Transportation of far-IR beams for use in plasma diagnostics

M. R. Siegrist; I. Kjelberg; R. Behn

doi:10.1364/AO.22.001318

Applied Optics
Vol. 22,
Issue 9,
pp. 1318-1324
(1983)
•https://doi.org/10.1364/AO.22.001318

Transportation of far-IR beams for use in plasma diagnostics

M. R. Siegrist, I. Kjelberg, and R. Behn

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M. R. Siegrist, I. Kjelberg, and R. Behn, "Transportation of far-IR beams for use in plasma diagnostics," Appl. Opt. 22, 1318-1324 (1983)

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Abstract

In this paper we discuss certain aspects concerning the transport and focusing of a high power far-IR laser beam into a plasma for Thomson scattering measurements. To attain the required megawatt power level in a D₂O laser, it is important to use efficiently the volume of the optically pumped vapor. The best known method to achieve this is use of an unstable resonator which produces a beam with an annular intensity profile. This has a negative effect on the quality of the focused beam and on the intensity profile incident on the beam dump. A system utilizing a Cassegrainian telescope and spatial filtering techniques is found to be a good solution.

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feedback of unstable resonator (%)	diameter of hole in beam (cm)	distance of propagation (m)	fraction of intensity in central lobe (%)
25	10	19	20
		25	30
		40	40
		∞	48
20	8.9	19	20
		24	30
		33	40
		68	50
		∞	54
15	7.7	18	20
		22	30
		28	40
		38	50
		∞	60
10	6.3	19	20
		22	30
		24	40
		30	50
		40	60
		∞	67
5	4.5	18	20
		20	30
		25	40
		31	50
		41	60
		∞	75

cavity feed-back of unstable resonator (%)	diameter of hole in beam (cm)	focal length (cm)	$\frac{r (I = 10 %)}{r (I = 50 %)}$	$\frac{r (I = 20 %)}{r (I = 50 %)}$	$\frac{r (I = 80 %)}{r (I = 50 %)}$	$\frac{r (I = 90 %)}{r (I = 50 %)}$
25	10	25	.74	.81	1.15	1.21
		50	.74	.81	1.13	1.20
		100	.74	.86	1.17	1.27
		200	.75	.84	1.18	1.39
20	8.9	25	.70	.77	1.17	1.22
		50	.71	.78	1.14	1.22
		100	.72	.82	1.18	1.29
		200	.73	.84	1.19	1.41
15	7.7	25	.65	.74	1.18	1.24
		50	.66	.75	1.17	1.24
		100	.68	.77	1.17	1.30
		200	.70	.84	1.22	1.42
10	6.3	25	.59	.72	1.20	1.26
		50	.61	.71	1.19	1.27
		100	.62	.73	1.18	1.29
		200	.64	.81	1.26	1.43
5	4.5	25	.52	.68	1.23	1.30
		50	.54	.68	1.22	1.30
		100	.55	.68	1.20	1.31
		200	.57	.76	1.27	1.45

Thin annular profile *)			1.	1.	1.	1.
Flat profile			.45	.63	1.26	1.34
Gaussian profile			.40	.58	1.44	1.63

	r₀ (mm)	transfer efficiency (%)	intensity ratio of lobes (%)	$\frac{r (I = 10 %)}{r (I = 50 %)}$	$\frac{r (I = 20 %)}{r (I = 50 %)}$	$\frac{r (I = 80 %)}{r (I = 50 %)}$	$\frac{r (I = 90 %)}{r (I = 50 %)}$
System with one focusing mirror	1.1	73.2	3.6	.56	.68	1.19	1.27
System with telescope	1.6	71.6	2.8	.48	.67	1.29	1.48
System with telescope and aperture	1.9*	71.6	0.0	.40	.57	1.48	1.73
	$\underset{}{\underset{︸}{}}$			$\underset{}{\underset{︸}{}}$
	referring to focal plane P4			referring to plane of beam dump P5

feedback of unstable resonator (%)	diameter of hole in beam (cm)	distance of propagation (m)	fraction of intensity in central lobe (%)
25	10	19	20
		25	30
		40	40
		∞	48
20	8.9	19	20
		24	30
		33	40
		68	50
		∞	54
15	7.7	18	20
		22	30
		28	40
		38	50
		∞	60
10	6.3	19	20
		22	30
		24	40
		30	50
		40	60
		∞	67
5	4.5	18	20
		20	30
		25	40
		31	50
		41	60
		∞	75

cavity feed-back of unstable resonator (%)	diameter of hole in beam (cm)	focal length (cm)	$\frac{r (I = 10 %)}{r (I = 50 %)}$	$\frac{r (I = 20 %)}{r (I = 50 %)}$	$\frac{r (I = 80 %)}{r (I = 50 %)}$	$\frac{r (I = 90 %)}{r (I = 50 %)}$
25	10	25	.74	.81	1.15	1.21
		50	.74	.81	1.13	1.20
		100	.74	.86	1.17	1.27
		200	.75	.84	1.18	1.39
20	8.9	25	.70	.77	1.17	1.22
		50	.71	.78	1.14	1.22
		100	.72	.82	1.18	1.29
		200	.73	.84	1.19	1.41
15	7.7	25	.65	.74	1.18	1.24
		50	.66	.75	1.17	1.24
		100	.68	.77	1.17	1.30
		200	.70	.84	1.22	1.42
10	6.3	25	.59	.72	1.20	1.26
		50	.61	.71	1.19	1.27
		100	.62	.73	1.18	1.29
		200	.64	.81	1.26	1.43
5	4.5	25	.52	.68	1.23	1.30
		50	.54	.68	1.22	1.30
		100	.55	.68	1.20	1.31
		200	.57	.76	1.27	1.45

Thin annular profile *)			1.	1.	1.	1.
Flat profile			.45	.63	1.26	1.34
Gaussian profile			.40	.58	1.44	1.63

feedback of unstable resonator (%)	diameter of hole in beam (cm)	distance of propagation (m)	fraction of intensity in central lobe (%)
25	10	19	20
		25	30
		40	40
		∞	48
20	8.9	19	20
		24	30
		33	40
		68	50
		∞	54
15	7.7	18	20
		22	30
		28	40
		38	50
		∞	60
10	6.3	19	20
		22	30
		24	40
		30	50
		40	60
		∞	67
5	4.5	18	20
		20	30
		25	40
		31	50
		41	60
		∞	75

feedback of unstable resonator (%)	diameter of hole in beam (cm)	distance of propagation (m)	fraction of intensity in central lobe (%)
25	10	19	20
		25	30
		40	40
		∞	48
20	8.9	19	20
		24	30
		33	40
		68	50
		∞	54
15	7.7	18	20
		22	30
		28	40
		38	50
		∞	60
10	6.3	19	20
		22	30
		24	40
		30	50
		40	60
		∞	67
5	4.5	18	20
		20	30
		25	40
		31	50
		41	60
		∞	75

feedback of unstable resonator (%)	diameter of hole in beam (cm)	distance of propagation (m)	fraction of intensity in central lobe (%)
25	10	19	20
		25	30
		40	40
		∞	48
20	8.9	19	20
		24	30
		33	40
		68	50
		∞	54
15	7.7	18	20
		22	30
		28	40
		38	50
		∞	60
10	6.3	19	20
		22	30
		24	40
		30	50
		40	60
		∞	67
5	4.5	18	20
		20	30
		25	40
		31	50
		41	60
		∞	75

feedback of unstable resonator (%)	diameter of hole in beam (cm)	distance of propagation (m)	fraction of intensity in central lobe (%)
25	10	19	20
		25	30
		40	40
		∞	48
20	8.9	19	20
		24	30
		33	40
		68	50
		∞	54
15	7.7	18	20
		22	30
		28	40
		38	50
		∞	60
10	6.3	19	20
		22	30
		24	40
		30	50
		40	60
		∞	67
5	4.5	18	20
		20	30
		25	40
		31	50
		41	60
		∞	75

Abstract

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Figures (6)

Tables (3)

Equations (3)

Applied Optics

feedback of unstable resonator (%)	diameter of hole in beam (cm)	distance of propagation (m)	fraction of intensity in central lobe (%)
25	10	19	20
		25	30
		40	40
		∞	48
20	8.9	19	20
		24	30
		33	40
		68	50
		∞	54
15	7.7	18	20
		22	30
		28	40
		38	50
		∞	60
10	6.3	19	20
		22	30
		24	40
		30	50
		40	60
		∞	67
5	4.5	18	20
		20	30
		25	40
		31	50
		41	60
		∞	75

feedback of unstable resonator (%)	diameter of hole in beam (cm)	distance of propagation (m)	fraction of intensity in central lobe (%)
25	10	19	20
		25	30
		40	40
		∞	48
20	8.9	19	20
		24	30
		33	40
		68	50
		∞	54
15	7.7	18	20
		22	30
		28	40
		38	50
		∞	60
10	6.3	19	20
		22	30
		24	40
		30	50
		40	60
		∞	67
5	4.5	18	20
		20	30
		25	40
		31	50
		41	60
		∞	75