Raman Scattering

We measured Raman and Rayleigh scattering from cold atomic cloud through the cavity.

Experiment Rayleigh

The detection scheme of Rayleigh photons

We send one beam from a side (purple color on a picture) with some detuning from the main laser MBR (80/110 MHz), this laser should be first set-up to be in resonance with atoms, could be seen on a screen by the MOT disturbance. Main laser MBR serves as a local oscillator for heterodyne detection of scattered light. The trick to get the signal was to detune MBR+110/80 10-20 MHz away from resonance.

Signal from homodyne detector was sent to spectrum analyzer having next settings: RBW = 5MHz, VBW = 300 Hz, linear amplitude scale, zero span at central frequency 80/110MHz, triggered to cavity scan ( 2 Hz, sweep 500ms)

Experiment Raman scattering

The detection scheme of Raman photons

Then we want to detect non-elastic scattering on transition 5P(1/2) -> F=1 (5S(1/2)) ;see picture (blue photons). We use second homodyne detector (HD #2) and toptica serves as local oscillator (salad color line). Toptica is phase locked to MBR and its fequency is set to be: Toptica = MBR + HFS + 30 MHz For a lock we use signal generator, which frequency is difference between MBR and toptica frequencies, ans is set as follows: SG = (HFS+30 MHz)/384=(6834.68261090429(9)+30)MHz/384=17.87677763 MHz

The emitted photon is obliged to have frequency = MBR + 80 MHz + HFS (see picture with Rubidium level structure). And our heterodyne detection would be performed on the frequency difference between photon emitted and local oscillator (toptica):

Heterodyne = photon - toptica = 50 MHz

In actual experiment due to AC-stark shift we detected signal on 46.5 MHz

Exp-t Raman with detuning

The Raman signal we had got while were scanning the cavity

toptica = MBR+HFS+60 MHz =6894.68261090429(9) MHz;

SG(reference)= /384 = 17.95490263;

toptica = MBR+HFS+140 MHz= 6974.68261090429(9) MHz;

SG(reference) = 18.16323596;

Exp-t classical four-wave mixing

The Raman signal we had got while were scanning the cavity

The level scheme

The Anti-Stocks signal we get while pumping the Stocks transition

We send through the cloud three beams(see picture) toptica (salad), toptica-Y (orange), MBR+X (purple). There are a few conditions which should be fulfilled.

(1) toptica (direct) and anti-Stocks photon should be both resonant with the cavity, what means that toptica-Y (orange) must be set to 56 MHz (Y=56 MHz). toptica (should be in resonance with stocks or Raman photon)

(2) toptica (direct) must have the same frequency as Stocks photon. For this we perform exp-t Raman with detuning

(3) Difference between MBR (direct) and AS- photon should be <100 MHz (preferable <50MHz)

AOMs set to

AOM #	Frequency [MHz]	SG [MHz]	AOM Central freq [MHz]	Role
yellow	80	10	92.8	MBR spectroscopy
violet	100	12.5	86.4	MBR pump side
orange	56	7	85.6	Toptica pump side

First we set toptica = MBR + HFS + 110 MHz and expect to find Stokes photon @ 10 MHz, in real experiment signal was @ 16 MHz:

Detuning	SG [MHz]	Central freq	Role
110	18.08511096	6944	-

Then we set toptica to MBR + HFS + 110 -16 and we looked for a signal @ 44 MHz:

Detuning	SG [MHz]	Central freq	Role
94	18.0434443	6928	-

For an experiment we removed lambda/4, so toptica from a fiber won't go to HD#1.

MBR side	toptica side	toptica fiber
1.75 mW	3 mW	125 uW

26th of May We optimized cavity detuning:

Orange SG, [MHz]	AOM freq [MHz]	Heterodyne freq [MHz]	Signal amplt, [uV]	Power, topt - AOM, [mW]
9.5	76	24	300	2.3
9	72	28	400	2.3
8.5	68	32	475	2.3
8	64	36	500	2.3
7.5	60	40	550	2.3
7	56	44	500	2.3
7	56	44	400	1.7
6	52	48	400	1.7

The next task is to check where is double photon resonance (to make sure that both toptica(green) and MBR(violet)). So we want to tune toptica, although make both stokes and anti-stokes in resonance with a cavity.