Attachment 1 - Laser System Specifications.docx

Ultrafast Tunable Laser System for the Naval Research Laboratory’s Materials Science and Technology Division

05 August 2021

Introduction

The Materials Science and Technology Division at the Naval Research Laboratory (NRL) conducts basic and applied research for the development of advanced materials and functionality to support the Navy’s long term mission in sensing and advanced electronics. The Materials Science and Technology Division has a requirement for an ultrafast tunable laser system to facilitate a variety of time-resolved studies on new classes of materials and devices created by the Division. The system will include a femtosecond Ti:sapphire oscillator, an optical parametric oscillator with signal, second harmonic and idler outputs, a separate second harmonic generator, and all necessary power supplies, chillers, cabling, electronics and control software required for operation.

Background

The requirement for a femtosecond laser system stems from two of the research objectives that the Materials Science and Technology Division pursues.

1) Over the past several years, the Division has conducted intensive research into novel materials such as transition metal dichalcogenide monolayers and heterostructures using a variety of analytical techniques to characterize these emerging materials. Chief amongst them has been optical methods such as photoluminescence, reflectance and absorption studies. The Division has acquired two Horiba LabRam Spectrometer systems along with several discrete and tunable continuous wave lasers to facilitate these methods. The Division now requires new additional measurement tools to further characterize the temporal evolution of the optical properties of novel materials on very short time scales, and requires a pulsed laser system to facilitate the build out of spectroscopic techniques such as time-resolved Kerr rotation and reflectivity amongst others.

2) The Division also conducts research on using topological materials to manipulate magnetic systems using spin-orbit torque. As part of the Division’s ARAP program, the Division requires time-resolved Kerr rotation to track the evolution of magnetic layers that have been perturbed by ultrafast electrical pulses.

Objective

For this effort, the NRL seeks to acquire the necessary laser system to build the time-resolved experiments that are referenced in the background above. These experiments will permit the measurement of the optical and magnetic dynamics of the materials and devices the Division creates on timescales shorter than 1 picosecond. These experiments all will have elements in common (e.g. the laser, mechanical delay line), but may use different detection schemes based on what the experiment aims at measuring.

Scope

The vendor shall deliver, install and service a secure, ultrafast tunable laser system as described above while adhering to the requirements as described below:

System Specifications

I. Ti:sapphire Oscillator

1) Automated tuning range of at least 680-1080nm without any operator adjustment other than request of wavelength. System must be able to tune the entire range without requiring an external gas purge. Power output requirements are,

a. > 3.5 Watts at 800 nm

b. > 400 mW at 680 nm

c. > 150 mW 1080nm

2) Spatial mode of TEM00 with M^2 < 1.1 (at peak of tuning range)

3) A pulse width of between ~100 and ~150 fs (at peak of tuning range)

4) Repetition rate >75 MHz

5) Noise < .15% (measured RMS in a 10 Hz to 10 MHz bandwidth, at peak of tuning range)

6) Output Power Stability < ± .5% (Percent power drift in any 2-hour period with <±1°C temperature change after a 1-hour warm up.)

7) Beam astigmatism < 10% (at peak of tuning range)

8) Beam ellipticity .9 to 1.1 (at peak of tuning range)

9) Pointing stability of < 50 microradians/100nm tuning

10) Polarization horizontal or vertical, >500:1 (at peak of tuning range)

11) Integrated spectrometer

12) The laser head must be permanently aligned and sealed. The system should have automatic means to maintain the pump alignment within the cavity to maximize output power and to stabilize the pulse width for all wavelengths

13) The laser should be able to be operated via either a panel interface or computer.

14) The pump laser diodes must be user replaceable

15) A chiller should be included if necessary

II. Optical Parametric Oscillator (OPO) (assuming being pumped by entire output of Ti:sapphire)

1) The OPO should have tunable output of at least the following:

a. 1000 to 1600nm (‘IR’)

b. 510 to 720nm (‘Visible’)

c. 1750 to 4000nm (‘Idler’)

2) The wavelength tuning of the OPO should be automated and computer controlled

3) Pulse width < 250 fs

4) M^2 < 1.2 (excepting idler)

5) Output power > 75 mW over the visible and IR ranges given in 1), depending on OPO configuration.

6) Noise < .5% (measured RMS in a 10 Hz to 10 MHz bandwidth)

7) Repetition rate matched and synchronized to pump

8) Capable of being configured for simultaneous visible and IR output.

9) For optimal mode quality and power, the visible output must be generated by means of intracavity doubling of the IR OPO signal beam.

10) The OPO should be of such a design to allow for independent tuning of Ti:sapphire input and the visible output. The OPO should be able to accept at least a 100nm range of the TI:sapphire’s output between 700nm and 900nm (e.g. 730nm to 830nm), and over that entire range, have tunable output in the visible that spans at least 100nm.

11) For at least one given pump wavelength of the Ti:sapphire oscillator, the OPO should be tunable from at least 520nm to 700nm

12) The OPO should be field upgradable to operate in picosecond mode when paired with an appropriate laser

13) The OPO system should be internet capable to allow for the possibility of remote diagnostics

III. Second Harmonic Generation (SHG) Module

1) The SHG module should be able to communicate with the laser software and onboard spectrometer to automatically optimize crystal phase matching as the pump laser wavelength is tuned

2) Conversion efficiency of >30% (at peak of tuning range)

3) A beam splitter that can direct 20% of the laser power to the SHG should be included

IV. Acceptance Tests

Upon delivery and installation, the following must be demonstrated:

1) Automated tuning through the entire required wavelength ranges of the Ti:sapphire oscillator and the visible output of the OPO.

2) The output power of both the Ti:sapphire oscillator and the visible output of the OPO meeting the specs given above.

3) The conversion efficiency of the SHG module.

V. Warranty

1) 1 year warranty, parts and labor. Contractor shall be single service point of contact.