Klaus J. Siemsen, John Reid, and D. J. Danagher, "Improved cw lasers in the 11–13-μm wavelength region produced by optically pumping NH3," Appl. Opt. 25, 86-91 (1986)
An improved technique for creating gain in the ν2 band of NH3 by optically pumping mixtures of NH3 in N2 is described. Conventional (<10-W power) cw CO2 lasers were used to pump both 14NH3 and 15NH3. Lasing was obtained on more than thirty NH3 transitions in the 11–13-μm region, with a maximum output power of 1.2 W and conversion efficiencies as high as 17%. A simple rate equation model is used to explain the inversion mechanism.
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626 = 12C16O2, 0001 = 0001 − [1000, 0200]I,II, 0002 = 0002−[1001,0201]I,II.
Offsets measured by the Lamb-dip technique11
Table II
Observed Laser Lines in 14NH3 and 15NH3 for a Variety of Pumping Transitionsa
Transition
14NH3 Frequency (cm−1)
15NH3 Frequency (cm−1)
+20°C, 14NH3sR(5,0) line center 9-W pump powerb (mW)
−78°C, 14NH3sR(5,0) line center 2-W pump power (mW)
−78°C, 14NH3aR(3,3) ∼50-MHz off. 4-W pump power (mW)
−78°C, 15NH3aR(2,0) ∼40-MHz off. 8-W pump power (mW)
aP(9,6)
753.59
750.24
√
—
—
—
aP(9,3)
760.69
757.37
√
—
—
—
aP(8,6)
770.91
767.47
√
—
—
20
aP(8,3)
778.29
774.88
√
—
—
√
aP(8,0)
780.57
771.16
√
—
—
√
aP(7,6)
788.51
785.00
√
—
—
√
aP(7,3)
796.13
792.64
200
20
—
√
sP(8,3)
807.47
802.88
√
—
—
√
aP(6,3)
814.24
810.66
200
√
40
√
aP(6,0)
816.65
813.08
500
√
—
300
sP(7,0)
827.88
823.21
760
100
—
√
aP(5,3)
832.63
828.98
540
√
70
960
sP(6,3)
847.58
842.75
250
—
—
√
aP(4,3)
851.33
847.60
180
√
100
√
aP(4,0)
853.82
850.11
630
50
20
1200
sP(5,0)
868.00
863.12
710
√
—
500
aP(2,0)
892.16
888.32
190
√
—
200
sP(3,0)
908.19
903.15
150
√
—
—
aQ(6,6)
927.32
923.45
160
—
—
—
aQ(3,3)
930.76
926.84
160
20
—
20
aP(7,1)
798.22
aR(5,1) line center pumped, 1.5 W, −78°C, output 20 mW
aP(8,5)
770.60
aR(6,5) line center pumped, 3.5 W, −78°C, output 150 mW
a A check mark indicates that lasing took place, while a dash indicates that no lasing was observed. Optimum power levels are given for a range of lines. b Results from Ref. 1 for comparison.
Table III
Calculated Inversion and Gain Coefficients Produced In a 2% NH3 In N2 Mixture at 2-Torr Total Pressurea
Pump intensity is 60 W/cm2 in each case. N1/N0 is the ratio of populations in the ν2= 1 vibrational level to that in the ν2= 0 level. A high value of N1/N0 is best for laser action.
These three transitions indicate the range of tunability of the laser. None is directly pumped.
Table IV
Calculated Inversion for Para-NH3 Transitions, Q-Branch Transitions, and ND3 Transitionsa
All transitions are pumped at line center with 60 W/cm2 pump intensity. Gas mixture is 2% ammonia in 2-Torr N2.
Optimum temperature, 200 or 300 K, chosen for calculation. r1/r1e is the ratio of rotational population in the upper pumped level to the value in equilibrium at a total vibrational population of N1. Thus, in the absence of a population spike in the directly pumped level, r1/r1e = 1.
The collisionally pumped transition with maximum gain is given in this column.
Tables (4)
Table I
Best Coincidences Between CO2 Laser Lines and NH3 Absorber Lines
626 = 12C16O2, 0001 = 0001 − [1000, 0200]I,II, 0002 = 0002−[1001,0201]I,II.
Offsets measured by the Lamb-dip technique11
Table II
Observed Laser Lines in 14NH3 and 15NH3 for a Variety of Pumping Transitionsa
Transition
14NH3 Frequency (cm−1)
15NH3 Frequency (cm−1)
+20°C, 14NH3sR(5,0) line center 9-W pump powerb (mW)
−78°C, 14NH3sR(5,0) line center 2-W pump power (mW)
−78°C, 14NH3aR(3,3) ∼50-MHz off. 4-W pump power (mW)
−78°C, 15NH3aR(2,0) ∼40-MHz off. 8-W pump power (mW)
aP(9,6)
753.59
750.24
√
—
—
—
aP(9,3)
760.69
757.37
√
—
—
—
aP(8,6)
770.91
767.47
√
—
—
20
aP(8,3)
778.29
774.88
√
—
—
√
aP(8,0)
780.57
771.16
√
—
—
√
aP(7,6)
788.51
785.00
√
—
—
√
aP(7,3)
796.13
792.64
200
20
—
√
sP(8,3)
807.47
802.88
√
—
—
√
aP(6,3)
814.24
810.66
200
√
40
√
aP(6,0)
816.65
813.08
500
√
—
300
sP(7,0)
827.88
823.21
760
100
—
√
aP(5,3)
832.63
828.98
540
√
70
960
sP(6,3)
847.58
842.75
250
—
—
√
aP(4,3)
851.33
847.60
180
√
100
√
aP(4,0)
853.82
850.11
630
50
20
1200
sP(5,0)
868.00
863.12
710
√
—
500
aP(2,0)
892.16
888.32
190
√
—
200
sP(3,0)
908.19
903.15
150
√
—
—
aQ(6,6)
927.32
923.45
160
—
—
—
aQ(3,3)
930.76
926.84
160
20
—
20
aP(7,1)
798.22
aR(5,1) line center pumped, 1.5 W, −78°C, output 20 mW
aP(8,5)
770.60
aR(6,5) line center pumped, 3.5 W, −78°C, output 150 mW
a A check mark indicates that lasing took place, while a dash indicates that no lasing was observed. Optimum power levels are given for a range of lines. b Results from Ref. 1 for comparison.
Table III
Calculated Inversion and Gain Coefficients Produced In a 2% NH3 In N2 Mixture at 2-Torr Total Pressurea
Pump intensity is 60 W/cm2 in each case. N1/N0 is the ratio of populations in the ν2= 1 vibrational level to that in the ν2= 0 level. A high value of N1/N0 is best for laser action.
These three transitions indicate the range of tunability of the laser. None is directly pumped.
Table IV
Calculated Inversion for Para-NH3 Transitions, Q-Branch Transitions, and ND3 Transitionsa
All transitions are pumped at line center with 60 W/cm2 pump intensity. Gas mixture is 2% ammonia in 2-Torr N2.
Optimum temperature, 200 or 300 K, chosen for calculation. r1/r1e is the ratio of rotational population in the upper pumped level to the value in equilibrium at a total vibrational population of N1. Thus, in the absence of a population spike in the directly pumped level, r1/r1e = 1.
The collisionally pumped transition with maximum gain is given in this column.