1995 Fiscal Year Final Research Report Summary
Nonlinear Laser Spectroscopy of vibrationally excited molecules using a high-finesse cavity
| Project/Area Number |
06640532
|
|---|
| Research Category |
Grant-in-Aid for General Scientific Research (C)
|
| Allocation Type | Single-year Grants |
|---|
| Research Field |
物理学一般
|
|---|
| Research Institution | Keio University |
|---|
Principal Investigator |
SASADA Hiroyuki Keio University, Department of Physics, Assistant Professor, 理工学部, 専任講師 (30146576)
|
|---|
| Project Period (FY) |
1994 – 1995
|
| Keywords | saturated absorption spectroscopy / laser spectroscopy / optical resonator / methane / acertylene / overtonebands / semiconductor laser |
|---|
| Research Abstract |
In the first year, an external-cavity semiconductor laser was constructed for spectroscopy of the 1.65-mum region. This year an optical-cavity absorption cell having a finesse of 300 was made. Resonant radiation forms a standing wave in the cavity, and the radiation power at the antinode of the standing wave is enhanced by 150 times larger than tha incident power, which makes it easy to perform saturation spectroscopy. With a servo loop, laser frequency is always locked at the resonant frequency of the cavity. Saturation spectrum has been recorded on the overtone band of methane. Its spectral Iinewidth is about 0.5 MHz, which is much smaller than Doppler width of 290 MHz, hoence some lines overlapped in Doppler-limited spectroscopy are cleary resolved. Another opical-cavity absorption cell having a pair of Stark electrodes has been built to study Stark effects of methane. The magnitude of the vibrationally-induced permanent dipole moment detarmined from easurements of the Stark shift shows a clear dependence on the Coriolis sublevels.This dependence is observed for the first time, and a theoretical anlysis has been made.
An optical-cavity absorption cell was built using a pair of mirrors having a reflectivity of 99.97% around 790 nm. Using this cell, absorption spectroscopy of a weak combination band of acetylene was carried out. Because radiation is reflected many times in the cavity, an absorption length is effectively enhanced. Absorption strength in this cell is a thousand times larger than that in a single-pass absorption cell. A finesse of cavity is determined to be 1400, which is, however, far less than 10000 expected from the reflectivity of the mirrors. The main reason of this degrading is probably due to spots on the mirror surface. Frequency of a titanium-sapphire laser and the optical cavity resonance is not stable enough to observe saturation spectrum.
|
