Lee H. Sentman, Munir H. Nayfeh, Steven W. Townsend, Kevin King, Gus Tsioulos, and Jay Bichanich, "Time-dependent oscillations in a cw chemical laser unstable resonator," Appl. Opt. 24, 3598-3609 (1985)
The amplitude, frequency, and Fresnel number dependence of the time-dependent oscillations which were predicted to occur on lines whose saturated gain does not fill the unstable resonator were measured. The time-dependent oscillations had a period of ~40 nsec independent of flow rates, do not occur for Fresnel numbers less than a demarcation Fresnel number which lies between 1.5 and 3.0, and their amplitudes increased as the fraction of the resonator filled by the saturated gain of the oscillating line decreased. The period of the time-dependent oscillations was determined by the resonator magnification. There was a strong cascade coupling between the oscillating 2 → 1 and 1 → 0 lines. The a priori prediction of these characteristics of the time-dependent oscillations by the MNORO3UR computer model was in agreement with the data. A 7-nsec oscillation, which was probably a mode beat of the laser, was superimposed on top of the 40-nsec oscillation. The time-dependent oscillations occurred in both 2-D and 3-D unstable resonators.
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MNORO3UR Time-Dependent Oscillation Periods, Frequencies, and Amplitude Modulations [% Pv(J)] for a 50% Geometric Outcoupled Confocal Unstable Resonator with a 5-mm Slit at Run 34 Flow Rates with a 5.4-Torr Cavity Pressure
Frequency and Amplitude of the Time-Dependent Oscillation of Total Power as a Function of Fresnel Number for the Flow Rates of Run 34 at 5.3 Torr
Run 34, 50% geometric outcoupled, symmetric, confocal, unstable resonator
Scraper mirror slit (mm)
NF
Pcav (Torr)
PT (W)
OSC period (nsec)
Amplitude modulation (%PT)
1.0
0.357
5.31
7.25
7
—
2.0
1.428
5.30
11.7
7
—
3.0
3.214
5.29
9.5
40/7
3.0
4.0
5.714
5.31
7.0
40/7
22.0
5.0
8.929
5.34
2.25
40/7
25.0
6.0
12.857
5.31
0.98
40
50.0
Table III
Frequency and Amplitude of the Time-Dependent Oscillations on Individual Lines for the Flow Rates of Run 34 at 5.3 Torr as a Function of Fresnel Numbera
—Means the line lased but was too weak to operate the fast detector
Individual line data were not obtained for the 5- and 6-mm slit widths because the individual lines in these cases were too weak to operate the fast detector. A PbSe detector was used to measure time-averaged power spectral distributions. Lines too weak to operate the fast InAs detector would operate the PbSe detector.
Table IV
Frequency and Amplitude of the Time-Dependent Oscillation of Total Power as a Function of Fresnel Number for Flow Rates of Run 36 at 6.5 Torr
Run 36, 50% geometric outcoupled, symmetric, confocal, unstable resonator
Scraper mirror slit (mm)
NF
Pcav (Torr)
PT (W)
OSC period (nsec)
Amplitude modulation (% PT)
1.0
0.357
6.55
10.5
2.0
1.428
6.5
17.2
7
3.0
3.214
6.5
12.2
40/7
3.7
4.0
5.714
6.5
6.55
40/7
33.0
5.0
8.929
6.5
1.55
40/7
37.5
Table V
Frequency and Amplitude of the Time Dependent Oscillations on Individual Lines for the Flow Rates of Run 36 at 6.3 Torr as a Function of Fresnel Numbera
—Means the line lased but was too weak to operate the fast detector
A PbSe detector was used to measure time-averaged power spectral distributions. Lines too weak to operate the fast InAs detector would operate the PbSe detector.
Table VI
Period and Frequency of the Time-Dependent Oscillations on Individual Lines for a Scraper Mirror with a Rectangular hole 1.5 mm High by 7.07 mm Long (Corresponding to an Effective Slit of 5.0 mm in the Flow Direction) for Run 34 Flow Rates at 5.2 Torr as a Function of xc
MNORO3UR Time-Dependent Oscillation Periods, Frequencies, and Amplitude Modulations [% Pv(J)] for a 50% Geometric Outcoupled Confocal Unstable Resonator with a 5-mm Slit at Run 34 Flow Rates with a 5.4-Torr Cavity Pressure
Frequency and Amplitude of the Time-Dependent Oscillation of Total Power as a Function of Fresnel Number for the Flow Rates of Run 34 at 5.3 Torr
Run 34, 50% geometric outcoupled, symmetric, confocal, unstable resonator
Scraper mirror slit (mm)
NF
Pcav (Torr)
PT (W)
OSC period (nsec)
Amplitude modulation (%PT)
1.0
0.357
5.31
7.25
7
—
2.0
1.428
5.30
11.7
7
—
3.0
3.214
5.29
9.5
40/7
3.0
4.0
5.714
5.31
7.0
40/7
22.0
5.0
8.929
5.34
2.25
40/7
25.0
6.0
12.857
5.31
0.98
40
50.0
Table III
Frequency and Amplitude of the Time-Dependent Oscillations on Individual Lines for the Flow Rates of Run 34 at 5.3 Torr as a Function of Fresnel Numbera
—Means the line lased but was too weak to operate the fast detector
Individual line data were not obtained for the 5- and 6-mm slit widths because the individual lines in these cases were too weak to operate the fast detector. A PbSe detector was used to measure time-averaged power spectral distributions. Lines too weak to operate the fast InAs detector would operate the PbSe detector.
Table IV
Frequency and Amplitude of the Time-Dependent Oscillation of Total Power as a Function of Fresnel Number for Flow Rates of Run 36 at 6.5 Torr
Run 36, 50% geometric outcoupled, symmetric, confocal, unstable resonator
Scraper mirror slit (mm)
NF
Pcav (Torr)
PT (W)
OSC period (nsec)
Amplitude modulation (% PT)
1.0
0.357
6.55
10.5
2.0
1.428
6.5
17.2
7
3.0
3.214
6.5
12.2
40/7
3.7
4.0
5.714
6.5
6.55
40/7
33.0
5.0
8.929
6.5
1.55
40/7
37.5
Table V
Frequency and Amplitude of the Time Dependent Oscillations on Individual Lines for the Flow Rates of Run 36 at 6.3 Torr as a Function of Fresnel Numbera
—Means the line lased but was too weak to operate the fast detector
A PbSe detector was used to measure time-averaged power spectral distributions. Lines too weak to operate the fast InAs detector would operate the PbSe detector.
Table VI
Period and Frequency of the Time-Dependent Oscillations on Individual Lines for a Scraper Mirror with a Rectangular hole 1.5 mm High by 7.07 mm Long (Corresponding to an Effective Slit of 5.0 mm in the Flow Direction) for Run 34 Flow Rates at 5.2 Torr as a Function of xc
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