Consider Angle-Resolved Photo-Emission Spectroscopy with a Laser
Laser-based ARPES (Angle-Resolved Photo-Emission Spectroscopy) is a form of ARPES that uses a laser as the light source. Comparing to a synchrotron light source, laser-based ARPES offer some advantages: It fits on a table (ok … a large table) and makes experiment schedules independent from rare beam times at synchrotron facilities. The UV-laser provides an ultra-high energy resolution of down to 0.1 meV while providing a very high photon flux. Moreover, the bulk sensitivity is enhanced and the momentum resolution increased by using low energy photons of around 6 eV. This photon energy is sufficient to induce photoemission in many samples. However, due to the lower photon energy – compared to synchrotron radiation – Laser-ARPES probes typically only electronic states which are close to the Fermi level.
Laser ARPES/ARUPS with a High-Power UV Source
Tunable deep-UV pulses from 190 … 215 nm / 6.5 … 5.77 eV are available with APE’s HarmoniXX FHG in combination with Levante Emerald HP.
The tunable system provides high laser power in the range of several mW. Its brillant and monochromatic laser light is ideally suited for high-resolution ARPES (Angle-resolved Photoemission Spectroscopy) or ARUPS (Angle-resolved Ultraviolet Photoemission Spectroscopy).
- Tunable (Vacuum)-UV from 190 … 215 nm / 6.5 … 5.77 eV
- Extremely narrow spectral bandwidth of < 0.2 meV
- High photon flux of > 10^15 photons/s
- Exceptional beam quality of M2 < 1.2
- Automated wavelength tuning via software
- Ideally suited for table-top laser-based ARPES / ARUPS
Laser ARPES/ARUPS with a Narrow Spectral Bandwidth Down to 0.1 meV
ARPES on Graphene/Ir(111)
The following measurement were performed with APEs 190 nm / 6.5 VUV system. The ARPES measurement were taken on a SPECS GmbH system with a PHOIBOS 150 hemispherical analyzer with 2D-CCD detector.
ARPES maps of graphene/Ir(111) sample measured with laser around normal emission geometry showing the Rashbasplit of graphene/Ir(111) surface state. Two different entrance slits of the Electron Analyzer were used, resulting in different energy resolution (marked in the figure).
hv = 6.31 eV
Lens mode: WAM
Nr of energy points: 251 (Sweep mode)
Nr of 0-angle channels: 300
Dependence on Temperature. 3D ARPES data sets for graphene/Ir(111) sample measured with laser (lens mode: WAM). Measurements were performed at T=300 K (RT, see image) and T=120 K (LT, not shown here).
polar β-scan around NE
hv = 6.31 eV
Nr of energy points: 251
Nr of Θ-angle channels: 300
Nr of β-angle steps: 101
Total acquisition time: 50 min
Turning Complexity into a Turn-Key System
This light source enables spectroscopy and pump probe measurements in the deep UV range < 200 nm. The system consists of the following sub-components:
Creating a 190 nm / 6.5 eV Table-top System
The HarmoniXX allows access to the wavelength range of 190 … 215 nm (6.5 … 5.77 eV) by mixing the THG with a fundamental wavelength to create the fourth harmonic. The harmonic pulses are of narrow bandwidth nature, enabling a high resolution across the entire tuning range.
Levante Emerald HP OPO
The generation of high power tunable UV radiation is based on a widely tunable picosecond OPO with computer controlled tuning, pumped by an industrial high power green laser and with subsequent frequency conversion to reach UV wavelengths below 200 nm.
Paladin 532 – 20000 from Coherent Inc. is ideal for pumping the OPO. It is enabling a wide tuning range and high-average powers of the OPO output. Of course, other pump lasers can be incorporated into the setup as well.
|Levante Emerald HP + HarmoniXX FHG (incl. THG, SHG)|
|Wavelength Range||< 192 ... 215 nm | > 6.5 ... 5.77 eV (FHG)|
|< 240 ... 320 nm | > 5.12 ... 3.87 eV (THG)|
|< 360 ... 480 nm | > 3.44 ... 2.58 eV (SHG)|
|< 690 ... 990 nm (Levante Emerald HP OPO Signal)|
|Power Output||> 11 mW at 207 nm | 6 eV (FHG)|
|> 75 mW at 280 nm | 4.4 eV (THG)|
|> 410 mW at 800 nm | 1.55 eV (SHG; THG components removed)|
|> 6000 mW at 760 ... 960 nm (OPO Signal)|
|Pulse Width||approx. 15 ps|
|Spectral Bandwidth FHG||5 pm | 0.16 meV at 196 nm | 6.46 eV|
|Repetition Rate||80 MHz|
|M2||< 1.2 (typical 1.1)|
|Polarization||Linear / Horizontal|
|Power||> 20 W|
|Pulse Width||Approx. 15 ps|
|Manufacturer||Coherent Inc. (Paladin 532 -20000 )|
|Remote Control||Possible via USB / Ethernet TCP/IP / Serial RS232|
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