Laser system

1 . A single arm laser system comprising:

a first in-phase quadrature modulator (IQM), the first IQM configured to:

receive a single frequency fibred laser beam from a frequency locked laser seed,

generate a first single side-band frequency based on a carrier frequency of the single frequency fibred laser beam and suppress the carrier frequency, and

output a first fibre laser beam having a single side-band suppressed carrier frequency; and

a second IQM in line with the first IQM, the second IQM configured to:

receive the first fibre laser beam from the first IQM,

generate a second single side-band frequency based on the first single side-band frequency and maintain the first single side-band frequency as the carrier frequency, and

output a second fibre laser beam having the first and second single side band frequencies;

the single arm laser system being further configured to change the phase modulation of I and Q components in at least one of the first IQM and the second IQM so that at least one of the first and second single side band frequencies is changed.

2 . A single arm laser system according to claim 1 , wherein the first IQM receives two radio-frequency (RF) signals of the same frequency in phase quadrature, the generation of the first single side-band frequency being driven by the frequency of the two RF signals input into the first IQM, and wherein the second IQM also receives two RF signals of the same frequency in phase quadrature, the generation of the second single side-band frequency being driven by the frequency of the two RF signals input into the second IQM.

3 . A single arm laser system according to claim 2 , the single arm laser system further comprising a microwave chain to generate the two RF signals in phase quadrature received by the first IQM, and the two RF signals in phase quadrature received by the second IQM.

4 . A single arm laser system according to claim 3 , wherein the RF signals generated by the microwave chain are to drive an electro-optic modulator (EOM) which is used to modulate the laser for the spectroscopy locking.

5 . A single arm laser system according to claim 3 , wherein the microwave chain comprises an oven controlled crystal oscillator (OCXO) as its single frequency reference.

6 . A single arm laser system according to claim 1 , wherein the single frequency fibred laser beam has a wavelength of about 1560 nm.

7 . A single arm laser system according to claim 1 , the single arm laser system further comprising an Erbium doped fibre amplifier (EDFA) to amplify the power of the second fibre laser beam.

8 . A single arm laser system according to claim 1 , the single arm laser system further comprising an acousto-optic modulator (AOM) to switch the second fibre laser beam on and off and to control the power of the second fibre laser beam.

9 . A single arm laser system according to claim 1 , the single arm laser system further comprising a second harmonic generator (SHG) configured to double the frequencies of the second fibre laser beam, in order to halve the wavelength of the second fibre laser beam from about 1560 nm to about 780 nm.

10 . A single arm laser system according to claim 1 , the single arm laser system further comprising an optical fibre switch to select an optical delivery of the second fibre laser beam.

11 . A gravity gradiometer comprising:

a single arm laser system according to claim 1 configured to generate a plurality of optical frequencies as recited in claim 1 ; and

an optical system comprising an arrangement of lenses and optics, the optical system configured to, using the optical frequencies generated by the single arm laser system:

trap and cool atoms to form two vertically separated cold atom clouds;

select a hyperfine level of atoms of the cold atom clouds;

trap atoms of each cold atom cloud in an optical lattice;

perform Raman interrogation of the two cold atom clouds simultaneously with the same laser beam; and

detect the atomic states of each cold atom cloud by fluorescence to find a gravity gradient.

12 . A method for generating multiple frequencies from a frequency locked laser seed, the method to be performed by at least two in-phase quadrature modulators (IQMs) the method comprising:

receiving a single frequency fibred laser beam from a frequency locked laser seed;

shifting a frequency of the laser seed from a locking frequency;

generating a generated frequency based on the shifted frequency; and

outputting a laser beam through a selected optical delivery having the shifted frequency and the generated frequency;

the method further comprising changing the phase modulation of I and Q components in at least one of the two IQMs so that at least one of the shifted frequency and the generated frequency is changed.

13 . The method of claim 12 , the method further comprising:

amplifying a laser power;

controlling the laser power; and

doubling laser frequencies.