Residual Pump Research Articles

Design of an Optimized Terahertz Time-Domain Spectroscopy System Pumped by a 30 W Yb:KGW Source at a 100 kHz Repetition Rate with 245 fs Pulse Duration

Ytterbium laser sources are state-of-the-art systems that are increasingly replacing Ti:Sapphire lasers in most applications requiring high repetition rate pulse trains. However, extending these laser sources to THz Time-Domain Spectroscopy (THz-TDS) poses several challenges not encountered in conventional, lower-power systems. These challenges include pump rejection, thermal lensing in nonlinear media, and pulse durations exceeding 100 fs, which consequently limit the detection bandwidth in TDS applications. In this article, we describe our design of a THz-TDS beamline that seeks to address these issues. We report on the effectiveness of temperature controlling the Gallium Phosphide (GaP) used to generate the THz radiation and its impact on increasing the generation efficiency and aiding pump rejection while avoiding thermal distortions of the residual pump laser beam. We detail our approach to pump rejection, which can be implemented with off-the-shelf products and minimal customization. Finally, we describe our solution based on a commercial optical parametric amplifier to obtain a temporally compressed probe pulse of 55 fs duration. Our study will prove useful to the increasing number of laboratories seeking to move from the high-energy, low-power THz time-domain spectroscopy systems based on Ti:Sapphire lasers, to medium-energy, high-power systems driven by Yb-doped lasers.

High-efficiency anti-stokes Raman blue laser in CO2 enables high-luminance RGB laser-driven white light

Stimulated Raman scattering (SRS) is an efficient nonlinear frequency conversion method, enabling simultaneous generation of red, green, and blue (RGB) lasers. In order to synthesize a white light source for laser display by SRS, a 532 nm laser was used as pump source, and high purity gaseous carbon dioxide (CO2) was used as the Raman active medium. First, by optimizing experimental parameters, with an f = 1.5 m focal lens, in 0.8 atm CO2 pumped at 304 mJ, a first-order anti-Stokes (AS1) 495 nm blue laser was achieved, with an energy of 31.9 mJ, peak power of 10.9 MW and conversion efficiency (CE) of 10.5 %. Then, Then, the second-order Stokes light (S2) at 624 nm, residual pump laser (S0) at 532 nm, and AS1 laser were utilized as RGB primary colors. By the variation of pressure below 1 atmosphere (atm), the laser-driven white light (LDWL) with adjustable correlated color temperature (CCT) below 4700 K were simulated. Finally, LDWL up to 2.6 × 1018cd/m2 of a CCT of 3300 K could be synthesized at an RGB power ratio of PR: PG: PB = 0.447:0.094:0.459, resulting in a white light power CE of 44.4 % and luminous efficacy of 113.7 lm/W. In addition, use of the 574 nm yellow Raman light is expected to realize a four-primary (RGBY) laser display scheme with higher Luminance and broader color gamut. Moreover, the feasibility of using a 515 nm Yb: YAG laser as pump source to widen the range of CCT and improve the brightness of LDWL was discussed.

Effect of thermal expansion to the coupling efficiency of (1 + 1) long distance side pumping fiber

With the same fiber preform, two long distance side pumping fibers were fabricated and measured based on a master oscillator power structure. The residual pump power tendency of the two fibers were obtained in experiment. It was found the residual pump power would arise rapidly when the power reached turning point, which was defined by derivative value of residual pump power to pump power equal to 2.5%. Numerical analysis reveals that the thermal expansion of low refractive polymer between signal and pump fibers, will increase the distance between fibers, deteriorate the coupling efficiency, and lead to an exponential increasing of the residual pump power.

Study on the mechanism of fiber-optic hot-wire sensing based on DFB-FL thermally induced chirp effect

In this paper, we propose an intensity demodulated fiber-optic hot-wire sensing method based on the thermally induced chirp effect of distributed feedback fiber lasers. The cobalt-doped fiber is fused at the rear end of the erbium-doped distributed feedback fiber laser to constitute a hot fiber wire with a gradient temperature distribution. The cobalt-doped fiber is heated up under the excitation of the residual pump light. Then the thermally chirp of the erbium-doped phase-shifted fiber grating brings out the change of the lasing threshold condition of the distributed feedback cavity and a significant reduction of the output power. When this structure is further altered by thermal induced chirp under external thermal field, the lasing output power will be further changed. The experimental results of the dynamic fluid thermal field and the static thermal field shows that, the fiber-optic hot-wire structure can sensitively detect the weak airflow and the thermal field of the environment by monitoring the laser power.

Quiet point engineering for low-noise microwave generation with soliton microcombs

Low-noise microwave signals can be efficiently generated with microresonator-based dissipative Kerr solitons (microcombs). However, the phase noise level in integrated microcombs is presently several orders of magnitude above the limit imposed by fundamental thermorefractive noise, resulting from residual pump laser frequency noise transduction to the soliton repetition rate. This effect can be substantially reduced by accessing a quiet point (QP) in the parameter space, where the transduction is compensated by the dispersive wave (DW) recoil, which conventionally relies on accidental mode crossings. Here we present a method to deterministically engineer the QP, both in terms of spectral width and position, and we discover a continuum of possible QPs within the soliton existence region. Using two controlled mode crossings, we obtain regions where the QPs interact with each other, extending the noise suppression range. Our work demonstrates a promising way to reach the fundamental limit of low-noise microwave generation in integrated microcombs.

The resistive heating, defrosting, and thermal performance of CFRPs as a heat transfer unit in a frozen environment

This study explored the feasibility of substituting the traditional aluminum heat exchanger units of the residual heat pump systems with carbon fiber reinforced polymers (CFRPs). The main objective was to investigate the potential advantages of employing a self-heating heatsink in frozen ambient regarding CFRPs resistive heating feature. The in-plane and through-plane thermal conductivity of PAN-based and Pitch-based carbon fiber laminates, as well as their resistive heating characteristics and surface temperature under various electrical conditions, were studied. Also, the impact of piping (fins to pipe connection) on CFRPs heat generation and defrosting performance of the heatsinks was examined. As a solution, the suggested three-point electrical connection demonstrated a positive effect on reaching uniform temperature throughout the samples, especially for the PAN-based case. In general, the PAN-based laminate exhibited lower power consumption to obtain the desired average surface temperature compared to Pitch-based CFRPs. However, the higher thermal conductivity of the Pitch-based samples led to better heat dissipation and a more uniform temperature contour. Finally, the thermal performance of the Pitch-based CFRPs and aluminum heatsinks were compared in a freezing chamber. The results revealed that under the given time interval, amount of transferred heat for the Pitch-based CFRPs heatsink equipped with defrosting feature was 2260 (kJ), 2.23 times higher than the aluminum (without defrosting element) with 967 (kJ).

Observation of Anomalous Orbital Angular Momentum Transfer in Parametric Nonlinearity.

Orbital angular momentum (OAM) conservation plays an important role in shaping and controlling structured light with nonlinear optics. The OAM of a beam originating from three-wave mixing should be the sum or difference of the other two inputs because no light-matter OAM exchange occurs in parametric nonlinear interactions. Here, we report anomalous OAM transfer in parametric upconversion, in which a Hermite-Gauss mode signal interacts with a specially engineered pump capable of astigmatic transformation, resulting in Laguerre-Gaussian mode sum-frequency generation (SFG). The anomaly here refers to the fact that the pump and signal both carry no net OAM, while their SFG does. We reveal experimentally that there is also an OAM inflow to the residual pump, having the same amount of that to the SFG but with the opposite sign, and thus holds system OAM conservation. This unexpected OAM selection rule improves our understanding of OAM transfer among interacting waves and may inspire new ideas for controlling OAM states via nonlinear optics.

Systemic exposure of floxuridine after hepatic arterial infusion pump chemotherapy with floxuridine in patients with resected colorectal liver metastases

BackgroundFloxuridine’s high hepatic extraction ratio and short elimination half-life allows maximum liver exposure with minimal systemic side-effects. This study attempts to quantify the systemic exposure of floxuridine. MethodsPatients undergoing continuous hepatic arterial infusion pump (HAIP) floxuridine after resection of colorectal liver metastases (CRLM) in two centres underwent six cycles of floxuridine at start dose 0.12 mg/kg/day. No concomitant systemic chemotherapy was administered. Peripheral venous blood samples were drawn during the first two cycles: pre-dose (only in the second cycle), 30 min, 1 h, 2 h, 7 h, and 15 days after floxuridine infusion. Foxuridine concentration in the residual pump reservoir was measured on day 15 of both cycles. A floxuridine assay with a lower boundary of detection of 0.250 ng/mL was developed. Results265 blood samples were collected in the 25 patient included in this study. Floxuridine was mostly measurable at day 7 and day 15 (86 % and 88 % of patients respectively). The median dose corrected concentrations were 0.607 ng/mL [IQR: 0.472–0.747] for cycle 1 day 7, 0.579 ng/mL [IQR: 0.470–0.693] for cycle 1 day 15, 0.646 ng/mL [IQR: 0.463–0.8546] for cycle 2 day 7, and 0.534 ng/mL [IQR: 0.4257–0.7075] for cycle 2 day 15. One patient had remarkably high floxuridine concentrations reaching up to 44 ng/mL during the second cycle, without a clear explanation.The floxuridine concentration in the pump decreased by 14.7 % (range 0.5 %−37.8 %) over a period of 15 days (n = 18). ConclusionOverall, negligible systemic concentrations of floxuridine were detected. However, remarkably increased levels were detected in one patient. Floxuridine concentration in the pump decreases over time.

Generation of single solitons tunable from 3 to 3.8 μm in cascaded Er3+-doped and Dy3+-doped fluoride fiber amplifiers

High-power tunable femtosecond mid-infrared (MIR) pulses are of great interest for many scientific and industrial applications. Here we demonstrate a compact fluoride-fiber-based system that generates single solitons tunable from 3 to 3.8 μm. The system is composed of an Er:ZBLAN fiber oscillator and amplifier followed by a fusion-spliced Dy:ZBLAN fiber amplifier. The Er:ZBLAN fiber amplifier acts as a power booster as well as a frequency shifter to generate Raman solitons up to 3 μm. The Dy:ZBLAN fiber amplifier transfers the energy from the residual 2.8 μm radiation into the Raman solitons using an in-band pumping scheme, and further extends the wavelength up to 3.8 μm. Common residual pump radiation and secondary solitons accompanying the soliton self-frequency shift (SSFS) are recycled to amplify Raman solitons, consequently displaying a higher output power and pulse energy, a wider shifting range, and an excellent spectral purity. Stable 252 fs pulses at 3.8 μm with a record average power of 1.6 W and a pulse energy of 23 nJ are generated. This work provides an effective way to develop high-power widely tunable ultrafast single-soliton MIR laser sources, and this method can facilitate the design of other SSFS-based laser systems for single-soliton generation.

High-temperature linearly polarized single-frequency fiber lasers based on a non-polarization-maintaining FBG preparation through a femtosecond laser

A high-temperature-resistant linearly polarized single-frequency distributed Bragg reflector fiber laser is demonstrated by using a femtosecond laser and directly fabricating a pair of fiber Bragg gratings (FBGs) into an erbium-doped fiber (EDF). A high-reflection FBG with high birefringence prepared by femtosecond laser overexposure is used as a polarization selector. The integrated resonator cavity is 0.82 cm to ensure single-frequency operation. After annealing treatment, the laser can work stably at 600°C, and no mode hopping happens at different temperatures. By using the residual pump light and a suitable EDF to amplify the laser, a narrow linewidth laser with an output power of 26.3 mW, a degree of polarization reaching 0.984, and a linewidth less than 4 kHz is obtained.

Effective all-fiber pump recycler for kilowatt fiber lasers.

We report an effective pump recycler for industrial kilowatt fiber lasers. The pump recycler is a (6+1)×1 tapered fiber bundle, with signal ports of Ge-doped fiber (GDF) with core/cladding diameters of 20/400 µm and pump fiber ports (PFPs) with core/cladding diameters of 135/155 µm. By splicing PFPs in pairs, 77.9% of the residual pump light reaching the pump recycler is sent back to the cladding of the GDF. The insertion of a pump recycler increases the power conversion efficiency (PCE) of a fiber laser using an Yb-doped fiber (YDF) from 61.0% to 70.5%, with a maximum output power of 2.78 kW. The laser with a 20 m long YDF and pump recycler compares well to another laser using a 40 m long YDF without pump recycler. In both cases, the PCE is comparable but the laser with a 20 m long YDF and pump recycler benefits from reduced stimulated Raman scattering (SRS), thus enabling an 80% increase in Raman threshold. By giving access to short YDF length, the tapered fiber bundle represents an effective pump recycler since it enables reducing SRS while keeping a large PCE.

Mode-resolved analysis of pump and Stokes beams in LD-pumped GRIN fiber Raman lasers.

All-fiber Raman lasers have demonstrated their potential for efficient conversion of highly multimode pump beams into high-quality Stokes beams. However, the modal content of these beams has not yet been investigated. In this work, based on a mode decomposition technique, we are able to reveal the details of intermodal interactions in the different operation regimes of continuous wave multimode graded-index fiber Raman lasers. We observed that, above the laser threshold, the residual pump beam is strongly depleted in its transverse modes with principal quantum number below 10. However, the generated Stokes signal beam mainly consists of the fundamental mode, but higher-order modes are also present, albeit with exponentially decreasing population.

Femtosecond tunable light source with variable repetition rate between 640 kHz and 41 MHz with a 130 dB temporal pulse contrast ratio.

We demonstrate a femtosecond tunable light source with a variable pulse repetition rate based on a synchronously pumped fiber-feedback optical parametric oscillator (FFOPO) that incorporates an extended-cavity design. The repetition rate can be reduced by an acousto-optical modulator in the FFOPO pump beam. The extended FFOPO cavity supports signal oscillation down to the 64th subharmonic. The high nonlinearity of the FFOPO threshold suppresses signal output for residual pump pulses that are transmitted by the pulse picker. We characterize the temporal pulse contrast ratio of the FFOPO signal output with a second-order cross-correlation measurement. This FFOPO system enables pulse picking with extraordinarily high values up to 111 dB suppression of adjacent pulses and exhibits a temporal contrast ratio that exceeds 130 dB. It generates fs-pulses with tunable wavelength from 1415-1750 nm and 2.5-3.8 µm and variable repetition rates ranging from 640 kHz to 41 MHz.

An efficient wide flatness gain bandwidth with parallel hybrid fiber amplifier

AbstractIn this article, we experimentally propose an efficient wide flat gain bandwidth with a parallel hybrid fiber amplifier. The setup includes parallel amplifier branches. In the first branch, serial erbium‐doped and Raman fiber amplifiers are used. In the second branch, only a Raman fiber amplifier is used. Three Raman pump power units (i.e., 1410, 1480, and 1495 nm) are used to achieve Raman gain at different optical communication bands. At optimum pump powers and at a small‐signal power of −30 dBm, an average gain of 18.5 dB with a maximum gain variation of 3 dB and a gain flatness bandwidth of 83 nm, that is, from 1527 to 1610 nm, is achieved. This gain flatness is expanded to 92 nm (1525–1617 nm) at a large input signal power of −5 dBm with an average gain level of 13 dB. In our proposed amplifier, the Raman amplification peaks (1510 and 1595 nm) are chosen to be far from the erbium amplification peak (1530–1570 nm) in order to avoid the overlapping and the saturation in the first amplifier branch. Therefore, due to such wavelength optimization in addition to the recycling the residual Raman pump power, a wide flatness gain bandwidth is achieved for both of low and large input signal powers.

Quality Management of a Comprehensive Blood Conservation Program During Cardiopulmonary Bypass

BackgroundRed blood cell transfusion is common and associated with adverse outcomes for cardiac surgery, while present blood conservation guidelines have not been fully implemented until now. This study evaluated our comprehensive blood conservation program after quality management and explored its impact on blood transfusion and outcomes in patients undergoing cardiopulmonary bypass (CPB). MethodsWe retrospectively compared blood transfusions and outcomes of patients from 2 different periods, before and after initiation of the quality management of the comprehensive blood conservation program. The comprehensive program included restrictive transfusion protocols, conventional ultrafiltration, cell salvage, residual pump blood ultrafiltration, and a modified minimal extracorporeal circulation system. A 1:1 propensity score matching and subgroup analysis were conducted. ResultsThere were 3977 pairs. A significant decrease of red blood cell transfusion was observed before vs after the comprehensive blood conservation program during CPB (28.4% vs 18.6%, P < .001), in the operation (40.7% vs 34.3%, P < .001), and after the operation (6.2% vs 4.3%, P < .001). Also reduced were 30-day mortality and some major complications. Subgroup analysis showed that the comprehensive blood conservation program was more beneficial for patients aged >60 years, male, and with a medium-risk European System for Cardiac Operative Risk Evaluation (EuroSCORE) of score 3 to 5. ConclusionsThe comprehensive blood conservation program during CPB is safe and effective in adult cardiac operations, reducing blood use, with no adverse outcomes. For patients who are older, male, and have a EuroSCORE of 3 to 5, blood transfusion should be more cautious.

Study on Physical Effects of Optical Fiber Transmission Characteristics Under Nonlinear Optical Effects

Photonic crystal fiber has a special light guiding mechanism and structural tunability, which can produce singular dispersion characteristics and high nonlinearity, which provides new conditions for the research in the field of nonlinear fiber optics. Due to the combined action of a variety of nonlinear optical effects, photonic crystal fibres with different structural parameters and transmission characteristics can produce rich nonlinear spectra under different pump light pulse parameters. We use the photonic crystal fiber cladding section to conduct nonlinear optical experimental research, and obtain the broadband spectral output of soliton wave and dispersive wave. The theoretical analysis and experimentally measured spectra include blue-shifted dispersion waves in the visible light band near 0.5 μm, residual pump light in the 0.82 μm band, soliton waves in the 1.1 μm band, and red-shifted broadband dispersive waves near 2 μm. Corresponding to this, the formation and redshift of solitons can be clearly seen in the time domain, and there is no more oscillation secondary peak in the femtosecond transmission pulse.

Comparison of terahertz time-domain spectroscopy based on photoconductive antenna and electro-optic sampling and the optical parameter measurement of GaSe nanofilm in THz band

Due to the advantages of THz wave in nondestructive examination (NDE) of materials, terahertz time-domain spectrometer (THz-TDS) has become a mature device for THz detection. Thus, improving signal-to-noise ratio (SNR) and reliability of THz-TDS are considered as the vital work. In this paper, photoconductive antenna (PCA) and electro-optic sampling (EOS) were used to measure the intensity of THz wave. Under the same laser conditions, the residual pump laser and probe laser polarization in THz-TDS were studied for influence on the SNR of THz wave. The experimental results demonstrated the significance of the existing THz-TDS. In THz band, the refractive index of GaSe nanofilm varied from 3.3 to 4.1 with the frequency range from 0.3 THz to 0.6 THz.

Intraoperative Cell Saving: Is the Solution the Actual Problem?

Allogenic blood is a scarce, precious, and expensive resource that is not always available on demand. After termination of cardiopulmonary bypass, a large amount of residual pump blood remains in the extracorporeal circuit. The cell saver washes and concentrates this blood with .9% normal saline (NS), making autologous blood available and reducing the demand for allogenic blood. To quantify the quality of residual pump blood it was washed with either NS or a bicarbonate-buffered solution (Balsol). A qualitative in vitro analysis was conducted. Residual cardiopulmonary bypass blood from forty bypass circuits was processed with a cell saver device, using NS or Balsol solution. Measurements made compared the pH, electrolytes, metabolites, hematocrit, hemoglobin, osmolality, albumin, total protein, and strong ion difference. There were significant differences between the NS and Balsol groups. In the Balsol group, osmolality, electrolytes, and strong ion difference were similar to the constitution of Balsol solution after washing, but not with the normal saline group. Washing residual cardiopulmonary bypass pump blood with Balsol solution results in a resuspended red cell concentrate with a superior electrolyte profile and a strong ion difference similar to that of residual pump blood.

Gain and Noise Figure Analysis of Erbium Doped Fiber Amplifier Based on Double Pass Configuration Using Forward Pumping

In this paper, gain and noise figure of Erbium Doped Fiber Amplifier (EDFA) is analyzed based on double pass with Wave Selective Coupler (WSC). The main contribution in this study the use of a (WSC) to eliminate the residual pump power out of the signal and attain optimal result in L-band. This method decreases the self-saturation effect of ASE. Also, the study shows the effect on input and output signal power in L-band Erbium Doped Fiber Amplifiers with pump power using forward pumping. Moreover, the researchers analyzed the high-yield behavior and characterization details of the new double-pass EDFA with WSC. Finally, the study shows the effects of pump power on gain and noise figure with input and output signal power in L-band at 1590 nm.

400-W single-mode single-frequency laser output from homemade tapered fiber

In recent years, the high-power single-frequency fiber lasers have developed rapidly, and they have been used in nonlinear frequency conversion and gravitational wave detection. The main factors limiting the output power of single-frequency fiber lasers are the nonlinear effect and transverse mode instability (TMI) effect. In general, large-core fibers can mitigate nonlinear effects while small-core fibers help to suppress the TMI effect. Owing to the core diameter varying in the longitudinal direction, tapered double clad fiber (T-DCF) is a promising solution to simultaneously suppress the nonlinearity and TMI effects. In the present study, we have fabricated a piece of 2.2-m-long Ytterbium-doped T-DCF. The core diameter and the cladding diameter of this fiber vary gradually from 30.3 μm to 49.3 μm and from 245 μm to 404 μm, respectively. Using this homemade fiber, we constructe an all-fiberized single-frequency master oscillator power amplifier system, which is pumped by laser diodes with a central wavelength of 976 nm. The seed of the system has a central wavelength of 1064 nm, and output power of 30 mW. The T-DCF is coiled on a piece of cooling plate, whose output end is cleaved at a 8° angle. The laser is output to free space and collimated by a free-space collimator. After the collimator, dichroic mirror is utilized to strip out the residual pump power for measuring power, spectrum, time-domain signal and beam quality. The output power increases linearly with the pumping power increasing. When the pumping power is 502 W, the output power reaches 400 W. And there is no stimulated Brillouin scattering (SBS) nor TMI under the power level. The corresponding slope efficiency is 81.7% while the &lt;i&gt;M&lt;/i&gt;&lt;sup&gt;2&lt;/sup&gt; is measured to be 1.29, exhibiting the single-mode output characteristic of the system. When the output power is further increased to 418 W, the TMI effect is observed, which limits further the power scaling of the single-mode output. To the best of our knowledge, this is the highest output power of single-frequency fiber laser based on home-made gain fibers. The results indicate that T-DCFs can simultaneously suppress the nonlinearity and TMI, thus providing a useful reference for further power scaling of single-frequency fiber lasers. Higher output power is expected by optimizing the parameters of T-DCF and the structure of system.