Abstract

We present what is to our knowledge the first measurement of a two-photon transition excited in Rb with a commercial diode laser. In addition to the limitation imposed by diode lasers’ characteristic low powers, their relatively large bandwidths and sensitivity to optical feedback effects impede their application to two-photon spectroscopy. However, we show that optimized signal detection and careful minimization of optical feedback with an acousto-optic modulator combined with a Faraday isolator result in good two-photon signals with an off-the-shelf diode laser.

© 1993 Optical Society of America

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References

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  1. G. Grynberg, B. Cagnac, Rep. Prog. Phys. 40, 791 (1977).
    [CrossRef]
  2. C. E. Wieman, L. Hollberg, Rev. Sci. Instrum. 62, 1 (1991).
    [CrossRef]
  3. J. C. Camparo, Contemp. Phys. 26, 443 (1985).
    [CrossRef]
  4. E. Arimondo, M. Inguscio, P. Violino, Rev. Mod. Phys. 49, 31 (1977).
    [CrossRef]
  5. See, for example, G. P. Agrawal, N. K. Dutta, Long-Wavelength Semiconductor Lasers (Van Nostrand Reinhold, New York, 1986), p. 247.
  6. Y. Yamamoto, ed., Coherence, Amplification, and Quantum Effects in Semiconductor Lasers (Wiley, New York, 1991).
  7. R. Lang, K. Kobayashi, IEEE J. Quantum Electron. QE-16, 347 (1980); D. Lenstra, J. S. Cohen, in Laser Noise, R. Roy, ed., Proc. Soc. Photo-Opt. Instrum. Eng.1376, 245 (1991).
    [CrossRef]
  8. See, for example, M. Osinski, J. Buus, IEEE J. Quantum Electron. QE-23, 9 (1987).
    [CrossRef]
  9. L. A. Orozco, State University of New York at Stony Brook, Stony Brook, New York 11794 (personal communication, 1992).

1991

C. E. Wieman, L. Hollberg, Rev. Sci. Instrum. 62, 1 (1991).
[CrossRef]

1987

See, for example, M. Osinski, J. Buus, IEEE J. Quantum Electron. QE-23, 9 (1987).
[CrossRef]

1985

J. C. Camparo, Contemp. Phys. 26, 443 (1985).
[CrossRef]

1980

R. Lang, K. Kobayashi, IEEE J. Quantum Electron. QE-16, 347 (1980); D. Lenstra, J. S. Cohen, in Laser Noise, R. Roy, ed., Proc. Soc. Photo-Opt. Instrum. Eng.1376, 245 (1991).
[CrossRef]

1977

G. Grynberg, B. Cagnac, Rep. Prog. Phys. 40, 791 (1977).
[CrossRef]

E. Arimondo, M. Inguscio, P. Violino, Rev. Mod. Phys. 49, 31 (1977).
[CrossRef]

Agrawal, G. P.

See, for example, G. P. Agrawal, N. K. Dutta, Long-Wavelength Semiconductor Lasers (Van Nostrand Reinhold, New York, 1986), p. 247.

Arimondo, E.

E. Arimondo, M. Inguscio, P. Violino, Rev. Mod. Phys. 49, 31 (1977).
[CrossRef]

Buus, J.

See, for example, M. Osinski, J. Buus, IEEE J. Quantum Electron. QE-23, 9 (1987).
[CrossRef]

Cagnac, B.

G. Grynberg, B. Cagnac, Rep. Prog. Phys. 40, 791 (1977).
[CrossRef]

Camparo, J. C.

J. C. Camparo, Contemp. Phys. 26, 443 (1985).
[CrossRef]

Dutta, N. K.

See, for example, G. P. Agrawal, N. K. Dutta, Long-Wavelength Semiconductor Lasers (Van Nostrand Reinhold, New York, 1986), p. 247.

Grynberg, G.

G. Grynberg, B. Cagnac, Rep. Prog. Phys. 40, 791 (1977).
[CrossRef]

Hollberg, L.

C. E. Wieman, L. Hollberg, Rev. Sci. Instrum. 62, 1 (1991).
[CrossRef]

Inguscio, M.

E. Arimondo, M. Inguscio, P. Violino, Rev. Mod. Phys. 49, 31 (1977).
[CrossRef]

Kobayashi, K.

R. Lang, K. Kobayashi, IEEE J. Quantum Electron. QE-16, 347 (1980); D. Lenstra, J. S. Cohen, in Laser Noise, R. Roy, ed., Proc. Soc. Photo-Opt. Instrum. Eng.1376, 245 (1991).
[CrossRef]

Lang, R.

R. Lang, K. Kobayashi, IEEE J. Quantum Electron. QE-16, 347 (1980); D. Lenstra, J. S. Cohen, in Laser Noise, R. Roy, ed., Proc. Soc. Photo-Opt. Instrum. Eng.1376, 245 (1991).
[CrossRef]

Orozco, L. A.

L. A. Orozco, State University of New York at Stony Brook, Stony Brook, New York 11794 (personal communication, 1992).

Osinski, M.

See, for example, M. Osinski, J. Buus, IEEE J. Quantum Electron. QE-23, 9 (1987).
[CrossRef]

Violino, P.

E. Arimondo, M. Inguscio, P. Violino, Rev. Mod. Phys. 49, 31 (1977).
[CrossRef]

Wieman, C. E.

C. E. Wieman, L. Hollberg, Rev. Sci. Instrum. 62, 1 (1991).
[CrossRef]

Contemp. Phys.

J. C. Camparo, Contemp. Phys. 26, 443 (1985).
[CrossRef]

IEEE J. Quantum Electron.

R. Lang, K. Kobayashi, IEEE J. Quantum Electron. QE-16, 347 (1980); D. Lenstra, J. S. Cohen, in Laser Noise, R. Roy, ed., Proc. Soc. Photo-Opt. Instrum. Eng.1376, 245 (1991).
[CrossRef]

See, for example, M. Osinski, J. Buus, IEEE J. Quantum Electron. QE-23, 9 (1987).
[CrossRef]

Rep. Prog. Phys.

G. Grynberg, B. Cagnac, Rep. Prog. Phys. 40, 791 (1977).
[CrossRef]

Rev. Mod. Phys.

E. Arimondo, M. Inguscio, P. Violino, Rev. Mod. Phys. 49, 31 (1977).
[CrossRef]

Rev. Sci. Instrum.

C. E. Wieman, L. Hollberg, Rev. Sci. Instrum. 62, 1 (1991).
[CrossRef]

Other

L. A. Orozco, State University of New York at Stony Brook, Stony Brook, New York 11794 (personal communication, 1992).

See, for example, G. P. Agrawal, N. K. Dutta, Long-Wavelength Semiconductor Lasers (Van Nostrand Reinhold, New York, 1986), p. 247.

Y. Yamamoto, ed., Coherence, Amplification, and Quantum Effects in Semiconductor Lasers (Wiley, New York, 1991).

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Figures (10)

Fig. 1
Fig. 1

Two-photon spectroscopy setup. The laser beam is focused and retroreflected through a Rb oven. The light fluorescing from the two-photon-excited state is collected by an f/1 lens and is imaged onto the photocathode of a cooled photomultiplier detector (PMT). The light from the diode laser is optically isolated from the retroreflected beam by an optical isolator and AOM combination. Laser power at the oven is 4.0 mW.

Fig. 2
Fig. 2

The diode laser tuned to 778.1 nm excites the two-photon transition from the 5S1/2 state to the 5D5/2 state in Rb. The light at 420.2 nm fluorescing from the 6P3/2 to the 5S1/2 state is detected.

Fig. 3
Fig. 3

Detected fluorescence from two-photon-excited 5D5/2 through the 6P3/2 state. Peaks A and D are due to the 6P3/2 → 5S1/2 decay and the 5P3/2 → 6S1/2 decay of the 87Rb isotope, respectively. Peaks B and C are from the 6P3/2 → 5S1/2 decay and the 6P3/2 → 5S1/2 decay of the 85Rb isotope, respectively. This scan was taken in 8 s with a detector bandwidth of 1.0 kHz.

Fig. 4
Fig. 4

Five consecutive scans of the fluorescence from the two-photon-excited Rb 5D1/2 states with (a) the optical isolator deliberately misaligned and (b) optimum alignment of the optical isolation system. In (a) the feedback causes the heights and the widths of the 85Rb and 87Rb isotope peaks to fluctuate from scan to scan by approximately a factor of 2. In (b) the fluctuations are reduced to ~20%. The arrows indicate examples of the flyback of the laser’s tuning ramp.

Fig. 5
Fig. 5

Graphical solution for Eq. (2). The intersections of the line with the various sine curves correspond to the modes in which the laser can operate as allowed by optical feedback. Here we have taken α = 5, ω0 = 2πc/(778 nm) = 2.423 ×1015 s−1 and ϕ = ω0τext + tan−1α = π.

Fig. 6
Fig. 6

C parameter plotted as a function of distance for light reflected from external optics. Each line represents Eq. (3) plotted for isolation (=−fext) varied between 20 and 80 dB for (a) an AlGaAs diode laser with R = 0.3, α = 5, τL = 6.67 ps and (b) a dye laser with R = 0.98, α = 0, τL = 2 ns.

Fig. 7
Fig. 7

Numerical solution of Eq. (2) for the frequency shift of the laser induced by optical feedback from a surface nominally 50 cm away. A 100-nm change in the cavity length can result in a change in the laser’s operating frequency as great as 10 MHz.

Fig. 8
Fig. 8

The change in laser bandwidth induced by optical feedback for a surface nominally 50 cm away as a function of external round-trip length. The laser bandwidth can change by as much as 10% for a 100-nm change in the round-trip length.

Fig. 9
Fig. 9

Comparison of the maximum frequency shift due to optical feedback as a function of the amount of optical isolation between the laser and the feedback surface for a diode laser and a dye laser.

Fig. 10
Fig. 10

Injection-locking half-width given by Eq. (7) as a function of optical isolation of the injecting beam from the laser’s output beam. The linewidth enhancement factor of the Sharp LT021 is estimated to be α = 5.

Equations (8)

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d d t E ( t ) = 1 2 g ( 1 + i α ) n ( t ) E ( t ) + K E ( t τ ext ) exp ( i ω 0 τ ext ) ,
d d t n ( t ) = [ 1 T 1 + g | E ( t ) | 2 ] n ( t ) Γ 0 [ | E ( t ) | 2 I 0 ] ,
Δ ω 0 τ ext = C sin [ tan 1 α + ( ω 0 + Δ ω 0 ) τ ext ] ,
C = K ( 1 + α 2 ) 1 / 2 τ ext .
K = 1 R τ L ( f ext R ) 1 / 2
[ δ v δ v 0 ] = 1 F c 2 ,
F c = 1 + C cos [ tan 1 α + ( ω 0 + Δ ω 0 ) τ ext ] .
Δ f = f L 2 π ( P in P o ) 1 / 2 ( 1 + α 2 ) 1 / 2 ,

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