EXCIMER LASER AND NEW SCHEME FOR TRAVELLING-WAVE PUMPING OF X-RAY LASERS

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Submitted on 1 Jan 1986

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EXCIMER LASER AND NEW SCHEME FOR

TRAVELLING-WAVE PUMPING OF X-RAY LASERS

F. Schäfer

To cite this version:

F. Schäfer. EXCIMER LASER AND NEW SCHEME FOR TRAVELLING-WAVE PUMP- ING OF X-RAY LASERS. Journal de Physique Colloques, 1986, 47 (C6), pp.C6-149-C6-150.

�10.1051/jphyscol:1986620�. �jpa-00225863�

JOURNAL DE PHYSIQUE,

Colloque C6, supplbment au no 10, Tome 47, octobre 1986

EXCIMER LASER AND NEW SCHEME FOR TRAVELLING-WAVE PUMPING OF X-RAY LASERS

F.P. SCHAFER

Max-Planck-Institut far Biophysikalische Chemie, Abteilung Laserphysik,

GBttingen, F.R.G.

There are two new developments that encouraged us to start an X-ray-laser project:

1, the availability of excimer laser pulses of very high power and subpicosecond duration, which should result in a greatly increased efficiency creating an inversion with various X-ray laser schemes,

2 . a

new scheme for focussing the excimer laser beam on a cylin-

drical symmetry and at the same time giving a travelling-wave excitation of the target.

Figure 1 shows the conceptually simple and reliable experimental arrangement for the production of subpicosecond pulses at 308 or

248

nm [I]. It is essentially a two-channel commercial excimer laser, with one channel used as an oscillator, whose output first pumps a short pulse dye laser (which itself is used to pump a tiny distributed feedback dye laser and a multi-stage dye laser ampli- fier, whose output is frequency-doubled and then amplified in a double-pass through the amplifier channel of the excimer laser.

Theoutput is 10 mJ at 308 nm or 30 mJ at

nrn at subpicosecond pulse duration. Later this pulse will be further amplified in a power amplifier now under construction with which we hope to Dbtain a pulse energy of 1 J in hopefully 150 fs.

Figure

shows a cross-section of the focussing optics, which is essentially a cone of quartz-glass with an exactly centered bore and dielectric anti-reflection coatings. The excimer-laser beam entering from the bottom in the direction of the optical axis A-A' is focussed in a line extending from the tip of the cone along the axis for a distance L given by the refraction of the outermost rays. When a target of 7 tii and 7 mm length is positioned at this itne, t e average intensity of a > 4 * 1 0 W/cm on the target surface. 9 1 J-, 150 fs-pulse is

It is immediately seen that this geometry results in a travelling- wave excitation with the advantageous property of the excitation travelling along the optical axis slightly faster than the ampli- fied spontaneous X-ray emission front, since the length labelled x in the slide is shorter than the distance labelled L. Thus the X-ray pulse travelling down the optical axis sees always fresh inversion [2].

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986620

JOURNAL

DE

EMGKO

h z l l l l t o r

Fig.

- Experimental arrangement for the generation of high-power ps excimer laser pulses (from ref.

. ^EMG

commercial excimer laser (Lambda Physik, Gottingen, FRG)

PTP

dye cells with paraterphenyl solution

Sulforho- damin B

dye cells with solutions of sulforhodamin B

frequency- doubling KDP-crvstal.

REFERENCES

Fig. 2 - a) Cross-section through a glass cone with an excimer laser beam of diameter D entering from the right. The length of the pulse (cross-hatched area) is greatly exaggerated for clarity.

b) Enlarged view of the target area near the tip of the cone at the moment, when the laser pulse exits from the cone launching travelling-wave excitation of the target.

c) Detail showing how the target is centered and reloaded through the axial bore.

[ l ] S. ~ z a t m 6 r i and F. P. Schafer: Simple Generation of High Power, Picosecond Tunable Excimer Laser Pulses, Opt. Comrn. 48

(1983) 279-283.

[2] F. P. Schafer: On some Properties of Axicons, Appl. Phys. B 39

(1986) 1-8.