**5. Finding the spectral lines for repumping and cooling laser**

To find the spectral lines for the repumping and cooling laser it is necessary to change the current and temperature of each laser controller and scan the laser piezo element attached at the grating at large amplitudes and measure the whole absorption spectrum from the atoms in the rubidium cell with a photodiode. This should be made for each laser. A typical absorption spectrum of rubidium is shown in Fig.22. Lamb dips are useful to identify the lines.

Fig. 22. Saturated absorption spectra used to find spectral lines for the repumping and cooling laser.

## **6. Doppler free spectra of cooling and repumping laser**

A detailed view of the Doppler free spectra for the cooling and repumping lasers is shown in Fig. 23. To obtain these spectra we reduced the scan amplitude of the grating piezo and changed slowly the offset voltage of the piezo to isolate each line. Additionally it was possible to heat the rubidium cell with a nichrome wire to obtain more defined lines.

176 Quantum Optics and Laser Experiments

To find the spectral lines for the repumping and cooling laser it is necessary to change the current and temperature of each laser controller and scan the laser piezo element attached at the grating at large amplitudes and measure the whole absorption spectrum from the atoms in the rubidium cell with a photodiode. This should be made for each laser. A typical absorption spectrum of rubidium is shown in Fig.22. Lamb dips are useful to identify the


Rb85 a

1.8 cm

Rb87 a

relative frequency (MHz)

Fig. 21. Construction of anti Helmholtz coils.

12.9 cm

10.4 cm

lines.

0.5

Rb87 b

transmission (a.u.)

cooling laser.

1

**5. Finding the spectral lines for repumping and cooling laser** 

Rb85 b

**6. Doppler free spectra of cooling and repumping laser** 

Fig. 22. Saturated absorption spectra used to find spectral lines for the repumping and

possible to heat the rubidium cell with a nichrome wire to obtain more defined lines.

A detailed view of the Doppler free spectra for the cooling and repumping lasers is shown in Fig. 23. To obtain these spectra we reduced the scan amplitude of the grating piezo and changed slowly the offset voltage of the piezo to isolate each line. Additionally it was

Fig. 23. Doppler free spectra of a) repumping and b) cooling lasers. The arrows indicate the frequencies to be locked.

### **7. Signals needed to stabilize the repumping and cooling laser**

Fig.24 shows a typical measured modulated laser spectra and Fig.25 shows the error function obtained experimentally. In both cases, the interferometer cavity length was held fixed and the laser was scanned continuously. The alignment procedure of the light reflected from the interferometer into the fast photodiode can be best done using a surveillance camera an trying to group the multiple reflections on a single point at the photodiode.

Fig. 24. Laser modulated profile recorded with interferometer.

Cold Atoms Experiments: Influence of Laser Intensity Imbalance on Cloud Formation 179

Fig. 27. Image taken with modified Samsung camera. The chamber can be seen.

diameter was nearly 2.0 mm at its full width.

image and right a 3D plot of intensity of the same cloud.

Fig. 28 shows the cloud image obtained with the IR Altec Vision CCD camera. The cloud

Fig. 28. Cloud of atoms obtained with our Altec Vision IR CCD camera. Left is the cloud

**8.1 Optical method: using a Glan Thomson polarizer for laser intensity imbalance** 

laser field polarization would be kept fixed after passing the Glan Thomson.

We introduced an optical method, previously developed for laser printers (Duarte, 2005), to study the effect of the laser intensity imbalance on the cloud formation. The method uses two Glan Thomson polarizers to produce a controlled imbalance between pump and probe laser. Each Glan Thomson polarizer was installed in front of the polarizing beam splitter cubes the produces the first division of the cooling and repumping laser respectively as seen in Fig.13. The laser intensity was controlled at will by rotating the Glan Thomson polarizer. The polarizing beam splitter cube contributes for further reduction of the laser intensity. We measured the intensity behind the beam splitter cube after each intensity reduction and recorded simultaneously the cloud with our camera. The laser polarization was slightly rotated after passing the beam splitter polarizing cube not affecting the overall functioning of the cloud. A more precise method could be realized by fixing the Glan Thomson polarizers for maximum transmission and rotating at will the field in front ofs each Glan Thomson polarizer by means of a half wave plate disposed in front of it. By this method the

Fig. 25. Experimental error function.

To lock the laser frequency to the needed resonance, we have stored one single Doppler free spectrum and recalled and displayed it on the oscilloscope screen. The amplitude scan was decreased close to the zero crossing of the error function. Adjustments of the error signal position relative to the Doppler free spectra could be done by changing the absolute cavity length of the interferometer. This was done by changing the offset bias voltage of the interferometer.
