Tunable lasers handbook phần 3 pps

84 Charles Freed r Laser-Cavity Mirrors 7 (4.3~) PFL Detector (Saturation 4 Resonance) FIGURE 8 Graphic illustration of the saturation resonance observed in CO, fluorescence at 4.3 pm. Resonant interaction occurs for v = vo (when k 1’ = 0). The figure shows an internal absorption cell within the laser cavity. External cells can also be used. (Reprinted with permission from SooHoo et d. [76]. 0 1985 IEEE.) In the initial experiments. a short gas cell with a total absorption path of about 3 cm was placed inside the cavity of each stable CO, laser [72] with a Brewster angle window separating the cell from the laser g& tube. Pure CO, gas at various low pressures was introduced inside the sample cell. A sapphire window at the side of the sample cell allowed the observation of the 4.3-pm spontaneous emission signal with a liquid-nitrogen-cooled InSb detector. The detector element was about 1.5 cm from the path of the laser beam in the sample cell. To reduce the broadband noise caused by background radiation. the detec- tor placement was chosen to be at the center of curvature of a gold-coated spher- ical mirror, which was internal to the gas absorption cell. The photograph of the laser with which the standing-wave saturation resonance was first observed via the fluorescence signal at 4.3 pm is shown in Fig. 9. More than two orders of magnitude improvements in signal-to-noise ratios (SNRs) were subsequently achieved with improved design low-pressure CO, stabilization cells external to the lasers [73]. One example of such improved design is schematically shown in Figure 10. In the improved design, the low-pressure gas cell, the LN,-cooled radiation collector, and the infrared (IR) detector are all integral partsbf one evacuated housing assembly. This arrangement minimizes signal absorption by windows and eliminates all other sources of absorption. Because of the vacuum enclo- sure. diffusion of other gases into the low-pressure gas reference cell is almost completely eliminated; therefore, the time period available for continuous use of the reference gas cell is greatly increased and considerably less time has to be wasted on repumping and refilling procedures. One LN, fill can last at least several days. 4 CO, Isotope Lasers and Their Applications 85 FIGURE 9 Two-mirror stable laser with short intracavity cell. This laser was used for the first demonstration of the standing-wave saturation resonance observed via the 4.3-pm fluorescence signal. FIGURE 1 0 Schematic illustration of improved external CO, reference gas stabilization cell. With the improved cells, significantly larger signal collection efficiency was achieved simultaneously with a great reduction of noise due to background radiation, which is the primary limit for high-quality InSb photovoltaic detec- tors. We have evaluated and tested several large-area InSb detectors and deter- mined that the LN,-cooled background greatly diminished llf noise in addition to the expected reduction in white noise due to the lower temperature back- ground radiation. Figure 11 shows a typical recorder tracing of the observed 4.3-ym intensity change as the laser frequency is tuned across the 10.59-ym P(20) line profile 86 Charles Freed fm=260Hz r = 0.1 aec (single pole) 16.4% DIP Ps1.75W; PO p = a034 Torr FIGURE 1 1 Lamb-dip-like appearance of the resonant change in the 4.3-pm fluorescence. The magnitude of the dip is 16.4% of the 4.391 fluorescence signal. The pressure in the reference cell was 0.034 Torr and the laser power into the cell was 1.75 W in the I-P(20) transition. A frequency dither rate of 260 Hz was applied to the piezoelectric mirror tuner. with a 0.034-Torr pressure of 12C160, absorber gas. The standing-wave satura- tion resonance appears in the form of a narrow resonant 16.4% “dip” in the 4.3- pm signal intensity, which emanates from all the collisionally coupled rotational levels in the entire (OOOl)+(OOO) band. The broad background curve is due to the laser power variation as the frequency is swept within its oscillation band- width. Because collision broadening in the CO, absorber is about 7.5 MHzRorr FWHM [72], in the limit of very low gas cell pressure the linewidth is deter- mined primarily by power broadening and by the molecular transit time across the diameter of the incident beam. The potentially great improvements in SNR, in reduced power and transit-time broadening, and in short-term laser stability were the motivating factors that led to the choice of stabilizing cells external to the laser’s optical cavity. The one disadvantage inherent with the use of external stabilizing cells is that appropriate precautions must be taken to avoid optical feedback into the lasers to be stabilized. For frequency reference and long-term stabilization, it is convenient to obtain the derivative of the 4.3-pm emission signal as a function of frequency. This 4.3-pm signal derivative may be readily obtained by a small dithering of the laser frequency as we slowly tune across the resonance in the vicinity of the absorption-line center frequency. With the use of standard phase-sensitive detec- tion techniques we can then obtain the 4.3-pm derivative signal to be used as a frequency discriminator. Figure 12 shows such a 4.3-pm derivative signal as a function of laser tuning near the center frequency of the 10.59-pm P(20) transi- tion. The derivative signal in Fig. 12 was obtained by applying a f200-kHz fre- quency modulation to the laser at a 260-Hz rate. A 1.75-W portion of the laser’s output was directed into a small external stabilization cell that was filled with 4 CO, Isotope Lasers and Their Applications 87 S/N = -1000 Af = -f 200 kHz tm = 260 Hz T = 0.1 we (ringla pole) Po = 1.m W; P(20); l0.6~ p = 0.034 Torr FIGURE 12 nance shown in Fig. 11. SNR - 1000, Af - f200 kHz, and t = 0.1 sec (single pole). Derivative signal at 4.3 pm in the vicinity of the standing-wave saturation reso- pure CO, to a pressure of 0.034 Torr at room temperature. It is a straightforward procedure to line-center-stabilize a CO, laser through the use of the 4.3-pm derivative signal as a frequency discriminant, in conjunction with a phase-sensi- tive detector. Any deviation from the center frequency of the lasing transition yields a positive or negative output voltage from the phase-sensitive detector. This voltage is then utilized as a feedback signal in a servoloop to obtain the long-term frequency stabilization of the laser output. Figure 13 shows a block diagram of a two-channel heterodyne calibration system. In the system, two small, low-pressure, room-temperature C0,-gas ref- erence cells external to the lasers were used to line-center-stabilize two grating- controlled stable lasers. The two-channel heterodyne system was used exten- sively for the measurement and calibration of C0,-isotope laser transitions [36,37]. Figure 14 shows the spectrum-analyzer display of a typical beat-note of the system shown in Fig. 13. Note that the SNR is greater than 50 dB at the 24.4 GHz beat frequency of the two laser transitions with the use of varactor photodiode detection developed at MIT Lincoln Laboratory [74,75]. Figure 15 illustrates the time-domain frequency stability that we have rou- tinely achieved with the two-channel heterodyne calibration system by using the 88 Charles Freed FIGURE 1 3 Block diagram of the two-channel line-center-stabilized C0,-isotope calibration system. In the figure, wavy and solid lines denote optical and electrical paths, respectively. (Reprinted with permission from Freed [75]. 0 1982 IEEE.) -20 -30 52 dB m^ -40 'D 0 9 -50 I 7 -60 -70 -80 4 + 200kHz FIGURE 14 The 24.4104191-GHz beat note of a 16012CfSO laser I-P(l2) transition and a l*C1602 laser I-P(6) transition. The power levels into the photodiode were 0.48 mW for the 16012C180 laser and 0.42 mW for the 12C160, laser. The second harmonic of the microwave local oscillator was generated in the varactor photodiode. The intermediate-frequency noise bandwidth of the spectrum analyzer was set to 10 kHz. 4 CO, Isotope Lasers and Their Applications 89 I I I I1111~ I I I I I Ill[ I I I I Ill 10-10 M = 50 h - d g 10.11 : 2 A HP 5061 CESIUM u) P 0 ATOMIC STANDARD z 2 W ; 10-12 E @ C02 SHORT-TERM STABILITY 0.01 0.1 1 .o 10 I00 SAMPLE TIME, T (s) FIGURE 1s Time-domain frequency stability of the 2.6978618-GHz beat note of the 'jCl30, laser i-Ri21) transition and the lTl6O0, reference laser I-P(?Oj transition in the two-channel hetero- dyne calibration system (Fig. 13) with the 4.3-pm fluorescence stabilization technique For the sake of comparison. the stabilities of a cesium clock and short-term stabilities of individuai CO, lasers are also shown. Note that the frequencj stabilities of the CO, and the cesium-stabilized systems shown are about the same and that the CO, radar has achieved short-term stabilities of at least tlbo to three orders of magnitude better than those of microwave systems. (Reprinted with permission from SooHoo eral. [76]. 0 1981 IEEE.) 4.3-ym fluorescence stabilization technique [56.76.77]. The solid and hollow circles represent two separate measurement sequences of the Allan variance of the frequency stability Each measurement consisted of M = 50 consecutive samples for a sample time duration (observation time) of T seconds. Figure 15 shows that we have achieved OJT) <?x 10-12 for T-10 sec. Thus a frequency measurement precision of about 50 Hz may be readily achieved within a few minutes. 90 Charles Freed The triangular symbols in Fig. 15 represent the frequency stability of a Hewlett-Packard (HP) model 5061B cesium atomic frequency standard, as spec- ified in the HP catalog. Clearly, the frequency stabilities of the CO, and the cesium-stabilized systems shown in Fig. 15 are about the same. The two cross-circles in the lower left corner of Fig. 15 denote the upper bound of the short-term frequency stabilities, as measured in the laboratory (Fig. 6) and determined from CO, radar returns at the Lincoln Laboratory Firepond Facility [56,58]. Note that the CO, radar has achieved short-term stabilities of at least two to three orders of magnitude better than those of microwave systems. Figure 16 shows the frequency reproducibility of the two-channel line- center-stabilized CO, heterodyne calibration system. The figure contains a so- called drift run that was taken over a period of 8.5 hours beginning at 1:OO P.M. [56,76,77]. The frequency-stability measurement apparatus was fully automatic; it continued to take, compute, and record the beat-frequency data of the two line- center stabilized CO, isotope lasers even at night. when no one was present in the laboratory. Approxinlately every 100 sec the system printed out a data point that represented the deviation from the 2.6976648-GHz beat frequency, which was '2C'602 I-P(Z0); '3C'802 I-R(24); T = 10 s; M = 8 -2 E 31 -3 I NOON 1 2 3 4 5 6 7 8 9 ELAPSED TIME (h), TIME OF DAY FIGURE 16 Slow drifts in the 7.6978648-GHz beat frequency due to small frequency-offset- ting zero-voltage variations of the electronics. The frequency deviations were caused by ambient temperature variations. The beat note was derived from the 13C1800: I-R(24) and the 12C'602 I-P(Z0) laser transitions. An obsemation time of 'I = 10 sec and a sample size of :21 = 8 were used for each data point. (Reprinted with permission from SooHoo er nl. [76]. 0 1985 IEEE.) 4 CO, Isotope Lasers and Their Applications 91 averaged over 8.5 hours. The system used a measurement time of T = 10 sec and A4 = 8 samples for each data point. yielding a measurement accuracy much better than the approximately f 1-kHz peak-frequency deviation observable in Fig. 16. The frequency drift was most likely caused by small voltage-offset errors in the phase-sensitive detector-driven servoamplifier outputs that controlled the piezoelectrically tunable laser mirrors. Because 500 V was required to tune the laser one longitudinal mode spacing of 100 MHz, an output voltage error of i2.5 mV in each channel was sufficient to cause the peak-frequency deviation of fl kHz that was observed in Fig. 16. By monitoring the piezoelectric drive voltage with the input to the lock-in amplifier terminated with a 50-SZ load (instead of connected to the InSb 4.3-ym fluorescence detector), we determined that slow output-offset voltage drifts were the most probable cause of the il- kHz frequency drifts observed in Fig. 16. It is important to note that no special precautions were taken to protect either the lasers or the associated electronic circuitry from temperature fluctuations in the laboratory. The temperature Wuc- tuatians were substantial-plus or minus several degrees centigrade. Significant improvements are possible with more up-to-date electronics and a temperature- controlled environment. Perhaps the greatest advantage of the 4.3-ym fluorescence stabilization method is that it automatically provides a nearly perfect coincidence between the lasing medium's gain profile and the line center of the saturable absorber, because they both utilize the same molecule. CO,. Thus every P and R transition of the (0001 j-[lOOO. 02@0],,,, regular bands and the (Olll) [Ol@O, 0310],.,, hot bands [78-811 may be line-center-locked with the same stabilization cell and gas fill. Furthermore, as illustrated in Fig. 8, the saturation resonance is detected sepa- rately at the 4.3-pm fluorescence band and not as a fractional change in the much higher power laser radiation at 8.9 to 12.4 ym. At 4.3 ym, InSb photovoltaic detectors that can provide very high background-limited sensitivity are available, However, it is absolutely imperative to realize that cryogenically cooled InSb photovoltaic elements are extremely sensitive detectors of radiation far beyond the 4.3-pm CO, fluorescence band. Thus, cryogenically cooled IR- bandpass fil- ters and field-of-view (FOV) shields. which both spectrally and spatially match the detector to the CO, gas volume emitting the 4.3-ym fluorescence radiation, should be used. If this is not done. the detected radiation emanating from other sources (ambient light, thermal radiation from laboratory personnel and equip- ment, even electromagnetic emission from motors, transformers, and transmit- ters) may completely swamp the desired 4.3-ym fluorescence signal. This proce- dure is a very familiar and standard technique utilized in virtually every sensitive IR detection apparatus; surprisingly, however, it was only belatedly realized in several very highly competent research laboratories. because the most commonly used and least expensive general-purpose IR detectors are bought in a sealed-off dewar and may not be easily retrofitted with a cryogenically cooled bandpass fil- ter and FO'V shield. 92 Charles Freed Additional precautionary measures should be taken in using the saturated fluorescence signal. The Einstein coefficient for the upper lasing level (0001) is about 200 to 300 sec-1 and. therefore, the modulation frequency must be slow enough so that the molecules in the upper level have enough time to fluoresce down to the ground state; here radiation trapping [82,83] of the 4.3-~m sponta- neous emission (because CO, is a ground-state absorber) will show up as a vari- ation of the relative phase between the reference modulation and the fluores- cence signal as the pressure is vaned. The phase lag between the reference signal and the molecular response would increase as the pressure increases because there are more molecules to trap the 4.3-ym radiation and, therefore, hinder the response. This phase lag will increase with increasing modulation frequency, since the molecules will have less time to respond; thus, caution must be taken when selecting the modulation frequency. A large phase lag will reduce the out- put voltage (feedback signal) of the phase-sensitive detector; however, it will not cause a shift in the instrumental zero [76]. In addition to optimizing the frequency at which to modulate the laser, the amplitude of the modulation (the frequency excursion due to the dithering) was also considered in the experiments at Lincoln Laboratory [76]. The modulation amplitude must be large enough such that the fluorescence signal is detectable, but the amplitude must be kept reasonably small to avoid all unnecessary para- sitic amplitude modulation and nonlinearities in the piezoelectric response. in order to avoid distorting the 4.3-pm Lorentzian. The maximum derivative signal is obtained if the peak-to-peak frequency excursion equals 0.7 FWHM of the Lorentzian. But such a large excursion should be avoided in order to minimize the likelihood of introducing asymmetries in the derivative signal. A compro- mise modulation amplitude based on obtaining sufficient SNR for most J lines was used. This modulation amplitude corresponded to a frequency deviation of approximately 300 kHz peak-to-peak on a Lorentzian with an FWHM of about 1 MHz. Experimental results indicated that the modulation frequency should be kept well below 500 Hz. At such low frequencies, InSb photovoltaic detectors may have very high llfnoise unless operated at effectively zero dc bias voltage. This may be best accomplished by a low-noise current mode preamplifier that is matched to the dynamic impedance of the detector and is adjusted as close as possible to zero dc bias across the detector (preferably less than 0.001 V). There are other advantages of the 4.3-pm fluorescence stabilization; because the fluorescence lifetime is long compared to the reorientating collision time at the pressures typically employed in the measurements, the angular distribution of the spontaneous emission is nearly isotropic. This reduces distortions of the lineshape due to laser beam imperfections. Furthermore, only a relatively short (3- to 6-cm) fluorescing region is monitored, and the CO, absorption coefficient is quite small (-10-6 cm-1-Torr-1); this eliminates laser beam focusing effects due to the spatial variation of the refractive index of the absorbing medium pro- duced by the Gaussian laser beam profiles [84,85]. Indeed, we have found no 4 CO, Isotope Lasers and Their Applications 93 significant change in the beat frequency after interchanging the two stabilizing cells, which had very different internal geometries and volumes, and (within the frequency resolution of our system) no measurable effects due to imperfect and/or slightly truncated TEMoo, beam profiles. We have used external stabilizing cells with 2-cm clear apertures at the beam entrance window. Inside the cell, the laser beam was turned back on itself (in order to provide a standing wave) by means of a flat, totally reflecting mirror. Slight misalignment of the return beam was used as a dispersion-independent means of avoiding optical feedback. External stabilizing cells were used, instead of an internal absorption cell within the laser cavity, in order to facilitate the opti- mization of SNIP, in the 4.3-pm detection optics, independent of laser design con- straints. External cells w-ere also easily portable and usable with any available laser. The FWHM of the saturation resonance dip ranged from 700 kHz to 1 or 2 MHz as the pressure was varied from 10 to about 200 to 300 mTorr within the relatively small (2-crn clear aperture) stabilizing cells employed in our experi- ments. By using a 6.3-cm-diameter cell, 164-kHz RVHM saturation resonance dips were reported by Kelly [86]. Because the FWHM of the CO, saturation res- onance due to pressure is about 7.5 kHz/mTorr. much of the lin&idth broaden- ing is due to other causes such as power and transit-time broadening, second- order Doppler shift. and recoil effects. More detailed discussions of these causes can be found in [76,112], and in the literature on primary frequency standards but any further consideration of these effects is well beyond the scope of this chapter. The saturated 4.3-pm fluorescence frequency stabilization method has been recently extended to sequence band CO, lasers by Chou et al. [87,88]. The sequence band transitions in CO, are designated as (000~)-[100(u- 1). 020 (u- l)lI.*. where li > 1 (u = 1 defines the-regular bands discussed in this and previous sections of this chapter). Sequence band lasers were intensively studied by Reid and Siemsen at the NWC in Ottawa beginning in 1976 [89,90]. Figure 17 shows the sinnplified vibra- tional energy-level diagram of the CO, and N, molecules, with solid-line arrows showing the various cw lasing bands observed so far. The dotted-line arro\vs show the 43-pm fluorescence bands that were utilized for line-center stabilization of the great multitude of individual lasing transitions. Figure 17 clearly shows that for the (0002)-[1001, 0201],,, first sequence band transitions the laver laser levels are approximately 2300 crn-1 above those of the regular band transitions and therefore the population densities of the first sequence band laser levels are about four orders of magnitude less than in the corresponding regular band laser levels. Chou er al. overcame this problem by using a heated longitudinal C07 absorption cell (L-cell) in which the 4.3-ym fluorescence was monitored through a 3.3yrn bandpass filter in the direction of the laser beam [87,88]. Due to the increased CO, temperature, photon trapping [82,83,87] was reduced. and by increasing the fluorescence collecting length they increased the intensity of sequence band fluorescence so that z. good enough SNR was obtained at relatively low cell temperatures. [...]... P(14) P( 13) P(12) P (11) P (10) P[ 9) FREQUENCY (MHZ1 30 54 30 57 30 60 30 63 3066 30 69 30 73 3076 30 79 30 R2 30 85 30 8E 30 91 30 94 30 97 31 00 31 02 31 05 31 08 31 11 31 14 31 17 31 20 31 23 3125 31 28 31 31 31 34 31 36 31 39 31 42 31 45 31 47 31 50 31 52 31 55 31 58 31 60 31 63 3165 31 68 31 ?1 31 73 3176 31 78 31 80 31 83 3185 31 88 31 90 31 93 3195 32 44.7021 4756 .38 72 61 23. 1746 734 4.4579 8419.6268 934 8.0678 0129.1655 0762 .30 30 1246.8 631 1582.2290... 31 99 32 04 32 09 32 13 3218 32 23 3227 32 31 32 36 32 40 32 44 32 48 32 50 32 55 32 59 32 63 3266 32 70 32 74 32 78 32 82 32 85 32 89 32 92 32 96 32 99 33 02 33 06 33 09 33 12 33 15 33 18 33 21 33 24 33 27 33 30 33 32 9427.2028 30 12.1187 6056.1 633 8556.0987 0508.7885 1911.2012 2760.4 139 30 53. 61 53 2788.1092 1961 .31 73 0570.7820 8614.1691 6089.2707 2994.0069 932 6.4282 5084.7176 0267.19 23 4872 .30 53 8898.6464 234 4.9440 5210.0656 74 93. 0190... (28) R (30 ) R ( 3 2j R (34 ) R (36 ) R (38 ) R(40) R(42) R(44) R(46) R(48) R(50) R(52) R154) R(56) RI58) 2 933 2940 2946 2952 2959 2965 2971 2977 2982 298% 2994 2999 30 05 30 10 30 16 30 21 30 26 30 31 30 36 30 41 30 46 30 50 30 53 3057 30 62 30 66 30 70 30 75 30 79 30 83 3087 30 91 30 95 30 98 31 02 31 05 31 09 31 12 31 15 31 19 31 22 31 25 31 28 31 31 31 33 3 136 31 39 31 41 31 44 31 46 31 48 31 51 98 13. 330 1 37 95.4270 6976.8409 935 1.4664 09 13. 4284... R( 53) RE54) R8!55) R(56) R(57) R(58) R'l59) FREQUENCY (MHZ1 32 97 32 99 33 00 33 01 33 03 330 4 33 06 33 07 33 08 33 09 33 11 33 12 33 13 331 5 33 1Q 33 17 STD DEV (MHZ1 6479.2160 0 836 .8567 5 033 .30 92 9068.9988 2944 .35 60 6659.8155 0215.81 63 3612.8006 6851.2 130 9 931 .50 03 2854.1107 5619.4927 8228.0944 0680 .36 29 2976.7 434 5117.6781 0.4554 0.6169 0.8207 1.0750 1 .38 93 1.77 43 2.24 23 2.8069 3. 4 839 4.2906 5.2465 6 .37 36 7.6959... 02 83. 9296 32 02 33 73. 1687 32 04 62 93. 232 2 32 06 90 43. 9565 32 09 1625.1911 32 11 4 036 .7984 32 13 6278.6540 32 15 835 0.6465 32 18 0252.6776 32 20 1984.6620 32 22 35 46.5277 32 24 4 938 .2155 32 26 6159.6795 32 28 7210.8868 32 30 8091.8175 32 32 8802.4647 32 34 934 2. 834 7 32 36 9712.9467 32 38 9912. 832 8 32 40 9942. 538 0 32 42 9802.1204 32 44 9491.6508 32 46 9011.2129 32 48 836 0.9 032 32 50 7540. 830 6 32 52 6551.1172 32 54 539 1.8971 32 56... 1421. 632 0 4629.5011 7086.8467 8788. 230 5 9728.0006 2926 2 932 2 938 2944 2949 2955 2961 2966 29-72 2977 29 83 2988 29 93 2999 30 04 30 09 30 14 30 19 30 24 30 29 30 33 3 038 30 43 3048 30 52 30 57 30 61 30 65 30 70 30 74 30 78 30 80 30 84 30 88 30 92 30 96 4508. 533 6 37 20.08 83 238 6.9924 05 03. 8821 8065.5045 5066.7 231 1502.5 235 736 8.0181 2658.4516 736 9.2056 1495.8 037 5 033 .9156 7979 .36 20 032 8.1180 2076 .31 81 32 20.2591 37 56.4042 36 81 .38 63. .. 1 4 ) 32 21 7091.27 43 R(16) 32 25 730 3 .34 00 R(18) 32 29 6717.0518 R(20) 32 33 533 4.0411 R(22) 32 37 31 56.20 43 R(24) 32 41 0185.7000 R(26) 32 44 6424.9456 R(28) 32 48 1876.6140 R (30 ) 32 51 65 43. 6298 R (32 ) 32 55 0429.16 53 R (34 ) 32 58 35 36. 636 0 R (36 ) 32 61 5869.6965 R (38 ) 32 64 7 432 . 235 4 R(40) 32 67 8228 .37 02 R(42) 32 70 8262.4421 R(44) 32 73 7 539 .0104 R(46) 32 76 6062.8469 R (48) 32 79 38 38.9297 R (50) 32 82 0872. 436 8 R... 6551.1172 32 54 539 1.8971 32 56 40 63. 3174 32 58 2565. 537 4 32 60 0898.7287 32 61 90 63. 07 53 32 63 7058.7 733 32 65 4886. 030 8 32 67 2545.0679 32 69 0 036 .1164 32 70 735 9.4198 32 72 4515. 233 1 32 74 15 03. 8227 32 75 832 5.4660 32 77 4980.4516 32 79 1469.0786 32 80 7791.6570 32 82 39 48.5069 32 83 9 939 .9585 32 85 5766 .35 18 32 87 1428. 036 6 32 88 6925 .37 17 32 90 2258.7249 32 91 7428.4725 32 93 2 434 .9992 32 94 7278.6976 32 96 1959.9675 - BAND I1... 957.8005 97 93 3608 2961 2 931 7860 136 1 632 4 4927 8 632 8202 36 91 0.0 035 0.0 035 0.0 035 0.0 034 0.0 034 0.0 033 0.0 033 0.0 032 0.0 032 0.0 032 0.0 031 0.0 031 0 0 031 0.0 031 0.0 031 0.0 032 0.0 033 0.0 033 0.0 034 0.0 035 0.0 035 0.0 036 0.0045 0.0070 0.0117 0.01 93 0. 030 7 966.25 03 967.7072 969. 139 5 910.5472 971. 930 2 9 73. 2885 974.6219 975. 930 4 977,2 139 978.4722 979.7054 980.9 132 982.0955 9 83. 2522 984 .38 32 985.48 83 986.56 73 987.6201... 634 3 8665 31 66 7818 1 13 1 14 Charles Freed TABLE 5 (continued) BAND II tcontinuedr FREQUENCY P ( 2) V ( 0) R ( 0) R( 2 ) STD DEV, (MHZ1 (MHZ1 0.0 038 0.0 038 0.0 038 0.0 037 0.0 037 0.0 037 0.0 037 0.0 037 0.0 037 0.0 037 0.0 037 0.0 037 0.0 037 0.0 037 0.0 037 0.0 037 0.0 037 0.0 038 0.0 038 0.0 038 0.0 039 0.0 039 0.0 039 0.0 039 0.0 039 0.0 039 0.0 039 0.0 039 31 43 3149 31 54 31 59 31 65 31 70 31 75 31 80 31 85 31 90 31 95 31 99 32 04 . 957.8005 36 91 0.0 035 0.0 035 0.0 035 0.0 034 0.0 034 0.0 033 0.0 033 0.0 032 0.0 032 0.0 032 0.0 031 0.0 031 0 0 031 0.0 031 0.0 031 0.0 032 0.0 033 0.0 033 0.0 034 0.0 035 0.0 035 0.0 036 0.0045. 0.0 036 R(10) 32 13 4266.89 53 0.0 036 R(12) 32 17 6079.4907 0.0 036 R(16) 32 25 730 3 .34 00 0.0 037 R(18) 32 29 6717.0518 0.0 037 R(20) 32 33 533 4.0411 0.0 038 R(22) 32 37 31 56.20 43 0.0 039 R(24). 0.0 039 0.0 039 0.0 039 0.0 038 0.0 038 0.0 038 0.0 038 0.0 037 0.0 037 0.0 037 0.0 038 0.0 038 0.0 038 0.0 037 0.0 037 0.0 037 0.0 037 0.0 037 0.0 037 0.0 037 0.0 037 (CM-1) 1018.9006 932 2