DE2142868C3 - Gas ion laser - Google Patents

Description

of elemental selenium has a temperature between 250 and 280 ⁰ C.

F i g. Figure 2 is a schematic view of a second embodiment using a closed one Laser discharge tube,

F i g. 3 is a diagram showing the dependence of the laser power on the discharge current for the in F i g. 1 laser shown,

F i g. 4 and 5 typical changes in the laser power with the He pressure or the side arm

The invention relates to a gas ion laser for continuous wave operation with one within an optical one Resonator arranged, the stimulable medium containing discharge tube with at least a source for a substance to be vaporized and with devices for generating a continuous Direct current discharge is provided, wherein the stimulable medium consists of helium of at least

2 Torr pressure and a temperature between 35 temperature in the embodiment according to FIG. 2, 200 and 300 ⁰ C vaporized substance consists. In the illustrated embodiments of

It has recently been recognized that the normal invention produces a selenium ion laser in which the ions present in solid or liquid form by cataphoresis through the discharge tube elements, e.g. For example, most metals that are likely to be pumped with relatively low currents will be the most likely source for new ion lasers. Because 40 continuous operation a broad spectrum of laser lines, with the help of the noble gas ion laser (e.g. the neon-helium laser generally known from the near infrared to the blue) it is not possible to spread the spectral range. The Schwin radiation at sufficiently different frequencies are generated with a mixture of helium gas in the entire visible range of the spectrum in a pressure of more than 2 Torr and selenium vapor continuous wave operation. On the other hand, 45 would be obtained, as this is obtained from ^{elementary selenium which is heated to 200 to 300 °} C., in particular in message transmission-resistant elementary selenium. Throughout

46 transitions between 4467 and 12,600 Å were observed. Nineteen of the transitions from 4605 to 6444 Ä in the visible range oscillate at the same time when using broadband reflectors. There were Output powers between 3 and 5 milliwatts in the spectral range from 4467 to 12 600 Å (1.26 micrometers) measured using various combinations of laser mirrors. A Spiegelmium laser but is a stimulated emission at only 55 combination produced a combined output two Lines, namely at 4416 and 3250 A, in the continuous signal with a power of 250 milliwatts for the line operation achievable. The known laser is therefore six strongest blue-green transitions, unable to meet the need for stimulated It was found during operation that a

Emission selenium vapor pressure achieved to contribute to as many different lines optimally at a temperature in the optical spectral crucial statement 60 of the selenium supply from about 250 to 280 ⁰ C. would. Optimal helium pressures were in the range between

It is also already known to see certain non-metallic 5 and 15 torr. The maximum overall performance Solid elements in pulsed lasers at very low was at a discharge current of 400 to gen to use steam pressures. For example, 500 milliamperes are achieved.

wise selenium, arsenic and bromine ion lasers, which in 65 The infrared transitions have for integiated pulsed HF ring discharges are excited from optical circuits and for optical transmission Article by W. E. Be 11 et al., IEEE Journal of systems is of particular importance, as it was earlier with ent-Ouantum Electronics, Vol. 1, p. 400 (1965). wound optical devices can be combined.

technology require as many different carrier frequencies as possible.

Thus it is known (see. Applied Physics Letters, H ^. 15 (196 ¹ J), 1j9-161), for a laser of the kind described in the introduction, a mixture of helium of at least 2 Torr and at temperatures between 200 and 300 ⁰ C. to provide vaporized potassium as the stimulable medium. With this helium cad

The in F i g. 1 shown embodiment beam as an alternative to a monochromator or • _or m of the invention used quartz discharge spectrometer for precise wavelength measurement tube 11, which glue a narrow area 17 with 3 mm.

Has inner diameter and a length of In addition, the front reflector 18 was partially

50 cm, can be carried out casually by a direct current source 16 in order to be able to draw off another part of the resonance-supplied discharge currents in the order of magnitude of radiation. This radiation can carry 1 ampere between anode 14 and cathode 15. used for example in a consumer 31 The tube 11 has two side arms 12 and 13 on the be used, with the consumer for example as a front height on anode and cathode side arms and direction for determining the spectroscopic outside the narrow range 17 in order to have a more accurate io To ensure Raman properties of a crystal over the frequency band spanned by the control of the vapor pressure at high discharge of the laser lines. Helium gas flows from one can be forms.

Reservoir 28 through inlet port which the anode 14 coherence of the extracted radiation can through

or side arms including cathode 15 and a slight tilting or detuning of one of the ends through the side arms 12 15 aligned with these reflectors 18 and 19 are tested, and 13 with the aid of a mechanical pump 20 The enlarged sections 81 of the tube 11 as well

leads. The cross flow of the helium = supports which the associated side arms can be made of tempered glass Discharge and protect the windows. The discharge consists of graduated seals or incoming current supplies enough heat to reach the tight fittings with the quartz tube 17 at a higher Tempeiatur than the reserve 20 forangen area 17 is connected. The extended voire 21 and 22 to keep and condensation of the sections can have an inner diameter of 2.5 cm To prevent selenium in the narrow area 17. to have. The areas near the end windows can

The selenium vapor can have an inner diameter of 1.7 cm from solid elemental selenium, are obtained in the reservoirs 21 and 22 When operating the selenium ion laser according to FIG. 1

is included, which towards the narrow area 17 was the helium pressure above 2 Torr, and are open. The reservoirs 21 and 22 have a depth preferably set at 5 to 15 Torr. It was of about 5 cm, are piston-shaped and found that cataphoresis, the movement more positive have in the area of their opening to the narrow area 17 ions under the influence of the direct current field, one towards a diameter of 3 mm. You can have a 4 cm decisive effect on the functioning of the in of the expanded sections of the quartz tube 11 30 F i g. 1 has shown the laser. The intensity of the be remotely located and are reflected by the output signal drops only weakly when the Standing heating coils 23 and 24 are heated, with the reservoir 22 on the right-hand side not being heated. The positive ones cylinder 25 and 26 the heating coils of the reser selenium ions are therefore longitudinally by cataphoresis Keep voirs 21 and 22 at a distance. If necessary, the tube from the anode-side reservoir 21 easily the coils 23 and 24 can by in F i g. 1 not 35 distributed and pumped towards the cathode, The 24 visible laser junctions shown in the

to reduce consumption. 50 cm tube 11 of the FIG. 1 shown

The temperature of the reservoirs 21 and 22 and thus the guide form are obtained in the subsequent steam pressure of the selenium is indicated by a controllable table I. Heating current source 27 was controlled for all wavelengths. The source 27 can be ^{measured from 40 with a 3} / _4- m spectrometer and can be controlled manually or automatically via feedback from transitions in the spectrum from the reservoirs 21 and 22 that are known per se. With auto-simply ionized selenium (Se II). matic adjustment can be done at the reservoirs The change in laser power with the current

attached thermocouples the feedback the strongest junction at 5227 A is in FIG. 3 for deliver signals. 45 shows the 50 cm discharge tube shown in FIG. 1 shown.

The optimal partial pressures of the two gases increased approximately linearly with the current, carried approximately 6 to 8 Torr He and 5 · 10 ^-3 Torr until it reached a saturation range at 400 mA. However, approximate optimal conditions can be achieved. The power reaches its peak value at 500 mA over a wide range of vapor pressures and then drops to a current of 1 ampere, as will be explained in more detail below . It is assumed that all transitions The gain at each transition is for the

from the excited 4s ² 4p ² 5p electron configuration 4 mm discharge tube 41 according to FIG. 2 originate in a cation in singly ionized selenium (Se II). Current of 200 mA indicated in Table I below. This electron configuration is energetically close. Even so, the gain per meter was on for the Hc ion ground state. This means that most of the transitions in the 3 mm tube correspond to this energy with the energy of the helium ion F i g. 1 higher than in the hard glass tube according to F 1 g. Basic condition almost coincides. The quartz tube 17 according to FIG. 1 could also

In one embodiment, the rear reflector carries larger currents than that according to F 1 g. 2. The gate 19 (Fig 1) partially permeable to a part of the maximum gain that in the embodiment To be able to subtract resonance radiation, the 60 according to FIG. 2 measured was 11% / meter derived part by a grid 29 in different the 5227-A junction at a current of 500 rnA. Diffraction orders on a display screen 30 for The relative intensities of all lines are in tables

Display is brought. In the first diffraction I beauty with strong, medium and weak indicated as order and at higher diffraction orders can in the embodiment according to FIG. 2_mit the separation or distance between the comparable 6 ₅ 4 mm tubular portion and a different colors can be distinguished with the eye meter-long discharge path in a He pressure. Since the different colors are not separated in the zero of 8 Torr and a discharge current of 200 mA order beam, it was observed.

Table I.

Wavelengths and level assignments liemesxene Wcllcn- (Ί nlcran / t 0.5 Λ)

4604.6 4648.6 4764.1 4840.6 4845.0 4 ^U 76.1 4992.9 5068.7 5096.1 5141.9 5176.0 5227.6 5252.6 5253.2 5271.3 5305.5

5522.8

5591.6 5697.9 5747.9 6056.3 6443.9 6490.1 6534.6

ISI'-WcllcnkinjiclAl

4604.34 4648.44 4763.65 4840.63 4844.96 4975.66 4992.75 5068.65 5096.50 5142.14 5175.98 5227.51 5253.07 5253.63 5271.11 5305.35

5522.42 a

5591.16 5697.88 5747.62 6055S6 6444 25 6490.48 6534 ^ 95

Ni \ c: iu- / iK <riliuini!

> P " ¹⁵ p ⁴ D ₄ * 5 s ⁴ P,
■> ⁴ P ₄ ² P ₁
2 5 p ^4th H ^{4 [} \ ► 5s ⁴ P, ⁴ ps ⁴ P _f ^ P ⁴ I). • 5 s ⁴ P ₄ ⁴ 1 -; _ ^4p f 5 p % ² D ^ ♦ 5 s ⁴ P, > P * 5 s ⁴ P ₅
2 ⁴ P ₁ 5 p ⁴ IX . 4s4p ^{4 2} P, ⁴ > \ 5 p ⁴ P, • 5 s ² P ₄ 5P * 5s ⁴ P, 5 P ⁴ D- 1 ♦ 4d ⁴ F- ^ P ⁴ P ^
2 ■ - * 5s 5 p 1
2 > 5s ⁴ ps sp ⁴ D _f ■ * 5 s - 4s4p ^{4 2} P, 5 π 2 * 5 s - »5s Sp 5P ² D ₅
2 * 5s - 5s 5 p 5p ·· 4d -> 5s 5 p - 5 s SP - 5s - * 7 5 p - » 5s 5p 5P 5p 5P

5p

Kcliili \ c Inlcnsiljl

mil lei weak weak weak medium strong strong strong weak medium strong strong medium medium weak strong

medium

weak weak weak medium medium medium weak

(icmcssciic Reinforcement

("• n McIiTl

2.3

3.3

1.3 4.6

5.4 1.7 1.7

2.6

1.3

a = assignment doubtful.

The execution of the "closed discharge tube 65 The tube consisting entirely of hard glass" According to the embodiment according to FIG. 2, it has a tubular area 47 with a 4 mm interior Cataphoresis Pmnpen of the selenium ions has an even better diameter and has a length of 11 suitable as the embodiment according to FIG. 1. where the extended sections near the end windows:

have an inner diameter of 12 mm. The Brewster angle of the quartz end window was chosen for a wavelength of about 4420 A in the blue region , although these windows cause only very little loss for the lines of longer wavelengths, even for the red lines.
A selenium reservoir 51 cm at a distance of about 2 in the direction of the discharge axis of the anode 44 is disposed side arm containing, in the reference to the embodiment according to F i g. 1 heated way. A uniform selenium vapor distribution is maintained with the aid of cataphoresis ion pumping through the direct current discharge in the tubular region 47. The heat that forms during the discharge also prevents selenium condensation in the tubular region 47 in this embodiment.

The heating power source 57 controlling the temperature can be adjusted either manually or automatically in order to control the temperature of the reservoir 51 via a resistance heating coil 53 which drives the glass cylinder 55 in the manner shown in FIG. 1 surrounds the manner shown.

A degassing cathode 50 arranged in a separate side arm replaces the main cathode 45 during the degassing process and causes the discharge, whereby the main cathode is protected from deterioration. A high vacuum pump 82, which is connected via a valve, evacuates the tube 41. The tube is then filled from the helium reservoir 58 with helium under a pressure of 8 Torr. Under these conditions a total output of 30 mW could be achieved in almost the same quantities as the 4976-, 4993-, 5069-, 5176-. 5227 and 5305 A transitions (lavender green to yellow green) can be obtained using an exit mirror 48 having a transmittance of 2-3% over this wavelength range. The output mirror 48 was not optimized for these transitions, and it can be assumed that higher powers could have been achieved with a correspondingly adapted degree of output coupling. In the embodiment according to FIG. 2, a power of 1.2 mW at 4605 A and 0.3 mW at 4649 A could be observed at these wavelengths with an output mirror 48 which has a transmittance of 0.7%. Some competition has been observed among some of the lines and it may therefore be necessary to use a prism selector, not shown, in the laser cavity in order to achieve maximum performance at each transition. If many lines vibrate at the same time, a rotatable transmission grating 60 can be used in practice, with which a line can be selectively transmitted to a consumer 61. The grating 60 is particularly suitable for promoting the oscillation of a selected wave lying in the infrared range.

F i g. 4 and 5 show the change in the laser power with the He pressure and the side arm temperature for a discharge at a current of 20OmA in the 4 mm tubular area in the embodiment according to FIG. 2. The output consisted of the above six lines using the 2-3% output mirror 48. The change with the helium pressure according to FIG. 4 at a selenium temperature in the side arm of 265 ° C has a relatively broad maximum in the range from 6 to 10 Torr. The lower pressure threshold is 2 Torr, and stimulated emission or laser effect could still be observed at pressures in the order of magnitude of 22 Torr. The tube with a tubular area of 3 mm showed a similar curve shape with an optimum at 6 Torr.

The change in laser output power with selenium temperature in the side arm is shown in FIG. 5 at one Helium pressure of 8 torr shown. The half width

ίο the curve extends over a temperature range of approximately 30 ° C with a maximum at 265 ° C. The vapor pressure corresponding to this temperature is approximately 5 × 10 ^-3 Torr. If the temperature deviates by ± 15 ° C, the laser power drops to about half. The narrow selenium vapor pressure range at which stimulated emission occurs can be recognized by a relatively white discharge. This white discharge is in contrast to a reddish discharge of pure helium at too low a selenium temperature and to the blue discharge in selenium vapor at too high a temperature.

The upper laser levels of these transitions, which include all thirteen 5p levels, all result from the 4s ² 4p ² 5p electronic configuration in the spectrum of singly ionized selenium (Se II). All of these levels are close to the helium ion ground state. Only three levels are above (within about 0.2 eV) with a maximum energy difference of about 4 kT. This very precise energy adjustment, together with the linear current dependence and the high helium pressure for an optimal output signal, indicates the possibility that the levels are stimulated by charge exchange collisions between helium ions and neutral selenium atoms in the ground state. It can be assumed that the discharges are effective in every case in the sense of ionizing a significant part of the helium, the degree of ionization being approximately 0.01% or more.

If electron impacts were responsible for the excitation at the levels, then the optimal helium pressure would be significantly lower (and a high electron temperature would be generated) in order to achieve the level described in the article by B e 11 et al. to meet the specified conditions. In addition, stimulated emission did not occur in similar mixtures of Ar-Se. This observation is consistent with the fact that there is no energy coincidence between the argon ion levels and the 5p selenium ion levels .

It is believed that selenium vapor is present in the form of Se ₂ , Se ₄ , Se ₈ and Se _a molecules, although the relative concentrations of the various forms are not precisely known. The dissociation energy of Se ₂ is 3.55 eV, so that the dissociation process is probably due to collision of Se molecules with either electrons and metastable helium atoms or ions. It is therefore also possible that the molecules dissociate and are in an excited ion state calmly white. Nevertheless, electrons would be the only energy carriers or species that have sufficient energy for this purpose, and the optimal laser output signal would then be at a much lower helium

pressure occur. Based on the above considerations The charge transfer ionization of Selei single atoms is likely to play the main role. In a modified embodiment of the Ai

ίο

Order according to fig. 1 a two meter long quartz tube 11 was used to make the 22 new transitions in simply ionized selenium. The modified discharge tube had a centrally located one Cathode as well as an anode at each end. Broadband reflectors with improved reflectance in the infrared were used. It was found that the optimal currents were slightly lower, when the helium flow has stopped and the tube has been closed.

The data given in Table II were observed in such a 2 m long tube with an internal diameter of 3 mm. With such a Tube was under optimal discharge conditions and when using an output mirror with a average transmittance of 3% a total power of 250 mW at 4976.1, 4992.9, 5068.7, Measured at 5176.0, 5227.6 and 5305.5 Å. Outputs on the order of 50 milliwatts were at 5068.7, 5176 and 5227.6 A measured.

Table II reproduced below is structured in the same way as Table I. In Table II The 22 new laser transitions gained are included.

Table Il
Wavelengths and level assignments 15th - 5S-P ₁ Kchilixc 111lc11si1.il (icmessene
Wrslürkun
("0 MiMcr) (it'incsscnc Well
| Λ | cnliinpc IS-Wcllcnliinuc
(Λ) Nneiiu-assignnunt! - 5 s ⁴ P, mi UeI 1.4 446S.0 4467.60 5 P ² P _V -> 3 weak <!. () 4619.1 461P.77 Col ⁴ P ₄ -> 4s4p ^{4 2} P,
-> weak <OK 4716.5 4718.23 5 P ⁴ S, - »5 s ² P ₁ weak <!. () 4740.6 4740.97 Col ¹ P ₁ - 5 s ⁴ P, medium 1.6 4765.1 4765.52 5p ² P, - 5 s ⁴ P ₁ weak < 1.0 5567.1 5566.93 5P ⁴ D, - 5s ² P ₄ weak <1.0 5622.S 5623.13 5P ⁴ P ₁ - 5s ² P ₄ medium 1.6 5X42.S 5X42.68 5 p ² S ₁ - 5 s ² P, medium 1.6 5X66.7 5X66.27 5P ⁴ P, - 5s ² P ₄ medium 1.6 6066.1 6065.X3 5P ⁴ P ₁ - 5s ² P; weak <OK (ι 102.1 6101.96 5P ² D ₁
2 ♦ 1 medium 1.8 7064.2 7063.89 Col ⁴ P ₁ - ► 5 s' ² D ₅
2 medium 1.4 73914 739 1 .99 5p ⁴ P ₅
2 - 5s ² P ₃
1 weak 1.0 7674.9 7674.82 5P ² P ₃
2 - 5 s' ² D ₃
-f medium IJ 7723.6 7724.04 5P ⁴ D ₁ - 5s ² P ₃
2 medium 1.3 7796.2 7796.15 Col ² P ₁
2 - 5s' ² D ₅ medium 1.9 7839.3 7838.81 5P ¹ P ₁
2 - 5s' ² D ₅
2 medium 1.9 8308.9 8309.52 5P ² D ₃
2 - 6 weak
medium <1.0
U 9249.3
9954.7 9955.15 5P ⁴ P ₅
2 - 10 strong 2.8 10409.7 10408.81 Col ⁴ D ₁ strong 4.3 12587.9 12586.78 Col ⁴ P ₃

Since it has not been observed that preferentially those 5p levels or states are excited which are energetically close to the He ⁺ ground state, it can be assumed that mixed collisions with electrons or He atoms play an essential role in the distribution of the initial charge transfer excitation among the Play 5p levels. It is to be expected that the cross-sections for these collisions or impacts are large, since the middle one

The energy gap between the levels is approximately kT in the discharge.

The He-Se laser described above is capable of scanning a wide range of the near infrared and the to cover the visible spectrum. In addition, power would have to be in the range of 5 to 100 mW per Line over most of the spectrum with longer discharge tubes and optimized output coupling be achievable.

For this purpose 3 sheets of drawings

Claims (2)

Patent claims:
1. Gas ion laser for continuous wave operation with a These lasers preferably operate at an optimal neon buffer gas pressure on the order of 100 mt. These known designs could but only a few laser oscillations (according to the 5 selenium noble gas lasers arranged within an optical resonator, only two laser oscillations) Generate discharge containing the stimulable medium, and this only in pulse mode, tube with at least one source for a continuous wave operation was known with these evaporating substance and with facilities for lasers not possible. Generation of a continuous direct current The problem outlined above with a gas ion discharge is provided, the stimulable io laser a variety of both in the visible and Medium made of helium with a pressure of at least 2 Torr laser lines in the infrared spectral range To generate continuous wave operation is based on the gas ion laser of the type specified at the outset, solved according to the invention in that the evaporated Substance made from elemental selenium. As will be shown in detail below, it is possible with the laser according to the invention to generate stimulated emission at up to 46 lines within the optical spectral range in continuous wave operation. 3. Gas ion laser according to claim 2, thereby generating 20 z \\. indicates that the source of evaporation is the following, the invention is at hand in the Drawing illustrated embodiments explained in detail; it shows F i g. 1 is a schematic view of the first embodiment, where a transverse helium flow is used, and a substance evaporated at temperatures between 200 and 300 ⁰ C, characterized in that the evaporated substance consists of elemental selenium. 2. Gas ion laser according to claim 1, characterized in that the helium gas is in the mixture is under a pressure of 5 to 15 torr with the selenium vapor.