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Absolute frequency measurements of 12C16O and 13C16O laser transitions
Volume 10, number 3
ABSOLUTE
FREQUENCY
OPTICS COMMUNICATIONS
MEASUREMENTS
March 1974
O F 12C~ 6 0 A N D ~ 3C~ 6 0 L A S E R T R A N S I T I O N S
B.G. WHITFORD, K.J. SIEMSEN and H.D. RICCIUS Division o f Physics, National Research Council. Ottawa, Canada
Received 18 January 1974 The absolute frequencies of one 5.2 ,zm 12C160 laser line and one 5.3 um 13C160 laser line have been measured against 10 ~m band transitions of the CO 2 laser by heterodyning in a tungsten nickel diode. The frequencies, wavelengths and wave numbers of these lines are reported to an accuracy of one part in 107. The absolute frequencies of the 5/ira transitions, P(14) of tile 8--7 vibrational band of 12C160 and P(19) of the 7 - 6 band of 13C160, have been measured relative to the accurately known frequencies of the 10/lm band transitions P(28) and P(10), respectively, of the CO 2 cw laser. The results are believed to be accurate to within -+ 1 part in 107 ; the work provides additional frequency and wavelength references for the 5 gm region. Sokoloff et al. [1] have measured the frequency of the P(13) transition of the 7 - 6 vibrational band in 12C160. A t u n g s t e n - n i c k e l diode set-up similar to that first used by Hocker et at. [2] and others [3,4] was used for the frequency comparisons. The tungsten wire of 25/ira nominal diameter was electro-chemically etched in 3N KOH solution to give a tip near 2 / i r a diameter and a tip radius near 50 nm (electron microscope study). This was m o u n t e d in a coaxial-line connector and the assembly rigidly fastened in a L-shaped brass block containing the polished nickel post on a differential screw drive which facilitated making the mechanical contact of tungsten to nickel. CW radiant energy from both CO and CO 2 lasers was focussed on the diode point-contact with j / 4 optics. The incident electric field vectors were polarized in the horizontal direction: the tungsten wire was horizontal. The directions of incidence of the focussed CO and CO 2 beams were inclined 5 ° and 10 ° respectively relative to the tungsten wire. The diode generated the second harmonic of the CO 2 frequency and, simultaneously, mixed this with the CO frequency to produce a beat in the low GHz range. The dc signal generated by the diode was gener288
ally in the range o f - 15 mV throughout the measurem e n t s ; i t was used as an indicator of diode behaviour until the beat signal itself could be observed. Tile beat frequencies were observed and measured with a spectrum analyzer which had been specially calibrated against the NRC Cs standard to permit determination of beat frequencies to within _+0. l MHz. Both CO and CO 2 lasers had discharge tubes 0.8 m long and resonant cavities 1.2 m long. Transitions were selected by gratings at one end of each cavity;piezoelectric translation of the output mirrors was used for fine tuning. The CO 2 laser was operated with a flowing 15% CO 2 12% N 2 - 7 3 % He gas mixture giving a total pressure of 8 torr in the tube. The discharge current was 4 mA; power output was kept in the range of 200 roW. Each CO 2 frequency was servo-locked to the center of the laser gain profile to within -+ 100 kHz. The CO laser discharge tube was operated sealed, and was cooled with a methyl alcohol-dry ice system. The discharge current was 6 mA and power output in the range 50 to 150 mW. For the 12C160 measurement the gas mixture had partied pressures, in tort, of 2.5 He, 3.0 Xe, 2.0 12C160, and 3.0 N2; and for the 13C 160 measurement the mixture was 2.5 He, 3.0 Xe, 1.5 13C160, and 3.5 N 2. Before each frequency measurement, file CO laser was adjusted to the center of its gain profile with the aid of a 520 Hz dither o f thelaser output mirror to within -+3 MHz. CO 2 and CO transitions were identified with grating spectrometers. For the determination of the beat frequency between P(14) of 12C160 a n d t h e second harmonic of P(28) of CO 2 a total of 14 measurements were made.
Volume 10, number 3
OPTICS COMMUNICATIONS
March 1974
Table 1
C02 transition frequency [MHz] Measured beat frequency [MHz] I?requency of CO transition [MHz] 'Vacuum wavelength [/~m] 'Vacuum wave number [cm-1 ]
The value 2198.8 lVlHz is the mean of these data. The maximum deviation of any one data from the mean was 2.2 MHz. In the case of P ( 1 9 ) o f 13C160 and P(10) of CO 2 825.0 MHz is the mean of 9 readings of the beat frequency; 2.5 MHz was the m a x i m u m deviation of any one value from the mean. The CO frequencies were computed from the measured beat frequencies and CO 2 transition frequencies derived by the use of absolute values given by Evenson et al. [5] and rotational constants recently determined by Petersen et al. [6]. Wavelengths and wave numbers of the CO lines were obtained using 2.997 924 58 m/s as the speed of light. Our results are Nven in table 1. The m a x i m u m error in setting the CO laser to the centre of the gain curve is estimated to be -~t3 MHz. The absolute error in the value of each CO 2 frequency is estimated to be not more than -+ 1 Mttz. Experiments performed in this laboratory and the experience of other workers indicate that other contributions to the total error, such as those due to shifts of the gain profile centres with
P(14) of 8-7 band of 12C160
P (19) of 7-6 band of 13C160
28 084 669.78 2199 57 135 497 5.247 043 8 1905.8350
28 566 649.18 825 56 168 515 5.337 375 5 1873.5800
pressure, current, gas composition, etc., are negligible compared to the above. Errors in the actual measurement of the beat frequencies are also negligible. Accordingly, the constants given here are estimated to be accurate to within I part in 107.
References
[1] D.R. Sokoloff, A. Sanchez, R.M. Osgoode and A. Javan, Appl. Phys. Lett. 17 (1970) 257. [2] L.O. Hocker, D.R. Sokoloff, V. Daneu, A. Szoke and A. Javan, Appl. Phys. Lett. 12 (1968)401. [3] K.M. Evenson, J.S. Wells, L.M. Mataresse and L.B. Elwell, Appl. Phys. Lett. 16 (1970) 159. [4] T.G. Blaney, C.C. Bradley, G.J. Edwards and D.J.E. Knight, Phys. Lett. 36A (1971) 285. [5] K.M. Evenson, J.S. Wells, F.R. Petersen, B.L. Danielson and G.W. Day, Appl. Phys. Lett. 22 (1973) 192. [6] F.R. Petersen, D.G. McDonald, J.D. Cupp and B.L. Danielson, Phys. Rev. Lett. 31 (1973) 573.
289
ABSOLUTE
FREQUENCY
OPTICS COMMUNICATIONS
MEASUREMENTS
March 1974
O F 12C~ 6 0 A N D ~ 3C~ 6 0 L A S E R T R A N S I T I O N S
B.G. WHITFORD, K.J. SIEMSEN and H.D. RICCIUS Division o f Physics, National Research Council. Ottawa, Canada
Received 18 January 1974 The absolute frequencies of one 5.2 ,zm 12C160 laser line and one 5.3 um 13C160 laser line have been measured against 10 ~m band transitions of the CO 2 laser by heterodyning in a tungsten nickel diode. The frequencies, wavelengths and wave numbers of these lines are reported to an accuracy of one part in 107. The absolute frequencies of the 5/ira transitions, P(14) of tile 8--7 vibrational band of 12C160 and P(19) of the 7 - 6 band of 13C160, have been measured relative to the accurately known frequencies of the 10/lm band transitions P(28) and P(10), respectively, of the CO 2 cw laser. The results are believed to be accurate to within -+ 1 part in 107 ; the work provides additional frequency and wavelength references for the 5 gm region. Sokoloff et al. [1] have measured the frequency of the P(13) transition of the 7 - 6 vibrational band in 12C160. A t u n g s t e n - n i c k e l diode set-up similar to that first used by Hocker et at. [2] and others [3,4] was used for the frequency comparisons. The tungsten wire of 25/ira nominal diameter was electro-chemically etched in 3N KOH solution to give a tip near 2 / i r a diameter and a tip radius near 50 nm (electron microscope study). This was m o u n t e d in a coaxial-line connector and the assembly rigidly fastened in a L-shaped brass block containing the polished nickel post on a differential screw drive which facilitated making the mechanical contact of tungsten to nickel. CW radiant energy from both CO and CO 2 lasers was focussed on the diode point-contact with j / 4 optics. The incident electric field vectors were polarized in the horizontal direction: the tungsten wire was horizontal. The directions of incidence of the focussed CO and CO 2 beams were inclined 5 ° and 10 ° respectively relative to the tungsten wire. The diode generated the second harmonic of the CO 2 frequency and, simultaneously, mixed this with the CO frequency to produce a beat in the low GHz range. The dc signal generated by the diode was gener288
ally in the range o f - 15 mV throughout the measurem e n t s ; i t was used as an indicator of diode behaviour until the beat signal itself could be observed. Tile beat frequencies were observed and measured with a spectrum analyzer which had been specially calibrated against the NRC Cs standard to permit determination of beat frequencies to within _+0. l MHz. Both CO and CO 2 lasers had discharge tubes 0.8 m long and resonant cavities 1.2 m long. Transitions were selected by gratings at one end of each cavity;piezoelectric translation of the output mirrors was used for fine tuning. The CO 2 laser was operated with a flowing 15% CO 2 12% N 2 - 7 3 % He gas mixture giving a total pressure of 8 torr in the tube. The discharge current was 4 mA; power output was kept in the range of 200 roW. Each CO 2 frequency was servo-locked to the center of the laser gain profile to within -+ 100 kHz. The CO laser discharge tube was operated sealed, and was cooled with a methyl alcohol-dry ice system. The discharge current was 6 mA and power output in the range 50 to 150 mW. For the 12C160 measurement the gas mixture had partied pressures, in tort, of 2.5 He, 3.0 Xe, 2.0 12C160, and 3.0 N2; and for the 13C 160 measurement the mixture was 2.5 He, 3.0 Xe, 1.5 13C160, and 3.5 N 2. Before each frequency measurement, file CO laser was adjusted to the center of its gain profile with the aid of a 520 Hz dither o f thelaser output mirror to within -+3 MHz. CO 2 and CO transitions were identified with grating spectrometers. For the determination of the beat frequency between P(14) of 12C160 a n d t h e second harmonic of P(28) of CO 2 a total of 14 measurements were made.
Volume 10, number 3
OPTICS COMMUNICATIONS
March 1974
Table 1
C02 transition frequency [MHz] Measured beat frequency [MHz] I?requency of CO transition [MHz] 'Vacuum wavelength [/~m] 'Vacuum wave number [cm-1 ]
The value 2198.8 lVlHz is the mean of these data. The maximum deviation of any one data from the mean was 2.2 MHz. In the case of P ( 1 9 ) o f 13C160 and P(10) of CO 2 825.0 MHz is the mean of 9 readings of the beat frequency; 2.5 MHz was the m a x i m u m deviation of any one value from the mean. The CO frequencies were computed from the measured beat frequencies and CO 2 transition frequencies derived by the use of absolute values given by Evenson et al. [5] and rotational constants recently determined by Petersen et al. [6]. Wavelengths and wave numbers of the CO lines were obtained using 2.997 924 58 m/s as the speed of light. Our results are Nven in table 1. The m a x i m u m error in setting the CO laser to the centre of the gain curve is estimated to be -~t3 MHz. The absolute error in the value of each CO 2 frequency is estimated to be not more than -+ 1 Mttz. Experiments performed in this laboratory and the experience of other workers indicate that other contributions to the total error, such as those due to shifts of the gain profile centres with
P(14) of 8-7 band of 12C160
P (19) of 7-6 band of 13C160
28 084 669.78 2199 57 135 497 5.247 043 8 1905.8350
28 566 649.18 825 56 168 515 5.337 375 5 1873.5800
pressure, current, gas composition, etc., are negligible compared to the above. Errors in the actual measurement of the beat frequencies are also negligible. Accordingly, the constants given here are estimated to be accurate to within I part in 107.
References
[1] D.R. Sokoloff, A. Sanchez, R.M. Osgoode and A. Javan, Appl. Phys. Lett. 17 (1970) 257. [2] L.O. Hocker, D.R. Sokoloff, V. Daneu, A. Szoke and A. Javan, Appl. Phys. Lett. 12 (1968)401. [3] K.M. Evenson, J.S. Wells, L.M. Mataresse and L.B. Elwell, Appl. Phys. Lett. 16 (1970) 159. [4] T.G. Blaney, C.C. Bradley, G.J. Edwards and D.J.E. Knight, Phys. Lett. 36A (1971) 285. [5] K.M. Evenson, J.S. Wells, F.R. Petersen, B.L. Danielson and G.W. Day, Appl. Phys. Lett. 22 (1973) 192. [6] F.R. Petersen, D.G. McDonald, J.D. Cupp and B.L. Danielson, Phys. Rev. Lett. 31 (1973) 573.
289