Heterodyne detection of coherent Raman signals

In an apparatus for detecting coherent Raman signals from a Raman active sample comprising a pump laser having an output radiation at a frequency w.sub.1, a probe laser having an output radiation at a predetermined polarization and a frequency w.sub.2, w.sub.1 -w.sub.2 approximating a Raman mode frequency of said sample thereby resulting in a first portion of said probe laser output shifting polarization as it passes through said sample, means for directing said probe laser output and said pump laser output into said sample whereby to intersect each other within said sample, a polarization analyzer for passing some of said probe laser radiation having a predetermined polarization after having passed through said sample, and means for detecting said probe laser radiation that has passed through said analyzer, the improvement comprising means for optically heterodyning said first portion of said probe laser output with a second laser output portion thereby obtaining a heterodyned cross-term signal linearly proportional to the Raman cross-section of said sample.

In an apparatus for detecting coherent Raman signals from a Raman-active sample comprising a pump laser having a circularly polarized output radiation at a frequency w.sub.1, a probe laser having a linearly polarized output radiation at a frequency w.sub.2, w.sub.1 -w.sub.2 approximating a Raman mode frequency of said sample thereby resulting in a first portion of said probe laser output shifting polarization by 90 degrees as it passes through said sample, means for directing said probe laser output and said pump laser output into said sample whereby to intersect each other within said sample, a polarization analyzer for passing some of said probe laser radiation having a predetermined polarization after having passed through said sample, and means for detecting radiation that has passed through said analyzer, the improvement comprising means for passing through said polarization analyzer portions of said probe laser output not having shifted polarization and portions of said probe laser output having shifted polarization by 90 degrees, said not-shifted portion of said probe laser output constituting a local oscillator output;

• said probe laser outputs having passed through said polarization analyzer and combined at said detection means thereby forming a heterodyned corss-term signal linearly proportional to the Raman cross section of said sample.

In an apparatus for detecting coherent Raman signals from a Raman active sample comprising a pump laser having a circularly polarized output radiation at a frequency w.sub.1, a probe laser having a linearly polarized output radiation at a frequency w.sub.2, w.sub.1 -w.sub.2 approximating a Raman mode frequency of said sample thereby resulting in a first portion of said probe laser output shifting polarization by 90 degrees as it passes through said sample, means for directing said probe laser output and said pump laser output into said sample whereby to intersect each other within said sample, a polarization analyzer for passing radiation having the same polarization as that portion of said probe laser output having its polarization shifted by 90 degrees, and means for detecting radiation that has passed through said polarization analyzer, the improvement comprising means for isolating a portion of said probe laser output to be used as a local oscillator signal and combined with said polarization-shifted portion of said probe laser output, said combined portions thereby forming a heterodyned cross-term signal linearly proportional to the Raman cross-section of said sample.

In an apparatus for detecting coherent Raman signals from a Raman active sample comprising a pump laser having a circularly polarized output radiation at a frequency w.sub.1, a probe laser having a linearly polarized output radiation at a frequency w.sub.2, w.sub.1 -w.sub.2 approximately a Raman mode frequency of said sample thereby resulting in a first portion of said probe laser output shifting polarization by 90 degrees as it passes through said sample, means for directing said probe laser output and said pump laser output into said sample whereby to intersect each other within said sample, a polarization analyzer for only passing radiation having a polarization the same as said probe laser first portion, and means for detecting radiation that has passed through said polarization analyzer, the improvement comprising means for changing a second portion of said probe laser output so that subsequent to passage though said sample it has the same polarization as said probe laser first portion, said second portion comprising a local oscillator signal, said first and second probe laser portions when combined at said detecting means creating a heterodyned cross-term signal linearly proportional to the Raman cross-section of said sample.

In an apparatus for detecting coherent Raman signals from a Raman-active sample comprising a pump laser having a circularly polarized output radiation at a frequency w.sub.1, a probe laser output having a linearly polarized output radiation at a frequency w.sub.2, w.sub.1 -w.sub.2 approximating a Raman mode frequency of said sample thereby resultng in a first portion of said probe laser output shifting polarization by 90 degrees as it passes through said sample, means for directing said probe laser output and said pump laser output into said sample whereby to intersect each other within said sample, a polarization analyzer for only passing radiation having a polarization the same as said probe laser first portion, and means for detecting radiation that has passed through said polarization analyzer, the improvement comprising means for routing a second portion of said probe laser output prior to its entrance into said sample to said detecting means and bypassing said sample and said polarization analyzer, said second portion comprising a local oscillator signal, said first and second probe laser portions when combined at said detecting means creating a heterodyned cross-term signal linearly proportional to the Raman cross-section of the sample.