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Comparative study of diode-pumped alkali vapor laser and exciplex-pumped alkali laser systems and selection principal of parameters | Optical Engineering | SPIE
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Abstract .
Abstract Introduction Kinetic Model Results and Discussions Conclusion Acknowledgments References
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Abstract.? A theoretical model based on common pump structure is proposed to analyze the output characteristics of a diode-pumped alkali vapor laser (DPAL) and XPAL (exciplex-pumped alkali laser). Cs-DPAL and Cs-Ar XPAL systems are used as examples. The model predicts that an optical-to-optical efficiency approaching 80% can be achieved for continuous-wave four- and five-level XPAL systems with broadband pumping, which is several times the pumped linewidth for DPAL. Operation parameters including pumped intensity, temperature, cell’s length, mixed gas concentration, pumped linewidth, and output coupler are analyzed for DPAL and XPAL systems based on the kinetic model. In addition, the predictions of selection principal of temperature and cell’s length are also presented. The concept of the equivalent “alkali areal density” is proposed. The result shows that the output characteristics with the same alkali areal density but different temperatures turn out to be equal for either the DPAL or the XPAL system. It is the areal density that reflects the potential of DPAL or XPAL systems directly. A more detailed analysis of similar influences of cavity parameters with the same areal density is also presented.
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Figures in this Article.
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Introduction .
Abstract Introduction Kinetic Model Results and Discussions Conclusion Acknowledgments References
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The diode-pumped alkali vapor laser (DPAL) enjoys great attention for its promising properties of high efficiency, high beam quality, and extremely high power from a single aperture. Since the first demonstration of Rb in 2001 by Krupke,1 several important improvements of this three-level laser system have been achieved, including reasonable theoretical models,2–7 experimental investigations, and demonstrations.8–10 Above 1-kW continuous wave for Cs-DPAL11 and a 1.5-kW resonantly pumped potassium (K) DPAL with a slope efficiency of 50%12 were reported in 2012 and 2016, respectively, which demonstrated its cw operation potential of high power and high efficiency.
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A new kind of alkali laser, exciplex-pumped alkali laser (XPAL), which is similar to the DPAL system, was proposed. It is expected to solve the problem of linewidth matching, which increases the cost and complexity of the system, by invoking a molecular interaction to allow one to pump away from the atomic resonance in a broadband absorption blue satellite created by naturally occurring collision pairs. The concept of four- and five-level Cs-Ar XPAL systems has been proposed and demonstrated by Readle et?al.13,14 For both DPAL and XPAL, pumping parameters including temperature, cell’s length, pumped intensity, linewidth of pumped laser, mixed gas pressure, and output coupling have crucial influences on the performance of laser systems. In this paper, the influences of pumping parameters on the performances of Cs-DPAL and four- and five-level Cs-Ar XPAL are investigated and compared by theoretical calculation. In addition, some practical implications on these results based on recent diode technology are discussed at the end of this paper.
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Kinetic Model .
Abstract Introduction Kinetic Model Results and Discussions Conclusion Acknowledgments References
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Models for Diode-Pumped Alkali Vapor Laser and Exciplex-Pumped Alkali Vapor Laser .
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Figure?1 shows the typical schematic diagram of an end-pumped DPAL/XPAL system. The incident pumped laser is assumed to be delivered into the vapor cell by a polarizing beam splitter or a thin film polarizer. After the incident pumped laser Ip passes through the alkali vapor cell, the population inversion is formed within the gain medium. Il± represents the laser beam, which circulates inside the cavity and is coupled out as Iout through the output coupler with the transmittance of Toc . The main intracavity losses include the transmission loss of cell windows Tl and Tp for the laser and pumped laser wavelengths, respectively, and single-pass scattered loss Ts , which is assumed to be located at the back reflector end. Rp is the reflectivity of the back reflector. End-pumped geometries of different incident directions are demonstrated to be equivalent by the simulation.
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Graphic Jump Location Fig. 1
F1 : Calculated (solid curve) and experimental (dots) dependence of output power on the input power with different output coupler.
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In this paper, the Cs-based DPAL and XPAL systems are considered as examples. The energy levels and main kinetic processes of the Cs-DPAL laser are shown in Fig.?2. D1 and D2 lines are laser and pump transitions. In the presence of small hydrocarbons, taking methane as an example, the mixing rate between levels 3 and 2 is γ=nmethaneσ32vr , where nmethane is the number density of methane, σ32 is the mixing cross section, and vr is the relative velocity between cesium atoms and methane molecules. ni is the population density on the i ’th energy level. Aij is the spontaneous emission rate from the i ’th energy level to the j ’th one. gi is the degeneracy factor of the i ’th energy level.
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Graphic Jump Location Fig. 2
F2 : The main kinetic processes of Cs-DPAL.
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According to these kinetic processes, the rate equations of the alkali laser are listed as
dn1(z)dt=?[n1(z)?12n3(z)]×∫0∞σ13(ν)[Ip(z,ν)]hvpdν+[n2(z)?n1(z)]·σ21[Il+(z)+Il?(z)]hvl+n2(z)τD1+n3(z)τD2,(1)
dn2(z)dt=?[n2(z)?n1(z)]·σ21[Il+(z)+Il?(z)]hvl+γ[n3(z)?2?exp(?ΔEkT)·n2(z)]?n2(z)τD1,(2)
dn3(z)dt=[n1(z)?12n3(z)]×∫0∞σ13(ν)[Ip(z,ν)]hvpdν?γ[n3(z)?2?exp(?ΔEkT)·n2(z)]?n3(z)τD2,(3)
where σ13(ν) is the spectrally resolved absorption cross section and σ21 is the emission cross section.
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Equations?(4) and (5) describe the spatial propagating intensities of the pumped laser and laser through the gain medium.
dIp(z,ν)dz=?[n1(z)?12n3(z)]σ13(ν)Ip(z,ν),(4)
dIl±(z)dz=±[n2(z)?n1(z)]σ21Il±(z).(5)
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The XPAL system invokes a molecular interaction to allow one to pump away from the atomic resonance in a broadband absorption blue satellite created by naturally occurring collision pairs. The linewidth of the broadband absorption blue satellite is as wide as the one of a commercial diode laser. For conceptual clarity, the four- and five-level laser operation mechanisms for Cs-Ar are shown in Fig.?3.
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Graphic Jump Location Fig. 3
F3 : The main kinetic processes of four- and five-level XPAL operation.
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The collision pair state of X2Σ1/2+ is pumped by the broadband pumped laser to the dissociative state of B2Σ1/2+ . Taking the Cs-Ar collision pair as the example, the exciplex rapidly dissociates into Cs(62P3/2) and Ar atom resulting in lasing on the Cs(62P3/2)→Cs(62S1/2) transition at 852.3?nm for the four-level XPAL system. For the five-level XPAL system, the dissociating process is followed by kinetic relaxation of the Cs(62P3/2) state to the Cs(62P1/2) state via collisions with the buffer gas (CH4 ) and lasing on the D1 transition at 894.6?nm. kij in Fig.?3 are the rate constants from i to j state, which are listed in Ref.?15. gi are the degeneracy factors of the energy level of i .
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According the kinetic processes shown in Fig.?3, the four- and five-level XPAL rate equations are expressed, respectively.
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For four-level XPAL system,
dn0(z)dt=[n3(z)?2n0(z)]σ30[Il+(z)+Il?(z)]hνl+n3(z)τ30?k01n0(z)M+k10n1(z),(6)
dn1(z)dt=k01n0(z)M?k10n1(z)?[n1(z)?n2(z)]∫0∞σ12(ν)Ip(z,ν)hνpdν,(7)
dn2(z)dt=[n1(z)?n2(z)]∫0∞σ12(ν)Ip(z,ν)hνpdν?k23n2(z)+k32n3(z)M,(8)
dn3(z)dt=k23n2(z)?k32n3(z)M?n3(z)τ30?[n3(z)?2n0(z)]σ30[Il+(z)+Il?(z)]hνl.(9)
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For five-level XPAL system,
dn0(z)dt=[n4(z)?n0(z)]σ40[Il+(z)+Il?(z)]hνl+n3(z)τ30?k01n0(z)M+k10n1(z)+n4(z)τ40,(10)
dn1(z)dt=k01n0(z)M?k10n1(z)?[n1(z)?n2(z)]∫0∞σ12(ν)Ip(z,ν)hνpdν,(11)
dn2(z)dt=[n1(z)?n2(z)]∫0∞σ12(ν)Ip(z,ν)hνpdν?k23n2(z)+k32n3(z)M,(12)
dn3(z)dt=k23n2(z)?k32n3(z)M?n3(z)τ30?γ[n3(z)?2?exp(?ΔE34kT)n4(z)],(13)
dn4(z)dt=?[n4(z)?n0(z)]σ40[Il+(z)+Il?(z)]hνl?n4(z)τ40+γ[n3(z)?2?exp(?ΔE34kT)n4(z)],(14)
σ12 is the cross section for the pumped laser and M is the gas concentration of Ar. And the spectrally resolved stimulated absorption cross section for the pumped laser is defined as σ12(ν)=σ12·Δνabs/2π(ν?νabs)2+(Δνabs/2)2,(15)
where νabs is the central frequency of the blue satellite (836.7?nm) and Δνabs (supposed to be 2?nm) is the FWHM of the absorption line.
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The cross section for the pump laser σ12 is determined through the reduced absorption coefficient kabs and equilibrium fraction f10 .16 Their relationship can be described as
σ12=kabs[n0][n1][M]=kabs[M][f10],(16)
where f10 provides the relation between n0 and n1 at the condition of thermal equilibrium. f10=n1n0=[CsAr(X2Σ1/2)][Cs(S1/22)]=g1g04πR02ΔR?exp(?ΔE10kbT)[M],(17)
where kb is the Boltzmann constant, R0 is the optimal internuclear separation (4.5?? for Cs-Ar) for the blue satellite, ΔR is the range of distances over which the resonance absorption condition is maintained (1??), T is the temperature of the cell, and ΔE10 is the difference in the potential energy between the collision pair state at R0 and the unbound state ( 10??cm?1 ). 17
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The sum of the alkali atom containing species must obey conservation for both DPAL and XPAL systems, therefore
∑i=04ni=ntot,(18)
ntot is the number density of the Cs atom, and ntot=PCskbTNA , 18 where NA is the Avogadro constant.
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The initial pumped laser is assumed to be in the Gaussian spectral profile. Ipin(ν) represents the spectrally resolved pumped laser intensity, and Ipin(ν) can be described as
Ipin(ν)=I02Δνp(ln?2π)1/2?exp{?[4?ln?2(ν?νp)2Δνp2]},(19)
where I0 is the total intensity of the pumped laser, νp is the center frequency of the pumped laser, and Δνp is the FWHM of the pumped laser. Ip(z+Δz,ν)=Ip(z,ν)exp{?[n1(z)?n2(z)]σ12(ν)Δz},(20)
Il±(z+Δz)=Il±(z)exp{±[n4(z)?n0(z)]σ40Δz},(21)
Il±(z+Δz)=Il±(z)exp{±[n3(z)?2n0(z)]σ30Δz}.(22)
Equation?(20) describes the spatial propagating intensities of the pumped laser through the gain medium. Equations?(21) and (22) describe the propagating intensities of laser for four- and five-level XPAL systems, respectively. As Fig.?1 shows, the locations z=0,L represent the boundaries of the gain medium, respectively. The boundary conditions that connect the pumped laser intensity Ip and forwards and backwards laser intensities Il± for both DPAL and XPAL are as follows: Ip(0,ν)=Ipin(ν)Tp,(23)
Il+(0)=Il?(0)Tl2Roc,(24)
Il?(L)=Il+(L)Tl2Ts2Rp,(25)
Iout=Il?(0)Tl(1?Roc),(26)
where Roc is the reflectivity of output coupler ( Roc=1?Toc ). Equation?(23) describes the boundary condition for the pumped laser, and Eqs.?(24) and (25) for the lasers of Il± . Equation?(26) is the relation of the output intensity with the intracavity laser intensity.
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The output laser intensity is defined as Pout=Ioutπωlaser2 , where ωlaser is the beam radius. The mode volume is assumed to be the same as the pumped laser volume, so the optical-to-optical efficiency is defined as ηo?o=PoutPin=IoutIin .
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Numerical Methodology .
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Some assumptions are set to simplify and solve the models. These assumptions include:
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Only the energy states and transitions listed in Figs.?2 and 3 are considered. .
Intensity in the beam cross section is assumed to be uniform for the pump and laser light. .
Pumped laser single passes the vapor cell. .
Neglect the decrease of alkali number density in high temperature regions and natural convection caused by temperature gradient in the cell. .
The processes of ionization in both DPAL and XPAL systems are neglected. .
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In general, gas heating,19 natural convection,20 and ionization21 are also important physical effects for both DPAL and XPAL. But the selective value range of pumped intensity considered in this paper is very large. To unify the models of DPAL and XPAL and simplify the calculation, aforementioned, three factors are ignored.
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The algorithm to solve the equations is described as follows: as we are considering the continuous-wave mode, all the time derivatives are set to zero in rate equations for both DPAL and XPAL. From the rate equations and Eq.?(18), we can obtain the expressions of ni(z) . Suppose a value of Iout as the solution, Il+(0) and Il?(0) can be calculated through the Eqs.?(24) and (26) with a certain value of Ipin(ν) . Then, ni(0)(i=0,1,2,3) can be calculated. Gain medium is supposed to be divided into n segments, which are decided by the value of Δz (n=L/Δz ). In every segment, particle densities are considered to be uniform. The propagation of pump and laser intensity from one segment to the next segment can be simulated by Eqs.?(4), (5), and (20)–(22) for DPAL and XPAL systems, respectively. By this iterative algorithm, population densities and laser intensity can be obtained from all over the gain medium and the relation of whether Il+(l) and Il?(l) meet the boundary condition is checked, Eq.?(25). If the relation is true, the assumed Iout is what we need, and if the relation is not true, we continue to search for the proper Iout , which could make the solution meet the boundary condition.
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Results and Discussions .
Abstract Introduction Kinetic Model Results and Discussions Conclusion Acknowledgments References
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By employing the simulation models, the influences of different parameters on performances of DPAL and four- and five-level XPAL systems are investigated. In this paper, the Cs-DPAL and Cs-Ar XPAL systems are considered as examples. The main parameters used are listed in Table?1.
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Table Grahic Jump Location Table 1 The main parameters. View Large??Save TableSpeciesCs-DPALFour-level Cs-Ar XPALFive-level Cs-Ar XPAL
Mixed gas (torr/atm at the temperature of 300?K).
He: 360?torr.
Ar: 4 atm.
Ar: 4 atm.
CH4: 300?torr.
CH4: 300?torr.
Cell’s length.
10?cm.
10?cm.
10?cm.
Pumped laser linewidth.
0.1?nm.
2?nm.
2?nm.
Toc.
0.7.
0.7.
0.7.
Tl.
0.98.
0.98.
0.98.
Tp.
0.98.
0.98.
0.98.
Ts.
0.9.
0.9.
0.9.
Rp.
0.98.
0.98.
0.98.
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It is known that pumped intensity, cell’s temperature, cell’s length, output coupling, mixed gas pressure, and output coupler are the main influence factors of DPAL and XPAL output characteristics. Previous research has shown that the pumped intensity, the temperature, and the length of the alkali cell are the key parameters influencing the output characteristics, for both DPAL and XPAL systems due to the similar type and pumped structure.2,5 Additionally, these three factors are tightly coupled. The composition of the buffer gas and impact mechanism of mixed gas on DPAL and XPAL systems are different. For the DPAL system, the buffer gas influences the absorption linewidth and fine-structure mixing rate. The noble gas in the four-level XPAL system influences the N-A (noble-alkali) atomic collision pairs’ concentration. The alkane in the five-level XPAL system can result in fine-structure mixing from P3/22 to P1/22 . The influence of the output coupler on the output characteristics is the same as other types of the laser. In this part, the influence law of these factors and output characteristics are investigated by model simulation.
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Figure?4 describes the optical-to-optical efficiency versus input intensity and the temperature of the cell. It is indicated that optical-to-optical efficiencies for both four- and five-level XPAL systems that approach diode-pumped alkali lasers with the same alkali vapor are possible. The maximum efficiencies for four- and five-level XPAL systems are 78.5% and 77.6%, respectively. Although our analysis indicates that DPAL have an efficiency advantage over XPALs, it also indicates that XPALs systems have an efficiency advantage over DPAL systems at higher pump irradiances that are due to four- or five-level structure. Figure?4 not only outlines the values of efficiency but also sensitivities of these two various parameters. We conducted trade-off studies of pumped intensity versus cell’s temperature on optical-to-optical efficiency in both DPAL and XPAL. The result shows that a higher temperature with higher pumped intensity leads to higher efficiency, but within the different scopes for DPAL and XPAL systems. The efficiency for DPAL is more sensitive to these two parameters than that for the XPAL system. Moreover, the XPAL system has a larger and broader parameter selection range for pumped intensity and temperature to achieve the optimal optical-to-optical efficiency. Because of the high potential efficiency advantages in different power scopes for these two types of laser systems, end-pumped DPALs and XPALs can be used in different fields with different power requirements. With the development of diode laser technology, narrower linewidths ranging from picometer at very low power levels to sub-100 picometers stacks around 1?kW of output power have been reported recently. It is possible to achieve the pumped intensity needed for DPAL with <0.01??nm linewidth. However, the needed pumped intensity for XPAL is still hard to achieve. In addition, such a high power for the XPAL system may lead to ionization and damage the optics in the experiment especially in a side-pumped structure.
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Graphic Jump Location Fig. 4
F4 : Pseudo-color map of optical-to-optical efficiency (a)?for Cs-DPAL, (b)?four-level Cs-Ar XPAL, and (c)?five-level Cs-Ar XPAL systems as a function of input intensity and temperature.
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Note that the pumped threshold intensities are 0.08??kW/cm2 at 350?K and 3.98??kW/cm2 at 420?K for DPAL, 67??kW/cm2 at 400?K and 89??kW/cm2 at 600?K for four-level XPAL, and 24??kW/cm2 at 400?K and 31??kW/cm2 at 600?K for five-level XPAL. The efficiency value increases with alkali cell temperature with a certain input intensity, which is much larger than the pumped threshold. The result is limited to the rate at which pumped power can be absorbed by the Cs-Ar collision pairs (Cs atoms for DPAL) based upon the actual number density of Cs. With a higher temperature, one is able to couple in more energy and subsequently couple out more laser energy simply based upon the higher density number of Cs. Therefore, the conclusion from these simulations is that the efficiency of the cw-DPAL and XPAL systems is strongly dependent upon temperature.
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Further, one of the known challenges for XPAL will be to properly absorb the broadband pump radiation on the n1→n2 transition. There are two ways to increase the absorption per cm. One is increasing the cell’s temperature (thereby raising the gain medium concentration). The other is increasing the gain length with the assumption of abundant rare gas for XPAL. Then, the study analyzes how these two factors influence the performances of DPAL and XPAL systems.
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The nL parameter is defined as the product of the alkali density and cell’s length. Here, L is the length of the vapor cell, and n is the density number of alkali atoms, which relates to the temperature of the alkali vapor. For cesium, it can be described as
n=pkT=109.171?3830TkT,(27)
The nL parameter can be regarded as equivalent to “alkali areal density,” which could decide the absorption capacity of the gain medium for DPAL and XPAL systems. Figure?5 describes the contours of the nL parameter and optical-to-optical efficiency for Cs DPAL and four- and five-level Cs-Ar XPAL systems as functions of a cell’s length and temperature. The input intensities for DPAL and four- (five-) level XPAL systems are 3 and 3000??kW/cm2 . It is clear that the contour of nL overlaps the one of constant optical-to-optical efficiency. The same performances for either DPAL or XPAL can be achieved with the same nL parameter. This is a result of assuming that the intensity in the pump beam cross section is uniform. In the case of high-power operation, it is reasonable to assume that the intensity in the beam cross section is uniform. Figure?5 also shows that there exists an optimal nL parameter at which the laser system could achieve the maximum optical-to-optical efficiency with a certain input intensity.
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Graphic Jump Location Fig. 5
F5 : Pseudocolor map of optical-to-optical efficiency and contours of nL parameter (a)?for Cs DPAL, (b)?for four-level Cs-Ar XPAL, and (c)?for five-level Cs-Ar XPAL systems as a function of cell’s length and temperature.
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Figure?6 shows predicted performances of DPAL and four- and five-level XPAL systems as a function of pumped intensity with the same nL parameter. As shown in Fig.?6, it can be concluded that the efficiency versus the pumped intensity is the same for either DPAL or XPAL systems with different cell parameters (temperature and cell’s length) but the same nL parameter. The output performances of the four- and five-level XPAL system are similar, but the optimal pumped intensity for the five-level XPAL system is higher than the one in the four-level XPAL system with the nL parameter of 8.2×1020/m2 .
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Graphic Jump Location Fig. 6
F6 : The influence of pumped intensity on optical-to-optical efficiency with the same constant of nL (a)?for DPAL and (b) and (c)?for four- and five-level XPAL system.
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The dependences of optical-to-optical efficiency on input intensity with different constants of nL for DPAL and four-level XPAL are shown in Fig.?7. It can be seen that the optical-to-optical efficiencies of DPAL and four-level XPAL increase to the maximum and then begin to decrease with the increase of the input intensity. The input intensity corresponding to the maximum optical-to-optical efficiency is the optimal input intensity. The optimal input intensity increases with the nL parameter. It is also shown that higher efficiency can be achieved with a higher nL parameter. The maximum efficiency that can be achieved for both DPAL and XPAL is decided by nL. The efficiency is high, to 91.9%, for the DPAL system with the nL of 7.14×1014/cm2 , while the efficiency is only 75.5% for the XPAL system with the nL of 1.17×1017/cm2 , which is much larger than the one in the DPAL system.
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Graphic Jump Location Fig. 7
F7 : The optical-to-optical efficiency versus input intensity with different constant of nL (a)?for DPAL and (b)?for four-level XPAL system.
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With the different roles of buffer gas for DPAL and XPAL systems, we compared the influences of buffer gas pressure and pumped linewidth on optical-to-optical efficiency for DPAL and four-level XPAL systems. It is instructive to explore the dependence of DPAL and XPAL performances on both buffer gas pressure and pumped linewidth simultaneously. For this analysis, we consider the DPAL and four-level XPAL systems, as analyzed in Fig.?5, except now the linewidths of the pumped laser and the mixed gas pressure of the cell are both varied independently. Not surprisingly, for the range of pump linewidths and mixed gas pressures considered in Fig.?8, peak efficiencies are achieved with the narrowest linewidth for both DPAL and XPAL systems. The difference is that the XPAL system is more sensitive to buffer gas pressure than the DPAL system, while the DPAL system is more sensitive to pumped linewidth. Also evident in Fig.?8 is that for a given value of buffer gas pressure (He for DPAL and Ar for XPAL), the XPAL optical-to-optical efficiency increases slower with decreased pumped laser linewidth than the DPAL system due to its broader spectral absorption characteristic.
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Graphic Jump Location Fig. 8
F8 : (a)?Contours of optical-to-optical efficiency for Cs DPAL system as a function of pump linewidths between 0.01 and 1?nm and He pressures between 0.25 and 2.7 atm. (b)?Contours of optical-to-optical efficiency for four-level Cs-Ar XPAL system as a function of pump linewidths between 0.1 and 4?nm and Ar pressures between 0.5 and 10 atm.
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For evident comparison, the dependences of optical-to-optical efficiency on reflectivity of output coupler for DPAL and four- and five-level XPAL systems are shown in Fig.?9. It is shown that the optical-to-optical efficiency for both DPAL and XPAL systems have similar reflectivity of output coupler dependence. The high output coupling is beneficial to optical-to-optical efficiency.
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Graphic Jump Location Fig. 9
F9 : Dependence of optical-to-optical efficiency on the output coupler.
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Conclusion .
Abstract Introduction Kinetic Model Results and Discussions Conclusion Acknowledgments References
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In this paper, we propose models to analyze and to compare the influences of pumping parameters on the performances for either a DPAL or XPAL system (four-level and five-level). The model predicts that XPAL systems have an efficiency advantage over DPAL systems at higher pump irradiances. In addition, it is observed that there is an optimal pumped intensity under which the efficiency reaches the maximum. According to the investigation, the nL parameter is proposed in this paper. It is defined as the product of the concentration of alkali and cell’s length. The result shows that the DPAL (or XPALs) with the same “nL” but different cell temperatures and cell lengths reveals the same output characteristics. Moreover, higher maximal efficiency can be achieved with the higher nL value. In addition, there is a maximal efficiency for each nL value, and a higher nL value corresponds to higher maximal efficiency. Considering these results, the nL parameter can be used as a design guide. Both for the DPAL and for the XPAL, the optical-to-optical efficiency decreases with the increase of linewidth, but the efficiency for the DPAL decreases faster, while for the XPAL, it decreases rather slowly. Finally, the analysis on the influence of the output coupler shows that high output coupling is beneficial to the performances of both DPAL and XPAL systems. In view of the recent developments of the diode laser, it is scarcely possible to achieve the cw pumped intensity XPAL system needed. In addition, there are still pending issues for the XPAL system, such as ionization and gas heating, in the condition of a high power pump. However, the parameter selection principle proposed in this paper is of importance in designing a static alkali laser.
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Acknowledgments .
Abstract Introduction Kinetic Model Results and Discussions Conclusion Acknowledgments References
.
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This work was supported by the National Natural Science Foundation of China (Grant No.?61505212) and Foundation of State Key Laboratory of Pulsed Power Laser Technology (Grant No.?SKL2014/2016KF02). The authors appreciate all discussions and help provided by our colleagues.
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References .
Abstract Introduction Kinetic Model Results and Discussions Conclusion Acknowledgments References
.
1
Krupke ?W. F. ?et al., “Resonance transition 795-nm rubidium laser,” Opt. Lett.. 28,?(23?), 2336?–2338 (2003).?0146-9592?CrossRef
2
Beach ?R. J. ?et al., “End-pumped continuous-wave alkali vapor lasers: experiment, model, and power scaling,” J. Opt. Soc. Am. B. 21,?(12?), 2151?–2163 (2004).?0740-3224?CrossRef
3
Yang ?Z. N. ?et al., “Theoretical model and novel numerical approach of a broadband optically pumped three-level alkali vapour laser,” J. Phys. B: At. Mol. Opt. Phys.. 44,?(8?), 085401? (2011).CrossRef
4
Carroll ?D. L., and Verdeyen ?J. T., “A simple equilibrium theoretical model and predictions for a continuous wave exciplex pumped alkali laser,” J. Phys. B: At. Mol. Opt. Phys.. 46,?(2?), 025402? (2013).?0953-4075?CrossRef
5
Huang ?W. ?et al., “Theoretical model and simulations for a cw exciplex pumped alkali laser,” Opt. Express. 23,?(25?), 31698?–31715 (2015).?1094-4087?CrossRef
6
Barmashenko ?B. D., and Rosenwaks ?S., “Modeling of flowing gas diode pumped alkali lasers: dependence of the operation on the gas velocity and on the nature of the buffer gas,” Opt. Lett.. 37,?(17?), 3615?–3617 (2012).?0146-9592?CrossRef
7
Waichmann ?K., , Barmashenko ?B. D., and Rosenwaks ?S., “Laser power, cell temperature, and beam quality dependence on cell length of static Cs DPAL,” J. Opt. Soc. Am. B. 34,?(2?), 279?–286 (2017).CrossRef
8
Zameroski ?N. D. ?et al., “Experimental and numerical modeling studies of a pulsed rubidium optically pumped alkali metal vapor laser,” J. Opt. Soc. Am. B. 28,?(5?), 1088?–1099 (2011).CrossRef
9
Page ?R. H. ?et al., “Multimode-diode-pumped gas (alkali-vapor) laser,” Opt. Lett.. 31,?(3?), 353?–355 (2006).?0146-9592?CrossRef
10
Zhdanov ?B. V. ?et al., “Potassium diode pumped alkali laser demonstration using a closed cycle flowing system,” Opt. Commun.. 354,?, 256?–258 (2015).?0030-4018?CrossRef
11
Bogachev ?A. V. ?et al., “Diode-pumped caesium vapour laser with closed-cycle laser-active medium circulation,” Quantum Electron.. 42,?(2?), 95?–98 (2012).?1063-7818?CrossRef
12
Pitz ?G. A. ?et al., “Advancements in flowing diode pumped alkali lasers,” Proc. SPIE. 9729,?, 972902? (2016).?0277-786X?CrossRef
13
Readle ?J. D. ?et al., “Cs 894.3?nm laser pumped by photoassociation of Cs-Kr pairs: excitation of the Cs D-2 blue and red satellites,” Opt. Lett.. 34,?(23?), 3638?–3640 (2009).?0146-9592?CrossRef
14
Readle ?J. D. ?et al., “Lasing in Cs at 894.3?nm pumped by the dissociation of CsAr excimers,” Electron. Lett.. 44,?(25?), 1466?–1467 (2008).?0013-5194?CrossRef
15
Palla ?A. D. ?et al., “XPAL modeling and theory,” Proc. SPIE. 7915,?, 79150B? (2011).?0277-786X?CrossRef
16
Carroll ?D. L., and Verdeyen ?J. T., “XPAL theory and predictions,” Proc. SPIE. 8238,?, 823804? (2012).?0277-786X?CrossRef
17
Hedges ?R. E. D., and Gallagher ?D. L., “Extreme-wing line broadening and Cs-inert-gas potentials,” Phys. Rev. A. 6,?(4?), 1519?–1544 (1972).CrossRef
18
Alcock ?C. B., , Itkin ?V. P., and Horrigan ?M. K., “Vapor-pressure equations for the metallic elements—298–2500-K,” Can. Metall. Q.. 23,?(3?), 309?–313 (1984).CrossRef
19
Oliker ?B. Q. ?et al., “Simulation of deleterious processes in a static-cell diode pumped alkali laser,” Proc. SPIE. 8962,?, 89620B? (2014).?0277-786X?CrossRef
20
Barmashenko ?B. D., and Rosenwaks ?S., “Detailed analysis of kinetic and fluid dynamic processes in diode-pumped alkali lasers,” J. Opt. Soc. Am. B. 30,?(5?), 1118?–1126 (2013).?0740-3224?CrossRef
21
Knize ?R. J., , Zhdanov ?B. V., and Shaffer ?M. K., “Photoionization in alkali lasers,” Opt. Express. 19,?(8?), 7894?–7902 (2011).?1094-4087?CrossRef
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Wei Huang received his BS degrees in physics from Inner Mongolia University in 2012 and will receive his PhD in physical electronics in June 2017. He is a doctor candidate at the Institute of Electronics, Chinese Academy of Sciences. He is the first author of four journal papers. His current research interests include the diode-pumped alkali laser (DPAL), exciplex-pumped alkali laser, and transversely excited atmospheric CO2 laser. He is a student member of SPIE.
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Rongqing Tan received his BS degree in physics from Peking University and his PhD in physical electronics from the Institute of Electronics, Chinese Academy of Sciences. He is a professor at the Institute of Electronics, Chinese Academy of Sciences. His current research interests include gas lasers and their applications.
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Zhiyong Li received his BS degree in optics information sciences and technology from Harbin Institute of Technology in 2009 and his PhD in physical electronics from the Institute of Electronics, Chinese Academy of Sciences, in 2014. He is an assistant professor at the Institute of Electronics, Chinese Academy of Sciences. His current research interests include alkali vapor lasers, beam shaping, and applications of volume Bragg gratings.
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Gaoce Han is pursuing her master’s degree in physical electronics from the Institute of Electronics, Chinese Academy of Sciences. Her current research interest includes microfabricated alkali cells.
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Hui Li is pursuing his Ph D in physical electronics from the Institute of Electronics, Chinese Academy of Sciences. His current research interest includes diode-pumped alkali vapor lasers.
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? 2017 Society of Photo-Optical Instrumentation Engineers
Citation
Wei Huang ; Rongqing Tan ; Zhiyong Li ; Gaoce Han and Hui Li "Comparative study of diode-pumped alkali vapor laser and exciplex-pumped alkali laser systems and selection principal of parameters", Opt. Eng . 56(3), 036112 (Mar 23, 2017). ; http://dx.doi.org/10.1117/1.OE.56.3.036112
Figures.
Graphic Jump Location Fig. 1
F1 :Calculated (solid curve) and experimental (dots) dependence of output power on the input power with different output coupler.
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Graphic Jump Location Fig. 2
F2 :The main kinetic processes of Cs-DPAL.
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Graphic Jump Location Fig. 3
F3 :The main kinetic processes of four- and five-level XPAL operation.
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Graphic Jump Location Fig. 4
F4 :Pseudo-color map of optical-to-optical efficiency (a)?for Cs-DPAL, (b)?four-level Cs-Ar XPAL, and (c)?five-level Cs-Ar XPAL systems as a function of input intensity and temperature.
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Graphic Jump Location Fig. 5
F5 :Pseudocolor map of optical-to-optical efficiency and contours of nL parameter (a)?for Cs DPAL, (b)?for four-level Cs-Ar XPAL, and (c)?for five-level Cs-Ar XPAL systems as a function of cell’s length and temperature.
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Graphic Jump Location Fig. 6
F6 :The influence of pumped intensity on optical-to-optical efficiency with the same constant of nL (a)?for DPAL and (b) and (c)?for four- and five-level XPAL system.
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Graphic Jump Location Fig. 7
F7 :The optical-to-optical efficiency versus input intensity with different constant of nL (a)?for DPAL and (b)?for four-level XPAL system.
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Graphic Jump Location Fig. 8
F8 :(a)?Contours of optical-to-optical efficiency for Cs DPAL system as a function of pump linewidths between 0.01 and 1?nm and He pressures between 0.25 and 2.7 atm. (b)?Contours of optical-to-optical efficiency for four-level Cs-Ar XPAL system as a function of pump linewidths between 0.1 and 4?nm and Ar pressures between 0.5 and 10 atm.
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Graphic Jump Location Fig. 9
F9 :Dependence of optical-to-optical efficiency on the output coupler.
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Tables.
Table Grahic Jump Location Table 1 The main parameters. View Large??Save TableSpeciesCs-DPALFour-level Cs-Ar XPALFive-level Cs-Ar XPAL
Mixed gas (torr/atm at the temperature of 300?K).
He: 360?torr.
Ar: 4 atm.
Ar: 4 atm.
CH4: 300?torr.
CH4: 300?torr.
Cell’s length.
10?cm.
10?cm.
10?cm.
Pumped laser linewidth.
0.1?nm.
2?nm.
2?nm.
Toc.
0.7.
0.7.
0.7.
Tl.
0.98.
0.98.
0.98.
Tp.
0.98.
0.98.
0.98.
Ts.
0.9.
0.9.
0.9.
Rp.
0.98.
0.98.
0.98.
MultiMedia .
References.
1
Krupke ?W. F. ?et al., “Resonance transition 795-nm rubidium laser,” Opt. Lett.. 28,?(23?), 2336?–2338 (2003).?0146-9592?CrossRef
2
Beach ?R. J. ?et al., “End-pumped continuous-wave alkali vapor lasers: experiment, model, and power scaling,” J. Opt. Soc. Am. B. 21,?(12?), 2151?–2163 (2004).?0740-3224?CrossRef
3
Yang ?Z. N. ?et al., “Theoretical model and novel numerical approach of a broadband optically pumped three-level alkali vapour laser,” J. Phys. B: At. Mol. Opt. Phys.. 44,?(8?), 085401? (2011).CrossRef
4
Carroll ?D. L., and Verdeyen ?J. T., “A simple equilibrium theoretical model and predictions for a continuous wave exciplex pumped alkali laser,” J. Phys. B: At. Mol. Opt. Phys.. 46,?(2?), 025402? (2013).?0953-4075?CrossRef
5
Huang ?W. ?et al., “Theoretical model and simulations for a cw exciplex pumped alkali laser,” Opt. Express. 23,?(25?), 31698?–31715 (2015).?1094-4087?CrossRef
6
Barmashenko ?B. D., and Rosenwaks ?S., “Modeling of flowing gas diode pumped alkali lasers: dependence of the operation on the gas velocity and on the nature of the buffer gas,” Opt. Lett.. 37,?(17?), 3615?–3617 (2012).?0146-9592?CrossRef
7
Waichmann ?K., , Barmashenko ?B. D., and Rosenwaks ?S., “Laser power, cell temperature, and beam quality dependence on cell length of static Cs DPAL,” J. Opt. Soc. Am. B. 34,?(2?), 279?–286 (2017).CrossRef
8
Zameroski ?N. D. ?et al., “Experimental and numerical modeling studies of a pulsed rubidium optically pumped alkali metal vapor laser,” J. Opt. Soc. Am. B. 28,?(5?), 1088?–1099 (2011).CrossRef
9
Page ?R. H. ?et al., “Multimode-diode-pumped gas (alkali-vapor) laser,” Opt. Lett.. 31,?(3?), 353?–355 (2006).?0146-9592?CrossRef
10
Zhdanov ?B. V. ?et al., “Potassium diode pumped alkali laser demonstration using a closed cycle flowing system,” Opt. Commun.. 354,?, 256?–258 (2015).?0030-4018?CrossRef
11
Bogachev ?A. V. ?et al., “Diode-pumped caesium vapour laser with closed-cycle laser-active medium circulation,” Quantum Electron.. 42,?(2?), 95?–98 (2012).?1063-7818?CrossRef
12
Pitz ?G. A. ?et al., “Advancements in flowing diode pumped alkali lasers,” Proc. SPIE. 9729,?, 972902? (2016).?0277-786X?CrossRef
13
Readle ?J. D. ?et al., “Cs 894.3?nm laser pumped by photoassociation of Cs-Kr pairs: excitation of the Cs D-2 blue and red satellites,” Opt. Lett.. 34,?(23?), 3638?–3640 (2009).?0146-9592?CrossRef
14
Readle ?J. D. ?et al., “Lasing in Cs at 894.3?nm pumped by the dissociation of CsAr excimers,” Electron. Lett.. 44,?(25?), 1466?–1467 (2008).?0013-5194?CrossRef
15
Palla ?A. D. ?et al., “XPAL modeling and theory,” Proc. SPIE. 7915,?, 79150B? (2011).?0277-786X?CrossRef
16
Carroll ?D. L., and Verdeyen ?J. T., “XPAL theory and predictions,” Proc. SPIE. 8238,?, 823804? (2012).?0277-786X?CrossRef
17
Hedges ?R. E. D., and Gallagher ?D. L., “Extreme-wing line broadening and Cs-inert-gas potentials,” Phys. Rev. A. 6,?(4?), 1519?–1544 (1972).CrossRef
18
Alcock ?C. B., , Itkin ?V. P., and Horrigan ?M. K., “Vapor-pressure equations for the metallic elements—298–2500-K,” Can. Metall. Q.. 23,?(3?), 309?–313 (1984).CrossRef
19
Oliker ?B. Q. ?et al., “Simulation of deleterious processes in a static-cell diode pumped alkali laser,” Proc. SPIE. 8962,?, 89620B? (2014).?0277-786X?CrossRef
20
Barmashenko ?B. D., and Rosenwaks ?S., “Detailed analysis of kinetic and fluid dynamic processes in diode-pumped alkali lasers,” J. Opt. Soc. Am. B. 30,?(5?), 1118?–1126 (2013).?0740-3224?CrossRef
21
Knize ?R. J., , Zhdanov ?B. V., and Shaffer ?M. K., “Photoionization in alkali lasers,” Opt. Express. 19,?(8?), 7894?–7902 (2011).?1094-4087?CrossRef .
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