and photorefractive detection can have good contrast-to-noise ratio at significant depths. The speckle contrast method has a smaller penetration depth comparatively.

Computational study of wavelength conversion based on XGM by photonic crystal semiconductor optical amplifier

In this paper, a numerical study of wavelength conversion based on cross-gain modulation (XGM) has been conducted for the first time using the photonic crystal semiconductor optical amplifier (PC-SOA). A PC-SOA and an optical filter have been used in this design. Nonlinear effects, such as carrier depletion (CD), carrier heating (CH), and spectral hole burning (SHB), have been included in the PC-SOA. The rate and propagation equations have been solved using the finite difference method (FDM). The optimal wavelength conversion based on XGM has been obtained in the PC-SOA through the application of 3.2fJ and 1.0pJ energies for the input and the continuous wave (CW) signals, respectively, and a 15mA injection current for the biasing. The effects of the injection current and input signal energies on wavelength conversion have also been investigated for further examination of the impact of the XGM mechanism on wavelength conversion. It has finally been demonstrated that the PC-SOA exhibits better conditions and performance than the conventional bulk SOA in wavelength conversion based on XGM. Furthermore, the PC-SOA provides a far more appropriate alternative than the bulk SOA for all-optical integrated circuits due to the smaller length of the device and the lower value of injected current.

Extreme Double/Triple Asymmetric Epitaxial Structure Based Diode Lasers for High Powers and High Efficiencies

In edge-emitting high power laser diodes, the longitudinal spatial hole burning (LSHB) effect induced by the inhomogeneous photon and carrier distributions and the non-linear process, two-photon absorption (TPA), are demonstrated to the key causes of power saturation at the high injection level even in the absence of thermal roll-over. Laser diodes based on extreme, double/triple asymmetric (EDAS/ETAS) epitaxial structures show great potentials in high-power and high-efficiency applications owing to the reduced series resistance, low optical loss, and suppressed power saturation. In this paper, a novel semi-analytical calculation method is proposed to systematically analyze the impact of LSHB and TPA effects on the output characteristics of EDAS/ETAS-based broad area lasers (BALs). By leveraging the feature that it is flexible to adjust the confinement factor of ETAS epitaxial structure without compromising the internal loss and resistance level, the laser parameters are first optimized to minimize power saturation of ETAS-based BALs under pulsed and Continuous Wave (CW) operation.

Surface plasmon polariton at the interface of dielectric and graphene medium using the Doppler broadening effect

We theoretically investigate the control of surface plasmon polariton (SPP) generated at the interface of dielectric and graphene due to effective variation of dielectric functions. The input light pulse is controlled and modified in a Doppler broadening dielectric medium. The controlled and modified output, from Doppler broadening dielectric medium is used to excite SPPs at the interface of graphene and dielectric medium. It is noted that at high Doppler width the absorption/dispersion and propagation length of SPPs become saturated and significantly affected by strength of the control fields. The inverse Doppler effect enhances the group speed of SPPs but suddenly decreases at the region of SPPs hole burning. These results have potential applications in optical tweezers, nano-photonics, radiations guiding, plasmonster technology, photovoltaic devices, data storage devices, biosensor technology and solar cells.

Nanosecond pulsed single longitudinal mode diamond Raman laser in the 1.6 µm spectral region.

We demonstrate the first nanosecond pulsed single longitudinal mode (SLM) intracavity-pumped diamond Raman laser, to the best of our knowledge. The eye-safe coherent source at 1634 nm, which was converted from the actively Q-switched 1342 nm Nd:YVO4 laser, yielded 4.35 W of multimode average output power with a pulse duration of 6 ns and peak power of 29 kW. By exploiting the spatial hole burning free gain mechanism in the Raman media, stable SLM operation was observed at low output power (0.46 W) for the free-running case. Furthermore, by incorporating an etalon in the fundamental standing-wave cavity, the spectral linewidth of the fundamental field was suppressed substantially below the diamond Raman gain linewidth and slightly less than the free spectral range of the mm-scale Raman resonator. Thereby, a much higher SLM output power of 1.63 W was obtained with a pulse duration of ∼9 ns and a spectral linewidth of ∼77 MHz.

Limits to the sensitivity of a rare-earth-enabled cryogenic vibration sensor

Cryogenics is a pivotal aspect in the development of quantum technologies. Closed-cycle devices have recently emerged as an environmentally friendly and low-maintenance alternative to liquid helium cryostats. Yet the larger level of vibrations in dry cryocoolers forbids their use in most sensitive applications. In a recent work, we have proposed an inertial, broadband, contactless sensor based on the piezospectroscopic effect, i.e., the natural sensitivity of optical lines to strain exhibited by impurities in solids. This sensor builds on the exceptional spectroscopic properties of rare earth ions and operates below 4 K, where spectral hole burning considerably enhances the sensitivity. In this paper, we investigate the fundamental and technical limitations of this vibration sensor by comparing a rigid sample attachment to the cold stage of a pulse-tube cryocooler and a custom-designed exchange gas chamber for acoustic isolation.

Manipulation of rotary photon drag in the region of spectral hole burning

Manipulation of rotary photon drag in the region of spectral hole burning

Analysis of light – current characteristics of high-power semiconductor lasers (1060 nm) in a steady-state 2D model

This paper presents a 2D model of a high-power semiconductor laser, which takes into account carrier transport across the layers of its heterostructure and longitudinal spatial hole burning (LSHB), an effect related to the nonuniform gain distribution along the cavity axis. We show that the use of the 2D model which takes into account carrier transport across the layers of the heterostructure allows an appreciable contribution of LSHB to saturation of light – current characteristics to be demonstrated. The LSHB effect, causing a decrease in the output optical power of semiconductor lasers, is shown to be stronger at high drive currents and low output mirror reflectivities. In the case of high drive currents, the LSHB-induced drop in power is related to the faster growth of internal optical and recombination losses because of the nonuniform current density distribution along the cavity axis, such that the highest current density can be almost twice the lowest one. LSHB is shown to increase the power stored in a Fabry – Perot cavity, which is an additional mechanism reducing the output optical power.