Research Development and Technological Challenge of Alkali Lasers with High Power

Fig. 5. Window damage in alkali cells in different flowing field and buffer gases^[31]. (a) Window damage in Cs alkali cells filled with static methane buffer gas; (b) window damage in Cs alkali cells filled with flowing methane buffer gas; (c) window damage in K alkali cells filled with flowing He buffer gas

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Fig. 6. Design of transversely pumped Cs laser with stable resonator and unstable resonator^[26]. (a) Stable resonator; (b) unstable resonator

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Table 1. Comparison of characteristic of D line for different alkali atoms
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Table 1. Comparison of characteristic of D line for different alkali atoms
Alkali atom Pump wavelength for D₂ line /nm Lasing wavelength for D₁ line /nm Quantum efficiency /%
Na 589.16 589.75 99.8
K 770.11 766.70 99.6
Rb 780.25 794.98 98.1
Cs 852.35 894.59 95.3

Table 2. Main achievement on concept research of DPAL in the beginning
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Table 2. Main achievement on concept research of DPAL in the beginning
Year Team Gain medium Main contribution
1958 Townes K Master amplified design for visible light
1961 Jacobs^[5] Cs Experiment of coherent light
1962 Rabinowitz Cs Cs DPAL CW output with extremely low power

Table 3. Achievement on power of DPAL during fast improving period

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Table 3. Achievement on power of DPAL during fast improving period

Year	Team	Gain medium	Pump power /W	Output power /W	Key technology
2003	Krupke^[4]	Rb	0.5	0.028	—
2005	Ehrenreich	Cs	0.4	0.13	—
2006	Zhdanov^[9]	Cs	0.57	0.35	—
2007	Zhdanov	K	0.86	0.014	—
2007	Zhdanov^[10]	Cs	16	10	—
2008	Zhdanov^[11]	Rb	37	17	Dual side pumped
2008	Zhdanov^[12]	Cs	100	48	Dual side pumped
2008	Zhdanov	Cs	200	28	End pumped
2008	Zhdanov	Cs	—	1.45	Amplifier
2008	Hostutler	Rb	0.05	0.33	Amplifier
2009	Zhdanov^[13]	Cs	157	49	End pumped/unstable cavity
2010	Zhdanov	Cs	5	25	End pumped/amplifier
2012	Bogachev	Cs	2000	1000	Dual side pumped/flow gas
2016	Pitz	Rb	168	571	Amplifier/flow gas
2016	Pitz	K	2750	1500	Flow gas

Table 4. MW DPAL main design parameters^{and evaluation of TRL}

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Table 4. MW DPAL main design parameters^{and evaluation of TRL}

Parameter	Value	Unit	TRL	Technological challenge
Gain cell length	30	cm	2	Optimization of configuration and fabrication
Gain cell diameter	11	cm	2
Laser mode diameter	10.8	cm	2
Rubidium density	4.3	10¹³cm^-3	2	New type of control for density
Rubidium cold temperature	160	℃	2	Uniformity control of temperature
Pump power	3.7	MW	1	Integrated technology of new LD with high efficiency and high matching rate
Output power	2.07	MW	1
Output power irradiance	22.5	kW∙cm^-2	1
Optical conversion efficiency	55.8	%	1‒2
Waste heat density	17	W∙cm^-3	2	Management of waste heat
Gain medium flow velocity	30	m∙s^-1	2	High stability control technology for medium flow velocity
Gain medium temperature rise	9	℃	2‒3	Very difficult for 3D temperature gradient

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Yu Qi, Hengyu Yi, Jijin Huang, Yan Kuang. Research Development and Technological Challenge of Alkali Lasers with High Power[J]. Laser & Optoelectronics Progress, 2021, 58(7): 0700003

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