Further measurements on the noise of a D.C. excited HeNe laser oscillator

Bolwijn, Piet

doi:10.1016/0031-9163(64)90024-1

Cited by 9 publications

(5 citation statements)

References 11 publications

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“…It can be shown that in most cases ~-l < 2a, except near threshold, and the dominant cutoff-frequency will then be 7-1, being largely independent of the laser operating conditions. Cutoff-frequencies in modulation noise spectra observed by us [4], see also [10] and others [3,[5][6][7] are in general agreewith these orders of magnitude. This was concluded independently also by Kubo et al [6,7].…”

Section: Cal 4]supporting

confidence: 73%

“…Experiments reported previously by us and other authors are in agreement with our analysis.The radiation of d.c. excited He-Ne lasers may show a large amount of low-frequency noise [1] which is due to modulation of the internal laser field by discharge current fluctuations [2][3][4][5][6][7]. Here we give an analysis of this modulation noise which includes explicitly the laser oscillator properties as derived by Lamb [8], in contrast to the analysis given by other authors [5,7].…”

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confidence: 57%

“…This noise source, however, was certainly not predominant in our case, since it cannot explain the observed crosscorrelation between laser noise and discharge-current noise [3][4][5].…”

Section: It Is Seen From Eq (2) That For a Given San(f)mentioning

confidence: 74%

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Discharge modulation noise in HeNe laser radiation

Bolwijn

1967

Physics Letters A

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Discharge modulation noise in He-Ne laser radiation is considered theoretically, including explicitly the laser oscillator properties. Experiments reported previously by us and other authors are in agreement with our analysis.The radiation of d.c. excited He-Ne lasers may show a large amount of low-frequency noise [1] which is due to modulation of the internal laser field by discharge current fluctuations [2][3][4][5][6][7]. Here we give an analysis of this modulation noise which includes explicitly the laser oscillator properties as derived by Lamb [8], in contrast to the analysis given by other authors [5,7].As a result of discharge current fluctuations the number of excited metastable He atoms and Ne atoms in the upper laser level fluctuate. This fluctuation in the driving force of the laser oscillation may be described by including a stochastic, slowly varying term AN(t) in N, which is defined by Lamb [8] as the excitation density in absence of optical oscillations. Thus we write N = N + +AN(t), with AN(t) << N. Using Lamb's differential equation for the amplitude E(t) of the electric field in the laser interferometer dE~dr = ~E -~E 3, and its steady-state solution, Eo2 = a/~, we find for the fluctuating part AE(t) in E [cf. 9,10] dAE/dt + 2otAE = (½v/Q) (Eo/N)AN(t),( 1) where we assumed AE(t) << E o. The quantities and ~ respresent the unsaturated net gain and the saturation, respectively, as defined by Lamb [8].Eq. (1) is a typical Langevin equation wellknown in noise analysis. The relation between the spectral noise intensities SAN(f) and SAE (f) can easily be found by making a Fourier analysis of eq. (1). The spectral noise intensity of the laser power output ccE2 follows from SA(E2 ) (f~ = = 4Eo2SAE (f). We have(2) where ¢o = 21rf. We assumed implicitly that f is much smaller than the decay rates of the laser levels (f << 10 Mc/s in case of He-Ne lasers). It is seen from eq. (2) that for a given SAN(f)the intensity fluctuations decrease with increasing average excitation density N and saturation B, as may be expected. The saturation of a gas laser transition is known to become stronger near atomic line center [8]. It follows then from eq. (2) that for w << 2a the noise intensity of a singlemode gas laser versus interferometer detuning should show a dipnear line center, which we observed indeed [4]*. In ref. 4 also reported the noise intensity near threshold detuning varied proportionally to the square of the d. c. laser output with varying interferometer detuning. Close to threshold we have w >> 2~ [cf. 10], so that according to eq. (2) SA(E 2) (f) cc (~/~)2 = Eo4 ' indeed.In discussing the noise spectrum of the laser radiation we have also to consider the noise spectrum SAN(f) , being determined by relaxation effects in the discharge. Let us discuss briefly some factors which affect the noise spectrum. In case of He-Ne lasers the slowest decay rate in the (de-)excitation processes involved is the inverse lifetime T of the metastable He atoms (23S or 21S) which at low electron densities describes t...

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confidence: 73%

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Discharge modulation noise in HeNe laser radiation

Bolwijn

1967

Physics Letters A

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“…The results of the experimental investigations of natural intensity fluctuations of the He-Ne laser at wavelengths of 0.63 and 3.39 p have beenexpounded in [1][2][3]; a comparison of the data obtained with the theory developed in [4] yielded satisfactory agreement. In the present communication we present the resuits of an experimental study of natural intensity fluctuations of a one-mode He-Ne laser at a wavelength of 1.15 #; at this wavelength a previous study [5] was made only of the fluctuations caused by engineering factors (the noise of the gas-discharge plasma). Note that the investigations described were conducted over a wide range of power and specifically at a larger excess above the lasing threshold than was the case in investigations at wavelengths of 0.63 and 3.39 #.…”

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On natural fluctuations of the intensity of a He?Ne laser operating at a wavelength of 1.15 ?

Gelikonov¹,

Zaǐtsev²

1970

Radiophys Quantum Electron

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“…In a previous paper [2] we reported that the a.c. power output of a single-mode He-Ne laser, which was obtained by modulating the discharge current [3,4], as a function of the detuning of the interferometer shows a dip at the peak frequency of the atomic transition. This modulation dip can be understood with the theory of Lamb [5], whose notation is followed throughout this paper.…”

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confidence: 99%